Extended Surface Heat Transfer Example - Part 2
 
Hello for quite a few lectures we are discussing regarding extended surfaces, extended surfaces are very important that’s why you were spending some time on it. We need to know what are the different options available we need to know using extended surfaces what different designs various designs of heat exchanger we can have how to estimate the rate of heat transfer from extended services sector show in continuation with my previously is the present collector we like to see again some extended success it extended if you recall we were doing some numerical examples to know how to calculate the heat transferred from extended surface without bringing in heat exchanger now we slowly go into heat exchangers and how extended services are utilised in heat exchangers house calculation can be done for extended surface it is dangerous to this is what we want to do with the telephone number of examples this is kind of a write-up I have given almost a very brief but but very very important that we texting with extended services in there could be two different type of design one is in plate heat exchanger now completed a heat exchangermight have number of variations I am not discussing over here because that will be taken care of so there is no point no point I mean one should not think that there are no variations of this thing so I want to write that variations variations that will be discussed later one should not think that clicking it exchanger doesn’t have any variation through what I have written variations will be discussed later this year and what we can do we can classify them between two very important categories that we have separate individuals and teams will have it’ll fit this we’ll see how they are designed then we will concentrate onI got single phase of SG buses to the inside and the gas passes over the fence so basically we will have you and on the tube we will have him and inside the tube there will be there was a job by the liquid or gas liquid or liquid vapour mixture and on the outer side of the tube which is free and there will be passage of gas YouTube may have a number of separate fish or a number of teams with penetrate legal team play please I am telling time and again so that you have some idea and we will have also a number of figures from the Earthunderstand what I am telling plates are parallel to each other and be produced in passages for the transport of gas what I am telling that only inside there are fast passage of gas this integral think they will provide the passage to which gases if you recall when we have started augmentation of the transfer I have told that basically the engineer has to analyse what is the overall heat transfer if we see normal case is there at five resistances let’s say there are two free and we call them to e1 and e2 show convective heat transfer fluid one filing of fluid 1 then the metallic surface then the filing of fluid to an convective heat transfer of free to visit the five resistances one has to see which resistance is more and if there is a gas leak in heat transfer equipment heat exchanger then one will find that their side resistance is much more to get side resistance first we have to reduce so that’s why I feel that provided on the gas side this Hai I have repeated number of times so here I am feeling the samewe are having something to get extended to have some idea on that you there please so let us see these three three figures they are not use and on the tube there is peace here you can see the tube and fin their integral if you see this cross-section the song the same material tube and Finney they’re happy and now this design is alright but here you see while making this kind of paper component there will be lots of material taken out cut out or wasted quote-unquote wasted because we have to make make these cloths between the fence on the other hand what you can help the cube is made up of the material and separate kind of Irfan Irfan Shaikh received an attorney that you can find in these two designs show designs are common but the design which is shown in the top-right has got the advantage that it is havingwhere it is I think I'm sorry it is starting from here and it is ending probably at the top so it can enter from here and we can go out to eat while having a very long while it is having a longer need it you sure it will exchange see it when the gas is fluid which is outside the tube and to enhance the heat transfer with the gases fluid outside that you will be happy so you can see if you and these are kind of integral see one thing that is fierce by number of 1301 team played that is pierced by a number of these so this is what I had mentioned so in this case we are seeing individual firms in this case we are having a wonderful with number of tubes piercing it that is if he played with these letters go to the next diagram show here again we can see different kind of geometry here again we will not use a single tube there will be number of tubes so each tubes can have a number of things these things could be individual things without getting any connection with another this is one kind of design and actually what we want to buy providing thing we have increased the rate of heat transfer so in that way we have increased the compactness but we are not satisfied with that we want to go for more contact design so then what we have done in between the fence there is some sort of a gap we want to we want to abolish this gap now we are having integral sin play which appears by number of and to feel plates are parallel to each other so in between gas passes so that becomes the gas message okay so this is kind of it is I we we try to evolve from this first design design design we are going for design CND design see what we can find that these tubes have been made flat there are several reasons why we like to make make the stupid one reason could be that you see a circular body is a black body and when we are making it flat so we are reducing the phone Greg when a gas bill passed this is one variation we can find here but only place they have some sort of a surface modification modification in the same maybe maybe there are some old salsa dancers so this will give some sort of education or good mixing of the gas cream which is passing over this feels so many things we have done first thing you see how this concept of compactness is increased how first thing there were two on the black tube who have provided number of the film where there was no material that gap we have a blessed by providing integrated then we have made these tubes flattened and then what we have done all this thing play we have provided Lewis or some sort of operations or some sort of a surface feature which is all these thing you can understand that we can reduce the size of the text in there and we can within a small volume we can have large amount of heat transfer that is the whole purpose and that is what I like the principal latest latest move to the I can tell you that by this time probably we are convinced that go in heat transfer books and I have also done the same way that we have analysed a single thing that we never use a single thing we use a large number oftemperature at things and these are different distances one registered should be provided by the fed and other logistical be provided by the surface area in between the feeling that on-field success library service so we can make some sort of a can have a purple Turkey as it has been shown over here but I also have told you that this isn't Griffin from the same material and the business has been made that means I have to I have to take away this much of costly material and sometimes we cannot permit this so we had to separately attach the file separately because I am attaching material with another here you can see that this contact resistance it could be called contact contact resistance ofearphone different kind of tubes and only one side of the issue has been shown the first one is the things are made from the same material itself in the second one this is the tube service on the top of that I have used some sort of a stream which is having things so it is around around the TV show this is one kind of it is okay for kids to make the fields and to make the fence very effectively transfer what we have to do we haveand cost of those kind of material will be large so what we have to do is like this that if that tube material is something else and on the top of that we provide fill material but now or some sort of a feature some sort of arrangement firefin said they’re made of highly conducting material should then probably our cost will be here again this is the tube materials and on the top of that there is a sleep which is having fun here again another kind of the design so that the themes are tightly attached to the tube material which is shown here so many different kind of designs are available and these are done that filling machines are available with the help of message one can provide defence on the air circulator nowassociated with using defence that is what we have to determine whether to find out the heat transfer by The office you see if this is the this is the thing of it iswe can think of idealized as it gets to get primary productwhat assumptions we can make steady-state condition let me tell you all the heat exchanger and how sweet you are going to do in in this course our state state tourney and tournament in a heat exchanger is also very important there are different type of analysis with time how the temperature changes so those kind of analysis are done and do the analysis are important because sometimes too strong and can give rise to thermal stress if we cannot we cannot allow highest thermal stress or one need to check the thermal stress and the problem is not an exception one dimensional radial conduction in heat will be conducted in this direction and then it will be convicted from the surface of the face constant properties properties are constantly exchange surrounding surroundingthis is an ideal number of times what I am telling that we provide provide the we make a change in the surface conditions and the convective heat transfer coefficient will be different but for many of the examples and some of the practical cases we do not differentiate between the heat transfer coefficient with feel or without faith this is one idealization we make and buy some sort of design after we take care of it then this car this car be similar because I’m in Amelia because this type of car by phone earlier if there is a way by Queens you can determine the efficiency of the of the radial fill out circular field because otherwise we need to calculate the sum function which is which is not very convenient to doif we neglect the heat transferred from the if we are taking insulated gift that is not correct so that’s why we’ll link can be corrected as has been mentioned yet this I have told our ears this is the heat transfer rate that is given by his on your face and hair the is the total area and then there are certain calculations which has been down here we had to calculate the fin efficiency should Stephen efficiency calculation has also been explained and fin efficiency for the fin efficiency calculation you have to calculate the LC order corrected link that has also been explained over here Kelsey and then definitely CNC were getting 95% reductions show you see if we have taken the examples and many examples we have calculated the fin efficiency and we are really getting them are we have gone below 50% so we are really designing furniture cutting high-efficiency in fact about the fin efficiency what will efficiency will take out design will depend on the application but really we go below 70 17 below 70 75% really we go we generally go for high efficiency all this weekend690 what we did total heat transfer from the cylinder of the internal combustion engine now this transfer comes from this heat transfer comes from again I like to draw your attention that sings let me go back a little bit so here’s what I wanted to tell you that the transfer will be there from the surface which is not filled or unfilled surface heat transfer will be there from the two surfaces of the field and then taking all the success is all the surfaces of the fence and all the injection services which I can find so the total heat transfer has been calculated this is very important to understand and buy this calculation we have got how much we have what we have got 69 and then if there are no fence then only there is beer cylindrical success and we can calculate assuming that the transfer coefficient has remained so assuming that we I can calculate and we get some heat transfer value as 236one thing we have to keep it in mind probably in a little later I will talk about that that when we do this in many of the cases there is extra amount of pressure dropthis is what we we try to address in our next lecture got some lecture afterwards so thank you and if you have got any queries etc. in the forum taking place it so we will try to address them there. Thank you