 How do you make air condition as noiseless? This is supposed to be split AC, is it? It is not window. It is only split, I think. It is better than, supposed to be better than split. Split will not give, as I said, window when compared to window. Central. Central AC if you put, you will not have any noise. Start, okay. Yeah, I think yesterday what we have discussed about fluid AC beds. You remember a little bit? Yeah, come to the class, I say. Okay, mentally. Okay, so we have discussed the definition of fluidization and... Yeah, types means what types we have discussed. Regimes and all that we have discussed. Good. Yeah, now to design fluidizer bed reactors, what are the parameters we should know? That is what we are going to list here. Number one is particle size and fluidization characteristics. Fluidization characteristics. Number two is pressure drop due to solids. Or sometimes you can also say bed. Pressure drop due to solids in the bed. Okay, so number three is pressure drop distributor plate or distributor. And number four is minimum fluidization velocity. Number five, terminal velocity is bed height. Right here static bed height. Seven, eight and mass transfer correlations. Yeah, the last one, eight is difficult to write. Reactor models. Reactor models. See how many things we should know. And actually this is a full course if you teach all of them. One by one, deeply. Good. Yeah, but I think all the points we will just touch. And this we have to go a little bit deeper just to develop the model. So you need to find out what are the particles that can be used for fluidization. What kind of fluidization you get if you use different size of the particles. That is one. Number two is that the pressure drop. How much maximum pressure drop that will be there for the solids. Okay, that is one. Then you have the distributor to support the solids. Right? So what is the maximum pressure drop this distributor plate should have? How do you design this distributor plate? That is very important. So then you know like for example what is the free area we allow? When you have the distributor plate you have perforations and what is the area? Is it 100 percent? 100 percent means same column, column diameter. So then 50 percent is 70 percent, 80 percent, 30 percent. How much you go for free area? So that is what you have to also find out and that correspondingly gives you the pressure drop. That is the one. Then we have the minimum fluidization velocity. I think I better write here this symbol ëumfí. Right? So that is the starting point of the fluidization. Then we have terminal velocity of the solids. Actually it does not have any meaning you know here terminal velocity. We are talking about single particle terminal velocity where in the bed we have lots of other particles. So in the presence of other particles definitely the terminal velocity will be different. But even then we would like to have an idea what is the maximum you know upper side what you can go but sometimes even plus or minus under times you will go around that velocity okay. Because multi particle systems even now it is very difficult to characterize and there is no theory where you can get all the solutions using you know from first principles and also closed form solution. Closed form solution means correctly you are having the solution you have the nice equation and when you solve it as a differential equation first order for example you will get a nice solution. All that is not possible for multi particle systems and that too in the presence of some other fluid either gas or liquid. So then you have the static bed height. What is the bed height to start with you have to take? You know we discussed at HP height of the packed bed before fluidization. What it should be? How many times L by D for example or how many times D? If I take 1 meter diameter how many times I can go as packed bed static bed before starting fluidization 2 times 5 times 10 times okay. So that also is important for us. Then you have heat and mass transfer correlations both will take place I think you know during reaction you have either exothermic reaction or endothermic reaction so heat transfer will automatically come into picture catalytic reaction so mass transfer again comes into picture so that due to diffusion the reactant gases have to go into the catalyst get reacted come out all that things okay. So that is what is heat and mass transfer correlations what we have then finally we have the reactor model okay. What kind of reactor models we have ideally only 2 flow systems PFR and MFR okay. So we have to also see which one is more suitable here either PFR or MFR or both that is what that is what is the overall picture I think I have to complete all this in 2-3 classes so that is why first let us take this parameter particle size and fluidization characteristics lot of you know all these things are mainly empirical and many researchers try to find out what kind of fluidization you get if I take for example 10 mechanical particles 100 mechanical particles 1000 mechanical particles 10,000 mechanical particles okay generally beyond that we do not go beyond 1 m m particle itself beyond that we do not go 1000 mechanical particles but still there are large scale fluidization particles where particularly fluidized by combustion they use around 5 to 6 m m coal particles because they cannot go to very fine powder if they go to very fine powder all the where all the energy what they produced in the thermal power plant will be used for crushing because tons and tons of coal has to be crushed to very fine powder means okay so that is why practically they found that around 5 to 6 m m size coal combustion for coal combustion so I think beyond that normally we do not use the fluidization operation that is the maximum right and if you want to use beyond that also some kind of good contact then what we call it as spouted beds spouts the bed you know heavy large amount of I mean large diameter particles will spout rather than entire bed moving that I think also I will mention when you are talking about this so that is why many people tried and then they try to give the good fluidization for example good fluidization means where you have smooth uniform fluidization like particulate fluidization particulate fluidization is good fluidization why because inter particle distance is same everywhere that means all particles are uniformly distributed in the bed nice things happening okay like western society where discipline is there okay to some extent there is discipline there not like our traffic and all that but whereas here in the real aggregative fluidization excellent representation of India chaos you cannot find out suddenly there may be bubbles you know suddenly there may be bubbles bursting suddenly there may be bubbles starting and in between there are good ordered people in between somewhere this corner one thus corner one the other corner one so that kind of chaos will be going on so that is why some of them try to put this information in terms of dimensionless numbers obvious first dimension number dimensionless number that will come is then also number very good good guess so afterwards that only we know next one next number you tell me Savita Charu number will not come here you know this for fluidization characteristics Charu number will come in this step you are playing chess thinking 10 steps ahead okay we are talking about only that particle and fluidization characteristics where we are not talking about heat transfer mass transfer anything any other number you see I told you know actually I am a good person why do you scold me I do not know I think all the time you know my guess and I am a very good psychologist I say I can easily find out how the students mind will work you see how much time you are taking to give second dimensionless number in fluidization it is a fluid particle system porosity is not a number no it is just a parameter dimensionless number Archimedes number is 1 other than that for fluidization 2 I think you would have never heard of what is called Froude number u square by gdp what does that tell you Froude number this is my problem I say once I start discussing it goes goes goes okay what is the definition of Froude number equation to be fair to you I do not ask Archimedes number okay because no one can tell definitely can you tell Archimedes equation tell me no into there only divided by divided by u square that will come anyway when you are discussing about minimum fluidization velocity yeah Froude number is another number which will come okay same of course friction factor has a dimensionless number also people use yeah so all these things will come and people try to characterize in terms of those numbers Froude number is u square by gdp velocity squared divided by g g is the acceleration due to gravity dp is the diameter of the particle that will tell us inertial upon gravitational or buoyancy also can say yeah okay so that is the kind of thing what we have got very successful then there was a person called Geldart so from then onwards it is called Geldart classification of solids okay so he published a paper in powder technology powder technology we have page number 7 sorry this is not page number I want to write page number and saying okay so this is volume 7 285 page number 1973 and again they modified this with another person called Abraham saying may be he speech is called okay Abraham son son of Abraham okay so this is Geldart plus plus Abraham son so these two people again published in the same that is after 5 years I think you know yeah 1978 okay so this is volume number 19 page number 133 1978 so they slightly modified the old graphs and then that is slightly more reasonable because it is an empirical observation this is very popular because straight forward and easy to use that is why all our research must be very simple as simple as possible but not simpler like who said that Einstein your model should be as simple as possible but not simpler wonderful statement good so they have made this one as simple as possible in the beginning but I think next one they did not it is not simpler a little bit complicated in the sense that some updating because it is mainly empirical observation they do experiments observe record there is no theory behind this so what they did was everything they have put in the form of a graph if you draw the graph you will get some experience about this and you will also know how to draw the straight lines this is rho s minus rho g normally expressed as grams per cc okay one can also express in kgs and this side we have we have p in microns okay microns so that is one and then the scale changes here from 10 I have here somewhere 100 here 1000 okay approximately 100 this is log scale this side and then this side the density change the density difference this is mainly for gas solid only okay 0.12 0.1 somewhere here ya this is 1 0.11 so okay this may be 2 3 5 normally decreases no okay initially this one will be larger than smaller smaller like that it goes actually it will be 6 7 like that okay good so this is the scale what we have and then they put their data in this format like divide the regions it will start okay this side also I have to put approximately so this again this may be 50 this is also 50 then somewhere here I have 500 500 ya so this is only just approximate plotting this is 50 100 it starts somewhere here this is a kind of diffusive region not so much ya I will tell you what is this later all this is one region then we have 1000 starting from here okay this is a this is one region then we have good so first draw the lines approximately like that you know till 1000 ends here it may start around 50 here or slightly inside 50 so this also may start around ya this is 500 so somewhere in between like this okay so then what he calls is this he calls as group A this he calls as group B this he calls as group C and this group D okay so now we have to see first of all what is this group C group A group D and all that right so group C particles are the cohesive particles you can see they are smaller size fine size see here even around may be 20 microns 50 microns less than 50 microns and in general but these boundaries are not exact I think you know they put all the data and then try to interpret but I think I will also give you some sizes later but generally when you have small particles you have cohesive powders one example is talcum powder what you put everyday morning okay if you have talcum powder will be around 1 micron 10 microns less than that very fine powder so that is an example of cohesive powder so that means when you have that kind of powders you know as the size is becoming smaller and smaller the surface energy is more they come together stick to the surface very difficult to fluidize that means the drag force which you are going to use to lift the entire bed may not be sufficient sometimes to break the inter particle forces that is why you will not get uniform fluidization some part the particles may fluidize where you have slightly loose and you know the structure there in some other parts it may not so that is why very difficult to fluidize is group C particles and group A particles are exactly I do not know whether you have seen the catalyst or not FCC catalyst is one of the very good examples there that will vary around 100 microns FCC catalyst I will tell you I think I will also tell you then group B particles you do not have to write that I will tell you group B particles are like sand particles this is an example so that you will have some idea group B means sand particles and this is the reason where all the laboratories in the world people like us who work in fluidization we take always only sand as fluidizing medium why you will get good fluidization and bubbles are also they are fast bubbles and all that will come there but bubbles all that can happen here to some extent here okay so that is why if you go to the literature and try to see either heat and mass transfer coefficients or fluidization minimum fluidization or terminal velocities or whatever you know even pressure drops everything if you go and see the literature 99 percent of the papers will be dealing with only sand okay if they want to increase the diameter sorry density for example sand density how much I will ask Abhinav Abhinav what would be sand density not a bad guess still that is okay Kg per meter I understood but is it correct is it higher or lower higher Renita you have any idea around 2000 okay I think Prabhu will tell 2500 1800 1800 okay it is 2600 you see this time this time you have missed it always you are trying to go in the middle path but this time I think you are tripping that is why I ask when he said 3000 I said Prabhu is the best bet to get the answer so 2600 okay so to see the effect of density sometimes we use the higher density like you know steel balls where you have around iron ore iron ore will be around 4.7 that means 4700 or 5000 okay Kg per meter cube all that so those things would have used but most of the time people love to use these particles or these particles these particles again this side okay this is the boundary this side particles are better and this side when you are coming to this fluidization may be difficult okay so now please take this I will give you notes you know quickly yeah group C you can now write group C okay underline these particles are very cohesive and fine powders so usually around 10 microns 20 microns like that okay normal fluidization is extremely difficult for these solids because inter particle forces are greater than those inter particle forces are greater than those resulting from the action of gas normally drag force right or greater than those resulting from the action of gas phase powder that is talcum powder what I said phase powder floor mays floor and all that floor and starch starch are typical of these solids now next one group C group B sorry group A we are moving this way group A okay group A particles are aeratable aeration I say you aeration I have A E or A T ABLE aeratable or materials having a small mean particle size and or low particle density and or low particle density in the bracket less than approximately 1400 kg per meter cube 1400 kg per meter cube okay full stop there these solids fluidize easily with smooth fluidization at low gas velocities and controlled bubbling with small bubbles at higher okay full stop FCC catalyst is representative of these solids those are the typical powders actually there is a lot of range here but still we are somewhere around here those are the good representation of group A okay next one group B the particles are sand like with size range of 40 micrometers to micron size just right sometimes micron M also one can write to 500 micrometers okay that is the normal size range but there you can see more than that also these are the typical group okay sand like particles with size range of 40 microns to 500 microns and density range of 1400 to 4000 kg per meter cube these solids fluidize well with vigorous bubbling action and bubbles that grow large particles are similar to sand like particles whatever particles you get similar to sand next one is group D these particles are spoutable spoutable large and dense in fact not large large and or dense combinations spoutable large and slash dense combinations deep beds of these solids are difficult to fluidize fluidize static bed if you take 5 or 6 for example okay l by d deep beds of these solids are difficult to fluidize they behave erotically giving they behave erotically erotically erotically erotically giving large exploding bubbles with severe channeling or spouting behavior if if the gas distribution is very uneven okay ya full stop drying grains and peas okay roasting of coffee beans comma gasifying coals and some roasting metal ores or examples of this group full stop or this group shallow beds are preferred okay shallow beds are spouting spouting beds are preferred for this group shallow beds are spouting or spouted beds are preferred understood now good okay ya so this graph was generated mainly at room temperature okay and varying because velocity is not told there right it is only the density difference and average size of the particle okay so normally the the flow through the beds are varied from 1 umf to 10 umf you know for the generation of this graph okay so that is one that is why it is highly empirical later of course I think in this paper or in this paper may be they also given equations here and also equations for this no equation here because this is a band where you have that error too much this side or that side so that is why it is drawn like this here atleast the boundary is short but with again difference between A B and all that this gives a beautiful idea for example if you have from the process normally you have a process okay mining for example you took from mining coal particles for example for gasification okay will you know some idea of fluidization what kind of fluidization you are going to get from this information correct no that is what we have discussed till now right so if I have 7mm or 8mm or sometimes we dry paddy paddy here only but in other countries they also dry wheat and all that roasting of beans okay so all these are large particles so then the moment I have that kind of particles which is the starting point B I will have this kind of fluidization for me so I better go for shallow beds shallow beds means very shallow it is if L by D is 0.4 or 0.5 or 0.2 that is shallow bed why because here for large particles if you have very deep beds fluidization is very difficult and when you are pushing the gas more and more for getting fluidization suddenly they explode because the you will get exploding bubbles channeling may occur particles may be throwing here and there very high aggregative fluidization which is not uniform fluidization right so that is the reason why you will have an idea okay when I have group D particles let me go for spouting spouting is another very nice operation in fact spouting beds alone there is a book also they do like this they have a cone and they have the particles this is gas introduction okay so this will go like this pushing the particle this is gas of course some amount will percolate also through the bed so you see here it goes like this it goes like this and some of the particles are caught and again coming here circulations okay you do not have uniform exposure of each and every particle but on the average if you take because of the circulations what you have circulation will be like this like this so circulation will be like this because of those circulations you will have good drying characteristics but you see here advantage is I do not have to use that kind of very high gas velocities because that spot only I have to manage where like you have here spouting velocity what is the minimum fluidization minimum spouting velocity where this can start okay like a fountain exactly like a fountain where these solids are going to this and then near the wall you have the sliding mechanism so the entire bed moves like this this entire bed moves like this then on the whole you have good exposure for the hot gas if it is drying operation okay good so that is the one that is called spouted bed we are not talking about that we are talking about in case you want to use a fluidized bed then go for only shallow bed shallow bed means if the diameter is one foot diameter probably you have to use only 4 inches 5 inches 6 inches then you will not have time or not we will not have time gas will not have time to become a big bubble easily it will come out that is the reason okay good so that is the one the moment you know that you are in B group B then we know that it is sand like particles good fluidization but see the bubbling is vigorous here here it is exploding bubbles here it is vigorous bubbles and here small and smooth bubbles which you prefer this or this or this this one because small number of not small number of large number of small bubbles you will get many good for us because that is how the contact in between solids and gas will improve so that is why this gives a wonderful picture for us of course there is lot of discussion again correctly how the fluidization takes place and all that we cannot go and I can tell you for example one here in the cohesive powders when you want to fluidize for example flour for drying purposes flour or what is the other one we have starch powder so what happens is when you are using that or talcum powder you have the distributor like this then you are sending the gas here you have the powder that is very fun powder so most of the time snakes will form here what are the snakes this one because of the inter particle forces if there is a weak structure inside so this will start it goes like this that is a snake if you put like this okay like this so like that here there may be another snake snake ya but if you go on doing that all the snakes will become one because they coalesce together and then you have the fluidization but that fluidization all the powder may be thrown out so that is why you can have a bigger cross section like that even though they fall again come back again okay safe so that is why so this kind of possibilities are there you have coalesce powders so that is why that is very difficult to fluidize now with nano technology these people are now trying to use fluidizer beds nano technology nano powders nano size powders okay and even of course japan has done wonderful work on this particularly when you have coalesce powders they used very nice techniques okay one technique is vibrating the bed ya so the moment you start vibrating the bed then snakes will not form what is that you are trying to do only you are trying to loosen the powder by shaking right when you are shaking like this the inter particle forces will be gone right so then easy to fluidize so that is why there is no end for human mind I say okay but only thing is you have to sit down and then think properly yes so this is what that can be done and then that kind of thinking should come first in the mind and then you have do the experiment and prove that your thinking, your hypothesis and what you have done experimentally both are right if both are right you are great okay do mtech beautiful or ms somewhere you are doing good very nice good so this is the particle size and fluidization characteristics that is this I think still I can tell many many things about that but all stories we do not have time that much then this first part is over now second one is pressure drop due to solids that is simpler one so let me quickly finish so here I have to draw the picture for fluidization yah okay we have the bubbles somewhere here so that is the manometer then we may have this is the manometric fluid that is the pressure drop which we can measure okay pressure drop due to solids we are taking good yah see okay what is that you are discussing yah you have an experiment definitely only thing is I am very happy you are able to recollect that you know you have the experiment for fluidized bed only or something else liquid solid why choices act beds fluidized bed both are important for chemical engineers what is the concession yah I mean I was giving 12 means 12 all 12 we have 12 experiments at that time okay yah good but anyway I think there is no choice between packet bed and fluidized both you should know thoroughly because I think packet bed is right hand and fluidized bed is left hand for you okay good anyway so this is what how the how I arrange it is gas solid fluidization same thing even liquid solid also when you measure this pressure drop delta P T total pressure drop through this okay as delta this one this also gives some pressure drop delta P D distributor plate pressure drop plus delta P S because of the solids that is here okay that is weight divided by unit area per unit area wall wall pressure that is what I measure okay so what I do is before starting the experiment that means before putting the solids inside this then I do the experiment for the same velocities for the same velocities without any solids what do I get I get the pressure drop due to distributor plate and also pressure drop due to wall delta P S I will subtract you know delta to get delta P S I subtract delta P T minus delta P D plus delta P W okay correspondingly if I also plot this when I am doing that experiment I think this also you could have done delta P versus U plotting graph initially when I have low flow rates initially when I have low flow rates then you that is nothing but packed bed so you may get a linear graph which is not true all the time okay and then it will go like this it goes like that but if you do not know this and then if you have plotted the total pressure drop this is delta P versus U like this I do not know whether you remember your graph whether this way you got that way you got that is the right one this is wrong one why why this is wrong one that is the right one this is only which is not fluidized this is also fluidized this is at this point you have fluidization but after that it is continuously increasing pressure drop so after fluidization our theory is that because there is no more additional solids so the total weight is constant weight per unit area is your pressure okay pressure drop must be constant okay so that is what is that this will come because without knowing yourself this distributor is there if you are measuring actually distributor will contribute much more pressure drop at higher velocities okay so that was added to that though that is the reason I mean when I was doing that laboratory in charge when I was also conducting those experiments you know for students so this kind of graph they used to plot then we used to explain no no that is not right you have to subtract the distributor pressure drop and then only you will get almost horizontal like that okay so this is the one okay good so this is of course at this point what we call it as Vmf if you go much much beyond this much much beyond this where terminal velocities come it is pressure drop only we are plotting then what will happen solids will go out okay then you will get something like this actually this is maybe approximately because solids will go out of the system that means total pressure drop is less right so this will happen I think I will stop here I have to develop an expression for this I think that that I mean I think Ravi has become to me also terror I think he made me like that shaker want to run okay run run this is delta ps okay even though you are right here delta ps this is wrong it should be removed subtract only this one you have to add okay okay you leave