 now let us take packet by it first i think when i have the c u plate what is the kind of contact in pattern we have i mean the distribution is there workflow no no then what is happening see this questions when i ask you what a phenomena is required it is not that easy to answer my questions even though they are simple stupid questions once you have common sense then i think it is very easy is very easy, what is happening on each plate? Exactly, overall plug flow, each plate is a CSTR, okay, you have tanks in series, overall you may have that, okay, so what is happening at each and every plate, I think the liquid will be bubbling, the gas will be bubbling through the liquid and after some time it will overflow if there is a wear, that means you know what is that, down comers, otherwise they will simply go through the sieves themselves, okay, but on the whole the amount of liquid that is retained on the, on the sieve will have some residence time that is and also there is perfect mixing between, mixing means you know all the bubbles are creating good mixing in the liquid, okay, now we are talking about only liquid or gas, for liquid only we said that, you know tanks in series, what about gas, gas what is overall flow, gas is starting from the bottom, bubbling through liquid on the bottom plate, then again going to next plate, again bubbling through, next plate again bubbling through, so if you take only residence times will be different, but if you sum up all the bubble times when it is coming out, that is equivalent almost 3 of all, plug flow, how many things are there, just imagine, that is why I was telling you instead of talking stupid things on this teacher is bad, that teacher is good, this teacher is lousy, good you would not tell normally, okay, good normally no one will tell, so only bad things only we will project you know in the hostels and all that, so instead of doing all that, why do not you sit down as groups and then start questioning, quizzing yourself, okay, really then only you learn the subject, you just sit down, you know all of you may be in one hostel or may be two, three hostels in that hostel whoever are there chemical engineers you come together and then say that at least, okay, today is Saturday, Saturday anyway I will take the class, Sunday morning, Sunday morning, sit down and then try to question yourself, okay, now I know there are different pumps, how do you choose them, right and particularly MSBHT scholars also, I am not only talking about MTech scholars, MSBHT you always talk about your guides, that is true, I mean they do not have any other work you know, because they do not realize also that brain is there and that brain if it also something is there then I think that they will sit down and then talk to, criticize their own guides, always you know other, okay I mean I should not say that here, yeah, so other people look very beautiful for us, right I think that is why other guides for you will look beautiful, Swami may be thinking that some other guide is beautiful, his guide is not beautiful, okay, so like that you know that other guide student will think that he is a lousy fellow, other guide is excellent, that is all you think, you are not thinking about the subject, you are thinking about the guide where there is no use of thinking about guide, you do not learn anything from that fellow, by discussing about him, so that is the reason why I think you know you have to start that kind of thing, you know we say MIT is great, you know why, because people will not talk about people, people will talk about subjects, that is why, but in India every institution is lousy we say because before anything we talk about people first, that is all, I think you know nothing else, we always talk about people, you can just imagine now, you can just see what you have talked till now, did you talk any subject to your friend, any type, if at all you would have asked whether, okay, next semester subjects are coming, which one is the easiest to pass, that is what you could have asked, not what he teaches and what you learnt, correct no, how do I get that 7.5, if it is MSPHD, correct no, 7.5 is the border for you, that is all, which courses if you take, easily you will get 7.5, no, Swami, correct no, I am telling the truth also, correct, M Tech people may be telling that, okay, without doing any work how do you get maximum marks, because they do not have that border, but maximum is 10 out of 10, if it is possible to take courses with some teachers where you get 10 out of 10, everyone will go to them, that is all, so this is what is happening, unfortunately that is why absolutely no, there is no learning, absolutely there is no learning, anyway same old story, okay, so now we will go to packed bed, we will take 1 or 2 columns and then just try to discuss, yeah, in packed bed I know that we have this kind of bottom and top distributor, then you send gas maybe from the top or bottom, so these are the packings, this may be catalyst, okay, that may be catalyst, but ideally we expected that this may be plug flow, because you can see the flat velocity profile and that is the requirement for our plug flow, that means when you have flat velocity profile only, you will have each and every particle exactly spending same time and but in reality, I think you know, this is only ideal case, where we imagine, in reality what kind of velocity profile you get in packed bed, because all this information is required, all that is required, what kind of profile you get, actual profile in packed bed, I am sure none of you would have thought about that, Purovali any idea, what kind of profile in actual system you may get, ideally we are assuming that you should be flat profile, because my mathematics will be simple and Rahul, why laminar, so you mean this kind of profile, what do you mean by turbulent with backflow, jigsaw poke, is this one you are talking or something else, what is sort of, what else you draw you tell me, more you cannot, you know the actual profile in this will be, you know why, now I gave the profile, at least you try to find the reason why it should be like that, particles are near the wall, you have you know the voidage is slightly more than, at this extent, okay and that is worse when you have smaller and smaller, so if you take may be 3 feet or may be 1 meter, 1.5 meters, 2 meters, you may not see that kind of profile there, but in the normal columns you will see that, right, so that is why we are now trying to flatten this and then say that ideally we have flat velocity profile, right, that is one, that is even that is ideal case, but the true profile will be something again like this, fluctuations, so that fluctuations will be our non-ideality, so the ideal profile for packed bed is ideal is ideal is P f, now tell me non-idealities, non-idealities because we have to identify in each and every column, okay, yeah, first of all solids batch and the fluid which is going in P f if it is ideal because I have liquid and, sorry, I think I have to write not, yeah, two phases but I would write, instead of writing this, this is batch, this is continuous I will write, in continuous if it is ideal plug flow then you have P f, right, okay, good, so this is the one and now non-idealities what are the non-idealities we can expect here, very fast if I write on my O without discussing, very channeling occurring in a packed bed because normally what is the height of the packed bed or L by D of the packed bed, D is the diameter, L is the length, L by D, what will be the L by D of normal packed beds, many can tell, may be knowing in industry, huh, so definitely more, okay, more may be 20, may be 30, right but you know when you have that kind of long columns do you expect channeling, I am just questioning, I am saying whether she is right or wrong, huh, towards the side, near the entrance, near the entrance, okay, for first one, now one non-ideality is axial mixing, that you will agree, axial mixing is one, right, why, because we do not expect, we expect only flat velocity profile but generally you will have the particles moving back and forth because of the packing and also because of the turbulence, okay, turbulence if you imagine, turbulence is like this only, even in normal turbulence does not mean that you know you have perfect mixing, that you have to separate it out, merit, yeah, right, so when you talk about turbulence we are not talking about perfect mixing, we are talking about over the turbulence when you have the velocity profile, that will be shown only like this, if there are slightly more turbulence then you may have a little bit like that, okay but even then that is always under axial mixing and what about the radial mixing is it perfect, non-ideal packet bit, what do you expect in radial mixing, radial mixing should be perfect, axial mixing must be 0, then you will get plug flow, right and the radial mixing also should be infinity but do you have infinity radial mix, that means infinity does, means that across that you will have same concentration and temperature but actually what should be because all packed beds are chemical reactions, you know whether they are endothermic or exothermic then you have to put a jacket outside or some kind of heating or cooling mechanism inside the, inside generally we do not put in packed bed but that is also possible, we can also put that, right, so imagine that I have the outside jacket then it is exothermic reaction, easy to imagine, then I have a coolant here, what will be the temperature profile inside, at any cross section if I look because heat transfer is taking place in this direction, exothermic heat inside the reactor, uniformly generating because of this profile but heat is removed and where do you have less temperature, where do you have more temperature, yeah more temperature you will have near the, you know at the centre, less temperature there, that means there is a gradient in temperature, right, so particularly when I have gas phase reaction do you have concentration gradient now, yes, how does that affect C A equal to P A by R T, at any point P A by R T, so when T is changing concentration also changes, when concentration changes along the length how can you assume that you have plug flow because plug flow definition is across the cross section you should have perfect mixing, perfect mixing means concentration must be uniform, that is why in fact the greatest problem with packed bed C is not axial mixing, radial mixing, radial non-uniformities will be there, what we expect is ideally there should be uniformity of concentration in the radial direction but that will not be there in most of the packed bed reactor, axial mixing actually it is not a problem, okay, so that is why radial non-uniformity, radial non-uniformity, okay, that is also a kind of non-ideality for us, okay, then what are the other things, this is one, this is two, where do you expect dead zones, near the walls we assume velocity equal to zero but you cannot say that is dead zone, yeah, see when actually I put this kind of cone, if I do not have that kind of cone, if I have only flat, anyway that is the distributor plate otherwise it cannot enter, so here you expect some kind of dead zone, similarly even here also you may expect some kind of dead zones, so dead zones also if you very badly designed this is what is happening, right, okay that means very badly designed means I have a packed bed something like this, okay and then entry, right and also height I do not know L by D must be 50, 60 or 100, so then I will put L by D equal to 1, I like 1, so that means it will be very very lousy, correct no, L by D, this D and L both are same, so this will be something like this and again you are putting this is one of the lousiest designs of the packed bed, then what Sushmita telling also will come there, channeling because by the time it goes like this and then again it has to come like this, so all these things are waste, dead, this is channeling, why it is channeling because it is supposed to spread throughout and then come but instead of that straight away it is coming because you have this much dead zone, this much dead zone, in fact that is the reason why you put the same shape here, correct no, the same shape is here because this is how if you are able to design this kind of packed bed, so then packing from here then you will have the velocity, entry at exactly plug flow entry, I do not know in transport phenomena when you are assuming you assume flat velocity profile entry into any equipment otherwise that variation itself is a big headache for us, that is an assumption that is why next time when you are taking, this time or next time you have, yeah next time when you are taking please be observant for this assumptions, each assumption has a tremendous meaning to simplify the mathematics, okay, yeah good, so yeah this is radial and also dead space and if packing is not properly put then if you have some kind of more wide edges there you may have even recirculation, so that means it is recirculating and then going back and again may be going back you know like turbulence, okay that it is but recirculation generally we do not expect but that is also a possibility, okay good, so this is the one. Now this is for because solid is batch we are happy, we are only talking about continuous phase and in general continuous ideal should be plug flow, liquid should be moving in the form or gas can be moving may be moving in the form of plug flow but if you do not have plug flow then what are the other non-idealities that are coming into picture, non-idealities are axial mixing which is not very serious but radial mixing is much more serious even mathematically also solving that is slightly complicated than axial mixing, right and you have dead space but dead space and all that can be easily you know there are some things which you can tackle on your own you can avoid dead space provided you design like this, so you do not have to worry about dead space but axial mixing and radial mixing you cannot avoid definitely there will be some kind of axial mixing and radial mixing definitely you also have because temperature gradient because of the term you have to remove the heat, right but if you have adiabatic system you may not have, if you have adiabatic packet bed that is the reason why for SO2 reaction and all that you know SO2 they use adiabatic packet bed even though it is exothermic reaction but where do you cool one bed heat exchanger another bed heat exchanger another bed heat exchanger there that packet bed will be almost ideal plug flow if you maintain again sufficient L by D so that is all for everything there is there is a beautiful explanation provided you want to think and then do it, okay so this is one the second one let us take as fluidized bed, right fluidized bed normally shown like this, okay so, okay these are the you also have what are called bubbles in fluidized bed these are the solids and this is gas most of the time fluidized bed is also used for as a reactor catalytic reactor so the solid will be catalyst, right when solid is catalyst I can put that as in batch condition may be batch, okay or it may be continuous also that means I am taking continuously and then solid continuously entering solid continuously leaving, right and this example of solid continuous solid coming out can be also all this ore reactions for example iron ore if you want to convert to iron, okay what is the reaction iron ore to iron, what is iron ore, reductionally, reductionally, reductionally F U 2 O 3 R F E 2 O 4, okay F U 2 O 3 let us take reductionally, F U 2 F E 2 O 3 solid plus what is the gas use carbon monoxide are or no other CO 2 hydrogen, hydrogen gas yeah what do you get F E solid plus H 2 O gas my god I am losing time here, okay good so now how do you balance this is 2 O this is 3, okay correct 3 H 2 O yeah O I have written smaller yeah here 3 H 2 this is the one so now solid can be continuous and solid can be continuously coming out, right and the gas is entering fluidizing and also reacting with the solid and that goes out you know H 2 O may come out in the form of vapor, right so what are the ideal conditions here now I have solid continuous now again you know slash continuous or batch sorry gas continuous gas always continuous so like this you know for every time every time you have to now analyze, okay you take an equipment how many phases entering whether they are continuous whether they are batch and once you know they are continuous then now you have to discuss whether they are plug flow or mixed flow now tell me gas how it moves is it in plug flow ideally first is ideal ideally is it in plug flow or is it in mixed flow, okay so now gas okay PF ideal why do you say PF ideal I mean gas ideal PF it is velocity profile by the way for gas because I think the gas is mostly going in the form of bubbles yeah so I think you know there is a lot of question it can be either plug flow or mixed flow this is a question mark, okay next course only we will clear this when under what conditions it is mixed flow and what conditions it is plug flow it is plug flow when you are maintaining the bed only just at the point of minimum fluidization velocity, okay Arya you heard of fluidizer bed fluidization is an operation where all the particles are kept in suspension by the drag force of fluid it can be liquid or it can be gas in environment engineering mostly we use liquid and in catalytic reactions and non catalytic reactions mostly we use gas, okay so and also that minimum fluidization velocity is the velocity that is minimum required to lift the entire particle and then just keep in suspension above minimum fluidization velocity when you go then these bubbles will form if you are able to exactly maintain at minimum fluidization velocity then you may assume plug flow and you can never maintain exactly at minimum fluidization velocity that is also there why you need some kind of good contact between gas and solids that is the reason why you are using fluidizer bed and when you are using just only minimum fluidization velocity that contact is not guaranteed that is why we go 1.5 times minimum fluidization velocity 2 times and in industry 40 times minimum fluidization velocity all this we can discuss in the next chemical ya chemical and catalytic reaction engineering but anyway so that is why I said P F R M F both are question mark under what conditions we do not know, right this is for gas we have to find out in fact if it is very simple plug flow or mixture flow there is no thrill in fluidizer bed at all like exothermic reactions we also have lot of thrill in the fluidizer beds fluidizer bed exothermic reactions are much more thrill because one thrilling is exothermic reaction another thrilling is fluidizer bed itself, okay good so that is the one now if I take solids solids are in batch in continuous it can be in batch but I think let us make continuous as for this reaction non catalytic reaction because continuously I feed continuously it comes out so how the solids move is it in plug flow or is it in the mixture flow ideal can be both why how can it be both normally what are the dimensions of fluidized bed what are the dimensions of fluidized bed L by D wise it will be diameter 1 inch and then height will be 100 inches so then L by D will be around 1 or maximum it can also go to 2 or 3, okay why beyond that you cannot go I can tell you in the next semester because there is what is called slugging and all that comes because particles will move in the form of slugs not as real fluidization all these problems are there so generally L by D 1 to 2 is the best design and less than 1 will be again shallow bed shallow bed less than 1 that means you take 1 inch diameter not 1 inch 1 foot diameter and only 6 inches height, okay 1 inch diameter 1 foot diameter and 6 inches height so that will be called shallow bed so we are wasting lot of things there in the bed so that is why we do not want to use that kind of thing L by D normally 1 to 2, right so when I have normally 1 by L by D equal to 1 to 2 what kind of flow I expect for the solids see this is why when we are discussing this I do not know other teachers are telling you like this are I think every teacher must be telling in the same way otherwise how can you explain you cannot explain so when it is actually when I ask you know what is really happening how the solids are moving you have to imagine a lot you have to imagine how gas is flowing through that and how gas is flowing through solids whether it is pulling pushing the solids away or it is lifting solids away what has happened to the lifted solids whether they are again falling all that imagination should go into your mind then only you can answer, okay, yeah now you tell me, why mixture flow of them, yeah mixture flow is right because these gas will try to take the solids up and somewhere it has to get separated and after that what will happen yeah for solids there is no more drag you know so that was the solids will simply fall when they are falling they go to bottom they just sink in so again some of those solids again picked up so when you look at that then you will have almost perfect mixing for solids because most of that means that that solid can be either here or here or here or here anywhere in the column that is what is the definition of perfect mixing and if you also take the temperature of the solids, okay or concentration of the solids throughout that means if you take reaction uniformly and same size particles then throughout the bed I will have the same conversion for a given time, okay, otherwise, yeah, because till here only you have the bed, no I think you are talking about pneumatic conveying but we are talking about fluidity, solid is continuously falling here I think, you have introduced here and then take out here, right and what he is telling is if I take very small bed, small diameter and a lot of solids there and then like slug what is the meaning by slug all the particles are just lifted up and there also after some time it will break because some of the solids will go and touch the walls and what is the velocity near the walls 0 then what should happen to the particles they have to fall down, right when you go to pneumatic conveying that means the velocity is much much higher than the terminal velocity of the solids so even those few solids which are near the wall they will be also taken away by the gas that is why that kind of high velocities but even then in a pipe where you have the boundaries pipe will have definitely boundaries even perfect pneumatic conveying you will never get why again near the wall velocity is 0 so some of the few solids 1 or 2 particles which are near the wall may slide down even if you go beyond pneumatic conveying all these things are you know nice way of telling like in breeze when you have lot of breeze there are no boundaries there so if you have very fine solids all those solid solids will be taken away you should have seen no recent cyclone what has happened lot of dust has come and fallen on us there is no boundary if there is a boundary or boundary is administrative block for example just imagine so those particles which hit administrative block and on the surface of administrative block there will not be that kind of velocities for particles would have slide same your body also acts as a boundary particles will come and it will be thrown on your body and face but once it starts here again velocity near the you know skin is that is 0 so some particles will fall down if it is fine dust that will stick okay then you have to go and wash your face otherwise people cannot recognize you who you are so that is why even truly pneumatic conveying also some particles will be sliding down okay good so that is why here you have for solids perfect mixing mixed flow now what are the non idealities that will come here okay the non idealities I think you know we started heterogeneous systems homogeneous systems we have discussed sometime I think in the beginning itself what are the non idealities that may come like if I have a CSTR single phase liquid for example okay what are the non idealities you may expect when you get dead zones near the corners that is why again we try to put bowl like thing right yeah then any other here are the recirculations near the end near the stirrer yeah the stirrer is very badly designed recirculations will be near the stirrer that means the fluid which is touching the that propeller you know that blades and that may be recirculating there itself all the time that will not mix with other components yeah one more bypassing by wrongly putting the inlet and outlet it may bypass bypassing is an inherent quality for mixing but natural bypass is different this is artificial bypass by putting wrongly the input and output things that means if I have yeah so if this is the pipe this is the tank this is the tank bottom is closed and this is entering here logically at least I should put in the opposite direction logically okay so by innovation okay I will put my inlet here also outlet here like why okay like why why I do not know how to put okay like this right so that means it enters and comes out it will not go down that is the reason why the best design for CSTR the mixed flow is bottom top okay so you will not have bypass there bottom inlet top outlet why cannot you do the reverse I can also do know here inlet here outlet yeah but you know the maintenance of level is not easy I told you know after sometime everything becomes common sense after sometime but you have to reach that level you have to use first sense then it becomes common sense okay yeah so that is the reason okay so that is why you can expect their bypass if you wrongly putting inlet and outlet pipes okay so that is what we call that one as bypassing oh no where is that non-idealities I am writing oh I have not written non-idealities okay so for mixed flow okay for plug flow when I have plug flow for gas the same non-idealities what we mentioned here will come anywhere plug flow you will definitely have axial mixing you will definitely have radial non-uniformity okay and then by wrongly designing the column you may have dead space the circulation that is what what you have to learn that means under plug flow conditions what are the non-idealities sorry to say this one but see I cannot say under plug flow conditions what are the non-idealities the moment you say plug flow it is ideal okay you may be imagining as ideal plug flow but what are the non-idealities possible under those conditions the first one is axial mixing the second one is radial non-uniformity because I think there will be mixing but it will not be perfect mixing the third one will be yeah the dead zones dead zones are in your hand you made it with your hand by wrongly designing the pipe you know by putting the you know without putting the cone right so that cone will allow you to develop the velocity profile then it becomes flat then it enters if you are not allowing that then you have dead zones and some kind of channeling will be there what he said is right channeling will be there if the L by D is very small okay L by D of packed bed is very small and one corner when you have more solids another corner you have less solids correct know because you are not properly adjusted the solids in packed bed so under those conditions channeling also will be there right so whenever you have plug flow general okay plug flow will have axial mixing as non-ideality radial radial mixing radial mixing non-uniformity that means okay that means it is supposed to be uniform across the cross section it will not be there then dead zones okay actually the dead zones are man-made or woman-made okay now it is as you cannot say only man-made person-made okay yeah so that is why you are dead zones you can actually stop dead zones by designing nicely right and some kind of channeling channeling double N or single N double L single L or okay so this is channeling these are the general things non-idealities that come into picture if I have non-idealities okay so when I have mixed flow mixed flow we may have dead zones re-circulations no okay and bypassing okay bypassing or short circuiting also we will say but bypassing you know generally the thumb rule is that for packet bed channeling is used and for mixed flow bypassing is used so the difference is in channeling at least the fluid will spend some amount of time but bypassing is almost instantaneous it may not spend even one second or two seconds or maybe two seconds it may spend if they again in comparison with your mean residence time mean residence time to if you have 10 minutes if you have the channeling may be having one minute and whereas bypassing will have only one second or five seconds that is the meaning of channeling at dead spots so now as I told you I promised you that you bring any kind of reactor to me which is there on this planet okay any kind of reactor like yesterday you said trickle beds yesterday you said moving beds of course fluidizer beds all these beds can be imagined in terms of only two mixed flow and plug flow any reactor you bring but you have to look at this thing like for example trickle bed in trickle bed you have solids in the batch condition then we have gases gas moving from the top liquid also moving from the top right how this movement is taking place in trickle bed we are fortunate because you know the solids are in batch condition we do not have to worry the other two phases we have to worry liquid will enter and also gas will enter depending on gas velocity and liquid velocity one will take the other like you know behind you in OAT if he is a very strong guy he will push you he will take you you do not have to only thing is he will not lift and take you but he will be pushing you and then you will enter but if there is a small kid and you are heavier than that small kid you will push that guy so similarly in trickle bed also that happens depending on which phase has more energy more velocity then that will push the other one so normally what we expect for both is plug flow or mixture flow also trickle bed diameter is small compared to that is why that shape also you should you should get immediately in your mind shape also shape of the reactor also immediately in your mind you have to imagine otherwise you cannot answer these questions right simply not telling trickle bed without knowing because somewhere you would have heard of trickle bed you come here trickle bed and say trickle bed unless you have that feeling I told you know finally nothing will work without feeling I say even your love will not work without feeling you have to say that love with so much feeling so for that you have to take training from Kamalasana or someone but I think you know really because that guy is a great actor so I think you should get ask her sometime so he will show what is that real feeling is okay so if you want to say that words go and take training and then you can say that otherwise simply I love you doesn't mean anything okay same thing with subject when I like CRT when I love CRT means that feeling should be there otherwise there is no you don't really enjoy that simply you are saying some words like trickle bed we don't know okay then fluidized bed we don't know whether there is solid or gas or anything okay so that kind of feelings will not help you at all you should have the real feeling and to develop the real feeling you have to totally immerse in that field okay nithu nithu simi simi nithu nithu ya okay ya so that is the what is the problem now I think I will leave you