viscoelastic and shear-thinning effects of aqueous exopolymer solution on disk and sphere settling - polymer gel powder

by：Demi     2019-09-07
In this study, the xanthan glue was used as an out-of-model polymer to demonstrate non-
Newton properties of natural aquatic systems on Particle sedimentation dynamics.
The visualization method combined with the flow measurement and sedimentation experiment found that the instantaneous velocity fluctuation and the flow pattern formed around the particles were solution viscosity elasticity and shear-
The average settling rate depends on the concentration and particle size of the outer polymer.
Our research shows that under the conditions of consideration,
The shape of the particle is best settled in a vertical position with a negative tail behind it.
Understanding of these processes is essential in technology and engineering, and for improving large-scale-
The scale deposition process in the ocean and the biochemistry cycle, including mineral precipitation, Ocean Snow, microplastics and microbial movement.
Impact of non-liquidity
The research on Particle sedimentation dynamics of Newton fluid has been widely studied in the background of applied science, and the same problem in nature has not received much attention, although the flow of natural waters has a significant impact on the deposition process.
Seawater may show off locally.
Newton nature was proposed in the 1980s s.
Further studies have found that extracellular polymers (EPSs)
, Also known as an external polymer, produced by bacteria and algae, accounting for a considerable part of dissolved organic matter (DOM)
In the ocean, natural waters may become non-local
Newton liquid.
It has been shown that there is a positive correlation between seawater viscosity and marine bacterial community, as well as seawater viscosity and chlorophyll concentration during algae bloom.
Flow analysis showed that EPSs aqueous solution secreted by marine organisms showed elasticity and higher viscosity compared with clear water.
However, recent studies have addressed the effects of increased seawater viscosity on the movement of marine microorganisms, and the effects of dissolved external polymers on the deposition of various particles: minerals, marine snow, larvae, plankton and micro-plastic contaminants, the flow properties of modified natural waters remain untouched research issues.
In order to better understand the sedimentation dynamics of particles at the micro-level, it is necessary to carry out such research
Scale, and better evaluate the particle settling flux, which plays an important role in the biochemical cycle, marine productivity, and climate.
Although interest in external polymers is increasing in industrial applications and process engineering, Particle sedimentation dynamics in external polymer solutions have not been fully resolved.
The above questions are the motivation of this study.
Previous research covered a wide range of non-
Newton fluid includes variable viscosity non-elastic fluid, constant viscosity elastic fluid, variable viscosity elastic fluid, and shows that the flow properties greatly change the settling behavior of particles compared with Newton fluid.
It has been proved that in Africa
Unlike Newton fluid, the fluid at the back of the settling ball may move up to form a negative tail.
A negative wake-up was observed behind the sphere in the polymer solution, glue mass suspension system, and a negative wake-up was also observed in the case of non-bubble rise
Newton fluid.
Some investigations provide various explanations for the physical mechanism of negative wake-up.
Usually, it has been admitted that the elasticity and shear-
Sparse is necessary for the occurrence of negative wake-up.
Otherwise, an extended wake-up of the flow along the direction of the particle motion has been determined.
The negative flow is attributed to the relative tensile stress and shear stress, or to the relationship between the elastic and tensile stress at the back of the sphere.
Through the interaction of two kinds of viscous elasticity, the appearance of extended wake-up and negative wake-up is explained.
The tensile stress downstream of the sphere and the elastic recoil of the lateral shear stress of the tail.
The first is the wake-up responsible for the extension, and the other is to make the fluid inside the wake-up move up.
The extensibility of the polymer chain is the cause of the mutual ratio between the above two types of viscous elasticity, and the prolonged wake-up and negative wake-up occur in the case of high and low scalability, respectively.
This explanation has been approved in other studies.
Terminal settling speed is the basic parameter to describe the motion behavior of particles in stationary fluid under the influence of gravity.
It depends on the size, shape, density and fluid physical properties of the particles.
When gravity is balanced by friction and buoyancy, particles released from rest to Newton fluid accelerate, eventually reaching a stable terminal speed.
Detailed measurements are shown in various non-
The settling speed of Newton liquid did not reach a constant value and showed fluctuations.
Unstable sedimentation has been observed in the suspension system of oh-propylene melon gel, Laponite, glue group solution, fiber suspension system and corn starch suspension system.
The oscillation of velocity is explained by the flow properties of non-fluid
Newton fluid and its internal structure.
There are several working assumptions.
The transient sedimentation in the suspension system of corn starch was explained by the interference mechanism.
The crowded corn starch layer forms around the sphere, hindering the particles.
When the sphere slows down, the layers relax, the resistance decreases, and the particles accelerate again.
The flow instability and the resulting fluctuation of particle settling velocity have been the most widely studied for the Tuan solution.
It was assumed that the short settling of the ball in the glue mass solution was due to the increase of tensile stress and the effect of entanglement of the glue mass network rupture after falling the ball.
The authors used the image analysis method to study the flow around the sphere and associated this instability with the breakdown of the filament studied by the resistance method.
Similar but less accurate explanations were provided earlier.
It is assumed that a wake-up formed behind the particle can act as a rubber band.
After stretching to the limit, the rubber band breaks and the particles accelerate.
Then a new wake-up is formed and the cycle is repeated.
According to another hypothesis, shear
The strip is the physical mechanism of the velocity oscillation of settling particles.
Formation of flow
According to the shear action, the induced structure of the settling of particles in the mass solution is assumed.
Therefore, the effective viscosity and resistance increase and the particles slow down.
The ball accelerates after rest
According to another study, flow curves and creep tests show that shear-
Tie in laponite suspension.
The authors assume that due to the destruction of the internal structure of the solution, a liquid layer of low viscosity is formed near the settling sphere, which results in particle acceleration.
Then the sphere reaches another layer of undisturbed fluid at a higher viscosity and slows down again.
Zhang and Muller use nonshear-
Solution with glue mass to eliminate potential effects of shear
They confirmed that the extended flow only in the tail wave may be the source of fluid instability and fluctuations in settling velocity.
The mechanism that triggered the settling of unstable particles in the glue group solution has not yet been fully determined.
Other effects such as elastic wave effects and sliding effects on the surface of the particles have been pointed out as potential directions for further study.
Low Renault numbers (Re)
Digital system, non
The spherical particles settling in the viscous elastic fluid are significantly different from the orientation in the Newton fluid.
This is due to the viscous effect present in the viscous fluid, as well as the inertia and viscosity acting on particle settling in the Newton fluid.
Elasticity is the cause of normal stress acting on particles.
Normal stress is strongest at two points where there is rapid flow and streamline congestion.
The high pressure of these points acts in the opposite direction on the particles and forms a rotating pair that produces rotation.
The torque generated is often not
Spherical particles perpendicular to the spindle.
In the state of crawling flow (Reu2009u20091, i. e.
Inertia without or negligible), a non-
Spherical particles with fluid dynamic stress centers (e. g. disk)
With the initial orientation of Newton fluid (
Where it was released).
The theoretical analysis presented in hapel and Brenner shows that in this flow state, settlement does not cause rotation, which is the effect of a coupling tensor whose fluid dynamic stress center is equal to zero.
On the contrary
Spherical particles settling in the crawling flow state in a viscous liquid tend to fall at a wide edge parallel to gravity.
Unless the particle is released in a vertical position, the particle rotates to achieve the effect of the stick torque.
When the number of Re is large, I. e.
Inertia is more important, the rotation pair appears at the two stagnation points where high pressure occurs, and the inertia torque is formed, which tends to make the particles at the spindle level turn.
Therefore, a non-
Spherical particles are in a horizontal position in Newton fluid.
Non-terminal direction
The spherical particles settling in a viscous fluid are controlled by the ratio between the inertia torque with the opposite symbol and the viscous elastic torque.
The equilibrium particle orientation depends on the net torque, and depending on the ratio between the viscous and inertial effects, may vary between 0 ° and 90 °.
In this study, we discuss the above aspects of Particle sedimentation behavior to show that
In natural water with dissolved external polymers, the Newton effect can be expected.
The purpose of this study is to evaluate how the flow properties of the external polymer aqueous solution affect the sedimentation dynamics of individual solid particles.
There are three goals for this study :(1)
To evaluate how the flow properties of the solution change with the content of the dissolved outer polymer ,(2)
In order to evaluate the effect of polymer content at home and abroad on particle settling speed and resistance ,(2)
The occurrence and features of the fluctuation of settling velocity are analyzed.
The settling behavior of the particles is quantified and described and potential mechanisms are explained.
The goal was achieved through experimental studies, including the test of the flow measurement of the external polymer solution, and the settlement experiment using visualization and particle tracking methods.
We studied the sedimentation of balls and plates in aqueous solution with different content of xanthan glue (XG)
A commercial external polymer for environmental experimental research as a model for EPSs in natural aquatic systems.
Xanthan glue is water-
Soluble sugar bodies secreted by bacteria.
Thanks to its unique shear properties, it is widely used in the food, pharmaceutical, cosmetic and petroleum industries
Thin and sticky properties.
Xanthan gum is a kind of polymer extracellular Miscellaneous polysaccharide that forms hydrocolloid in water environment.
The XG consists of connected glucose units, which are linked to three-
Sugar side chains located on the trunk.
Details on the structure of the XG are being debated.
In an ordered state, the XG forms a network, which includes aggregates made of polymers connected by hydrogen bonds and entanglement.
In a dilute solution, polymer molecules are separated, and when the concentration increases, they wrap together to amplify the elasticity and shear
Refine the effect.
The polymer belongs to the polyelectrolyte with negative electricity, which is due to the presence of amino groups in the structure.
In deionic water, the polymer has an extended configuration due to the electrostatic interaction between the negative side chains.
Electrostatic drive expansion of polymer in water leads to its larger volume and affects the flow properties of polymer solution.
At higher concentrations, the distance between the expanded particles becomes smaller, which increases the interaction between the polymer and enhances the rigidity of the physically formed weak polymer gel.
We hope that the results presented in this study will not only help us to understand the effects of external polymers in industrial applications, it will also be an inspiration for a deeper study of the influence of external polymers and the flow properties of the dynamic natural waters in the deposition process.
Custom message
Chat Online 编辑模式下无法使用
Chat Online inputting...