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Extended Surface Heat Transfer
Welcome back if you recall we were discussing regarding augmentation of heat transfer and why we have discussed augmentation because we wanted to have very efficient heat exchangers. And in technical terms what is known as compact it extension at least some of the competitive changes in business now and I have shown you earlier that there are many techniques many techniques or augmentation of heat transfer I have not shown in I let me tell you I have not shown an exhaustive is it is not possible because there are many techniques and probably in a course like this where our main focus is heat exchanger we cannot discuss much detail in much detail regarding techniques and thermal engineer technique isyou have studied about fins in heat transfer in your he transferred us which is a very fundamental topic in any undergraduate transfer and probably some of his religion assuming that you have got some background or you can pick up that background from a standard book ofTrump’s performance we want to improve the transfer performance of his primary suspect then the thing we like to do is look at me to eat in is it conducted convective surface show initially the place we had it use I mean it had transferred by conduction now we are providing things on it still it we have is transferred by convection but we are in our area they will not be as effective but in any case this will enhance the if we see the attribute of extended service or fee which is a conductor convicted surface I will explain the stuff so this is a passive device no auxiliary power is suitable for single-phase connection first in heat transfer heat transfer and radiation in summer enphase storage system is used extensive design variation can be used for peanuts can be used inside or outside the country it can be used as I have told that it can be used for single phase it can be used for both liquid and gas and liquid mixture then we can use it in a very small heat exchanger we can use it one thing that is another feature increase I think so some of the common Fields I have shown so let me let me let me try to explain some things over here and this is the primary site facility this is the primary surplus this is the primary sources and on this primary southwest I have added some sort of a secondary service or extend a selfish decision is a longitudinal for us as I have earlier told that it is a contact contact deep convective sister so let us understand why I have to look what no initially I had a surface area or surface like these like this iPad a surface I had a service like this this was my surface but this one myself now what is happening with this feel my surface area is like this is much tougher silly I got this much surface area I have got this much surface area I have got and at the back of the field then again the same amount of side I can see how much I could provide to my design this is one of the design industry there are many designs by the transfer case fluid is flowing through the through it and if it is to be cooled by providing some sort of cash flow over the outside of the new show where we can provide this kind of things on the tube is the longitudinal fissure similarly we can provide this kind of similar findings also feels and they’re called in case they look like it means I draw your attention thatwe are running late because sometimes it is gone circular circular fashion and finally one pin has been shown that is your this one in case of radial thing which is also called circular field or a new life in one you want Finn has been shown in case of fin fin only one thing has been shot but really any practical application is in defence is basically we use different surface as we have shown in this case but all the other cases for the clarity for understanding we can only one typical fee in actual practice there will be many number of Fields on the surface let us move to let us move to our next this oneobviously when we had attaching fence so it will improve because how it will improve because because we feel material has to be a good conductor up so we cannot use any material we have to use some costly material and then wait and volume of the heat exchangers that we definitely miss most of the cases we will have an increasing pumping power and then there could be falling down volume of Jess Lee it is not desirable in any system increases in question for you but particularly if it is a mobile let’s say for anti-aircraft we are trying to have a heat exchanger with teams for a racing car for an automobile you want to havewe have to be careful because in all these cases these additional Fields not only increases the volume but also increases the weight of the mobile system moving system and which is more traction power so we had to be careful dimensions of the film in the longitudinal direction that is in a direction normal to a primary services based service is much more compared to the others in the analysis of we can take the assumption of one-dimensional connection to this is very important that many of the cases our analysis is based on the assumption of one-dimensional background resources are not unfortunately but I want to improve I want to improve the performance of a test we are not satisfied with that I get the best return of my investment I had to decide where I had to go for what I am telling please let me explain it is like this that we know that there could be many heat transfer but it typically transport service we had to fluids on one side so there will be a surface on the surface there will be 13 or rather let me put it in this way back to fluids are separated by some sort of a solid wall so one surface of the solid wall is contacted by one and another surface of the solid one is contacted by another now the augmentation or enhance made particularly if you think of passive enhancement we can provide on either side of the solid to this point we have to take a decision on which side we are going to survive the outside at leastI’m going to be moving there are several resistance 41 there in the distance between one side there could be some howling for that there is a resistance in the story to all the regions in fluid to side there could be found in there in the resistance and indifferent to their assistance I think these have been already told so we can proceed so bringing in overall heat transfer coefficient bringing in overall heat transfer coefficient should hear the overall heat transfer coefficient an area I have brought in so we have got hybrid is dense is the convective heat transfer on the one side this is one of the founding resistance on the fluid one side I have put it in the form of convective heat transfer coefficient the and then releasing food that is in general most of the cases now we can have some sort of it because it is very difficult to separate the distance in the conviction in a particular through it and just beside it is the resistance due to failure due to paoli in that particular food we can grab them together suppose the situation is such that 4321 side these two resistances summation of these two resistances are much more compared to the summation of other expenses then we can take a clear-cut decision that the competition is to be done on this week this is how we have to decide there are some guidelines very simple guidelines because it comes from our day-to-day experience and these guidelines are course more or less commonly called commonly followed but sometimes it needs some sort of it is like this that if there is a gas leak detector Westside register if we are going as we had discussed that that thing is one kind of technique which we can adopt sure if we are going to provide fees so we had to provide first on the gas side in many cases on the liquid side we did not provide free sometimes we provide Small things etc for enhancing the heat transfer the rate of heat transfer coefficient of heat transfer but it is gas liquid that did almost 100% cases the decision is taken to enhance the rate of heat transfer in the gas side by providing feels if it is a gas heater course many times we provide pins on both side of the sunset on both sides this small kind of information small piece of information we can proceed for the next line we can proceed for the next lightyou can see that the cross section of the speed is constant that means the thickness of the penis constant two areas which are important one area we can think of let’s say we can think of this area from the heat transfer is taking place and for the heat transfer is taking place to this area so this is basically the cross-sectional area which is taking part in your conduction and it is so then we can see one fluid is flowing over the feedback side of the funeral so pretty face or primary service also so it is like this that fluid is flowing on the only on this surface fluid is flowing so let us use this so on this surface fluid is flowing here I have shown to it is going on this fluid is flowing so so fluid is flowing and due to that there will be some sort of a conversation so that’s why I have told that Finn is a contact if convicted sister and the length of the field that is in the thickness of the frame is a quality in this action we have taken x and y x is the temperature at a distance x the hard to understand or appreciate one thing that heat transfer is taking place I have shown the area to which conduction is taking place there is another area that is the surface area of the field from the air conditioner contactif we if we assume that the thing is when is very large leaf in is very large along this direction and along this direction so one can one did not consider a temperature variation in all of this collection I have told that this thing is very long in this direction compared to its thickness so along this direction there will be temperature variation but along this direction there will not be any temperature variation so basically this direction low temperature variation this direction no temperature variation this direction no temperature variation only temperature variation is a longitudinal this is what we do in Finn and this probably is known to you known to all of you from your transfer courseanalysis of active inmates the energy transferred from the surface of Earth is the increased by convection based on 18 conduction I will not spend much time because these are all this type of heat transfer I will not explain also because I expect you people to go back to transfer book if you cannot figure it out this is some minimum requirement for this particular show for the field which I have shown no one can write this kind of an equation the first equation which has been beating it is assumed that the surface area changes along exploration or longitudinal direction first dictionary also changes now if we if we take some sort of a longitudinal fin with constant thickness we can get this then we replace TX – 3 infinity which is the free temperature buy some theatre we get this kind of effort emulation and then it is having a non temperature and on the t-shirt is the other end of the field that is insulated with this boundary condition we can give the temperature difference sorry temperature distribution along beliefs and flow of heat through the field which is coming from the base so at the base what is the heat flow that is there in heat transfer by the fee to the surrounding free so that will be cured with this if we go for the next slide so we have got the transfer and we have got the temperature if you recall you will find that probably the most common type of thing we had taken which is a longitudinal Federer could be of rectangular cross-section or it could be some sort of face paint so it is our cross section is constant in there we are getting a very complex situation or other brother competition not very complex but complex situation but if the senior military is more complex all this simplicity that not there we can imagine that the mission will not be very easy to remember or easy to handle that is one point another point how do I know that whether the 15 I have decided that is good or that is not sure yet we introduce some figure of merit which will give us the goodness of my finger sign and at the same time we will explain that it will make my life simple that when I have to estimate how much is transferring from which it is like this if we go back to the slide ppt so we define fin effectiveness against these are all Star for a transfer and then what we do we get it like this that effectiveness is it transferred from the film heat transfer through the fan base without the fee so this is how we get all in terms of thermal resistance it should be is one way of doing it there is another figure of merit that is Philippines heat transfer through the field and maximum possible with transfer how we can get maximum possible to transfer if we assume that Finn is made of a material which is some sort of a highly conductive material there is no temperature drop across the field so we get that and then and this is a very important this is a very important kind of information and we get the Finnerty CNC kit RF which is given by teenage email by Emily tan hyperbolic email by email I am not going back but there is a which has been defined by I have shown the previous like it is some sort of it design parameter for metric parameter of the field which is very important for the design and a linkedin with this we get the efficiency of the field so we can tell by adding Stephen how how much is the day weekend if I had to compare between two fingers but at the same time once we know the inefficiency what we can do the same area can be multiplied with this winner receives so from the name apcalc it will be clear that what we are getting is less than hundred percent Philippine area will be x this that means the entire area of field or rather let me put it like this deep in area is not as efficient as front fairing not as efficient and transparent as he basically if we multiply eat with some sort of a factor which is less than 100% or less than 1 then the area of which year getting that is equally efficient alphabets ABC returns for how can we getthe pair will multiply with the efficiency and then we will have our age intuition see him to tell Kathy that will be transferred to this is the advantage of introducing officiants I have just explained it in nutshell knowing that that this has been done in your mouth this this you have done this you have done in your earlier class show I have an issue with some sort of some sort of some sort of electrical and thermal human kind of longitudinal analysisHappy belated birthday keep is not actually insulated so there will be certain amount of heat transfer through actual length of the field can be corrected with some sort of a collection through which is given here and that is what is used in many of the many of the many of the analysis so sad I feel so here also we will get the expression of Peter which is the non dimensional come temperature in terms of modified bessel function of the water and first product then if CNC we also get but you can see the how the efficiency formula has become complex that is what I was going to tell that sometimes define analysis is very complex for a circular field which I have shown earlier so the analysis becomes very complex and that in this case the efficiency generally we determine with the help of a chart or graph like this and how we can use this these two things what I have shown that the longitudinal being on a plane surface or circular field operatives are ugly and they will be very commonly used very expensive and we will discuss some of these things for you and I only used it because this is not connected directly or not included mandatory is it I like that there will be number so as we have define fin efficiency they also and the service is sometimes calledinformation on ABC back from there we need to calculate this we need to use it with this I like to end my in my lecture and I thank you all for attending this if there is any queries or confusion we can discuss that if you indicated but what I like to tell that knowing the transfer or remembering the recalling the basic heat transfer connecting it with what we are teaching is very important and I like you to do that. Thank you
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