Hello and welcome to lecture number 31 of this lecture series on turbo machinery aerodynamics. We have discussed quite a lot on different aspects of turbo machines over the last several lectures. We actually started off with very introductory topics and very fundamentals of the turbo machines starting with thermodynamics and its analysis as applicable to turbo machines. We then moved on to discuss about axial compressors and we had quite a lot of discussion, detailed discussions on axial compressors and the various design aspects of axial compressors and how an analysis, detailed analysis of axial compressors can be carried out. Subsequently, we spent some time on discussion on turbines and we first started off with the axial turbines, the design issues related to axial turbines, performance analysis of axial turbines and so on. What we are going to discuss today is a slightly different topic in the sense that the component that we are talking now about is not really an axial turbo machine. We are going to discuss about centrifugal compressors starting from today's lecture and we will continue with this on two more lectures. We will discuss some details about centrifugal compressors but in contrast to axial compressors, our discussion would be rather superficial in the sense that we will not be really taking up very detailed discussion on the design aspects of centrifugal compressors. The basic reason being that centrifugal compressors are not really widely used in modern day aircraft engines as compared to the axial compressors. They are still used but their usage has been limited to rather smaller sized aero engines and some other applications and that is the reason why we shall not really be discussing too many details about especially to do with design aspects of centrifugal compressors. But of course, we will spend some time discussing about the fundamental issues related to centrifugal compressors, the different aspects of analysis of centrifugal compressors as well as the performance characteristics in quite some detail over the next two or three lectures or so. Of course, we will also be having a tutorial session where we will get a chance to solve some problems associated with centrifugal compressors. So, in today's lecture we will start with the fundamentals, we will talk about the thermodynamics of centrifugal compressors and subsequently we will be discussing about the different elements of centrifugal compressors. What are the different components which constitute a centrifugal compressor and what is the flow characteristic associated with the flow through these different components. So, let us begin our discussion with the thermodynamics of centrifugal compressors. But of course, we will also have a quick introduction to centrifugal compressors as a whole and see what centrifugal compressors are and why is it that these compressors are not really used in that much popularly as compared to the axial compressors. So, there are two distinct aspects of centrifugal compressors as you can see thermodynamics as well as the components of centrifugal compressors. So, it will be very interesting to know that centrifugal compressor in fact, has a longer history than axial compressors. In fact, the earliest jet engines that flew one by Frank Bittel in England and the other by a German engineer named Franz Ohain, both of them developed the jet engine independently and both these initial developments of jet engines used centrifugal compressors. In fact, that continued for a very long time and even the very common aircraft which were used the fighter aircraft which were used during the second world war all of them had in fact, most of them had centrifugal compressors. There are certain inherent advantages with centrifugal compressors, but of course, the disadvantages are also equally substantial and that is the reason why as we look at larger and larger sized aero engines use of centrifugal compressors become rather disadvantages in the sense that centrifugal compressors require a larger frontal area that is probably the most important disadvantage of the centrifugal compressor that the pressure ratio that is developed per stage from a centrifugal compressor very much depends upon the overall diameter of the jet of the centrifugal compressor which means that if you look at a larger sized aero engine which is used in let us say modern day passenger or fighter aircraft they all require the thrust requirement from such an engine is tremendous and to be able to develop such a high level of thrust it is necessary that the compressor develops the corresponding pressure ratio required for developing or generating this kind of a thrust. From a centrifugal compressor if you were to develop such a high level of thrust the frontal area required by such an aircraft of such a compressor would be substantial and obviously, such an engine would also have a huge amount of drag. So, an aero engineer an aircraft airframe engineer would not really want an aero engine with a large frontal area because that is going to increase the overall drag of the aircraft and obviously, that is not a good idea. And so if you compare this with an axial compressor to develop the same pressure ratio an axial compressor requires a smaller frontal area, but of course, axial compressor requires multiple stages to develop the same pressure ratio. Centrifugal compressors can generate far higher pressure ratio per stage as compared to axial compressor and that is of course, one advantage huge advantage of centrifugal compressor that they can generate a large much larger pressure ratio per stage than an axial compressor. We will of course, be exploring the reasons for this and little later when I will explain thermodynamics of centrifugal compressor. We will see that centrifugal compressors have a slightly different mechanism of pressure rise than axial compressor and that is the reason why they can generate much higher pressure ratios per stage. Yet there is yet another difference or disadvantage so to say between centrifugal and axial compressor. For larger sized engines axial compressors have slightly higher or better efficiencies than centrifugal compressor and that is of course, if you look at an aero engine perspective the efficiency is of at most importance and even a slight improvement in efficiency means a big deal in terms of the overall engine performance and therefore, that is where axial compressor scores yet again over centrifugal compressor and these are primarily the two reasons why centrifugal compressors are not really used in larger sized aero engines. They are used very much in smaller sized engines because for smaller engines axial compressors in fact, have a certain disadvantage because as you reduce the engine overall diameter to smaller and smaller levels the losses associated with tip clearance and so on increase substantially and therefore, in fact for smaller sized engines centrifugal compressors may have performance or efficiencies as high or in fact, even better than axial compressors and so for smaller engines it is a common practice to use centrifugal compressors and therefore, smaller sized engines which are used in let us say business jet or smaller airplane they still have engines which have centrifugal compressors. So, to sum up centrifugal compressors obviously can generate much higher pressure ratios per stage they obviously, have larger frontal area and therefore, they are not as commonly used as axial compressors and of course, they are little less efficient and centrifugal compressors are used in auxiliary power units the APUs of many aircraft. Some aircraft also have centrifugal compressors as part of the air conditioning system which is used in the aircraft and in some engines centrifugal compressors are used in combination with an axial compressor that is centrifugal compressor would form the last stage of a set of axial compressor stages and such engines are also quite popularly used which are of course, the medium or smaller sized engines. Some examples being the T 700 from G P T 6 from Pratt & Whitney or the Honeywell T 53 engines. So, these are some engines which have centrifugal compressors which are used in combination with an axial compressor and the inherent advantage here is that one axial compressor can replace multiple centrifugal compressor stages because it is possible to generate a higher pressure ratio per stage by from an axial from a centrifugal compressor as compared to axial compressors and that is why having a centrifugal compressor as the last stage would actually replace several axial compressor stages and that is a big advantage because it leads to lot of saving possible savings in weight and part count and so on. So, there are some advantages of trying to do that kind of a configuration. So, let us now take a look at some typical centrifugal compressor rotors. So, I have here two different types of rotors. The one you see on the left hand side is a so called classical centrifugal compressor rotor which has a straight radial blade you can see this is the impeller of the centrifugal compressor and you can see that these blades are radial and straight and of course, there is a bend here at what is known as an inducer we will discuss little more details about this later on. So, an inducer actually turns an axial flow and guides it into the impeller and makes the flow radial. On the right hand side you can see the rotor of a centrifugal compressor which is much more complicated than what you see on the left hand side and this is a rather recent development and you can see that these blades are much more complicated than what you see in a conventional centrifugal compressor rotor and you can also see that at the exit of the impeller these are the diffuser veins of course, that is not really shown here these also would have diffuser veins. So, these are the veins of the diffuser and of course, we will discuss more details on why a diffuser is used in a centrifugal compressor. So, having understood or at least taken look at two different classes of centrifugal compressor rotor let us take a look at the schematic and understand what constitutes a centrifugal compressor. So, there are primarily three distinct components in centrifugal in a typical centrifugal compressor it has an inlet and followed by a rotor which is also referred to as an impeller in a centrifugal compressor and the impeller exhausts or discharges the flow into what is known as a diffuser. And from the diffuser there is a collector or a volute which guides the flow towards the outlet. So, the flow enters the impeller in an axial direction and then the impeller deflects the flow and turns it into a radial flow and this radial flow exits or exhaust the rotor exhaust the compressor through the collector or volute. And most of the impellers also have what are known as inducers. Inducers basically guide an axial flow and allow the flow to enter the impeller smoothly. The absence of inducer as we will see later the flow can actually say there is a tendency for the flow to separate from the impeller wings if one does not have an inducer. So, inducer is sort of like an inlet guide wing that we have seen in the case of an axial compressor. So, there are there is a there is a set of stationary components as well as one rotating component in a centrifugal compressor. The impeller forms the rotating component of the rotor of a centrifugal compressor. The inlet and the diffusers are the stationary components of the stator of a centrifugal compressor. So, once we have and so as now that we have as understood the working or basically the components or constituents of a centrifugal compressor. Let us now try to understand the operation of a centrifugal compressor from a little more fundamental sense from a thermodynamics perspective. We will try to understand what really happens as the flow passes through these different components of a centrifugal compressor. Now, I had shown the there are three distinct components which I had marked as 1, 2 and 3. Let us take a look at them once again. One is here being referred to as the inlet of the centrifugal compressor. Two is the diffuser and three is the exit of the diffuser or the volute or collector of the centrifugal compressor. Now, on a T s diagram this is temperature entropy diagram. You can see that of course, it looks quite complicated here. Let us try to understand what are what is basically being implied by these set of constant pressure lines that are shown here. So, station one as we have seen is this inlet of the compressor to corresponds to the diffuser and three is for the exit of the diffuser or the volute. So, there are static pressure lines as well as the corresponding total pressure lines which have been shown. Energy is added as you know in the impeller and so, the stagnation pressure rise takes place between 0 1 and 0 2 between stations P 0 1 and P 0 2 and in the volute there is a stagnation pressure loss. That is why you can see that there is a certain amount of loss which is being associated here because of the loss of stagnation pressure in the volute. Now, from station one static pressure rises between station one P 1 to P 0 1 and this is the corresponding stagnation parameter C 1 square by 2 C P. So, T 1 plus C 1 T 0 1 is T 1 plus C 1 square by 2 C P. There is no change in stagnation temperature between station two and three because there is no energy added after the impeller. So, energy is added between station one and two and that is why we see a change in stagnation temperature from T 0 1 to T 0 2 because that is where the energy is added. And actual process they are shown in two different lines here. There is a thicker one which is showing the process between 0 1 and 0 2 and there is another line which is showing the process between 0 2 and 0 1 to 0 3. So, it is possible of course, that in some centrifugal compressor there may not be a vaneless diffusion could be one may not really have this vaneless space between the inducer impeller exit and the diffuser and that is why these two distinct lines have been shown. But of course, they both lead to the same stagnation temperature there is no change in stagnation temperature here. If you want to look at the losses which are incurred in a centrifugal compressor then the total losses as shown here is between the stagnation temperature which it would normally achieve minus the stagnation temperature that it should have achieved if the process was isentropic. So, this is corresponding to the process if the whole process were to be isentropic and in which case there are of course, no losses taking place. And so the corresponding dynamic parameters are also shown here between station for let us say station 3 between P 3 and P 0 3. We have C 3 square by 2 C p and C 2 square by 2 C p between which basically takes the temperature from D 2 to T 0 2. So, if you look at if you compare this with the temperature entropy diagram that we had discussed for an axial compressor you will see you can quickly figure out the similarities between both these compressor operation at least in a thermodynamic sense. Even in an axial compressor we have seen that energy is added in the rotor and you may actually have a total pressure loss taking place in the stator. Even though static pressure continues to rise in the stator one may have total pressure loss taking place because of frictional effects. So, they are quite similar in the sense that in the case of centrifugal compressors also we have an impeller or the rotor where energy is added and that is followed by a diffuser where there is obviously no more energy addition taking place. One may have one continues to have a static pressure rise which is why P 3 is actually greater than P 2, but there could be some amount of total pressure loss taking place in the diffuser due to frictional losses and that is why we have P 0 3 which is less than P 0 2. So what we will do next is to look at the working of the centrifugal compressor as well as trying to estimate the work done or work required for driving a centrifugal compressor rotor and we will relate that to the velocity components very similar to the analysis we have done for an axial compressor as well. We will try to relate the work done or work required for driving the compressor to the velocity components because it would be easy for us to construct the velocity triangles and develop and calculate the work done or work required for a centrifugal compressor. So, let us look at the governing equations for centrifugal compressor stage. Now, in a centrifugal compressor rotor the torque required for or torque applied on the fluid by the rotor is a function of the mass flow rate of course and components of the tangential velocity. So, here we have torque required is equal to m dot into r times C w at station 2 minus r times C w at station 1 and so here the stations 1 and 2 are denoting compressor inlet and outlet respectively. Unlike an axial compressor where the those hardly any change in these tangential velocities between for a given station here what we will see little later as well that even the blade speed is not really a constant because the flow is radial the blade speed also changes with every radial location and so we have mass flow rate m dot times the r the velocity component tangential velocity C w at station 2 minus r times C w at station 1. So, the total work done per unit mass is w is basically a function of the rotational speed omega times the torque divided by the mass flow rate. This is in turn equal to omega times r times C w at station 2 minus r times C w at station 1. So, if you multiply omega times r we get the blade speed u therefore, work is equal to u times C w at station 2 minus u at u times C w at station 1. And so in axial compressors we had actually written this as u times delta C w because u at inlet and exit of the compressor was assumed to be the same here it does not remain the same and it changes with because the flow is indeed radial. Now, if you now look at the energy equation the steady flow energy equation and compare that with what we have written here for a centrifugal compressor rotor we have work is equal to the change in enthalpy stagnation enthalpy h 0 2 minus h 0 1. This is equal to the static conditions and the dynamic conditions. So, h 2 minus h 1 plus C 2 square by 2 minus C 1 square by 2. We have already calculated the change in enthalpy stagnation enthalpy in the previous equation here. So, if you substitute that here we have h 2 minus h 1 is equal to w minus this velocity changes where w has already been calculated as shown here. So, h 2 minus h 1 change in static enthalpy is equal to u times C w at station 2 minus u times C w at station 1 minus C 2 square by 2 plus C 1 square by 2. Where C 1 and C 2 are the absolute velocities entering the rotor entering the compressor and leaving the compressor respectively. Now, if you look at the impeller for example, let us take a look at the schematic of an impeller and we have an impeller inlet tip radius as shown here as r 1 and impeller outlet radius as r 2 and the corresponding blade speeds would be u 1 at this location and u 2 at the exit of the impeller. The velocity components for an impeller then the above equation which we have written earlier that is h 2 minus h 1 is the difference of u times C w at station 2 minus u C w at station 1 and the velocity components that gets transformed into h 2 minus h 1 is u 2 square by 2 minus u 1 square by 2 minus the relative velocities v 2 square by 2 minus v 1 square by 2. So, this in differential form we can write as d h is equal to d into omega square r square by 2 minus d into v square by 2. Now, if you recollect the basic thermodynamics the T d s equations T d s is also equal to d h minus d p by rho and therefore, we have on the left hand side d h we shall replace by d p by rho for an isentropic process T d s is 0. So, d p by rho is equal to d into omega square r square by 2 minus d v square by 2 minus T d s which for an isentropic flow becomes 0. Therefore, d p by rho is d into omega square r square by 2 minus d into v square by 2. So, what we have just now written down is an expression which relates the pressure change in pressure across a compressor to do two distinct parameters or terms. One is proportional to the rotational speed and the radius or radial location and the other is proportional to the change in relative velocity. Now, this is a generalized form of an equation that I have written down which also could be extended to an axial compressor in which case we have assumed that there is no change in the axial well the radial location for a given analysis. So, if you take up one radial plane then there is no change the d omega square r square term becomes basically 0 for an axial compressor which means that the pressure rise would now be equal to minus d v square by 2 for an axial compressor that is the pressure rise in an axial compressor is proportional to the amount of deceleration taking place in the compressor in the relative velocity in terms of the relative velocity. But in a in a centrifugal compressor as we have just seen the pressure rise is a function of one additional parameter which is d of omega square r square by 2 that is even if there is no deceleration taking place in a centrifugal compressor rotor which means that if the second term is equal to 0 one can still attain a certain amount of pressure rise simply because of the first term that is d omega square r square by 2 that is it is possible to achieve pressure rise in a centrifugal compressor even if there is no deceleration taking place which means that centrifugal compressors ideally should not be affected by boundary layer flows because we are saying that even if there is no deceleration taking place one can still achieve pressure rise because of the centrifugal effect and that is why it is called a centrifugal compressor. But most of the modern centrifugal compressors also have a certain amount of deceleration taking place that is pressure rise also because of deceleration or diffusion as well as because of displacement of the centrifugal flow field. So, there is a component of both in a centrifugal compressor and which is why even centrifugal compressors are indeed affected by boundary layer flows and that is not possible to eliminate the boundary layer effects all together even in a centrifugal compressor. But of course, it is possible to achieve much higher pressure ratios per stage in a centrifugal compressor as compared to an axial compressor. So, in an axial compressor where we can assume we have assumed the d r that is change in the radius is equal to 0 the equation that we have written here d p by rho is d omega square r square by 2 minus d v square by 2 will simply reduce to d p by rho as minus d v square by 2 that is in an axial compressor rotor the pressure rise can be obtained only by decelerating the flow. In a centrifugal compressor the first term is basically greater than 0 because omega square r square by 2 change of that is always greater than 0. Therefore, pressure rise can be obtained even without any change in relative velocity and which means that it is possible to have a rotor which does not have any deceleration and still develops a certain amount of pressure. But most of the modern compressors as I mentioned do have deceleration and also this means that centrifugal compressors are indeed affected by flow separation, but not to the extent that axial compressors are and therefore, it is possible to achieve much higher pressure ratio per stage from a centrifugal compressor as compared to axial compressors. Now, that is one set of governing equation that we have just discussed there is one more aspect of centrifugal compressor which is also true with some of these radial flow machines we shall discuss about what that equation of conservation is and that is also valid for a centrifugal compressor. So, this is to do with what is known as Rothalpy. Now, if you let us say assume a steady viscous flow without any heat transfer then in a radial flow scenario we have this particular conservation equation which is also valid for these radial flow machines that is h 1 plus c 1 square by 2 minus u 1 c w 1 is equal to h 2 plus c 2 square by 2 minus u 2 c w that is h plus c square by 2 minus delta u c w it is basically conserved parameter in a centrifugal compressor or even in any other radial flow machines. So, this is usually denoted by symbol I and this is known as the rotational lengthal p or Rothalpy for short it is called rotational lengthal p because it combines enthalpy in the conventional sense that is h plus c square by 2 and the component which is associated with u times c w which is to do with the tangential velocity and therefore, it has been observed that this parameter generally is conserved as it as the flow takes place through an impeller and any change in Rothalpy in some cases one does see that there is a change in in Rothalpy is primarily because of fluid friction which is acting on the stationary shroud. So, that is if you consider the impeller plus this shroud there could be certain amount of losses taking place as a result of this shroud and that probably would explain the amount of loss in Rothalpy which might be observed in some analysis. But in general in radial flow machines Rothalpy is a conserved quantity. So, in centrifugal compressors also in most of the analysis conservation of Rothalpy is assumed to be satisfied as the flow takes place through the impeller. So, having understood some of the fundamental governing equations of centrifugal compressor let us now look at the different components of centrifugal compressor and also look at how the flow develops as it passes through these different components. So, we will be discussing about three distinct components one is the impeller second is the inducer which is also a part of the impeller. In fact, and the third is the diffuser which is the other stationary component of the stator in a centrifugal compressor. So, let us begin with the impeller which is the rotor of a centrifugal compressor and the most crucial component in a centrifugal compressor. So, impeller is the component which draws the working fluid and it is like the rotor as we have discussed for an axial compressor. And impeller has diverging passages which diffuses the flow to a lower static pressure and higher static pressure and lower relative velocities and there are different ways or different configurations of an impeller it could be either single sided or double sided shrouded or unshrouded and so on. Now, in impeller the working fluid besides deceleration it will also experience centripetal forces because of the rotation itself and displacement of the rotational of the fluid elements. And therefore, besides the fact that the flow decelerates and diffuses there is also a certain amount of centripetal force acting on the fluid elements as it passes through an impeller. Now, there are three different types of impellers or impeller blades that are possible. Now, the simplest type is the straight radial type or one might have forward leaning blades or backward leaning blades. Now, forward leaning blades are considered to be inherently in unstable and we will see the reason for its instability probably in the next class where we will be talking about performance analysis or performance characteristics of centrifugal compressors. So, we will see the reason for why forward leaning blades are not really used that is probably something which I will be explaining in next class. The two other configurations which are commonly used are the straight radial blades and the backward leaning blades. So, both these configurations are commonly used in most modern day compressors centrifugal compressors. So, straight radial backward leaning and forward leaning blades. Let us take a look at what these three different blading configurations are. We will start with the straight radial first. So, this the one that is shown in the center is a typical straight radial blade. This is the direction of rotation and this is the velocity triangle of the flow as it leaves the impeller. So, V 2 is the relative velocity leaving the impeller, C 2 is the absolute velocity and U 2 corresponds to the blade speed at the tip of the impeller. So, as you can see the flow leaves the blade radially that is V 2 is indeed radial that is why it is called a straight radial blade. If you look at the forward leaning blade, V 2 leaves the blade tangentially that is why V 2 is at a certain angle to the impeller vanes at the exit and it leaves at an angle of beta 2 which is negative. So, forward leaning blades have a negative blade angle or beta and the velocity triangle is what you see here C 2 and U 2. Backward leaning blades on the other hand have a positive beta 2 and so you have V 2 in this direction and which has a positive blade angle beta 2 and C 2 is the absolute angle and U 2 is the blade speed at the tip. So, these are the three different configurations of impellers which are possible and the two of them as I mentioned straight radial and backward leaning are the ones which are commonly used. Of course, the straight radial blades are have conventionally been commonly used because it is simpler to construct as well as the fact that the blades do not have to undergo a lot of stress because as you bend the blades the stress on the blades becomes substantial, but modern day design hand materials permit us to use these complicated shapes as well. In fact, some of the blades have a combination of straight radial and backward leaning geometry. So, there are blades which have a combination of backward and straight radial as well. So, that is about the impeller where which is probably the more crucial component of a centrifugal compressor and we have seen the velocity triangle corresponding to these three different configurations of a centrifugal compressor impeller. Now, there is another component which is usually part of the impeller itself. We have already seen that in the pictures I had shown in the earlier probably the third slide in today's class where the initial part of the impeller as you have probably have noticed is bent. So, there is a curvature given to the initial part of the impeller and that is known as an inducer and an inducer is basically a component which is just ahead of the impeller or in fact, it is almost always initial part of the impeller itself. The basic function of an inducer is to guide the flow smoothly into the impeller. In the absence of any inducer when the impeller is rotating there is a relative component at the impeller inlet and in the absence of inducer the relative velocity enters the impeller at a certain angle and there could be flow separation taking place from the impeller veins. To avoid that one uses set of blades which are like guide veins and these are known as inducers. So, inducer is the inlet impeller entrance section where the tangential motion of the fluid is basically changed to the radial direction and one may have either acceleration or some amount of acceleration within the inducer as we will see later. Inducer the basic function of an inducer is to ensure that the flow enters the impeller smoothly. Without inducers the flow operation is likely to suffer from flow separation and high levels of noise because of flow separating from the impeller. So, this is a schematic of an inducer and there are two views of the inducer shown. So, the initial part of the impeller as you can see this part of the impeller is the inducer and if you take a cross section of the inducer one would see veins like what is shown here. So, the inlet velocity triangle of an impeller would look something like this that the flow assuming that the flow is coming at an axial in an axial direction C 1 and because of the inducer the relative velocity is v 1 and this is at an angle of beta 1. So, this is the inlet blade speed which is u 1 and the flow leaving the inducer could be at a velocity of v 1 prime let us say at the tip of the inducer. So, that is why it is called v 1 denoted by v 1 prime with a subscript t which corresponds to the tip of the inducer. Now, if you look at the velocity triangles you can see that since the blade speed changes all the way from hub to the tip the velocity triangle and the angles at the hub beta h beta mean and beta tip they are quite different that is because of the fact that the velocity triangle the blade speed continuously changes from the hub to tip. And therefore, if you take the velocity triangles at the hub the mean and the tip velocity triangles are different because of the fact that the blade angles are changing which means that there is a certain twist to the inducer itself as it as we look at the inducer from the hub and trace it all the way to the tip. So, there could be a certain amount of twist now from the velocity triangles we have seen that the velocity leaving the inducer, relative velocity leaving the inducer could be is denoted by v prime t. And therefore, v prime t is a component it is related to the inlet relative velocity through the blade angle.  And that means that there is a certain amount of diffusion also taking place in the inducer. And similarly, the Mach number is related to the inlet Mach number through the blade angle beta 1. Now, the third component that we will be discussing is the diffuser. So, we have seen the impeller the inducer and now we will talk about the diffuser. Now, diffuser is has a function very similar to that of a stator of an axial compressor that is the deceleration which was taking place in the impeller continues. And that continues in the diffuser where the flow is further decelerated. Of course, there is neither energy addition or of course, there is certain amount of pressure loss that is as I mentioned total pressure loss taking place in the diffuser vanes, but there is static pressure rise continuously taking place in the diffuser as well. So, the flow leaving the impeller is at a very high speed and so one can convert part of that kinetic energy into pressure rise of static pressure and that is basically through the diffuser. And there are different types of diffusers which have been used in different types of applications and there are vaned types diffusers and vaneless types pipe diffusers and channel diffusers and so on. So, we will discuss some of these aspects and different types of diffusers in the next few slides. So, the high velocity that is of the flow leaving the impeller is basically decelerated using a diffuser. And the diffuser basically decelerates the flow and thereby reduces the absolute velocity of the working fluid and how much deceleration takes place depends upon firstly the application for which the compressor is being used as well as the efficiency of the diffusion process itself. And since the diffusion is as we have discussed many times before is a process wherein the flow tries to encounter an adverse pressure gradient, the chances of the risk of flow separation is always there when the flow encounters an adverse pressure gradient. And therefore, the amount of diffusion that one can achieve in a stationary component like a diffuser will depend upon how much the flow can withstand the pressure gradients. Therefore, the diffuser flow is kind of always affected by or limited by the fact that there could be chances of flow separation taking place. And so, the flow basically leaves from the impeller in a radial direction and then there is a certain space or gap between the impeller exit and the diffuser beginning and that is called the vaneless space. And actually the diffuser as we will see little later that diffusion continues even in the vaneless space and after that the flow enters the diffuser or the vaned space and diffusion continues even further in the vaned space. So, the fluid which leaves the impeller, it leaves the impeller radially outward and then it passes through a vaneless region and subsequently through a vaned diffuser. Now, there are different types of diffusers as I mentioned, vaned type diffusers, vaneless type diffusers. These are diffusers which are conventionally being used and if you look at compressors, centrifugal compressors which have applications in aero engines, these conventional types of diffusers may not really serve the purpose, one needs to employ better diffusion mechanisms of the flow exiting the impeller. So, in aero engine centrifugal compressors one might encounter diffusers which are known as pipe diffusers or channel diffusers which are much more efficient and more amenable to integration with the combustion chambers. For example, if you have can type combustion chambers then it is easy for distributing the flow from these pipe diffusers and directing them towards these can type of combustors. So, these type of diffusers which are used in aero engines are normally not the vaned type diffusers which are used in other applications, diffusers used in aero engines are usually the pipe type of diffusers. We will do now a very simple analysis of the flow through a diffuser, we will restrict our discussion to diffuser the vane type of diffuser because it is much more simpler to in understanding and analysis and we will restrict our discussion to these conventional type of vane diffusers. So, this is the impeller vane and the flow exiting the impeller first enters into a certain region known as the vaneless space and then it is guided out of the compressor into the volute through the diffuser vanes. So, as the flow leaves the impeller it basically leaves the impeller with a radial velocity and this is the radial direction as you can see and so the absolute velocity that actually leaves the impeller is at an angle of c absolute velocity c and so as the flow leaves the impeller and it moves towards the vane diffuser because of the velocity triangle as you see here the flow actually follows what is known as a logarithmic spiral because of the fact that the flow leaves the impeller in a radial direction and then it suddenly encounters a vaneless space. So, if you consider an incompressible let us for the moment consider an incompressible flow in the vane less region which has a constant axial width the mass flow through the incompress through the vane less space let us represent that by m dot. So, from the continuity equation we have m dot is equal to rho times the annular area that is 2 pi r h where h is the width of the vane less space times the radial velocity c r. So, this is equal to a constant. Now, from the conservation of angular momentum we also know that r times c w is also a constant. Therefore, this means that this ratio c w by c r is also a constant that is velocity ratio the tangential velocity to the radial velocity as we have seen in the velocity triangle this is also a equal to a constant and the angle is given by tan alpha. So, here the angle alpha is basically the angle between the velocity and the radial direction the absolute velocity leaving the impeller to the radial direction. So, this means that this velocity is basically inversely proportional to radius and. So, as we increase the radius the velocity would kind of reduce. So, in the vane less space we have velocity which is inversely proportional to radius and therefore, with increase in the radius the velocity absolute velocity actually reduces which means that there is diffusion taking place even in the vane less space and once the flow leaves the vane less space and enters the diffuser vanes since the flow is guided through a diffusing passage which has an increasing area in the radial direction the flow continues to decelerate and there is further static pressure rise taking place even in the vane section of the diffuser. So, what we can see here is the fact that the vane less space also contributes to the diffusion overall diffusion process which begins right from the inducer as we have seen that diffusion also takes place in the inducer vanes it continues in the impeller. Of course, in the impeller there is another mechanism which contributes towards the pressure rise which is the centripetal forces which are coming there. Once the flow leaves the impeller and enters the vane less space the flow continues deceleration and that is because the velocity is inversely proportional to r and it follows a logarithmic spiral. From there from the vane less space the flow enters the vane diffuser space where the flow is further decelerated and the flow exiting the diffuser vanes then goes into the volute or the collector and then it is exhausted from the centrifugal compressor. So, this is the overall working of a centrifugal compressor. So, what I will do is quickly take a recap of what we had discussed in today's class we had discussed about two distinct aspects of centrifugal compressors. We started off our discussion today with the thermodynamics of a centrifugal compressor where we had looked at how diffusion is indeed achieved in a centrifugal compressor from a thermodynamics perspective in terms of temperature and entropy. We have seen that in a centrifugal compressor energy is actually added in the impeller where we have an increase in the stagnation temperature which also contributes to which also gets converted into the stagnation pressure rise taking place in the centrifugal compressor. After the impeller we have the vane less space and the diffuser where there is no energy addition taking place, but static pressure rise continues to take place through these components as well. So, after the temperature entropy diagram we also wrote down the governing equations for centrifugal compressor and how one can analyze the flow through a centrifugal compressor. After this we took up the individual components of a centrifugal compressor and how one can analyze the flow through these different components. We have seen that in impeller there are different configurations of an impeller, the straight radial, the backward face backward leaning blades and the forward leaning blades. I made a passing remark that forward leaning blades are unstable. We will discuss details of that in the next class where we take up the instabilities in centrifugal compressor and then we discussed about the flow through an impeller and the velocity triangles at the inlet of an impeller as well as the flow exits the impeller and how the velocity triangle gets modified as we change the configuration of the impeller from straight radial to backward leaning blades. We then discussed about inducer and the flow analysis of the as the flow passes through the inducer we have seen that it undergoes a deceleration and as the flow leaves the impeller it enters into a vaneless space. Diffusion continues in the vaneless space as well as in the diffuser or the vaned space which follows the vaneless space. So, this was in a nutshell about what we had discussed in the various slides we had for discussion today and we will continue with discussion of different aspects of centrifugal compressors in the next class as well. We will take up an important aspect of centrifugal compressors that is to do with Coriolis acceleration first and then we will define what is known as the slip factor associated with the centrifugal compressor. After that we will take up the performance characteristics of centrifugal compressors and we will also talk about details regarding stall, surge and choking associated with centrifugal compressors. So, we will take up these some of these topics for detailed discussion in the next class on centrifugal compressors. Subsequent to that of course, we will have one session which would be a tutorial on centrifugal compressors we will solve some problems which are related to centrifugal compressors and we will also have some exercise problems for you which you can solve based on our discussions. So, in the next class we will basically have these topics for discussion we will talk about Coriolis acceleration, the slip factor, the performance characteristics and stall surge and choking associated with centrifugal compressors. So, we will take up these topics for discussion in the next class which would be lecture number 32.


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Yeah, I think we should just start maybe and like people are gonna join us Who here has never heard of the limo update raise your hand in the channel? great This is a very good sign. So we're talking amongst connoisseurs No hand raised like okay people have questions today Which is a good thing because today we have check in home chow first let Let me wish you all a happy new year because we haven't talked since the new year started A more precise day than Q1 like you're starting with the hard questions already Let's keep that for a little bit later. So let me wish you a new year a happy new year A happy new upgrade a happy new a lot of things for a lithium and We worked on the limo update since the main next launch, which is more than a year ago We announced it officially in October We made another article in the day in December and now it's getting closer So now is the occasion to ask questions and to talk about technicals a little bit So we have Cheng and Hong Chao from far away and they both are here to talk about it And we couldn't be more happy and I think you'll join me in being happy you can maybe Happy smiley happy meme until you have something so as it as always said always the Happy DJ of this session. So thanks to him. We have a working discord session and last time we had a few issues, but today should work well and Sadly only the moderator and the guests can speak but like you can always ask the questions in the text channel in the channel on the side that you can reach out from the upper right and We'll take the questions at the end in the Q&A The last talk with we was with flux was a month and a half ago something like this and the next one will be with Nervous Next week actually But I'll tell you that after this talk today concludes again So without further ado Let's start So Hong Chao and Cheng maybe you can Unlock yourselves But people can see you Hey, Cheng, how are you? Oh good Hong Chao nice happy new year Thank you. It's happy new year in China, especially right now actually. Oh, it's coming, right? Yeah, I think it's the weekend It's the weekend. Yeah So we have to wait for next next tech talk to wish it actually so thanks for coming today and We want to talk about the lemon grade and start with the easy questions So what is the lemon upgrade? Like we've talked about it for a long time Is it in is it it's the first network upgrade? Is it what kind of upgrade is it so if you Cheng could enlighten us a little bit But as an introduction of what the limo upgrade is and the refreshing for everyone here Yeah, so normal upgrade is a hard fork is the first little network upgrade for a few I Generally don't know how to summarize in one sentence because Include so many new features and new changes like functionality to the virtual machine security and performance upgrade to the whole blockchain and Also improvements to the programming language improvements to the endpoints Yeah, a lot of things be Very hard on that for like modern one year It's hard folk because it includes a lot of new features and the breaking changes And it's something we kind of necessary to do it or bait death experience For a bait future of RFU basically cool So like the question that energy Asked actually is coming soon like when when will it activate? Can you tell us a bit more about this? I think he's definitely gonna be For the end of Q1 Initially, we thought that we probably Could do it by the end of this month, but now it looks like a bit harsh we Need a bit more time to test it and also to communicate it's very gates is is based in China, so we can only kind of coordinate with them after Chinese New Year Right now is the is the probably the longest longest holiday in China right now So we're gonna to coordinate everything after probably after the Chinese New Year to Make sure that the whole ecosystem will be First need to upgrade to 1.6 and then we're going to discuss when we're going to activate this Then we are ready to go So it's very very close, but we cannot give the exact time stamp right now. Can we say that it's never been closer than today? Hong Chao, can you tell us a bit about the main Features of the lemo upgrade please Yeah, as Chun said, it's very difficult to come up with an exhaustive list of everything So just talk about like a few areas number one we have introduced a new set of VM instructions and building functions to make smart contract development more efficient and This include for example a subcontract system, which you can think of it as a It's almost like a more secure version of a of a map concept we also introduced the dynamic array indexing and and Also some some some building functions to for example facilitate debugging and logging and so on We also have introduced features at both language and VM level to make smart contracts development more secure and That includes for example the a new asset permission system Which at the code level dictates what exactly a smart contracts can can spend so Which is a pretty big improvement over the solidity smart contracts development We also have a external introduced an external call check system which By default you have to be explicit about like who can call a public method of a smart contract If this method can mutate the state of the contract the reason is because this Was a source of security issues for for like smart contracts development, so we wanted want to address that at the language and the VM level We have also improved the node API is an SDK to use the development cycle for the smart contracts For example the common tasks such as coding unit tests integration tests and also the like the deployment to like testnet and Manette Well, we want to make it make that very very easy basically So I'll stop at that That's pretty good list That's a pretty good list. Thank you Like so you you you evoked the bridge Like about the bridge like so that's the that would be the start to enter a very interesting Interoperability for the network. So do we have Do we think that when is the bridge going to be available after the lemo upgrade like is it going to come soon? Is it going to take a little bit more time? Do you have a a bit more precision about that? Yeah, so so right after the the man at upgrade we plan to spend some time to monitor the network first and We don't have a specific date to to launch the bridge on the manette things It does we all know bridge is a very Critical piece of infrastructure and it's very critical for our ecosystem. So we want to be very careful about that But we have already deployed bridge on on the testnet which is Lemon compatible for a while now So we've been testing the full stack including the the UI the smart contracts the the guardian code The infrastructure and the goal is to be for us to be very confident about our code and also Like to gain some operational experience so that we know what to react when when things happen so so yeah, we will take a however, however it takes to You know be be confident that It is secure to to to to deploy So for people like cof who the clearly express curiosity while you were talking It's possible to come and test the bridge right on the testnet on the testnet. Yes on the testnet is possible. Yeah Okay and Which tokens will be supported by the bridge? Do you think? Like Like it's a bridge to ether, right Yeah, so it's a back-and-forth between LFVM and Ethereum so of course out will be supported and In theory like you can you can basically bridge any token as long as they're set up properly and there's like Couple of steps that you need to Do to to before you can transfer tokens, but yeah, there will be instructions to do that And Yeah, what's your next another question other question. Yeah, no. Yeah, I like so those the decks comes after the bridge Right. Yeah, and and it's true the other way around to right if we want to get listed on On uniswap then the bridge needs to be already up and running Is it right? Yeah, exactly if if we want to list for example off on Uniswap we need to bridge Off to the Ethereum side from simple and then we can yeah, then we can create a pool for that Okay Cool. Yep Like I want to ask you Cheng also. Do we have already plans to bridge to other chains? Oh Yes, definitely As I believe I'm personally I'm a believer of multi-chain futures. So the more we can Connect to the the base Interpreter interoperability we're going to have Right now we don't have exact or extra energy on that Number the rose and bridge of Ergo seems seems to be very promising and interesting and also the Community of Ergo is is great and yeah, we have been in good the very good relationship with them so You're going to re-research on that direction once we have more resources I know we have pretty much focused on the the upgrades and also improving our own ecosystem Makes sense makes sense. So like people are asking questions in the chat But I think we'll probably keep them for a little bit later In the meantime, we're gonna just move on like one thing that the demo upgrade brings is a great Improvement for the developer experience the tech and the security of the Alephine network a blockchain so it gets easier to make more powerful things and We want to understand a little bit more about this. Can you talk about how the tooling evolves like the SDK You've talked about in the past What changes have we made to this that makes it easier and more deaf-friendly, let's say So the SDK is one of the probably the most important piece of infrastructure for the For the whole ecosystem and it takes a lot of time and the energy to to make it well for example in the Eastern ecosystem, they In it took multiple iterations for them to have good tools like hard hides and Fungi So it's kind of the same for us. We started at the minute launch We have a very simple and a minimal SDK available and people can actually build the apps with that But it's not really friendly enough in the past Since the minute launch we have spent a lot of time to improve the SDK to add more features and more tools So now is it's really much more easy to build the apps with it. I want to highlight a few Changes or a few features that we added since the main launch. The first thing is We have much better API endpoints for a minute launch and Almost every release of the phone out. We have some either new APIs or some improvements to the existing APIs We also introduced Development development tool for smart contracts like comparison tasting and Deployments right now you can do all of them Three just one one line of commands We have kind of redesigned our our smart contract even system The initial version was a bit naive now is more structured and people can use the SDK to interact with the events or the on the phone out And Lastly we added a lot of kind of utility functions abstractions for common tasks and also we introduce Some standards to the in the SDK especially I want to mention that we introduce a standard for wallet and It's very good for depth experience. Yeah, so yeah that that's Kind of the main main features It all of them took a lot of time to polish and some some of them we Went back and forth in the design sometimes but now SDK is I think is in good shape. We have been using it for all of our Dapps like the bridge decks and also an FT projects. We are We we are enjoying using it at least So I guess it answers half of the question of the fix that is in the chat That he asked if will the team build functional dApps to start the ecosystem growth like we've actually been doing this already And since we've have been doing this I think it's fair. It's a fair question to ask you change for the people who are a little bit less technical than Then we then you are especially what does it change in the experience of the depth? Which new features like like in a more understandable way, like can you can you tell us me for depth or for users for devs for devs For devs, I think Being if you are not really familiar with the take the technical details of RFU You can still like You can still build a simple dApps with our SDK Following just the the tutorial we have So I think that that's that's a very Very a big achievement for adoption of RFU, right? We can on board more devs Like in the past or around many lunch we kind of need a very Very Very high key devs they can build on top of our RFU with With the minimal or basic SDK, but now I think You are just a web or web of the earth. You can probably already start to build on top of on top of us The I I also think that's Right now we have introduced a lot of security improvements to the Four nodes and to the to the SDK to the language kind of easier for new devs to to build production ready applications because you don't need to worry too much about the Tested of the the pitfalls security pitfalls So if I if I if I sum it up it gets way easier for way more devs To build much more powerful stuff on top of a lithium Yeah, I think so that's cool. And can you so devs are gonna have to write this in in Ralph the Development language the programming language we have On a lithium that is let's say the equivalent of what solidity is to a theorem Can you tell us a bit more about how like what it is now because I know you've been working a lot on this over the year Yeah, we have been on a lot on this because it's the language is core part of the whole idea system The language itself has evolved a lot since the maintenance as well. We introduced other great features like Dynamic array indexing constants error codes debugging Language debugging supports, etc Especially we introduced a new syntax for the asset permission system, which is much easier and more intuitive for devs to Approve approve assets the language So right now I think the the language is pretty much of Blitz and we initially we want to design a domain specific specific language for Writing the ups on RFU. We don't want it to be too complicated. We just want it to be very specific for for for the ups So that is much easier to learn and to use Think right now we have already achieved what we want you to do and We have some small features to to add in the future, but right now is very ready for production development Okay, that's cool. And how is the Like that's a question for both of you because you've both been hacking with it actually how does the experience of writing in Ralph compared to the one That is writing in solidity Okay, I start first Yeah, yeah, I personally build some dApps in the past in solid like some solidity dApps in the past I remember like one of the greatest auditors Called some some CZ. He won't say that he personally is afraid to write any production dApps Because of there's so many security issues to consider about So I I feel kind of the same Night ride solidity. I Feel like I was playing with fire You know it can it's very easy to shoot on the on on the foot Because of there's so many security potential security issues the also nowadays because because of the Network is kind of sometimes gets very congested and the gas gas can be very Expensive on each one a lot of people they start to write very They have to optimize the contract. Otherwise, it's not really usable And in some cases people have to write assembly codes and that is first on one hand is very Very hard to write, you know assembly code is like the the bytecode for machine is not really for programmers So on one hand is very hard to code on the other on the other hand the Introduce some new security issues to the system because it's Much hard to write so it's easy to write bugs in that approach but on that hand but If we build Similar stuff on our field It's going to be much easier first a lot of the a lot of those security issues have already been mitigating or complete Completely eliminated. So you don't need to worry about that much and you don't even need to worry about the gas issues at war because We all rich machine is much more optimized than veteran than the EBM The gas cost itself is is low and the second Seconds because we are a shadow blockchain. We can support Much much higher throughput. So the the gas will not be an issue until we reach a very very massive adoption in the future, right? So in general, I think writing my contract or Dapps in On RFU is going to be a much much easier and friendly experience and developers can Easily have fun Well, so home chart you concur. You're having fun writing some of the Dapps when people will I agree with Chen The the the compiler can definitely Guide you more to avoid some of the people's especially the security people's and also The the the code is more concise So just just as a Example like we only implemented the the bridge we have to implement like the smart contract logic Pretty much the same as like a theorem and solidity and so on and our code size is Like order of magnitudes like smaller basically and that that illustrates like how concise the the the code can be using this language Okay, great legs so talking about Talking about Dapps like that brings us to a little bit more to the utility chapter of this discussion, right? Again people who are asking questions in the chat. I will ask them I just come back to it later when we finished the discussion. So keep asking them. These are actually some very good questions um So I want to ask you in terms of like more like the the lemo upgrade comes at the same time as a let's say Big update also on the front end front actually So nfts and smart contract interactions will be a big part of the front end upgrade and also we're going to have very soon A browser extension wallet that you can already actually test on testnet Can you tell us more about the wallets like the mobile wallet the desktop wallet the browser extension? yeah, so we have a Lfm water connect implementation And our desktop wallet the mobile wallet the implement stage, which means that our dApps can talk to the our desktop wallet And the mobile wallet through the water connect And as you said, we also have a like a browser extension wallet so the dApps can also interact with the browser extension wallet as well And as Chen mentioned before we we in the SDK we actually define a standard water interface And our like other thing what it connects implementation and also the browser extension wallet Both implement that and this interface basically support a standard set of operations like Just give you a feeling These operations include for example, like how to Like connect and disconnect with the dApp and sign transactions or transfer deploy contracts sign like Transaction scripts and so on so Once we have connected to Like like any wallets Like including the desktop wallet mobile wallet and extension wallets From the perspective of perspective of the dApps developer We can just like use this interface to to to to Like for example execute a transfer A transaction and things for things like that We will provide Like some standard UI components such as like auth components, which can help you to basically connect to like Any wallets that we support to like water connect and and or like browser extension And from that point on you can just like continue developing the dApp um So, yeah, that's basically the status of the of the wallets when it comes to like the interaction with the dApps Yeah, okay. And so everything is going to be available on every platform basically Yeah, all of these things. Oh, that's cool. I like about just about that chain Can you do you know when the the mobile wallet we've been talking for a while? will be available And will it be available on all os platforms Yeah, I talked with miga About yesterday He told me that the android version is android code is ready And right now the team is working on the ios parts. So Hope hopefully Hopefully it's going to be ready soon. Yeah That's great. That's great. And about about wallets You've said on discord last week. I think that you were working on the ledger integration like for the hardware wallet Can you expand on that a bit? Because everyone is waiting for that for sure Yeah, I personally i'm looking forward to using it as well. That's why I started to work on it with high priority Right now. I have already finished the the the minimal ledger app. So It means the the hardware side is has a minimal version and Since this week i'm working on the i'm spending some of the time working on the Integration to the extension wallets But this turns out to be non-trivial because I need to refact the the wallet to Support a new type of wallet. It's it's tricky. So it will take some time But I I think probably in two weeks Kind of work in part time on that. So it will take more time. I think in two weeks, we're going to have a first release 40 yeah Oh, that's cool. So, so okay that that gives a let's say type of magnitude. That's really great and um, so that's a question that actually I think The objective alpha or the fix I don't remember Asked but like it's also a question. We have so the the core team has been working on dApps like key dApps like the bridge We have a dex code somewhere and some nft prototyping What will it work on next like how is the How is the core team seeing working itself on core dApps and what parts would be more Left or encouraged for the community to start working on I don't know nft is defy payment social networks gaming like how do you How do you see that? so ideally I think For the very long term ideally like the whole dApp development should be driven by the community because it's supposed to be centralized in the very long term But right now because the project is still early and I'm not so many devs so Core team still need to build something and also build some pro tabs to to give inspirations for the whole community Giving the our limited Time and resources right now our main focus is on the The core components of defy like dex bridge And also we are building we we have something for the name service stuff And in the coming several months, we are still going to focus on the well-known dApps that's kind of being proved by other ecosystem like a name service nft dex hsr And we we are going to start to encourage and support community community devs to to build new dApps on top of us Regarding direction or topic. I I think What kind of dApps Should be encouraged Because you never know what kind of innovations the community can bring up and Yeah, I personally Don't want to push for a direction But then maybe some new, you know, the Maybe some new directions a lot of people Suddenly want to Put more effort on like for example social network payments as such right now is They are very hard topics so if They are a lot of kind of demanding in in some of the directions we may space some more efforts on that as well Build something to showcase our students Because that can potentially bring up new new developers to our ecosystem, right? That's basically the the strategy right now And and we are a pretty small team and we are pretty agile. We always adapt ourselves to fit the to to Kind of build the in the most efficient way and We will we'll see what what kind of He kind of the space is going to evolve in the in this year Oh and like about about developing that so hong chai you've been working on NFTs already Partly working with With a project that is actually building Already an NFC platform on top of LFM. Can you tell us more a little bit about The NFTs on testnet for example, can we already mean the NFTs? today on the testnet at least And yeah, we have deployed the NFT prototype on the on the testnet So together with the extension wallets We will be able to mean NFT But since since the extension wallets not published yet, you will have to go to github and download the Download download the zip file. So it's a little bit more complicated. Um, but um, but yeah, we can mean the NFT on testnet Okay, so can I share the link about that for the people who are interested? Yeah, sure So here's the link to the NFT on testnet on testnet like you're just gonna have to go for the browser extension and github first um So we're getting to the end of the questions that are prepared So soon we're gonna take the questions that were asked in the in the group in the chat but still uh last week we We discussed uh at the occasion of the 1.6 Upgrade of the full node chang you We talked about a DAA adjustment, which is the difficulty adjustment algorithm There was a change that was implemented in 1.60 Uh, and uh, I wanted to give you a little bit more of an occasion to talk about this Live and also for the people to ask questions if they have some Yeah, um So in 1.60 we uh included a big update to the DAA Improved the existing DAA by to stabilize the block time and the The main issue in the the previous or in the original DA was that because the The mining difficulty can be different and the the block reward of different block chains can be different. It gives Miners minus different different incentives to mine on different block chains, and that can cause the block the block time to be a bit dynamic in some cases in this new version we Accurate the mining incentives by averaging the difficulty across different chains and also we with this new DA The transaction fees is going to be uh uh completely burnt The original is only 50 percentage spent the motivation that's um The transaction fee is including the block rewards and the block reward is going to be uh Effect the mining incentives or different blockchain So we have to make it also the same for different block chains and the burn it completely is going to To be one of the the solutions uh so the improvement is already Deep uh implemented and deployed deployed on the test net from what I have seen right now is Mining difficulty is much much more stable than uh than the previous version uh on test net so, uh I think is is really great for the Uh for the whole network And for the right now it's not the trigger for the maintenance yet and we are going to It's going to be triggered once the lemur upgrade is activated. Yeah Okay Like okay, so thank you and like last question before we get to the final section of this is uh So when we talked about the lemur upgrade a lot of people are often asking and it happens also today Uh, because uh the objective alpha also asked us a question about this uh The new listings makes more make more sense New exchange listing make more sense after the lemur upgrade. So, uh, what kind of exchange listing are we considering? uh, uh, we we have um, I think the strategy is uh, it's always the the same we have been uh, replied to this question multiple times in the community we're going to first try to deploy the bridge and Uh make decks available for the for the whole community This is the first priority and then of course for this year we're going to um to go forward to uh Work on the uh sex uh centralized exchange listing as well um Because uh a lot of people they end up deal You centralized exchange a lot. So that's definitely a direction we're going to to work on There's no No timeline for for now, but we're going to work on it So this is something we're actively working on is to take away. I I get from that So, okay, so thanks. Uh, I think we've covered most of the important aspects and before we get To the questions that people have asked I want to ask you. Okay very concretely. What happens now from now to the lemur upgrade What are the the steps? so right now, uh, I think, uh the core team is tasting and monitoring the 1.60 which already includes all of the features and the changes for the lemur upgrades. It's going to be several weeks and In parallel, we're going to communicate with the the services like exchange mining pool to to communicate that we are we are ready for the upgrades And then we're going to figure out a time stamp for with the whole community to activate the upgrades So, yeah not too much on the clinical side or on the community really only The community side right now. Okay. And then I feel like it's weeks A few weeks or do you say Yeah, yeah Everything goes well Yeah, but sometimes they might be surprises, but usually Uh, I I I feel very confident this time because we have been testing for long enough Cool, will there be a party at the lounge Are you from today? Oh the activation activation time stamp Okay, so let me get to the questions that the people have asked in the in the in the chat. So First the question from polto that asked if the bridging is if you have the suit correctly is from alf to erc 20 And eith to a token on a lefium and then any erc 20 to a lefium, right? We can import all your c20s from ethereum to alf to a lefium, right? Yes Yeah The bridge is going to be Permissionless you can bridge any token to alfium or bring bring bridge any token from alfium to ethereum There's no limit on that I'm not sure like all the Kind of the the bridge will evolve once it's ready We're going to see which stablecoin people would like to bridge Yeah Yeah As polto says like liquidity would be needed Like montail and the fix have a quite a similar question Not not really, but it's closed They're asking why ethereum But montail says they had some weird stuff going on in the background ever since they became pos and the fix says that Try like Being clever actually like james and solidity is known to be very insecure Why is the plan to create a bridge where they have to create a smart contract and solidity on eith network and open up the risk of a hack on the ethereum side? so Basically the the main question I think is why why ethereum first? I think uh, even though we are saying like the ethereum Vm has a lot of issues But it does not say As the current the the existing dApps is Not secure I think the main issue is that if you want to build new dApps on On ethereum, it's going to be much more It's going to be very challenging very difficult But the existing dApps like uniswap like USDT USDC SHR Have been tested by time and they have been audited multiple rounds they have been wasting a lot of money to Make sure that those contracts to be secure so uh I think the security of those existing Well-known dApps are pretty pretty high it's just the new dApps and the the learning curve and the The the cost for security is pretty high in general so uh, I I think like bridging with the well-known dApps or well-known tokens makes great things and right now Uh, it's also the same for bridge When it comes to bridges you have multiple options to Support for example, we choose Choose, uh, we choose wormhole to to integrate because it's been has the highest token value lucky token value and also It's been existing for like many many years Even though it has been hacking multiple times in the past The contracts itself they Uh, they have never been exploited in the past so The I think the security is very high. Yeah in general like It's no absolute security. It's always about the cost, right? The with with the new version machine and the new language you can Can provide a very high security by default There are still some there will still be some cases you need to be to be careful about so In I think it makes sense to bridge to the very mature and existing ecosystem like eth. Yeah We are going to explore the ecosystem as well Yeah And also, I think I would just add that you have to think both ways, right? We're building a bridge to eat, but we're also making it easier for people from with To come to LFM right and to discover it. So it's it's it's a way for it's a win Um Talking about security and hacking like we got a question about the hackathon. Is it gonna come around? Or just after the limo upgrade Um time now again. No I cannot give a precise answer to that We just try to do it the best timing uh at the best timing. Um No, we are still planning a lot of the details. Yeah That we uh, one of the Very important thing we want to before that is to pre is to prepare um Some very good tutorial a series of good tour tutorials for devs Um, so that's the it's much easier to onboard new devs from the community or from other ecosystems Oh, yeah, we'll do it when it's ready Yeah, my main point is that we're actively working on that um So we are like, what's the next question? Um So the objective alpha asked a long question It's which is most likely to come first a non k y c sex such as q coin trader auger ascend decks Or an amm base decks Also, that's relates to the listing question that we had before I personally feel like uh, the decks is going to be much easier giving our progress because the bridge is kind of ready and uh If we want to get a list on uniswap then as long as the bridge is ready you can get a list on uniswap We also made a lot of progress on the On our native decks So we can also once the bridge is ready We can deploy the decks and then people can use the the native decks to chat Um Yeah, so I I definitely think decks is going to be Is going to come earlier than sex But uh Hey, yeah, maybe maybe Sex after decks and like where like the objective alpha also asked like if it comes first on the decks Who would be providing liquidity for the am? I think the the project the The team will provide some initial liquidity and then The ecosystem will uh follow up. I think yeah Because being the liquidity provider you can you can make you can gain some Getting free from the protocol The by the way, we are not In our design of the decks Uh, there will be no Um Kind of development fee all of the freeway goes to the liquidity providers Uh, so probably this will give more incentives for the community community to provide liquidity That's cool. I like the the question came now two times On which side Will be the decks you you would want to be first Would be each side or half side I mean my answer would be both, but I don't know what your answer would be Um, my answer is also kind of I don't know uh It's really It's really hard to predict for now like which uh, which decks is going to be uh favored by Rather community. I I kind of my my current estimation is that um, both will be used because Both will have some user basis So we will see we will adjust based on the Reality, yeah, if if like really people Use the decks uh native decks much more than the Decks on other platforms, then we can probably focus on the native decks. Yeah Somehow I feel like it's It's good to use the native decks. So probably uh I personally hope that we are going to use the native decks much more I think it's going to be more efficient. So we'll end up like this. Anyway, Lemo is ready sex and decks are done and developers are building an alethium What will be the priorities of the team after these steps are reached? So it's a bit of a perspective question, I think chang you could chime in on this Um, I I think there are quite a lot of things to to to build uh need to be built first on the funnel side still like lights light clients abate p2b protocol And the More kind of optimizations to the storage The some probably refactorization to make sure that's the code basis Can have more Taste the coverage, etc So for another side a lot of things to build and it takes time uh, and then probably We're going to explore some New directions to to leverage the scalability of the blockchain Like For example, I personally I'm very interested in the social network applications because It's going to be good for massive adoption of blockchain If there are some good kind of good use cases to to explore we're going to explore a little bit on that as well um, and Payments as well, uh sounds very uh The necessary and also very uh promising for the very long term Then the bridges Bridge sides right now we have wormhole. We we probably can create connect to more blockchains Also, we can connect with more Other bridges to bridge to more ecosystem Yeah, and then we can talk on a lot of other integrations like uh wallets Uh, right now most of the wallets we are are kind of built by ourselves By the core team There are a lot of good kind of uh good wallets in the in the whole space If we can get connected to them, then it's going to be a good leverage for for us And we are going to also work with a lot of I need to work with a lot of different communities to attract devs Just right now most of the things done by the core team That's definitely not enough for the very long term and I personally believe that's a very open and very Active dev communities the key to the future of RFU. So we're going to work very much on that It's cool. I like Wally and the fix basically Asked the same question like besides the hackathon. Is there anything planned? How to find new developers to build Alephium and the fix Asked like why will attract developers to Alephium? So I mean, I I think you've answered part of the question People often ask what we're doing marketing, but like we're actually doing a lot Like for example, we're producing a lot of documentation so that when people come in the ecosystem They don't start From nothing So there's a lot of articles being written that make it way easier for the next guy to come in or to know where he looks You should look for to start building Then we do these partnerships that like a little by little make our name known everywhere and our features And there will be more of this A lot more of this coming So it's just not as visible as As a lot of things that you can see in the tech side, but it's it's it's we're doing it The the long way, let's say So I think we are done with the questions of the people and it's actually 657 So if you have Oh, yes, sorry the objective alpha asked this question like how does the number of shouts get decided Currently in the future that I think that points out to a very great question of decentralization actually That's a very good question. So right now, I think At the minute launch we choose to be we choose the the groups to be four and the number of shots to be 16 Because it can provides around like 400 to 500 tps this tps is kind of close to the tps of of paypal and and I personally believe that it's going to take a Take quite a long time to to to reach that And if one day we reach that tps It means we reach we we achieve the massive adoption and it's going to be very cool and after that Then it's going it's going to be easy like if if one day we we see that the network is kind of GST, then we can start to work on Increasing the number of groups We will need some engineering work to make it happen Yeah, once we We Get that's higher number of tps We will have time and resources to work on that Okay, yeah great I think it's a great question to to close today on Let's say on a Look to the future So thank you Cheng. Thank you Hong Chao for answering the questions and I think hopefully making it be Clear for everyone I want the limo upgrade was unlike what he allows for the future We will have more documentation on the limo upgrade coming and more updates to let you guys Know when and how it will go on from now Thank you for all your questions Actually, we love to have such an engaged audience and like you have to know that you can still ask the questions Either in discord or in telegram or in any ways you can reach us. We love those questions on twitter too So thank you, especially also like, you know, the usual suspects You will find this video. We will put it on youtube theomars. You don't need to worry So, yeah, thank you. We will have another tech talk next month It will I would like it to be with the frontend team, but we don't know yet So we'll we'll keep you guys updated and also next week on tuesday 24th at 7 p.m CET. So that's like basically now We chain will be talking in a twitter space with one of the tech leads at developer relations, I think at nervous So it should be a cool space In the same style that we did with the flux A month ago or something So thank you guys we're gonna close the video now and And we keep asking you questions always Maybe move to general now Thanks, Chiang. Thanks. Oh, ciao. You can Bye guys, and thank you said for organizing Cheers Bye


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