Computational Fluid Dynamics (CFD) Modelling and Application for Sterilization of Foods: A Review
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paper_title: Numerically Predicted Transient Temperature and Velocity Profiles During Natural Convection Heating of Canned Liquid Foods

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Numerically predicted transient flow patterns and temperature profiles during natural convection heat transfer of a liquid in a uniformly heated cylindrical can were presented for the first time. A recirculating flow pattern was predicted inside the cylindrical container. The liquid was found to be stratified inside the container with increasing temperatures towards the top. The slowest heating location in the fluid was a donut-shaped region close to the bottom of the can at about one-tenth the can height.
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paper_title: Quantifying Enhancement in Heat Transfer Due to Natural Convection During Canned Food Thermal Sterilization in a Still Retort

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Thermal sterilization of canned viscous liquid foods using saturated steam is enabled by natural convective heat transfer. However, the governing equations for two-dimensional convective heat transfer may be only rigorously solved by numerical calculations. On the other hand, if conduction is assumed to be the only mode of heat transfer, the thermal sterilization problem has analytical solutions for simple boundary conditions. However, the conduction model may not be appropriate in describing thermal sterilization of even viscous liquid foods and may cause considerable error in the prediction of the important parameters such as slowest heating zone (SHZ) temperature and lethality. The longer time for sterilization recommended by the conduction model may lead to overprocessing and an unacceptable food product. The objective of this work is to quantify the faster temperature rise in the food can due to natural convection when compared to the temperature rise obtained by only conductive heating. The consequent enhancement in lethalities is also reported. In addition, this work’s objective is to investigate how quickly the natural convective heat transfer effects begin to dominate over the solely conduction heating mode. The volume-averaged temperature as well as the SHZ temperature variations with time was calculated for the convection-augmented mode using computational fluid dynamics (CFD) simulations. Lethality values were then calculated based on volume-averaged temperature as well as the SHZ temperature. Food cans of different aspect ratios and food medium thermal conductivities are considered in this analysis. For the food system investigated, the critical Fourier number at which the transition to convection-augmented mode of heat transfer occurred is identified and explained from scaling considerations. In the conduction-dominated mode, it was possible to use analytical solutions to predict the volume-averaged and SHZ temperatures of the liquid food undergoing thermal sterilization. The Nusselt number correlation developed by Kannan and Gourisankar (2008) was used in the lumped parameter transient heat transfer model to predict the volume-averaged temperatures in the convection-dominated region. The volume-averaged temperatures from this approach were found to be in good agreement with the CFD simulation results. The time predicted for the SHZ to reach the minimum sterilization temperature was significantly lower when convective heating was also considered. The volume-averaged temperature and SHZ temperature enabled an estimation of overall sterility levels attained and minimum sterility levels prevalent inside the can, respectively. Even though the volume-averaged temperature increase due to convection was only about 10 K, the resulting accumulated lethality values were higher by an order of magnitude. The increase in SHZ temperatures was much higher in the convection-augmented mode, and consequently greater integrated lethalities were attained. The simple conduction model that is amenable to analytical solution cannot be used to approximate the heat-transfer-related phenomena even for “quick estimation” purposes when convection effects are significant. This precaution is found necessary even for the reasonably high viscous carboxy methyl cellulose system, whose average viscosity values ranged between 13 and 3 Pa s during the course of the sterilization process.
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paper_title: EXPERIMENTAL COMPARISON OF NATURAL CONVECTION AND CONDUCTION HEAT TRANSFER

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Magnitude of fluid motion is significant in convective heat transfer (the faster the fluid motion, the greater the heat transfer), while in conductive heat transfer, there is no physical movement of objects undergoing heat transfer. Due to this statement, it is a real fact that convection can be many times faster than conduction. The objective of this research was to compare natural convection and conduction by creating both heat transfer mechanisms in the same product. For this purpose, canned water and 1% agar-gelled water were used in the experimental and further computational fluid dynamics studies. Experiments were conducted at 70C and in boiling water, and ANSYS V.10 (Ansys Inc., Canonsburg, PA) was used in the numerical simulations. The results showed that addition of agar prevented the natural convection phenomena in the gels resulting in pure conduction while the effect of natural convection, which occurred due to thermal buoyancy effects in the given gravitational force field, was obvious in the case of water. Creation of both natural convection and conduction heat transfer mechanisms in the same medium is an important contribution as the effect of natural convection over the conduction heat transfer can directly be emphasized. ::: ::: ::: ::: PRACTICAL APPLICATIONS ::: ::: Creation of both natural convection and conduction heat transfer mechanisms in the same medium would be an important contribution as the effect of natural convection over the conduction heat transfer can experimentally be emphasized. The results of this study are significant to show the significant difference between these heat transfer modes as both mechanisms were created in the same medium, and these results will be useful especially for teaching heat transfer purposes.
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paper_title: Numerical simulation of transient temperature profiles for canned apple puree in semi-rigid aluminum based packaging during pasteurization

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Pasteurization of canned apple puree was simulated for a 3-D geometry in a semi-rigid aluminum based container which was heated from all sides at 378 K. The computational fluid dynamics code Ansys Fluent 14.0 was used and the governing equations for energy, momentum, and continuity were computed using a finite volume method. The food model was assumed to have temperature-dependent properties. To validate the simulation, the apple puree was pasteurized in a water cascading retort. The effect of the mesh structures was studied for the temperature profiles during thermal processing. The experimental temperature in the slowest heating zone in the container was compared with the temperature predicted by the model and the difference was not significant. The study also investigated the impact of head space (water-vapor) on heat transfer.
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paper_title: Numerical Simulation of Natural Convection Heating of Canned Thick Viscous Liquid Food Products

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Sterilization of a thick viscous liquid food in a metal can sitting in an upright position and heated from the side wall (Tw= 394 K) only in a still retort was simulated. The liquid had temperature dependent viscosity but constant specific heat and thermal conductivity. Equations of mass, motion and energy conservation for an axisymmetric case were solved and plots of temperature, velocity and streamlines were provided for natural convection heating and isotherms compared with pure conduction contour plots. Results indicated that the natural convection moved the slowest heating point to the bottom center. The bottom of the can heated up slower than predicted by pure conduction heating. The magnitude of the axial velocity was found to be of the order of 10−5 m/sec which varied with time and position in the can.
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paper_title: Heat transfer analysis of pasteurization of bottled beer in a tunnel pasteurizer using computational fluid dynamics

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Abstract Beer is one of the most widely consumed alcoholic beverages in the world. Pasteurization is an important unit operation in beer processing that inactivates the spoilage microorganisms present in beer thereby extending its shelf life. It is difficult to determine the temperature profile and slowest heating zone (i.e. minimum heating region) inside the bottle during industrial scale tunnel pasteurization. Computational fluid dynamics (CFD) modeling can be used as a tool to determine the temperature distribution pattern inside the bottled beer. This study is unique in terms of using the actual thermophysical properties of beer unlike in earlier published works. Further, CFD simulation prediction of the temperature profile in the bottled beer was validated with experimental measurements. The study was extended to investigate the effects of different zones' temperatures on inactivation of Saccharomyces cerevisiae , the most common beer spoilage organism. A tunnel pasteurizer with seven zones was selected to study the temperature profile inside the bottled beer and found to be in good agreement with the published temperature profiles in different zones. In addition, the effectiveness of pasteurization was investigated in terms of pasteurization unit (PU) and the resultant PU value (15 to 30 PU) was adequate for achieving the maximum sterility of beer. Industrial relevance In recent years, a rapid development in the application of CFD in food processing operations has been witnessed. The main need for CFD analysis of pasteurization is to determine the uniform and effective heat distribution inside the bottled beer and to examine the position of slowest heating zone (SHZ). Relatively few works have been published related to applications of CFD during beer pasteurization. However, all the studies were performed with water as a model fluid. So far no work has been published on the CFD simulation during the pasteurization process in bottled beer by using the thermophysical properties of beer. Hence, the present study was aimed at investigating the temperature distribution inside the beer bottle during the pasteurization process and in each zone of the industrial tunnel pasteurizer. This model can be used for the brewery industry to ensure that the required pasteurization temperature has been reached inside the beer bottle when conveyed through a tunnel pasteurizer. This is very essential to render a safe product with extended shelf life to the consumers.
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paper_title: Modelling and Multi-objective Optimisation of the VHP Pouch Packaging Sterilisation Process

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Abstract Spouted pouches are being increasingly used in the beverage sector. However, aseptic packaging technology used for spouted pouches requires a highly complex sterilisation and rinsing process for the packaging materials before filling. This paper deals with the pouch packaging sterilisation process used in aseptic technology. A mixture composed of vaporised hydrogen peroxide and hot sterile air is injected into the package through a sterilisation nozzle. A CFD multicomponent model in ANSYS CFX (version 14.5) has been created and validated in order to simulate the real process. Based on this model, the paper aims to minimise hydrogen peroxide consumption and optimise the sterilisation treatment of the packaging. This issue has been approached using multi-objective optimisation software applied to CFD multicomponent simulations. The most suitable nozzle position inside the pouch has been established, as well as the optimal treatment time, concentration and flow rate of the sterilising mixture.
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paper_title: Transient temperature and velocity profiles in a canned non-Newtonian liquid food during sterilization in a still-cook retort

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Abstract Natural convection heating of a canned liquid food during sterilization is simulated by solving the governing equations for continuity, momentum and energy conservation for an axisymmetric case, using a finite element code. The model liquid has constant properties except viscosity (temperature dependent and shear thinning) and density (Boussinesq approximation). The velocity field establishes itself much more rapidly than the temperature field. The maximum axial velocity is of the order of 10 −4 m s −1 because of low Grashof number. The coldest point is not fixed but migrates in a region that is 10–12% of the can height from the bottom of the can and at a radial distance approximately one-half of the radius. On the basis of the computed particle path it appears that the liquid initially located just below the top center is exposed to the minimum heat treatment and should be of most concern in the thermal process calculations.
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paper_title: INFLUENCE OF THE GEOMETRY ASPECT OF JARS ON THE HEAT TRANSFER AND FLOW PATTERN DURING STERILIZATION OF LIQUID FOODS

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Natural convection heating of liquid food packed in glass jars of different sizes and volumes during sterilization is simulated by solving the governing equations for continuity, momentum and energy conservation, using the finite element method. The effect of the aspect ratio of the container on temperature distribution, flow pattern, position of the slowest heating zone (SHZ) and cooking value were analyzed. The position of the SHZ varied ‐ depending of container volume and aspect ratio ‐ in the range of 49.39‐76.83% and 5.81‐19.09% of jar radius and height, respectively. Sterilization times were estimated and differences between 135 and 105 s for containers of a same size of 360 or 660 cm 3 , respectively, were predicted depending on jar shape. A prediction model was developed that allows to calculate ‐ with a simple procedure ‐ sterilization times as a function of container dimensions. PRACTICAL APPLICATIONS It is frequent in low-volume processing plants that work with foods packed in glass jars to change container size and/or shape between successive batches of production, but maintaining the same process schedule. This leads to products with lack of microbial innocuousness (underprocessing) or with low nutritional or sensory quality (overprocessing). In that sense, in this work velocity and temperature profiles, and the location of the “slowest heating zone” were modeled and simulated using the finite element method for liquid foods in glass jars of different volumes and shapes during their thermal treatment. This information allowed estimate sterilization times as well as quality losses during thermal treatment. Finally, a simplified method for the calculation of sterilization times as a function of container size and shape was developed. This method could be very practical for the design of thermal processes in low-volume productions, whose operators usually lack simulation software and personnel trained in process calculations.
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paper_title: Simulation of heat transfer for solid-liquid food mixtures in cans and model validation under pasteurization conditions

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Abstract During processing of canned mixtures of solid–liquid foods, conduction and convection occur simultaneously. The literature lacks in a complete simulation study where a large number of solids are dispersed in the liquid phase, e.g. canned peas. Therefore, the objectives of this study were to determine temperature changes inside a can containing solid–liquid food mixtures. For this purpose, dispersed stationary solids (canned peas in water) in a 2D (axi-symmetrical) configuration were applied. Ansys V11 (Ansys Inc., Canonsburg, PA) was used to solve continuity, energy and momentum equations. For experiments, canned pea samples were prepared in 500 g cans, and heating process was conducted in a retort under pasteurization conditions at ≈98 °C. Temperature changes were measured using needle type thermocouples, and simulation results were validated against experimental data. This study is expected to be a significant contribution to the literature for further optimization studies and to form basis of an industrial project to improve canning process of solid–liquid mixtures.
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paper_title: Computational Fluid Dynamics in Thermal Food Processing

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Computational fluid dynamics (CFD) is a simulation tool used to analyze fluid flow and heat-transfer problems. In food processing, CFD has been applied to simulate drying, mixing, refrigeration, and sterilization conditions. Basically, the method involves the solving of Navier-Stokes transport equations, describing the conservation of mass, momentum, and energy, which are numerically resolved to predict, for example, velocity, temperature, shear, and pressure profiles inside a studied system that can adopt any geometry ::: ::: $$ \frac{\partial \rho }{\partial t}+\rho \nabla \cdot \overrightarrow{v}=0\kern1em \mathrm{Conservation}\ \mathrm{mass}\ \mathrm{equation} $$ ::: ::: ::: ::: $$ \begin{array}{l}\rho \frac{\partial }{\partial t}\left(\overrightarrow{v}\right)+\rho \overrightarrow{v}\cdot \nabla \overrightarrow{v}=-\nabla p+\mu {\nabla}^2\overrightarrow{v}+{S}_{\mathrm{m}}\hfill \\ {}{S}_{\mathrm{m}}=-{\rho}_{\mathrm{ref}}\beta \left(T-{T}_{\mathrm{ref}}\right)g\hfill \end{array}\kern1em \mathrm{Momentum}\ \mathrm{equation} $$ ::: ::: ::: ::: $$ \frac{\partial T}{\partial t}+\overrightarrow{v}\nabla \cdot (T)=\frac{1}{\rho {C}_{\mathrm{p}}}\nabla \cdot \left(k\nabla T\right)\kern1em \mathrm{Energy}\ \mathrm{equation} $$ ::: ::: where \( \overrightarrow{v} \) is the velocity vector, ρ is the density, a is the acceleration, p is the pressure, μ is the dynamic viscosity, Sm is the Boussinesq approximation, β is the thermal dilatation coefficient, ρref is the density at the boundary wall condition, Tref is the temperature at the boundary wall condition, g is the gravitational force, k is the thermal conductivity, Cp is the specific heat capacity, and T is the temperature.
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paper_title: Developing an Effective Method to Determine the Deviation ofFValue upon the Location of a Still Can during Convection Heating Using CFD and Subzones

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A numerical simulation was applied to determine the temperature profiles of water in a can with a diameter of 52.3 mm and a height of 124.0 mm. Cold points at different heating times were determined, and the degree of pasteurization (F value) of each cold point was calculated. Subzones in both vertical and horizontal directions were introduced to determine the deviation of F value upon the location in the can during a convective heating, and the average F value of each subzone was estimated. The slow heating zone (SHZ) was determined by overwrapping the subzones with the lowest average F values in the vertical and horizontal direction. The cold point was continuously moved during the thermal treatment and even at 600 s, the SHZ determined by this subzone method maintained a single zone, unlike the cold points. The relative difference of F value between the SHZ and the cold point was approximately 0.575%. The subzone method is thus an effective way to determine the SHZ and F value, which is an indicator of the sterilization. ::: ::: ::: ::: Practical Applications ::: ::: For safety purposes, estimation of the degree of pasteurization is very important for the liquid food in a can. Determination of the slow heating zone (SHZ) and F value in the can is very difficult because of the convection flow during heating. Many previous studies indicated the importance of determining the SHZ for the liquid food in a can, but there was no clear advice to estimate the degree of pasteurization based on the temperature profile from the SHZ. This study suggested to use the subzones to estimate the SHZ and clearly demonstrate that the degree of pasteurization at the SHZ represented by the area average F value obtained from the subzone is more stable and consistent.
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paper_title: Computational fluid dynamics (CFD) modelling and experimental validation of thermal processing of canned fruit salad in glass jar

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Abstract In this paper the heat transfer of a fruit salad during the pasteurization treatment was investigated. The objective of the paper was to develop and validate a computational fluid dynamics (CFD) model for predicting the temperature profiles during the thermal processing of this sample. Samples of a commercial fruit salad, composed of five different fruits with different shapes, sizes and thermal properties, submerged in water/sugar syrup, were submitted to thermal treatments in a pilot plant and temperature profiles at different locations were experimentally recorded. Results showed that the slowest heating point (SHP) was positioned at 19–20% of the can height: fruit closest to the SHP such as pear presented the lowest F value . Moreover, F values resulted to be influenced by the distance from the jar bottom as function of natural convection motion of the syrup. CFD model simulations data were then successfully validated against the experimental ones: results, expressed as RMSE, showed a good fitting between calculated and experimental data, both for syrup (mean RMSE 1.47 °C) and fruit pieces (mean RMSE 1.63 °C). In addition, F values calculated from both experimental and simulated temperatures resulted very similar with only little differences. In conclusion, the proposed approach and mathematical model can thus be usefully applied for the simulation and prediction of thermal processes of canned fruit salad for process design and optimization.
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paper_title: On the Validity of Boussinesq Approximation in Variable Property Turbulent Mixed Convection Channel Flows

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ABSTRACTThe present study investigates the effects of fluid thermo-physical property variations on fully developed turbulent mixed convection flow in vertical and horizontal parallel plate channels where walls are kept at different temperatures. The main attention is paid to the validity of the Boussinesq approximation when the temperature differences are enhanced. Reynolds number based on the channel half-width and friction velocity is assumed to be 150. The governing equations are solved utilizing the large eddy simulation and the low Mach number approach on a finite-volume basis. Dealing with the sub-grid scale stress tensor and the heat flux vector, the dynamic Smagorinsky model is used. All the numerical simulations are carried out by developing a solver in OpenFOAM. The present results display that an increase in the walls' temperature difference, applying the Boussinesq approximation and neglecting the dependency of thermal conductivity and dynamic viscosity on temperature, can result in relatively...
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paper_title: Three-Dimensional CFD Simulation of a “Steam Water Spray” Retort Process for Food Vegetable Products

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This work aims at simulating a retort sterilization process of flexible packaging, performed in autoclave. ANSYS CFD© software has been used in this study to simulate the heat transfer inside the retort chamber. Flexible packaging filled with a pumpkin soup has been modelled. Three-dimensional (3D) geometrical configuration of the equipment has been designed and then simulated to evaluate the sterilization level achieved by each packaging inside the retort chamber. In particular, the internal temperature of the product situated in the cold spot of the chamber has been monitored during 5 min of the process (after reaching 85°C inside the product) in order to monitor the time/temperature trend. Experimental tests have been finally performed to validate the simulation model of heat exchange. The sterilization process takes place in a retort chamber by means of “overheated water sprayed” at 403 K and a pressure of 5 atm. Results show a good agreement between the simulated results and the real retort process and confirm the potential value of the simulation model to evaluate the process performance.
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paper_title: Effects of air movement in a hot air dryer on the drying characteristics of colored potato (Solanum tuberosum L.) using computational fluid dynamics

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The flow fields of hot air in the dryer for drying colored potatoes of which characteristics are highly sensitive to the temperature were simulated using computational fluid dynamics (CFD) simulation. The local air velocity decreased as the distance from the flow inlet increased. The mass and heat transfer coefficients increased from 0.666×10-2 m/s to 1.711× 10-2 m/s, and 6.555 W/(m2•K) to 16.834 W/(m2•K), respectively, as the air velocity increased from 0.207 m/s to 1.567 m/s at 60°C. The drying simulation model using the heat and mass transfer model made accurate predictions. The thermal properties of colored potato, such as the thermal conductivity and specific heat, decreased significantly from 0.440 W/(m•K) to 0.034 W/(m•K) and 3906.45 J/(kg•K) to 2198.52 J/(kg•K), respectively, as the moisture content decreased from 78% to 5%. With the variable thermal and physical properties, the heat transfer simulation model made accurate predictions of the hot-air drying characteristics for the colored potatoes, and the RMSE values for all cases were (1.85±0.27)°C. ::: Keywords: colored potato, hot air drying, drying characteristics, computational fluid dynamics, thickness, air velocity ::: DOI: 10.25165/j.ijabe.20181101.3293 ::: ::: Citation: Park H W, Yoon W B. Effects of air movement in a hot air dryer on the drying characteristics of colored potato (Solanum tuberosum L.) using computational fluid dynamics. Int J Agric & Biol Eng, 2018; 11(1): 232–240.
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paper_title: Computational fluid dynamics prediction and validation of gas circulation in a cheese-ripening room

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Abstract This paper discusses the application of a computational fluid dynamics (CFD) approach to predicting air velocity patterns and circulation of an exogenous gas inside a pilot cheese-ripening room in 3 dimensions (3D). Comparison of numerical results with experimental data showed a fairly close agreement in the qualitative prediction and a few inaccuracies in the quantitative prediction of the air velocity patterns, with mean absolute differences of 0.12 m s −1 in half the volume of the ripening room and about 0.05 m s −1 inside the stacks filled with cheese models. A sensitive study revealed that using the standard k – e model for modelling the turbulence of the flow in combination with the first-order upwind differencing scheme offered a good compromise solution between accuracy of results and computation time, given the 3D mesh of 1.2 million cells created. Moreover, numerical calculations indicated that using the blowing duct for adding an exogenous gas seemed to provide a more efficient solution for levelling off the gas distribution throughout the whole volume of the room than an injection performed directly into the core of the stacks.
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paper_title: Numerical study on heat transfer of turbulent channel flow over periodic grooves

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Abstract A numerical investigation of turbulent forced convection in a two-dimensional channel with periodic transverse grooves on the lower channel wall is conducted. The lower wall is subjected to a uniform heat flux condition while the upper wall is insulated. To investigate turbulence model effects, computations based on a finite volume method, are carried out by utilizing four turbulence models: the standard k − e , the Renormalized Group (RNG) k − e , the standard k − ω , and the shear stress transport (SST) k − ω turbulence models. Parametric runs are made for Reynolds numbers ranging from 6000 to 18,000 with the groove-width to channel-height ratio ( B / H ) of 0.5 to 1.75 while the groove pitch ratio of 2 and the depth ratio of 0.5 are fixed throughout. The predicted results from using several turbulence models reveal that the RNG and the k − e turbulence models generally provide better agreement with available measurements than others. Therefore, the k − e model is selected to use in prediction of this complex flow. In addition, the results of the heat transfer coefficient, friction factor, skin friction coefficient and thermal enhancement factor are also examined. It is found that the grooved channel provides a considerable increase in heat transfer at about 158% over the smooth channel and a maximum gain of 1.33 on thermal performance factor is obtained for the case of B / H = 0.75. This indicates that the reverse/re-circulation flow in a channel with transverse grooves can improve the heat transfer rate.
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paper_title: Investigation of nanofluid mixed convection in a shallow cavity using a two-phase mixture model

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Abstract Laminar and turbulent mixed convection heat transfer of water/Cu nanofluids in a rectangular shallow cavity was studied utilizing a two-phase mixture model. The upper movable lid of the cavity was at a lower temperature compared to the bottom wall. Simulations were performed for Grashof numbers of 10 5 (laminar flow) and 10 10 (turbulent flow) for Richardson numbers from 0.03 to 30, and nanoparticle volume fractions of 0.00–0.04. The two-dimensional governing equations were discretized using a finite volume method. The effects of nanoparticle concentration, shear and buoyancy forces, and turbulence on flow and thermal behavior of nanofluid flow were studied. The model predictions for very low solid volume fraction ( φ ≈ 0) were found to be in good agreement with earlier numerical studies for a base fluid. It is shown that for specific Grashof ( Gr ) and Richardson ( Ri ) numbers, increasing the volume fraction of nanoparticles enhances the convective heat transfer coefficient and consequently the Nusselt number ( Nu ) while having a negligible effect on the wall shear stress and the corresponding skin friction factor.
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paper_title: CFD model of the airflow, heat and mass transfer in cool stores

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A transient three-dimensional CFD model was developed to calculate the velocity, temperature and moisture distribution in an existing empty and loaded cool store. The dynamic behaviour of the fan and cooler was modelled. The model accounted for turbulence by means of the standard k-e model with standard wall profiles. The model was validated by means of velocity, air and product temperature. An average accuracy of 22% on the velocity magnitudes inside the empty cold store was achieved and the predicted temperature distribution was more uniform than predicted. In the loaded cold store, an average accuracy of 20% on the velocity magnitudes was observed. The model was capable of predicting both the air and product temperature with reasonable accuracy.
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paper_title: Airflow characteristics within a slot-ventilated enclosure

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Abstract The objective of this study is to numerically and experimentally investigate velocity characteristics throughout a long slot-ventilated enclosure as a function of inlet flow arrangement located on the same side of the exit section. This study focused on the effect of the enclosure’s confinement on the airflow pattern and more particularly on the wall jet characteristics concerning its decay and its stabilisation. An original approach is also proposed to evaluate the local effect of airflow pattern on ventilation efficiency. To improve the performance and the uniformity of ventilation in the enclosure, a new configuration with a lateral air inlet section was studied. The results concerning airflow characteristics and air-ventilation efficiency were compared and contrasted with the more common case with a central inlet section. A numerical approach based on computational fluid dynamics (CFD) Fluent code was used to test various turbulence closure models including the high and low Reynolds number form of the two-equation k – e model and the more advanced Reynolds stress model (RSM). Comparisons with experimental data obtained on a scale model under isothermal conditions allow a critical evaluation of the performance of these models in internal flows.
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paper_title: A CFD model as a tool to simulate β-lactoglobulin heat-induced denaturation and aggregation in a plate heat exchanger

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Abstract During the pasteurization process, the thermal treatment of milk and its derivatives in plate heat exchangers is limited by protein fouling. The deposition mechanism onto the heat transfer surface involves the denaturation and aggregation of β-lactoglobulin. In this work, a 2-D CFD analysis was conducted to simulate locally the heat-induced protein denaturation mechanisms. Firstly, we present various intermediate validations of the ability of the numerical model to capture the hydrodynamics, by showing the similarity of CFD results and experimental data. Finally, the close agreement between the denaturation level obtained by CFD and that obtained experimentally indicates the ability of the numerical model adopted to simulate the chemical reaction. The analysis of the species present in the plate heat exchanger is related to the deposit mass distribution along the heat exchanger using CFD data. It has been shown that the unfolded species are deposit precursors and that the distribution of the deposit is correlated to this source.
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paper_title: Computation of the airflow in a pilot scale clean room using K-ε turbulence models

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This work deals with the assessment of the airflow in a food-processing clean room. The flow pattern inside the working area of a pilot scale clean room was numerically investigated using a computational fluid dynamics code based on a finite volume formulation. Two versions of the k-e turbulence model were tested: the standard and the RNG version. The analysis of the velocity magnitude does not reveal sensitive differences between them. Moreover, both models well predict the main features of the flow and numerical results agree with experimental measurements. However, a further examination shows that the RNG k-e turbulence model predicts more swirls and more complex trajectories. As the standard k-e model overestimates the turbulent diffusion, the RNG version seems to be more suitable to calculate the airflow in clean rooms. The influence of initial turbulence intensity is also pointed out. Finally, the study of the airflow below a laminar flow unit confirms that the design of clean rooms can benefit from the numerical approach.
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paper_title: The numerical computation of turbulent flows

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Abstract The paper reviews the problem of making numerical predictions of turbulent flow. It advocates that computational economy, range of applicability and physical realism are best served at present by turbulence models in which the magnitudes of two turbulence quantities, the turbulence kinetic energy k and its dissipation rate ϵ, are calculated from transport equations solved simultaneously with those governing the mean flow behaviour. The width of applicability of the model is demonstrated by reference to numerical computations of nine substantially different kinds of turbulent flow.
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paper_title: CFD modeling of a pilot-scale countercurrent spray drying tower for the manufacture of detergent powder

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ABSTRACTA steady-state, three-dimensional, multiphase computational fluid dynamics (CFD) modeling of a pilot-plant countercurrent spray drying tower is carried out to study the drying behavior of detergent slurry droplets. The software package ANSYS Fluent is employed to solve the heat, mass, and momentum transfer between the hot gas and the polydispersed droplets/particles using the Eulerian–Lagrangian approach. The continuous-phase turbulence is modeled using the differential Reynolds stress model. The drying kinetics is modeled using a single-droplet drying model, which is incorporated into the CFD code using user-defined functions (UDFs). Heat loss from the insulated tower wall to the surrounding is modeled by considering thermal resistances due to deposits on the inside surface, wall, insulation, and outside convective film. For the particle–wall interaction, the restitution coefficient is specified as a constant value as well as a function of particle moisture content. It is found that the variation...
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paper_title: Effects of air movement in a hot air dryer on the drying characteristics of colored potato (Solanum tuberosum L.) using computational fluid dynamics

paper_content:

The flow fields of hot air in the dryer for drying colored potatoes of which characteristics are highly sensitive to the temperature were simulated using computational fluid dynamics (CFD) simulation. The local air velocity decreased as the distance from the flow inlet increased. The mass and heat transfer coefficients increased from 0.666×10-2 m/s to 1.711× 10-2 m/s, and 6.555 W/(m2•K) to 16.834 W/(m2•K), respectively, as the air velocity increased from 0.207 m/s to 1.567 m/s at 60°C. The drying simulation model using the heat and mass transfer model made accurate predictions. The thermal properties of colored potato, such as the thermal conductivity and specific heat, decreased significantly from 0.440 W/(m•K) to 0.034 W/(m•K) and 3906.45 J/(kg•K) to 2198.52 J/(kg•K), respectively, as the moisture content decreased from 78% to 5%. With the variable thermal and physical properties, the heat transfer simulation model made accurate predictions of the hot-air drying characteristics for the colored potatoes, and the RMSE values for all cases were (1.85±0.27)°C. ::: Keywords: colored potato, hot air drying, drying characteristics, computational fluid dynamics, thickness, air velocity ::: DOI: 10.25165/j.ijabe.20181101.3293 ::: ::: Citation: Park H W, Yoon W B. Effects of air movement in a hot air dryer on the drying characteristics of colored potato (Solanum tuberosum L.) using computational fluid dynamics. Int J Agric & Biol Eng, 2018; 11(1): 232–240.
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paper_title: Developing an Effective Method to Determine the Deviation ofFValue upon the Location of a Still Can during Convection Heating Using CFD and Subzones

paper_content:

A numerical simulation was applied to determine the temperature profiles of water in a can with a diameter of 52.3 mm and a height of 124.0 mm. Cold points at different heating times were determined, and the degree of pasteurization (F value) of each cold point was calculated. Subzones in both vertical and horizontal directions were introduced to determine the deviation of F value upon the location in the can during a convective heating, and the average F value of each subzone was estimated. The slow heating zone (SHZ) was determined by overwrapping the subzones with the lowest average F values in the vertical and horizontal direction. The cold point was continuously moved during the thermal treatment and even at 600 s, the SHZ determined by this subzone method maintained a single zone, unlike the cold points. The relative difference of F value between the SHZ and the cold point was approximately 0.575%. The subzone method is thus an effective way to determine the SHZ and F value, which is an indicator of the sterilization. ::: ::: ::: ::: Practical Applications ::: ::: For safety purposes, estimation of the degree of pasteurization is very important for the liquid food in a can. Determination of the slow heating zone (SHZ) and F value in the can is very difficult because of the convection flow during heating. Many previous studies indicated the importance of determining the SHZ for the liquid food in a can, but there was no clear advice to estimate the degree of pasteurization based on the temperature profile from the SHZ. This study suggested to use the subzones to estimate the SHZ and clearly demonstrate that the degree of pasteurization at the SHZ represented by the area average F value obtained from the subzone is more stable and consistent.
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paper_title: Three-dimensional CFD calculations for designing large food chillers

paper_content:

In industry solid foods such as vegetables and meat are mostly air-chilled and stored in refrigerated rooms. Plant performance depends on heat and water exchanges between the air and the products and thus on the spatial distribution of the air parameters: velocity, turbulence intensity, temperature and relative humidity. In theory the transient behaviour of chillers could be calculated using computational fluid dynamics (CFD) codes, but current computer capacity and the inaccuracy of models for evaluating heat and mass transfer coefficients make them inapplicable to very large rooms containing hundreds of individual products. To overcome these limits a four-step calculation is proposed to assess how changes in chiller design and operating conditions affect chilling kinetics: (1) 3D calculation of the air velocity field with a CFD code, (2) deduction of an average air velocity map, (3) determination of heat and mass transfer coefficients in relation to the air velocity map using independent measurements, and (4) calculation of the product chilling kinetics using specific software. This procedure was applied to a pork chiller containing 290 carcasses. Two design cases differing in inlet air direction and flow rate, and two functioning modes, batch and continuous, were analysed. A fairly good agreement was observed between the calculated and measured air velocities. It was shown from temperature and weight loss kinetics that with this type of design, batch chilling can only be achieved overnight at the cost of overcooling for low weight carcasses, and increased weight losses.
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paper_title: CFD modeling of an industrial continuous bread-baking process involving U-movement

paper_content:

Abstract In an industrial continuous bread-baking oven, dough/bread is travelling inside the oven chamber on its top and bottom tracks connected by a U-turn. The temperature profile of dough/bread during this whole travelling period, which depends on the distribution of temperature and air flow in the oven chamber, dominates the final product quality. In this study, a two-dimensional (2D) CFD model for the whole baking oven chamber has been developed to facilitate a better understanding of the baking process. The transient simulation of the continuous movement of dough/bread in the oven was achieved using the sliding mesh technique. The U-turn movement of bread was successfully simulated by dividing the solution domain into two parts, then flipping and aligning them along the travelling tracks. The 2D CFD modelling was proven to be a useful approach to study the unsteady heat transfer in the oven as well as the heating history and temperature distribution within dough/bread.
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paper_title: Direct numerical simulation of turbulent flow over a backward-facing step

paper_content:

Turbulent flow over a backward-facing step is studied by direct numerical solution of the Navier–Stokes equations. The simulation was conducted at a Reynolds number of 5100 based on the step height h and inlet free-stream velocity, and an expansion ratio of 1.20. Temporal behaviour of spanwise-averaged pressure fluctuation contours and reattachment length show evidence of an approximate periodic behaviour of the free shear layer with a Strouhal number of 0.06. The instantaneous velocity fields indicate that the reattachment location varies in the spanwise direction, and oscillates about a mean value of 6.28 h . Statistical results show excellent agreement with experimental data by Jovic & Driver (1994). Of interest are two observations not previously reported for the backward-facing step flow: ( a ) at the relatively low Reynolds number considered, large negative skin friction is seen in the recirculation region; the peak | C f | is about 2.5 times the value measured in experiments at high Reynolds numbers; ( b ) the velocity profiles in the recovery region fall below the universal log-law. The deviation of the velocity profile from the log-law indicates that the turbulent boundary layer is not fully recovered at 20 step heights behind the separation. The budgets of all Reynolds stress components have been computed. The turbulent kinetic energy budget in the recirculation region is similar to that of a turbulent mixing layer. The turbulent transport term makes a significant contribution to the budget and the peak dissipation is about 60% of the peak production. The velocity–pressure gradient correlation and viscous diffusion are negligible in the shear layer, but both are significant in the near-wall region. This trend is seen throughout the recirculation and reattachment region. In the recovery region, the budgets show that effects of the free shear layer are still present.
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paper_title: CFD studies on natural convective heating of canned food in conical and cylindrical containers

paper_content:

Enhancing natural convective heat transfer in canned food sterilization is explored through modifications to container geometry and its orientation. A conical geometry, of equal volume and height as that of the cylinder, pointing either vertically up or down was considered. The non-Newtonian fluid, 0.85% w/w sodium carboxy-methyl cellulose (CMC), was taken as the test food material and its laminar flow behavior was investigated using computational fluid dynamics (CFD). The movement of the slowest heating zone (SHZ) temperature was tracked and compared for the three geometries. The SHZ temperature was observed to attain the final sterilization fluid temperature of 100 °C fastest for an upright conical geometry followed by the cylinder and the downward pointing cone. There is scope for enhancing the thermal sterilization process through geometry modifications but without mechanical agitation or rotation. Further, the geometry modification if non-uniform must be complemented by its suitable orientation.
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paper_title: Two-dimensional CFD modeling and simulation of crustless bread baking process.

paper_content:

Abstract A special type of baking oven was developed where crustless bread was made by gently baking the dough at controlled temperature by spraying water at prefixed intervals on the surface of the dough. In this study, a two-dimensional (2D) CFD model for crustless bread during baking has been developed to facilitate a better understanding of the baking process. Simultaneous heat and mass transfer from the bread during baking was successfully simulated. It was found that core temperature of the bread reached at 95 °C at the end of baking where as moisture of the bread satisfies the normal bread quality. The model can be successively applied to study the unsteady heat and mass transfer from the crustless bread during baking.
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paper_title: A New Computational Technique For The Estimation Of Sterilization Time In Canned Food

paper_content:

Sterilization of liquid food in cans is complicated by the influence of natural convection currents induced by the hot walls of the can. In order to predict the temperature variation of the slowest heating zone (SHZ) with time, it is necessary to use computational fluid dynamics (CFD) analysis, which can be done with the help of a number of available commercial software. However, the required computational time is usually of the order of hours. In this paper, simple method of calculation is developed to predict the SHZ without the requirement of sophisticated computations. A generalized correlation was developed to predict the change of the SHZ with time for different fluids and can sizes.
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paper_title: Heat transfer analysis of canned food sterilization in a still retort

paper_content:

Computational fluid dynamics (CFD) analyses provide insight on the natural convective processes occurring during the sterilization of canned liquid food. The definition and estimation of heat transfer coefficients pertaining to the transient heat transfer occurring in cylindrical food cans is presented. The heat transfer coefficients defined on the basis of absolute mass flow averaged and volume-averaged temperatures are compared. The contributions to the overall heat transfer rate from different surfaces of the uniformly heated cylindrical can are evaluated. The influence of the temperature difference to viscosity ratio on the peculiar Nusselt number trends is discussed. Unified correlations are provided for the Nusselt number as functions of Fourier number, food can aspect ratio and thermal conductivity of the food medium in both the conduction and convection dominated heat transfer regimes.
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paper_title: Fluid dynamic numerical simulation of a gas phase polymerization reactor

paper_content:

This article presents preliminary fluid dynamic simulation results of ethylene polymerization dense fluidized bed using the two-phase flow numerical code ESTET-ASTRID developed by Electricite de France for CFB boilers and based on the two-fluid modelling approach. The continuous phase consists of gas and the dispersed phase consists of catalyst particles. The particle fluctuating motion is modelled using two-separate transport equations, on the particle kinetic energy and the fluid–particle covariance, developed in the frame of kinetic theory of granular medium accounting for particle–particle and fluid–particle interactions. Time-dependent 2D and 3D simulations have been performed for industrial and pilot reactor operating conditions. The numerical predictions are in good qualitative agreement with the observed behaviour in terms of bed height, pressure drop and mean flow organization, such as the down falling of the PE particle layer along the walls. Moreover, these simulations help to provide information about instantaneous and time-averaged solid concentration and velocity fields. Characteristic mechanisms and influence of model closure assumptions on flow predictions are also investigated. Finally, such numerical simulations look very powerful, when validated on exhaustive data collection, to improve design and performance of industrial facilities and to provide insight into the complex physical mechanisms involved. Copyright © 2003 John Wiley & Sons, Ltd.
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paper_title: Effects of mesh refinement, time step size and numerical scheme on the computational modeling of temperature evolution during natural-convection heating

paper_content:

Abstract A computational fluid dynamics (CFD) analysis includes creating geometry, dividing it into elements, discretizing governing equations and solving with suitable numerical schemes. Refining mesh and lowering time step size increase accuracy. However, this may not always give the best result since convergence depends upon parameters of time step size, mesh resolution and numerical scheme. Therefore, the objective of this study was to determine the effects of these on the accuracy of a CFD solution. For this purpose, canning example was used, and results obtained with ANSYS CFX (v12.1.) were experimentally validated. Effects of time step size, mesh resolution and numerical scheme on temperature and velocity field evolution were determined. Mesh refinement affected temperature distribution significantly and surprisingly led to less accuracy. The reasons for this behavior were presented and explained comprehensively.
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paper_title: CFD-aided retail cabinets design

paper_content:

Abstract Food requires strict temperature control throughout the so-called ‘cold-chain’, in which a particular storage temperature is needed for each link. Display cabinets are known to be the weakest link from this point of view and, therefore, particular attention is paid to their design. In this paper, the usefulness of Computational Fluid Dynamics ( cfd ) is illustrated, as a tool for the prediction of the air flow pattern and of food temperature inside the cabinet. The numerical method is described: the airflow pattern and the load temperature are solved in sequence, in order to save computation time. The results of simulations performed both on a vertical and a horizontal cabinet are reported, as an example of the capabilities of the method. The influence of warm air infiltration on the energy balance of the cabinet is investigated and the results are validated by comparison with experimental tests. The applications reported in this paper showed the model to be reliable, and of valuable help to the designer.
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paper_title: The use of CFD to improve the performance of a chilled multi-deck retail display cabinet

paper_content:

Maintaining food temperatures below critical values is the key to maximising the high quality display life of chilled foods. Studies were carried out to see if computational fluid dynamic (CFD) modelling could be used to rapidly identify the changes that would be required to an existing multi-deck display cabinet so that it would meet a higher test specification. Implementing the changes on a Pastorfrigor MV 200TP display cabinet reduced the average power consumption from 1.37 to 1.29 kW as well as significantly reducing the number of test packs which spent any time above 4 °C, from 12 to 1. © 2005 Elsevier Ltd and IIR. All rights reserved.
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paper_title: Mesh quality effects on the accuracy of CFD solutions on unstructured meshes

paper_content:

Abstract The order of accuracy and error magnitude of node- and cell-centered schemes are examined on representative unstructured meshes and flowfield solutions for computational fluid dynamics. Specifically, we investigate the properties of inviscid and viscous flux discretizations for isotropic and highly stretched meshes using the Method of Manufactured Solutions. Grid quality effects are studied by randomly perturbing the base meshes and cataloguing the error convergence as a function of grid size. For isotropic grids, node-centered approaches produce less error than cell-centered approaches. Moreover, a corrected node-centered scheme is shown to maintain third order accuracy for the inviscid terms on arbitrary triangular meshes. In contrast, for stretched meshes, cell-centered schemes are favored, with cell-centered prismatic approaches in particular showing the lowest levels of error. In three dimensions, simple flux integrations on non-planar control volume faces lead to first-order solution errors, while second-order accuracy is recovered by triangulation of the non-planar faces.
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paper_title: Numerical simulation for heat transfer and velocity field characteristics of two-phase flow systems in axially rotating horizontal cans

paper_content:

Abstract Volume of fluid (VOF) element method coupled with a finite volume (FV) discretization technique was used to simulate two-dimensional, transient, two-phase flow patterns (air–water and air–food material) in an axially rotating horizontal can for rotational speeds of 10–160 rpm. Rotational Reynolds number ranged from 1700 to 27200 and 0.88 to 14.1 for water and food phases, respectively. FV solution was performed on a moving mesh system representing the can motion in on-axis axial rotation with respect to an inertial-fixed frame. Since the two-phase flow pattern prediction was an important aspect of modeling fluid mixing and improved heat transfer in canning process, reliable time- and spatially-dependent flow pattern maps were given to identify the rotational effects on two-phase flow characteristics and to determine flow patterns prevailing at different rotational speeds. Single-phase and food-phase flow computations with the corresponding flow patterns were also provided for a direct comparison with air–water results to further determine the physical limitations of the rotational effects. Numerical results demonstrated that two-phase flow patterns were significantly influenced by increasing rotational speeds leading to distinguishable flow patterns in terms of air–liquid (water/food material) interface characteristics and associated headspace air bubble movement through the liquid phase.
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paper_title: Numerical simulation of natural convection heating of canned food by computational fluid dynamics

paper_content:

Abstract Natural convection heating within a can of liquid food during sterilization is simulated by solving the governing equations for continuity, momentum and energy conservation for an axisymmetric case using a commercial Computational Fluid Dynamics (CFD) package ( PHOENICS ). Transient flow patterns and temperature profiles within model liquids (sodium carboxy-methyl cellulose (CMC) and water) have been predicted. The model liquids, CMC and water, were assumed to have constant properties except for the viscosity (temperature dependent) and density (Boussinesq approximation). It has been shown that the action of natural convection forces the slowest heating zone (SHZ) to migrate towards the bottom of the can as expected. The shape and the size of the SHZ area are different for CMC and water. The magnitude of the axial velocity was found to be in the range of 10 −5 –10 −4 m/s for CMS and of 10 −2 –10 −1 m/s for water, these magnitudes of course vary with time and position in the can. The time required for the SHZ to reach the sterilization temperature of 100°C was 1800 s for CMC and only, 150 s for water.
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paper_title: Developing an Effective Method to Determine the Heat Transfer Model in Fish Myofibrillar Protein Paste with Computer Simulation Considering the Phase Transition on Various Dimensions

paper_content:

Abstract Numerical simulation was performed to evaluate thermal patterns of Alaska pollock (AP) surimi paste depending on the dimension and the phase transition of sol to gel during conventional water bath cooking. AP surimi paste (76 and 80 % moisture) was molded into 2, 3.5, and 5 cm cubes and heated at 90 °C. Three simulation models were developed: using average thermal properties in the cooking temperature range from 20 to 90 °C (model A); the thermal properties at the average temperature of each dimension (model B); and the thermal properties including the phase transition region of each dimension (model C). Model A showed a relatively large deviation between the simulation and experiment. Model B reflected the effect of dimension on gelation and showed better fitness (maximum RMSE=5.01 °C). The highest fitness (maximum RMSE=1.67 °C) was observed with model C reflecting both dimension difference and a phase transition.
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paper_title: Direct numerical simulation of turbulent flow over a backward-facing step

paper_content:

Turbulent flow over a backward-facing step is studied by direct numerical solution of the Navier–Stokes equations. The simulation was conducted at a Reynolds number of 5100 based on the step height h and inlet free-stream velocity, and an expansion ratio of 1.20. Temporal behaviour of spanwise-averaged pressure fluctuation contours and reattachment length show evidence of an approximate periodic behaviour of the free shear layer with a Strouhal number of 0.06. The instantaneous velocity fields indicate that the reattachment location varies in the spanwise direction, and oscillates about a mean value of 6.28 h . Statistical results show excellent agreement with experimental data by Jovic & Driver (1994). Of interest are two observations not previously reported for the backward-facing step flow: ( a ) at the relatively low Reynolds number considered, large negative skin friction is seen in the recirculation region; the peak | C f | is about 2.5 times the value measured in experiments at high Reynolds numbers; ( b ) the velocity profiles in the recovery region fall below the universal log-law. The deviation of the velocity profile from the log-law indicates that the turbulent boundary layer is not fully recovered at 20 step heights behind the separation. The budgets of all Reynolds stress components have been computed. The turbulent kinetic energy budget in the recirculation region is similar to that of a turbulent mixing layer. The turbulent transport term makes a significant contribution to the budget and the peak dissipation is about 60% of the peak production. The velocity–pressure gradient correlation and viscous diffusion are negligible in the shear layer, but both are significant in the near-wall region. This trend is seen throughout the recirculation and reattachment region. In the recovery region, the budgets show that effects of the free shear layer are still present.
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paper_title: EXPERIMENTAL COMPARISON OF NATURAL CONVECTION AND CONDUCTION HEAT TRANSFER

paper_content:

Magnitude of fluid motion is significant in convective heat transfer (the faster the fluid motion, the greater the heat transfer), while in conductive heat transfer, there is no physical movement of objects undergoing heat transfer. Due to this statement, it is a real fact that convection can be many times faster than conduction. The objective of this research was to compare natural convection and conduction by creating both heat transfer mechanisms in the same product. For this purpose, canned water and 1% agar-gelled water were used in the experimental and further computational fluid dynamics studies. Experiments were conducted at 70C and in boiling water, and ANSYS V.10 (Ansys Inc., Canonsburg, PA) was used in the numerical simulations. The results showed that addition of agar prevented the natural convection phenomena in the gels resulting in pure conduction while the effect of natural convection, which occurred due to thermal buoyancy effects in the given gravitational force field, was obvious in the case of water. Creation of both natural convection and conduction heat transfer mechanisms in the same medium is an important contribution as the effect of natural convection over the conduction heat transfer can directly be emphasized. ::: ::: ::: ::: PRACTICAL APPLICATIONS ::: ::: Creation of both natural convection and conduction heat transfer mechanisms in the same medium would be an important contribution as the effect of natural convection over the conduction heat transfer can experimentally be emphasized. The results of this study are significant to show the significant difference between these heat transfer modes as both mechanisms were created in the same medium, and these results will be useful especially for teaching heat transfer purposes.
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paper_title: Simulation of heat transfer to a canned corn starch dispersion subjected to axial rotation

paper_content:

Abstract A finite element based simulation software (FIDAP) was used to solve the governing mass, momentum and energy transport equations for heating a 3.5% corn starch dispersion (STD) at 121°C in a 303×406 axially rotating can. A thermorheological model for the STD was incorporated into the program. Results revealed non-uniform temperature distribution with different slowest heating point (SHP) in the can when it was stationary and continuously rotating at 15 and 146 rpm. At 146 rpm, a highly viscous layer of gelatinized starch that formed at the can wall hindered heat transfer in the radial direction resulting in slower heat penetration than at 0 and 15 rpm.
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paper_title: Effects of mesh refinement, time step size and numerical scheme on the computational modeling of temperature evolution during natural-convection heating

paper_content:

Abstract A computational fluid dynamics (CFD) analysis includes creating geometry, dividing it into elements, discretizing governing equations and solving with suitable numerical schemes. Refining mesh and lowering time step size increase accuracy. However, this may not always give the best result since convergence depends upon parameters of time step size, mesh resolution and numerical scheme. Therefore, the objective of this study was to determine the effects of these on the accuracy of a CFD solution. For this purpose, canning example was used, and results obtained with ANSYS CFX (v12.1.) were experimentally validated. Effects of time step size, mesh resolution and numerical scheme on temperature and velocity field evolution were determined. Mesh refinement affected temperature distribution significantly and surprisingly led to less accuracy. The reasons for this behavior were presented and explained comprehensively.
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paper_title: Heat transfer simulation and retort program adjustment for thermal processing of wheat based Haleem in semi-rigid aluminum containers

paper_content:

A mixed computational strategy was used to simulate and optimize the thermal processing of Haleem, an ancient eastern food, in semi-rigid aluminum containers. Average temperature values of the experiments showed no significant difference (α = 0.05) in contrast to the predicted temperatures at the same positions. According to the model, the slowest heating zone was located in geometrical center of the container. The container geometrical center F0 was estimated to be 23.8 min. A 19 min processing time interval decrease in holding time of the treatment was estimated to optimize the heating operation since the preferred F0 of some starch or meat based fluid foods is about 4.8-7.5 min.
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paper_title: INFLUENCE OF THE GEOMETRY ASPECT OF JARS ON THE HEAT TRANSFER AND FLOW PATTERN DURING STERILIZATION OF LIQUID FOODS

paper_content:

Natural convection heating of liquid food packed in glass jars of different sizes and volumes during sterilization is simulated by solving the governing equations for continuity, momentum and energy conservation, using the finite element method. The effect of the aspect ratio of the container on temperature distribution, flow pattern, position of the slowest heating zone (SHZ) and cooking value were analyzed. The position of the SHZ varied ‐ depending of container volume and aspect ratio ‐ in the range of 49.39‐76.83% and 5.81‐19.09% of jar radius and height, respectively. Sterilization times were estimated and differences between 135 and 105 s for containers of a same size of 360 or 660 cm 3 , respectively, were predicted depending on jar shape. A prediction model was developed that allows to calculate ‐ with a simple procedure ‐ sterilization times as a function of container dimensions. PRACTICAL APPLICATIONS It is frequent in low-volume processing plants that work with foods packed in glass jars to change container size and/or shape between successive batches of production, but maintaining the same process schedule. This leads to products with lack of microbial innocuousness (underprocessing) or with low nutritional or sensory quality (overprocessing). In that sense, in this work velocity and temperature profiles, and the location of the “slowest heating zone” were modeled and simulated using the finite element method for liquid foods in glass jars of different volumes and shapes during their thermal treatment. This information allowed estimate sterilization times as well as quality losses during thermal treatment. Finally, a simplified method for the calculation of sterilization times as a function of container size and shape was developed. This method could be very practical for the design of thermal processes in low-volume productions, whose operators usually lack simulation software and personnel trained in process calculations.
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paper_title: Simulation of heat transfer for solid-liquid food mixtures in cans and model validation under pasteurization conditions

paper_content:

Abstract During processing of canned mixtures of solid–liquid foods, conduction and convection occur simultaneously. The literature lacks in a complete simulation study where a large number of solids are dispersed in the liquid phase, e.g. canned peas. Therefore, the objectives of this study were to determine temperature changes inside a can containing solid–liquid food mixtures. For this purpose, dispersed stationary solids (canned peas in water) in a 2D (axi-symmetrical) configuration were applied. Ansys V11 (Ansys Inc., Canonsburg, PA) was used to solve continuity, energy and momentum equations. For experiments, canned pea samples were prepared in 500 g cans, and heating process was conducted in a retort under pasteurization conditions at ≈98 °C. Temperature changes were measured using needle type thermocouples, and simulation results were validated against experimental data. This study is expected to be a significant contribution to the literature for further optimization studies and to form basis of an industrial project to improve canning process of solid–liquid mixtures.
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paper_title: Velocity and Temperature Field Characteristics of Water and Air during Natural Convection Heating in Cans

paper_content:

Presence of headspace during canning is required since an adequate amount allows forming vacuum during the process. Sealing technology may not totally eliminate all entrapped gases, and headspace might affect heat transfer. Not much attention has been given to solve this problem in computational studies, and cans, for example, were mostly assumed to be fully filled with product. Therefore, the objective of this study was to determine velocity and temperature evolution of water and air in cans during heating to evaluate the relevance of headspace in the transport mechanism. For this purpose, canned water samples with a certain headspace were used, and required governing continuity, energy, and momentum equations were solved using a finite volume approach coupled with a volume of fluid element model. Simulation results correlated well with experimental results validating faster heating effects of headspace rather than insulation effects as reported in the literature. The organized velocity motions along the air-water interface were also shown. Practical Application: Canning is a universal and economic method for processing of food products, and presence of adequate headspace is required to form vacuum during sealing of the cans. Since sealing technology may not totally eliminate the entrapped gases, mainly air, headspace might affect heating rates in cans. This study demonstrated the increased heating rates in the presence of headspace in contrast with some studies in the literature. By applying the effect of headspace, required processing time for thermally processed foods can be reduced leading to more rapid processes and lower energy consumptions.
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paper_title: Convective Heat Transfer to Fluid Foods in Cans

paper_content:

Publisher Summary The chapter explains about the convection heating of foods in cans. Canning is the effective means to preserve large part of food supply. Heating characteristics of food products based on conduction and convection are illustrated. Conduction heated products exhibit slower heating rates and longer lag times and convection-heated products exhibit faster heating rates and shorter lag times. Methodologies to study convective heat transfer to foods are explained. The heat transfer rates to liquid foods are influenced by flow conditions such as viscosity, geometry, velocity of flow, and physical and thermal properties of liquid. Flow properties of Non-Newtonian fluids and viscoelastic fluids are also discussed. Heat transfer by natural convection takes place by conduction through a stagnant film of liquid on the inside surface of the can. Various factors affecting heat transfer by forced convection are explained in details. Methods of heat transfer in orbitor retorts, spin cooker, flame sterilization etc. are clearly illustrated. The process of heat transfer by convection in the presence of particulate matter is explained in detail. Heat is first transferred to the fluid and then to the particle. The presence of particulate matter will alter the flow patterns and contribute to the mixing of the can's contents due to their motion. The chapter also emphases the need for experimental studies that are applicable to non-Newtonian foods. It also illustrates the importance of dimensionless correlation in the field of heat transfer.
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paper_title: Developing an Effective Method to Determine the Deviation ofFValue upon the Location of a Still Can during Convection Heating Using CFD and Subzones

paper_content:

A numerical simulation was applied to determine the temperature profiles of water in a can with a diameter of 52.3 mm and a height of 124.0 mm. Cold points at different heating times were determined, and the degree of pasteurization (F value) of each cold point was calculated. Subzones in both vertical and horizontal directions were introduced to determine the deviation of F value upon the location in the can during a convective heating, and the average F value of each subzone was estimated. The slow heating zone (SHZ) was determined by overwrapping the subzones with the lowest average F values in the vertical and horizontal direction. The cold point was continuously moved during the thermal treatment and even at 600 s, the SHZ determined by this subzone method maintained a single zone, unlike the cold points. The relative difference of F value between the SHZ and the cold point was approximately 0.575%. The subzone method is thus an effective way to determine the SHZ and F value, which is an indicator of the sterilization. ::: ::: ::: ::: Practical Applications ::: ::: For safety purposes, estimation of the degree of pasteurization is very important for the liquid food in a can. Determination of the slow heating zone (SHZ) and F value in the can is very difficult because of the convection flow during heating. Many previous studies indicated the importance of determining the SHZ for the liquid food in a can, but there was no clear advice to estimate the degree of pasteurization based on the temperature profile from the SHZ. This study suggested to use the subzones to estimate the SHZ and clearly demonstrate that the degree of pasteurization at the SHZ represented by the area average F value obtained from the subzone is more stable and consistent.
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paper_title: Quantifying Enhancement in Heat Transfer Due to Natural Convection During Canned Food Thermal Sterilization in a Still Retort

paper_content:

Thermal sterilization of canned viscous liquid foods using saturated steam is enabled by natural convective heat transfer. However, the governing equations for two-dimensional convective heat transfer may be only rigorously solved by numerical calculations. On the other hand, if conduction is assumed to be the only mode of heat transfer, the thermal sterilization problem has analytical solutions for simple boundary conditions. However, the conduction model may not be appropriate in describing thermal sterilization of even viscous liquid foods and may cause considerable error in the prediction of the important parameters such as slowest heating zone (SHZ) temperature and lethality. The longer time for sterilization recommended by the conduction model may lead to overprocessing and an unacceptable food product. The objective of this work is to quantify the faster temperature rise in the food can due to natural convection when compared to the temperature rise obtained by only conductive heating. The consequent enhancement in lethalities is also reported. In addition, this work’s objective is to investigate how quickly the natural convective heat transfer effects begin to dominate over the solely conduction heating mode. The volume-averaged temperature as well as the SHZ temperature variations with time was calculated for the convection-augmented mode using computational fluid dynamics (CFD) simulations. Lethality values were then calculated based on volume-averaged temperature as well as the SHZ temperature. Food cans of different aspect ratios and food medium thermal conductivities are considered in this analysis. For the food system investigated, the critical Fourier number at which the transition to convection-augmented mode of heat transfer occurred is identified and explained from scaling considerations. In the conduction-dominated mode, it was possible to use analytical solutions to predict the volume-averaged and SHZ temperatures of the liquid food undergoing thermal sterilization. The Nusselt number correlation developed by Kannan and Gourisankar (2008) was used in the lumped parameter transient heat transfer model to predict the volume-averaged temperatures in the convection-dominated region. The volume-averaged temperatures from this approach were found to be in good agreement with the CFD simulation results. The time predicted for the SHZ to reach the minimum sterilization temperature was significantly lower when convective heating was also considered. The volume-averaged temperature and SHZ temperature enabled an estimation of overall sterility levels attained and minimum sterility levels prevalent inside the can, respectively. Even though the volume-averaged temperature increase due to convection was only about 10 K, the resulting accumulated lethality values were higher by an order of magnitude. The increase in SHZ temperatures was much higher in the convection-augmented mode, and consequently greater integrated lethalities were attained. The simple conduction model that is amenable to analytical solution cannot be used to approximate the heat-transfer-related phenomena even for “quick estimation” purposes when convection effects are significant. This precaution is found necessary even for the reasonably high viscous carboxy methyl cellulose system, whose average viscosity values ranged between 13 and 3 Pa s during the course of the sterilization process.
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paper_title: Evaluation of two-dimensional approach for computational modelling of heat and momentum transfer in liquid containing horizontal cans and experimental validation

paper_content:

Axi-symmetric approach in vertical cans lead to 2-dimensional (2D) model with shorter computational times. For horizontal cans containing liquids, this approach is not possible due to internally evolved natural convection. If an assumption is made to neglect gravitational effect in horizontal direction, it may be possible to use a 2D model. Therefore, the objective of this study was to evaluate this approach numerically and experimentally. In simulations, continuity, energy and momentum equations were solved in 2D and 3D using Ansys CFX 12.1 for horizontal cans containing water and another viscous liquid. In experiments, water filled cans were prepared, and temperature data were compared with simulation results. The results demonstrated the possible use of 2D approach in modelling for liquid containing horizontal cans with significant reduction in computational times. Optimization algorithms of simulation programs are also expected to be used in combination with simulation studies since computation times are reduced significantly.
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paper_title: EXPERIMENTAL COMPARISON OF NATURAL CONVECTION AND CONDUCTION HEAT TRANSFER

paper_content:

Magnitude of fluid motion is significant in convective heat transfer (the faster the fluid motion, the greater the heat transfer), while in conductive heat transfer, there is no physical movement of objects undergoing heat transfer. Due to this statement, it is a real fact that convection can be many times faster than conduction. The objective of this research was to compare natural convection and conduction by creating both heat transfer mechanisms in the same product. For this purpose, canned water and 1% agar-gelled water were used in the experimental and further computational fluid dynamics studies. Experiments were conducted at 70C and in boiling water, and ANSYS V.10 (Ansys Inc., Canonsburg, PA) was used in the numerical simulations. The results showed that addition of agar prevented the natural convection phenomena in the gels resulting in pure conduction while the effect of natural convection, which occurred due to thermal buoyancy effects in the given gravitational force field, was obvious in the case of water. Creation of both natural convection and conduction heat transfer mechanisms in the same medium is an important contribution as the effect of natural convection over the conduction heat transfer can directly be emphasized. ::: ::: ::: ::: PRACTICAL APPLICATIONS ::: ::: Creation of both natural convection and conduction heat transfer mechanisms in the same medium would be an important contribution as the effect of natural convection over the conduction heat transfer can experimentally be emphasized. The results of this study are significant to show the significant difference between these heat transfer modes as both mechanisms were created in the same medium, and these results will be useful especially for teaching heat transfer purposes.
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paper_title: CFD studies on natural convective heating of canned food in conical and cylindrical containers

paper_content:

Enhancing natural convective heat transfer in canned food sterilization is explored through modifications to container geometry and its orientation. A conical geometry, of equal volume and height as that of the cylinder, pointing either vertically up or down was considered. The non-Newtonian fluid, 0.85% w/w sodium carboxy-methyl cellulose (CMC), was taken as the test food material and its laminar flow behavior was investigated using computational fluid dynamics (CFD). The movement of the slowest heating zone (SHZ) temperature was tracked and compared for the three geometries. The SHZ temperature was observed to attain the final sterilization fluid temperature of 100 °C fastest for an upright conical geometry followed by the cylinder and the downward pointing cone. There is scope for enhancing the thermal sterilization process through geometry modifications but without mechanical agitation or rotation. Further, the geometry modification if non-uniform must be complemented by its suitable orientation.
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paper_title: A New Computational Technique For The Estimation Of Sterilization Time In Canned Food

paper_content:

Sterilization of liquid food in cans is complicated by the influence of natural convection currents induced by the hot walls of the can. In order to predict the temperature variation of the slowest heating zone (SHZ) with time, it is necessary to use computational fluid dynamics (CFD) analysis, which can be done with the help of a number of available commercial software. However, the required computational time is usually of the order of hours. In this paper, simple method of calculation is developed to predict the SHZ without the requirement of sophisticated computations. A generalized correlation was developed to predict the change of the SHZ with time for different fluids and can sizes.
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paper_title: Heat transfer simulation and retort program adjustment for thermal processing of wheat based Haleem in semi-rigid aluminum containers

paper_content:

A mixed computational strategy was used to simulate and optimize the thermal processing of Haleem, an ancient eastern food, in semi-rigid aluminum containers. Average temperature values of the experiments showed no significant difference (α = 0.05) in contrast to the predicted temperatures at the same positions. According to the model, the slowest heating zone was located in geometrical center of the container. The container geometrical center F0 was estimated to be 23.8 min. A 19 min processing time interval decrease in holding time of the treatment was estimated to optimize the heating operation since the preferred F0 of some starch or meat based fluid foods is about 4.8-7.5 min.
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paper_title: Numerical simulation of transient temperature and velocity profiles in a horizontal can during sterilization using computational fluid dynamics

paper_content:

Abstract In this work, sterilization of a canned liquid food (carrot–orange soup) in a metal can lying horizontally and heated at 121°C from all sides is simulated for a 3-D geometry. Transient temperature, flow pattern, and shapes of the slowest heating zone (SHZ) during natural convection heating of canned liquid foods are predicted. The partial differential equations describing the conservation of mass, momentum and energy conservation are solved numerically using a commercial computational fluid dynamics (CFD) software (PHOENICS), which is based on a finite-volume method of analysis. The simulation shows the influence of natural convection on the liquid-flow pattern and on the movement of the SHZ. The action of natural convection forces the SHZ to migrate towards the bottom of the can as expected. The SHZ eventually stays in a region that is about 20–25% of the can height from the bottom. The secondary flow formation and its effect on the shape of the SHZ are evident. The results of this work are compared with those for vertical can. It shows faster heating in the vertical can, which is expected due to the enhancement of natural convection caused by its longer height.
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paper_title: Simulation of sterilization of canned liquid food using sucrose degradation as an indicator

paper_content:

Abstract Numerical simulation of natural convection as well as changes of invert sugar concentration during sterilization of canned liquid food using CFX are presented in this study. The invert sugar, which resulted from sucrose inversion, was used as an indicator of thermal deactivation of microorganisms. The effect of surrounding temperature and F 0 calculation methods were also investigated. The simulation was validated with experiment by using a 300 × 407 can fully filled with 20% (w/w) sucrose syrup and subjected to steam at 100 °C. The temperature history, at 3.6 and 5.4 cm from the bottom of the can along the longitudinal axis, showed a good fit against the experimental data with relative deviations of 0.957% and 0.717%, respectively. The relative deviation of the average invert sugar concentration was 0.997%. At a low heating temperature (100 °C), the slowest heating zone did not affect to accumulative F 0 (at 2.0 min). The accumulative F 0 value obtained from the deactivation of spores increased slower than that obtained from the General Method at 100 and 110 °C but a reversed effect was found at 120 °C.
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paper_title: Transient temperature and velocity profiles in a canned non-Newtonian liquid food during sterilization in a still-cook retort

paper_content:

Abstract Natural convection heating of a canned liquid food during sterilization is simulated by solving the governing equations for continuity, momentum and energy conservation for an axisymmetric case, using a finite element code. The model liquid has constant properties except viscosity (temperature dependent and shear thinning) and density (Boussinesq approximation). The velocity field establishes itself much more rapidly than the temperature field. The maximum axial velocity is of the order of 10 −4 m s −1 because of low Grashof number. The coldest point is not fixed but migrates in a region that is 10–12% of the can height from the bottom of the can and at a radial distance approximately one-half of the radius. On the basis of the computed particle path it appears that the liquid initially located just below the top center is exposed to the minimum heat treatment and should be of most concern in the thermal process calculations.
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paper_title: Thermal Sterilisation of Liquid Foods in a Sealed Container - Developing Simple Correlations to Account for Natural Convection

paper_content:

In this study, two approaches to developing simple correlations have been described and analysed. The recent ‘effective thermal diffusivity’ model has been benchmarked and the advantages of the approach illustrated. The ‘uniqueness’ of this kind of approach has been discussed. The second approach, which is new and called the ‘effective velocity’ approach, has been described and tested, against the limited data sets available. It has been demonstrated that by preserving the first order effect (i.e. the convection effect) in the heating equation, the second approach gives an opportunity to correlate with good accuracy the experimental data (whether it is generated by CFD or field measurement). Here the essential features of the natural convection driven process is captured well. The predicted circulation velocity level matches well with the previous CFD simulations for the two dimensional situations, supporting the validity of the approach. More in depth and quantitative study is required before any of these models can be used in practice.
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paper_title: The application of computational fluid dynamics in the food industry

paper_content:

Computational fluid dynamics (CFD) is a numerical technique for the solution of the equations governing the flow of fluids inside a defined flow geometry. CFD has seen applications in many different processing industries, but it is only in recent years that the technique has been applied to food processing applications, including air flow in clean rooms, ovens and chillers; flow of foods in continuous-flow systems; and convection patterns during in-container thermal processing. In this review article, we discuss the current state of play of CFD in the food industry and also the future advances in the technique that will guarantee its use as a tool for food process engineers.
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paper_title: Numerical simulation for heat transfer and velocity field characteristics of two-phase flow systems in axially rotating horizontal cans

paper_content:

Abstract Volume of fluid (VOF) element method coupled with a finite volume (FV) discretization technique was used to simulate two-dimensional, transient, two-phase flow patterns (air–water and air–food material) in an axially rotating horizontal can for rotational speeds of 10–160 rpm. Rotational Reynolds number ranged from 1700 to 27200 and 0.88 to 14.1 for water and food phases, respectively. FV solution was performed on a moving mesh system representing the can motion in on-axis axial rotation with respect to an inertial-fixed frame. Since the two-phase flow pattern prediction was an important aspect of modeling fluid mixing and improved heat transfer in canning process, reliable time- and spatially-dependent flow pattern maps were given to identify the rotational effects on two-phase flow characteristics and to determine flow patterns prevailing at different rotational speeds. Single-phase and food-phase flow computations with the corresponding flow patterns were also provided for a direct comparison with air–water results to further determine the physical limitations of the rotational effects. Numerical results demonstrated that two-phase flow patterns were significantly influenced by increasing rotational speeds leading to distinguishable flow patterns in terms of air–liquid (water/food material) interface characteristics and associated headspace air bubble movement through the liquid phase.
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paper_title: NON‐NEWTONIAN CANNED LIQUID FOOD, UNSTEADY FLUID MECHANICS AND HEAT TRANSFER PREDICTION FOR PASTEURIZATION AND STERILIZATION

paper_content:

Unsteady fluid mechanics and natural convective heat transfer during pasteurization and sterilization for aqueous (CMC solution) and fatty (soybean oil) liquid foods were numerically predicted by means of noncommercial computational program developed in this work. This software is based on the finite volume method and the food simulants are assumed to be non-Newtonian fluids with a temperature-dependent power-law viscosity model. Different cylindrical container materials were analyzed (LDPE, PA, PP, galvanized steel), with h/d equal to 0.53, 1.56 and 3.12. Results obtained show that the time required for sterilization is strongly dependent on the liquid food rheological behavior. A recirculating flow pattern was found inside the cylindrical container for the aqueous food stimulant. The Tshz variation with the dimensionless time was faster heating when the h/d decreases. The fastest heating pasteurization and sterilization processes were obtained for CMC solutions inside cylindrical packages with a pseudoplastic behavior. ::: ::: ::: ::: PRACTICAL APPLICATIONS ::: ::: There is a vast body of literature about transport phenomena of thermal treatment of packaged food. However, this literature is restricted when the analyzed foods show a non-Newtonian behavior. The methodology described in this paper aims to contribute to the understanding of pasteurization and sterilization of packaged non-Newtonian liquid foods through the implementation of a fast and accurate tool for the optimization of the operational parameters in these treatments, as well as in the design of packaging materials. Commercially available computational fluid dynamics is a powerful tool for the analysis of transient heat transfer packages that allow it to simulate almost any geometry or even import it as Computer Aided Design (CFX, FLUENT and others). Also, rheological properties can be introduced by applying user-defined functions. The noncommercial computational program developed in this work allows modifying operation, rheological and design parameters without restrictions. The versatility of these tools can complement experimental studies decreasing the time required to the design of the package and its associated costs. ::: ::: ::: ::: On the other hand, an accurate prediction of the unsteady fluid mechanics and natural convective heat transfer during thermal treatments allows estimating the adequate conditions to preserve the quality of packaged foods, along with reduction in energy consumption, resulting in low contamination.
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paper_title: 3D numerical simulation of asparagus sterilization in a still can using computational fluid dynamics

paper_content:

Abstract The heating and cooling cycles during thermal processing of asparaguses in a still can using Computational Fluid Dynamics (CFD) is the subject of this paper. The CFD code “Fluent®” was used to predict the temperature distribution and the velocity profile in the can. Experiments were run using a metal can containing 1 and 8 asparaguses filled with 4% NaCl brine and immersed in boiling water. Results obtained by CFD for temperature profiles were in good agreement with experimentally determined values. After validation of the model, further simulations were carried out for cans containing 0, 1, 8 and 19 asparaguses and for glass jars containing 19 asparaguses. It was shown that the brine flow depends on the number and spacing of the asparaguses in the can. By increasing the number of asparaguses in the can, the brine velocity increased being higher at the beginning of the heating and cooling phases. The slowest heating zone and the slowest cooling zone are located at a height of about 13.5% of the can height from the bottom and about 13.5% of the can height from the top, respectively, and they are not affected by the number of asparaguses. The final temperature during the heating phase was slightly affected by the number of asparaguses, while the heating rate was affected by the type of the container. Brine velocity did not affect the temperature inside the asparaguses indicating that the main resistance to heat transfer lies inside the asparaguses. The results clearly show that heating of the asparaguses is not uniform but the top of the asparaguses receives higher heat treatment than the bottom since the top of the can is heated faster and is cooled at a slower rate. These results could contribute to the optimization of thermal processing of asparaguses in order to minimize quality losses, such as texture, flavor and nutritional value, while keeping the product safe.
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paper_title: Computational fluid dynamics (CFD) modelling and experimental validation of thermal processing of canned fruit salad in glass jar

paper_content:

Abstract In this paper the heat transfer of a fruit salad during the pasteurization treatment was investigated. The objective of the paper was to develop and validate a computational fluid dynamics (CFD) model for predicting the temperature profiles during the thermal processing of this sample. Samples of a commercial fruit salad, composed of five different fruits with different shapes, sizes and thermal properties, submerged in water/sugar syrup, were submitted to thermal treatments in a pilot plant and temperature profiles at different locations were experimentally recorded. Results showed that the slowest heating point (SHP) was positioned at 19–20% of the can height: fruit closest to the SHP such as pear presented the lowest F value . Moreover, F values resulted to be influenced by the distance from the jar bottom as function of natural convection motion of the syrup. CFD model simulations data were then successfully validated against the experimental ones: results, expressed as RMSE, showed a good fitting between calculated and experimental data, both for syrup (mean RMSE 1.47 °C) and fruit pieces (mean RMSE 1.63 °C). In addition, F values calculated from both experimental and simulated temperatures resulted very similar with only little differences. In conclusion, the proposed approach and mathematical model can thus be usefully applied for the simulation and prediction of thermal processes of canned fruit salad for process design and optimization.
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paper_title: Effect of Particle Orientation during Thermal Processing of Canned Peach Halves: A CFD Simulation

paper_content:

The objective of this work was to apply Computational Fluid Dynamics (CFD) to study the effect of particle orientation on fluid flow, temperature evolution, as well as microbial destruction, during thermal processing of still cans filled with peach halves in sugar syrup. A still metal can with four peach halves in 20% sugar syrup was heated at 100 °C for 20 min and thereafter cooled at 20 °C. Infinite heat transfer coefficient between heating medium and external can wall was considered. Peach halves were orderly placed inside the can with the empty space originally occupied by the kernel facing, in all peaches, either towards the top or the bottom of the can. In a third situation, the can was placed horizontally. Simulations revealed differences on particle temperature profiles, as well as process F values and critical point location, based on their orientation. At their critical points, peach halves with the kernel space facing towards the top of the can heated considerably slower and cooled faster than the peaches having their kernel space facing towards the bottom of the can. The horizontal can case exhibited intermediate cooling but the fastest heating rates and the highest F process values among the three cases examined. The results of this study could be used in designing of thermal processes with optimal product quality.
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paper_title: Numerical Simulation of Natural Convection Heating of Canned Thick Viscous Liquid Food Products

paper_content:

Sterilization of a thick viscous liquid food in a metal can sitting in an upright position and heated from the side wall (Tw= 394 K) only in a still retort was simulated. The liquid had temperature dependent viscosity but constant specific heat and thermal conductivity. Equations of mass, motion and energy conservation for an axisymmetric case were solved and plots of temperature, velocity and streamlines were provided for natural convection heating and isotherms compared with pure conduction contour plots. Results indicated that the natural convection moved the slowest heating point to the bottom center. The bottom of the can heated up slower than predicted by pure conduction heating. The magnitude of the axial velocity was found to be of the order of 10−5 m/sec which varied with time and position in the can.
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paper_title: Using the computational fluid dynamics to analyze the thermal sterilization of solid–liquid food mixture in cans

paper_content:

Abstract Flow pattern, temperature distribution and shapes of the slowest heating zone during heating of solid–liquid food mixture (pineapple slices saturated with its moisture) in a cylindrical can of 84 mm diameter and 82 mm height are predicted. The partial differential equations describing the conservation of mass, momentum and energy are solved numerically using commercial computational fluid dynamics (CFD) software (PHOENICS), which is based on a finite volume method of analysis. Saturated steam at 121 °C is used as a heating medium, where the metal can is heated from all sides. The model liquid is assumed to have constant properties except for the viscosity (temperature dependent) and density (Boussinesq approximation). Two methods of analysis are adopted in the simulation. In one of the methods, the pineapple slices are assumed permeable to natural convection flow in its pores, while in the second method, the pineapple slices are assumed impermeable. The results of the simulations of both cases are very similar. The simulations show, the action of natural convection on the rate of heating, liquid flow pattern and on the shape and movement of the slowest heating zone (SHZ). The SHZ eventually stays in a region that is about 30–35% of the can height from the bottom. Industrial relevance The authors indentified the interesting and obviousely so far neglected topic of natural convection during sterilization heating of solid-liquid food mixtures in containers. The by simulation results obtained suggest that the configuration of the solid in the container can significantly influence the rate of heating. This may also be of significance for other processes such as high hydrostatic pressure treatment or ohmic heating.
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paper_title: Computational Fluid Dynamics Modeling of the Thermal Processing of Canned Pineapple Slices and Titbits

paper_content:

Thermal processing of canned fruits is an important preservation technique used to increase the shelf life of canned foods through the inactivation of spoilage microorganisms and enzymes. The objective of this study was to develop a computational fluid dynamics model to investigate the temperature profiles during the thermal processing of canned pineapple products. Two different kinds of products such as canned pineapple slices and titbits were analyzed to investigate the effect of size reduction of the product on the efficacy of heat transfer during thermal processing. The simulation results were validated with the experimental measurements of temperatures. The temperature profile, slowest heating zone (SHZ), and the effects of natural convection and conduction heating on canned pineapple slices and titbits were studied. In the canned pineapple slices, the SHZ was found to lie inside the pineapple slices. In contrast, for the pineapple titbits, the SHZ was present at the bottom of the can. The pineapple titbits were found to achieve a rapid temperature increase owing to the combined effects of buoyancy-induced natural convection and increased surface area available for higher heat transfer. This finding signifies the retention of the nutritive properties of pineapple by preventing the loss of heat-labile nutrients like vitamins without compromising the commercial sterility of the product.
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paper_title: Analysis of Thermal Processing of Table Olives Using Computational Fluid Dynamics

paper_content:

In the present work, the thermal processing of table olives in brine in a stationary metal can was studied through computational fluid dynamics (CFD). The flow patterns of the brine and the temperature evolution in the olives and brine during the heating and the cooling cycles of the process were calculated using the CFD code. Experimental temperature measurements at 3 points (2 inside model olive particles and 1 at a point in the brine) in a can (with dimensions of 75 mm × 105 mm) filled with 48 olives in 4% (w/v) brine, initially held at 20 °C, heated in water at 100 °C for 10 min, and thereafter cooled in water at about 20 °C for 10 min, validated model predictions. The distribution of temperature and F-values and the location of the slowest heating zone and the critical point within the product, as far as microbial destruction is concerned, were assessed for several cases. For the cases studied, the critical point was located at the interior of the olives at the 2nd, or between the 1st and the 2nd olive row from the bottom of the container, the exact location being affected by olive size, olive arrangement, and geometry of the container. ::: ::: Practical Application ::: ::: The resulting knowledge from the present paper will help in thermal process optimization of table olives which will lead to the production of safe and high-quality product with reduced salt content. In the present paper, only the safety issue, through the determination of the location of the critical point, as far as microbial destruction is concerned, was addressed.
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paper_title: Simulation of heat transfer for solid-liquid food mixtures in cans and model validation under pasteurization conditions

paper_content:

Abstract During processing of canned mixtures of solid–liquid foods, conduction and convection occur simultaneously. The literature lacks in a complete simulation study where a large number of solids are dispersed in the liquid phase, e.g. canned peas. Therefore, the objectives of this study were to determine temperature changes inside a can containing solid–liquid food mixtures. For this purpose, dispersed stationary solids (canned peas in water) in a 2D (axi-symmetrical) configuration were applied. Ansys V11 (Ansys Inc., Canonsburg, PA) was used to solve continuity, energy and momentum equations. For experiments, canned pea samples were prepared in 500 g cans, and heating process was conducted in a retort under pasteurization conditions at ≈98 °C. Temperature changes were measured using needle type thermocouples, and simulation results were validated against experimental data. This study is expected to be a significant contribution to the literature for further optimization studies and to form basis of an industrial project to improve canning process of solid–liquid mixtures.
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paper_title: Theoretical and experimental investigation of the thermal inactivation of Bacillus stearothermophilus in food pouches

paper_content:

Abstract Numerical simulations are used to profile temperature, velocity vector and viable bacteria ( Bacillus stearothermophilus spores) concentration in a three-dimensional pouch filled with beef–vegetable soup during thermal sterilization. The partial differential equations of the continuity, momentum and energy equations are solved numerically, together with an equation defining viable bacteria concentration, based on finite volume method of analysis. Saturated steam at 121°C is used as a heating medium, and the model liquid is assumed to have constant properties except for the viscosity (temperature dependent) and density (Boussinesq approximation). The simulations show clearly the dependency of the concentration of live bacteria on both the temperature distribution and the flow pattern as sterilization proceeds. Experimental measurements are done to validate the bacteria concentration profiles. The experimental measurements are conducted at the Biotechnology Laboratory located at the Chemical and Materials Engineering Department, University of Auckland in New Zealand. The measured concentrations of B. stearothermophilus spores at different periods of heating are compared with those obtained from simulations, showing good agreements.
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paper_title: Theoretical and experimental investigation of the thermal destruction of Vitamin C in food pouches

paper_content:

Abstract In this study, theoretical analysis and experimental measurements for the determination of Vitamin C (ascorbic acid) concentration during thermal sterilization of a three-dimensional pouch filled with carrot-orange soup, are presented. Experimental validation was performed by measuring the concentration of ascorbic acid in the soup, using high performance liquid chromatography (HPLC) and a titration method. Transient temperature, velocity profiles and the shape of the slowest heating zone (SHZ) during heating were also studied. The simulation covered a heating cycle of 3000 s. The computational fluid dynamics (CFD) code PHOENICS was used for this purpose. Saturated steam at a temperature of 121 °C (250 °F) was assumed to be the heating medium, which is the sterilization temperature commonly used in the canning industry. Partial differential equations describing the conservation of mass, momentum and energy were solved numerically, together with the concentration equation for Vitamin C, using a finite volume method. The temperature dependence of the carrot-orange soup's viscosity and density was incorporated in the simulation. The results of the simulations showed that natural convection plays an important role in the heat transfer within the liquid food in the pouch. The SHZ was found to migrate towards the bottom of the pouch into a region within 30–40% of the pouch height, closest to its deepest end. These results also showed that the vitamin profiles depend not only on the temperature distribution, but on the velocity profiles in the pouch. The measured values were compared with those predicted, showing reasonable agreement with an average deviation of 4.5%.
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paper_title: Numerical simulation of transient temperature profiles for canned apple puree in semi-rigid aluminum based packaging during pasteurization

paper_content:

Pasteurization of canned apple puree was simulated for a 3-D geometry in a semi-rigid aluminum based container which was heated from all sides at 378 K. The computational fluid dynamics code Ansys Fluent 14.0 was used and the governing equations for energy, momentum, and continuity were computed using a finite volume method. The food model was assumed to have temperature-dependent properties. To validate the simulation, the apple puree was pasteurized in a water cascading retort. The effect of the mesh structures was studied for the temperature profiles during thermal processing. The experimental temperature in the slowest heating zone in the container was compared with the temperature predicted by the model and the difference was not significant. The study also investigated the impact of head space (water-vapor) on heat transfer.
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paper_title: Heat transfer analysis of canned food sterilization in a still retort

paper_content:

Computational fluid dynamics (CFD) analyses provide insight on the natural convective processes occurring during the sterilization of canned liquid food. The definition and estimation of heat transfer coefficients pertaining to the transient heat transfer occurring in cylindrical food cans is presented. The heat transfer coefficients defined on the basis of absolute mass flow averaged and volume-averaged temperatures are compared. The contributions to the overall heat transfer rate from different surfaces of the uniformly heated cylindrical can are evaluated. The influence of the temperature difference to viscosity ratio on the peculiar Nusselt number trends is discussed. Unified correlations are provided for the Nusselt number as functions of Fourier number, food can aspect ratio and thermal conductivity of the food medium in both the conduction and convection dominated heat transfer regimes.
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paper_title: Computational Fluid Dynamics Modeling of the Thermal Processing of Canned Pineapple Slices and Titbits

paper_content:

Thermal processing of canned fruits is an important preservation technique used to increase the shelf life of canned foods through the inactivation of spoilage microorganisms and enzymes. The objective of this study was to develop a computational fluid dynamics model to investigate the temperature profiles during the thermal processing of canned pineapple products. Two different kinds of products such as canned pineapple slices and titbits were analyzed to investigate the effect of size reduction of the product on the efficacy of heat transfer during thermal processing. The simulation results were validated with the experimental measurements of temperatures. The temperature profile, slowest heating zone (SHZ), and the effects of natural convection and conduction heating on canned pineapple slices and titbits were studied. In the canned pineapple slices, the SHZ was found to lie inside the pineapple slices. In contrast, for the pineapple titbits, the SHZ was present at the bottom of the can. The pineapple titbits were found to achieve a rapid temperature increase owing to the combined effects of buoyancy-induced natural convection and increased surface area available for higher heat transfer. This finding signifies the retention of the nutritive properties of pineapple by preventing the loss of heat-labile nutrients like vitamins without compromising the commercial sterility of the product.
---
paper_title: Heat transfer simulation and retort program adjustment for thermal processing of wheat based Haleem in semi-rigid aluminum containers

paper_content:

A mixed computational strategy was used to simulate and optimize the thermal processing of Haleem, an ancient eastern food, in semi-rigid aluminum containers. Average temperature values of the experiments showed no significant difference (α = 0.05) in contrast to the predicted temperatures at the same positions. According to the model, the slowest heating zone was located in geometrical center of the container. The container geometrical center F0 was estimated to be 23.8 min. A 19 min processing time interval decrease in holding time of the treatment was estimated to optimize the heating operation since the preferred F0 of some starch or meat based fluid foods is about 4.8-7.5 min.
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paper_title: Simulation of sterilization of canned liquid food using sucrose degradation as an indicator

paper_content:

Abstract Numerical simulation of natural convection as well as changes of invert sugar concentration during sterilization of canned liquid food using CFX are presented in this study. The invert sugar, which resulted from sucrose inversion, was used as an indicator of thermal deactivation of microorganisms. The effect of surrounding temperature and F 0 calculation methods were also investigated. The simulation was validated with experiment by using a 300 × 407 can fully filled with 20% (w/w) sucrose syrup and subjected to steam at 100 °C. The temperature history, at 3.6 and 5.4 cm from the bottom of the can along the longitudinal axis, showed a good fit against the experimental data with relative deviations of 0.957% and 0.717%, respectively. The relative deviation of the average invert sugar concentration was 0.997%. At a low heating temperature (100 °C), the slowest heating zone did not affect to accumulative F 0 (at 2.0 min). The accumulative F 0 value obtained from the deactivation of spores increased slower than that obtained from the General Method at 100 and 110 °C but a reversed effect was found at 120 °C.
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paper_title: Application of ultrasound-assisted thermal processing for preservation and quality retention of liquid foods

paper_content:

A continuously working pilot plant–scale prototype was used to evaluate the effects of continuous-flow ultrasound-temperature treatment for bacterial decontamination of model suspensions and various liquid food systems such as milk, fruit, and vegetable juices. Escherichia coli K12 DH 5 α and Lactobacillus acidophilus were used as test microorganisms. In addition, treated juices were investigated for damage caused by heat or ultrasound-induced degradation of sensory and nutritional properties after treatment and storage. Changes in color and destruction of heat-labile and slightly oxidizable l-ascorbic acid content were monitored as an index to measure processing effects. Results were assessed with respect to the total energy requirement and compared with those using a conventional, indirect heating method having similar processing conditions. For the bacteriological process evaluation, the temperature- and time-dependent process lethality was used as the basis; for the quality- and energy-related investi...
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paper_title: Pressure-assisted thermal sterilization effects on gas barrier, morphological, and free volume properties of multilayer EVOH films

paper_content:

Pressure-assisted thermal sterilization (PATS) alters the morphology and free volume distributions of polymers leading to a decrease in gas-barrier properties of polymer packaging materials, and hence compromising the quality and shelf life of PATS processed foods. Two multilayer ethylene–vinyl alcohol (EVOH) films, intended for high pressure applications, were investigated to understand the influence of free volume characteristics and film morphology on gas-barrier properties of PATS processed EVOH films. X-ray diffraction (XRD) and positron annihilation lifetime spectroscopy (PALS) were applied to investigate film morphology and free volume characteristics, respectively. Film A was comprised of polyethylene terephthalate (PET)/EVOH/polypropylene (PP). Film B consisted of PET laminated to a co-extruded structure of PP/tie/Nylon6/EVOH/Nylon6/tie/PP. Both oxygen and water vapor transmission rates increased in the two films after the selected treatments. However, the increase in film A is much larger which can be understood from the change in free volume distributions measured by positron lifetime and overall crystallinity observed from X-ray diffraction. This work shows that PALS and XRD are suitable tools to reason out the gas-barrier changes in multilayer EVOH films after PATS treatment.
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paper_title: Three-Dimensional CFD Simulation of a “Steam Water Spray” Retort Process for Food Vegetable Products

paper_content:

This work aims at simulating a retort sterilization process of flexible packaging, performed in autoclave. ANSYS CFD© software has been used in this study to simulate the heat transfer inside the retort chamber. Flexible packaging filled with a pumpkin soup has been modelled. Three-dimensional (3D) geometrical configuration of the equipment has been designed and then simulated to evaluate the sterilization level achieved by each packaging inside the retort chamber. In particular, the internal temperature of the product situated in the cold spot of the chamber has been monitored during 5 min of the process (after reaching 85°C inside the product) in order to monitor the time/temperature trend. Experimental tests have been finally performed to validate the simulation model of heat exchange. The sterilization process takes place in a retort chamber by means of “overheated water sprayed” at 403 K and a pressure of 5 atm. Results show a good agreement between the simulated results and the real retort process and confirm the potential value of the simulation model to evaluate the process performance.
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Title: Computational Fluid Dynamics (CFD) Modelling and Application for Sterilization of Foods: A Review

Section 1: Introduction
Description 1: This section introduces the significance of thermal processing in the food industry, the challenges in designing thermal processes, and the necessity of using CFD for predicting heat transfer and fluid motion during food sterilization.

Section 2: Thermal Inactivation of Microorganisms
Description 2: This section explains the concept of commercial lethality (F value), the importance of thermal inactivation during sterilization, and how CFD can be used to ensure both food safety and quality.

Section 3: The Governing Equations in Thermal Processing
Description 3: This section discusses the fundamental equations of fluid dynamics, such as the Euler and Navier-Stokes equations, and their application in CFD modelling for thermal processing.

Section 4: Turbulence Modelling
Description 4: This section details different turbulence models used in CFD simulations, the importance of turbulent flow in enhancing heat transfer rates, and the selection of appropriate models depending on application requirements.

Section 5: Constitution of the CFD Model
Description 5: This section covers the importance of model simplifications, meshing strategies, and time-stepping in CFD simulations to ensure accuracy and computational efficiency.

Section 6: Solid and Very Viscous Foods
Description 6: This section describes CFD simulations specifically for solid and very viscous foods, addressing determination of the slowest heating zone (SHZ), headspace effects, and structural changes of food.

Section 7: Liquid Foods
Description 7: This section covers the challenges in identifying the SHZ in liquid foods, the role of natural convection, and the effects of container geometry and orientation on fluid motion and heat transfer.

Section 8: Liquid-Solid Foods
Description 8: This section discusses CFD applications for liquid-solid food mixtures, the combined heat transfer mechanisms, and the impact of solid food presence on SHZ and heating rate.

Section 9: CFD Studies on Microbial Inactivation
Description 9: This section details how CFD is used to evaluate temperature changes at the SHZ, assess microbial inactivation, and predict food quality changes during sterilization.

Section 10: Current Limitations and Future Trends of CFD Modeling in Thermal Processing
Description 10: This section addresses the limitations of current CFD models for industry-scaled applications, the need for improved algorithms, and future trends in combining thermal and non-thermal processing techniques.

Section 11: Conclusions
Description 11: This section summarizes the review's findings, the importance of accurate CFD models for thermal processing, and the need for ongoing research to address current limitations.