you [Music] good afternoon my name is Samir Khan Decker and I'm professor in the Department of Mechanical Engineering so I am told that you are the the the ticket fellow so to say isn't it and you are all now located somewhere for three year program is that correct I think there was one more batch which came before this and this is the second batch okay yeah so I think we have only half an hour actually so I do not know I mean we I tried telling the last batch some things and I will try to sort of experiment with you also I'm an experimentalist anyway so it's basically to talk about teaching in thermodynamics and heat transfer okay and that is what I also teach we have a core thermodynamics course which is done by Moore almost all they cross the Institute and we also have a heat transfer course heat and mass transfer which is done by the mechanical engineering students it's a compulsory course in the sixth semester okay the present semester I'm teaching in fact and how many of you are trained in thermal or fluids one okay two three okay your most most of your M Tech's or pH DS also know most of your M Tech's oh you have submitted your PhD thesis okay so okay so anyway so what I wanted to tell you was that look thermodynamics is a vast course so I don't know whether you will be you will get a chance to teach or not heat transfer of course many of you may teach okay depending on your interest also and the type of Institute which you are in and there are plenty of books which are available in there both of them are classical subjects so to say okay so plenty of books are available some of the books are user friendly some are more matured some are for more matured students for mature teachers for example some of them are very user friendly and right now one of the most popular books which we are using here in iit also is the thermodynamics as well as heat transfer is by professor called you know shingle okay so shingles book is pretty good if you really devote your time reading it and try to now the what why that book is good and why I also like it as a teacher I can tell you that two things one is the book is very friendly it talks to the students I mean it talks to the reader okay there is a dialog which sets up you know between the author on huh it's like yeah it's like a teacher itself you know it's like it's like a speaking the other thing which is more important okay is the fact that two things are important one is that the examples which the book gives are very realistic okay that means the data which has been taken the assumptions which are done okay the the calculations which are done are very very realistic in what goes on in the industry for example or what goes on in the in in the market so to say yes in our surroundings so that is one the second thing is that it it it picks up that that word is important surroundings it picks up concepts from around you isn't it and then tries to put the theoretical framework and gives those examples and then connect the two so I think it is very very very important as a teacher okay that you the subject which you are to teaching whether it is thermodynamics or heat transfer of strength of materials or for that matter any other subject you should be able to teach you should be able in a way that the student connects to his environment okay the connect the connectivity with the environment that means the engineering is not in the book engineering came then the books came so we have to understand that the book is not where the knowledge lies the knowledge is actually spread up everywhere book has formalized it it has made your life easier it has been segregated into chapters so that the delivery or the consumption becomes much more lucid and and interesting for example however mullet is around us that means for example I was I usually give this common example of let's say your finger gets burnt you know you are ironing the clothes in the hostel okay or your mother is cooking something and you happen to touch you know the thought tebah for example and the finger gets burnt okay now one can one can take this example of a finger getting burned and then all the equations of heat transfer the energy conservation can be applied and you can teach them with that as an example isn't it you have you you have a mass of the object you have some specific heat of the object you have a thermal conductivity of the object okay then a certain amount of energy has been supplied to the system so you can make a control volume and the energy comes in no work is done so that means then the energy must be equivalent to the the heat supplied must go eventually to the internal energy of the system so DQ is equal to du plus DW there is no DW so DQ must be equal to D you isn't it and then what does what does that do you do naturally there is a row and there is CP and so that there is a delta T so there is it's a fixed temperature system and there is a big body which is isothermal and a small portion has been burnt so it you can take it as an semi in finite type of an object is it not and then the heat comes in the temperature rises okay now there is a pain threshold beyond which you start feeling uncomfortable so now as a transport engineer or as an engineer what is your job you want to get rid of this extra energy and bring down the temperature how fast you can do it is what you are looking at right now sometimes you have to do the other problem it's like how slow you can do it you know isn't it you want to preserve the heat you don't want to take it out isn't it so what do we do forget about books forget about everything else what do we do when our finger gets burned okay we can just keep it like that we don't do that even did we can it will cool down will it cool down or not yes it will it will cool down we can just keep it like that and there is a certain physics by which it will cool down you not because the the the temperature close to the a the the air which is close to this finger will get heated up it will expand there is a beta isn't it there is a there is a volumetric expansion coefficient okay for an ideal gas you can find it out for a non-ideal gas also you can find it out it will expand when it expands it will become lighter there is a buoyancy force now a row at temperature t1 and Rho at the ambient so there is a Delta Rho so G times Delta Rho will be a force which will act on the object and it will rise when it rises cold air will come in isn't it now this can be formalized in a book and you can talk about grashof number you can talk about you know nusselt number coming out as a function of the grashof number and things like that is it not that all formalization can come but the student should understand that this damn grashof number he already knows actually he already knows that it can cool down and this is how so this is where your role as a teacher comes in if you just derive nestled is equal to constant in crush off to the power a you know it will not click it will not that the student will not become happy to learn okay and then you will share your attendance okay our final attack you only give milk on your couch in half way is it not because I cheat milega padang Anna you understand so the value addition which you guys have to do is the connectivity of that equation with the outside world which we they already know actually even even a dog knows that when there is when his finger gets born you like that when do I say the career so dog knows that if you do like that the heat transfer increases is it not why because just keeping it like that the force which was there was only buoyancy now there is an inertia force there is a relative velocity between the finger and the ambient and then suddenly it comes at nusselt is proportional to R a Norris isn't it you do this Renault somebody increases is it not and then yes this is better is it not it's not that then what do you do you put it into ice you put it in cold water so that means previously some some air molecules were hitting this is it it now some water molecules are hitting it and you feel better even if the Reynolds number is the same even if you keep the Reynolds number same still you feel better because now the the molecules which are hitting there they something has changed isn't it something has changed now the same molecules when you change the molecules your cooling curve is better now is it not that means other than the Reynolds number there is something else which has to do with the molecule itself which is responsible for enhanced heat transfer is it not do you agree with me ok then now suppose you are still not comfortable what do we do we put we make it wet and then blow air now it is much better so what have we done we have changed the physics now from single phase heat transfer we have moved to two phase heat transfer we are now making use of the latent heat the HfG was not there in the previous example is it not now latent heat has come in and we suddenly see that the heat transfer coefficient is now much much much better if you put some ethanol you know and then do like that that will be still more better is it not so this is where you as a teacher have to come in okay you as a teacher have to come in for example all heat for example your mother you know when she she cooks aloo is that not a Luke or Duvall there then what do we do she keep she keeps it on a tap water or Purnima darken then she starts peeling off so the temperature must be been the temperature of the top surface must have come below 40 otherwise the haja lega 40 42 okay is it not after that though the hot Jen Elega how about the inside temperature is it still 100 is aloo inside also hot enough when the when the peeling takes place what the temperature outside is 40 42 what about the inside temperature if you break it open you see steam you see steam that means can you take a loo at the lumped parameter system no you cannot is it not is it not if you have a copper ball and if you put it in water isn't it what will happen the inside temperature and the outside temperature will be more or less the same more or less the same more or less the same isn't it so now you can now with this with this discussion then you say there is something called Bo number there is a thermal resistance of conduction thermal resistance of you know a convection and then you describe what is the numerator what is the denominator and then it will come alive is it not so I mean we take baths for example you know when we take baths if you just put the null you know very small what happens the water stops dropping it comes down how what is the shape of that water jet is it is it like that straight or is it like this why does it become forget formula forget fum and that's what I'm trying to tell you don't go into the go to the formula at the end first understand it speed is increasing that means it is accelerating and Rho AV has to be constant it's a therefore you will see that as the velocity increases the area of cross section will go down after a while it becomes unstandardized eetu give the drops because surface energy is needed to create drops who is supplying that energy so the kinetic energy the inertia of the system the kinetic energy the accelerating kinetic energy the gravitational pull is there and that kinetic energy part of it but why does it become unstable then you go into the rear then you have a navier-stokes equation you perturb you pulled up the navier-stokes equation you create a perturbation equation you subtract the two and have a linear theory for example for perturbation and then you will come to know that there is some really Taylor instability there is some there is some sort of an instability which will grow and when that instability grows this nice jet which was coming will now break down you know and you can have atomization for example so what I'm trying to tell you is very simple what I'm trying to tell you is please whatever subject you are teaching whether it is thermodynamics or heat transfer or solid mechanics or manufacturing process okay or fluid mechanics please see that subject around you how many of you have calculated the rate of heat transfer from human body how much heat are we dissipating can can a problem be simpler than that every day we dissipate energy every day we try to write now I am trying to reduce my energy as much as possible by putting multi-layer insulation in if this is MLI isn't it multi-layer insulation okay how much energy are we dissipating anybody any idea rough guess what 50 what he says I don't okay so that the first guess which he has made right let's say it is fixed let's say right now it is 25 so delta T is 20 degrees let us say how much is the typical area human body area either cylinder that's a very nice model you can but forget about cylinder also I can give you the area of the body also now you should know the area how much is the area of the body any idea a grown up body how much is the idea any idea a rough guess Mauro cylinder liquid 2 pi RL is it not so so this is no I'm not interested in the answer right now I will tell you the answer that's not but what is important to know is that you have all mtech all have studied heat transfer but we have never bothered to calculate how much heat is dissipated by me is it not this is what I am trying to tell you you understand you know how to do a differential equation you know what is homogeneous equation you know what is non-homogeneous equation you can derive you know you can if the boundary condition is known to you you can get C 1 C 2 you know and get some you know some values of of the constants okay you can convert you know you can have some you know separation of variables and integrate all that you can do but the connectivity with real engineering is not there that is where we have to be different and that is why I am different that is what you have to say also after five years that I am different because I made my students connect to the real world you understand I still remember my first interview was in Heathrow in a campus interview okay and I entered the room you know there was this door and I push I entered and I sat and then after some discussion the person asked me please tell me example of combined loading okay now a typical student will start thinking combined loading means beam vinayagar skipper Chris Walker egg are you point load this load moment I just told him that I just entered the room the handle I had to give a torque and push combined loading is it not this is what I want you to do and then you will be a good teacher you understand the student must be enthusiastic enough after your course that as soon as he starts going out he starts looking everywhere he come fluid mechanics decry miracle you know car heat transfer very good the karate is it not extended surface has fins we teach it not these fish we see fins everywhere is it not whenever we are feeling cold we sit like that when we are not feeling cold whereas you could not Jeremy on Alexa so is it not feeling system am I not extending my area you did not so Wieck why don't you take this as an example well made about handy Loctite oh my F a hot car TomSka if there is a fire here I don't put a hand in line with it so there is a shape factor you dip not as a cardigan we were very very Mira to shape factor can you cheat Ravana Omega area nose Nicobar micro Oh Karma I am not undermining it I'm not saying that you don't have to do that you can't you can't only talk they have to analyze also they have to understand but then with equation to use ven which boundary conditions to apply which what are the assumptions under which this equation will be valid okay and the spark which comes that oh this can be solved like this can only come if the teacher has done the due diligence that he has made his students aware of the connectivity of that equation the terms of that creation with real-time situations okay so if you want to do it it's it's it's hard work it's not easy see right now what has happened is unfortunately those people who don't do don't get anything else in life they want to become teachers I mean we are all part of the same community is it not but then once fine that's also fine you never got anything else now you want to become teacher that's also fine but once you want to become a teacher now then everything which is needed to make that profession worthy of it and you enjoy your teachers your your students enjoy your your colleagues enjoy is what now you have to do you have to inculcate an interest if the interest is not there if the interest is inherently there then there is absolutely no problem is it not absolutely no problem okay so coming back to that question you know so is radiation important when heat transfer takes place from human body why normally people say that radiation is only important at high temperatures we are not high temperature so why do you say radiation is important forget that but why is it why do you think that is an important thing when you are you when you are doing a human body calculation if I'm going on a motorcycle I am doing a calculation for the heat transfer from the engine fins I don't care radiation the temperature is much higher there but at human body the temperature is only 37 but weaker comparable to absolutely so what so the idea here is that there are several modes of heat transfer okay and all of them are probably playing a role all the time is it not most of our systems have convection conduction and radiation for example this building right now all of us are sitting here there is radiation there is convection there is conduction naturally okay in the human body so everything is important now which one to assume negligible or which one to focus on will depend on the relative magnitude of the things is it not so in a human body example the natural convective heat transfer and radiative heat transfer are almost equal and your answer has to be multiplied by two yes okay you do the calculation you understand so this is what I want to stress you know in half an hour I cannot tell you everything okay but the the underlining let's say message the take-home message which I want to give is that make an effort so that the equations which you derive in the class come alive talk about examples which can be related to that that that equation okay that equation is not a dead equation otherwise the same equation can be taught by a mathematic student also a mathematics teacher also is it not it's the same differential equation no lets say energy equation or partial derivative equations which are navies Stokes equation it can be taught by a mathematics mathematician also so why is a mechanical engineering engineer being asked to teach that equation to derive that equation okay boundary condition deliciously browned recondition you can write it but do you know what is directly boundary condition in terms of temperature how do you achieve it which systems are there around you wherein insulated boundary condition is really working or is it really possible to have an insulated boundary condition in real time scenarios how close can you go to a insulated boundary condition when you say convective boundary condition has H is equal to 10 what does it mean what is that ten how many systems are there which have H is equal to ten how many systems are there you have a PC for example there is a fan at the back isn't it what is the H in those systems is it 10 is it 50 is it 200 in the 2000 watts per meter square Kelvin see there is one order of magnitude coming in this class itself it must be around 53 answers have come this is important please try to get real-time values and that is why I said some of the books are good these books have examples these books have problems wherein the value which has been taken is not just because could be the idea Anthony all these books the good books will always assume values which are very close to real-time technological or real-time industrial problems ok so it is very important for you to get hold of these books solve these problems before you go to the class and then get a feeling of what is 100 watt what is H is equal to 20 which are the systems where H is increasing what do you mean by low Prandtl number systems what is the what is the meaning of high Prandtl number systems ok if an Indian oil is falling down of a hot wall is it a low Prandtl number system or a high pontal number system you have to keep thinking about it if you do that then your teaching will come alive that means people will be happy to come to you even then and then there is no problem of attendance or anything is it not so I think I have run out of my time no no no that's ok mullah is already here so Malaya will also discuss a few things he is also a fantastic teacher he also taught large classes fluid mechanics not thermodynamics also a fluid mechanic so he has start he has taught large classes 450 400 students like 380 students fluid mechanics I have taught large classes with thermodynamics ok so that also requires enormous amount of you know planning ok Emily I can be mad I can give a lot of ideas about how to plan for a class because the course is wide everything has to be covered and interest also has to be simultaneously let's say you know it has to be kept alive you cannot leave anything also and they are young students so you have to give them a lot of assignments you have to make sure that they are doing it you have to take a quiz also in between and there are only 40 hours or even less 35 36 hours which we get in a full semester so teaching fluid mechanics in 35 hours with lot of interest lot of examples and derivation and whatever I have told you how to make it alive and things like that is a very very challenging job ok and enormous amount of time has to be spent before you go to the class and maloi will also agree every class is different the same topic Bernoulli's equation every time you go you have to think you have to work you know how I am going to pitch it what diagrams I am - there are three black boards which black board I'm going to use how when all that has to be planned otherwise it goes haywire is it not so that that delivery is like a program it's like a it's like a you know it's like an you know some actor going in yeah yeah it's like an it's it's an act it's an act and every actor wants the full impact okay so you don't go to the class just like that okay so plan out things read these books talk to the students and before that you get hold of all these numbers you know what is hundred what if I just do like that how much what I am how much what is your heat is coming out is it not huh half way half multi-angle but keeps my energy be clear you know you should have some feeling of that so assume a friction coefficient okay think what is the velocity is it not and the weight of the hand is known to you more or less so you can find out a work done and all the work is now converted to heat nothing is happening is it not so it will increase the temperature okay so these are things which you have to do and that will then make it you are unique teacher so to say that not everybody will be happy to come to your class so with this I thank you and I invite Malloy to continue you [Music] you [Music]