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Module 1: Trasferimento di calore

    Study Reminders

    Enhancement of Heat Transfer compact Heat Exchangers
    Hello everyone so welcome back to the course heat exchangers fundamentals and design analysis. Now if you recall we have given some introduction and after that we have tried to have a general overview of different type of heat exchangers we are having and you should appreciate that this is a very wide variety. And in letter I have got the different classification of exchanges and one of the classification is based on the compactness of the heat exchangers can be divided into two groups compact heat exchangers and non-competitive changes based on surface area perimeter volume of the details I will or any of the instructors will try to provide as the case proceedsbut this is one of the important classification of heat exchangers and then then we have also seen that the compactness or the Field of compactness based on some magnitude of amount of surface area per unit volume of the heat exchanger that carries weather depending on whether our freezer gas or anything what we will do we will explain some principles of augmentation of the transfer and then some typical method of getting compact heat exchanger and design and analysis that is getting some sort of compactness in the heat exchanger with the use of extended successes of him that we will try to describe in Finglas to come today is the beginning this lecture is the meaning of that activity we like to have an overview of what is what are the different methods of augmentation of heat transfer the food that later see what are the desirable features of a good it is there are number of points I do not claim back the the points I have mentioned here are kind of exhausting so there could be some other activity but definitely I have it down the most important features most important features which we expect from a good design like Hai heat exchanger should have it should be qualify that flooring in volume on giving envelope same as it should have the highest key duty as far as possible as practicable by the technology and the potential for this transferall these things contact list is one point from that what we want to have we want to have less pressure drop generally what happens pressure drop depends on many parameters one of the most important parameter is the velocity but along with this if if we win in the heat exchanger has to possibly long Parkway then there will be high pressure drop so we have to also see that the pressure drops below and up to this I have given different colour because at the beginning or somewhere in the course we are going on mentioning that we will look into thermal hydraulic aspects of heat exchanger may not be the other design aspects are the manufacturers expect these four points are very important for us but on totality foreign exchange for an engineer who is designing heat exchanger or working on it exchange other points are important points could be less prone to cody is a cleaning and maintenance that is the serviceability of the heat exchanger and over and above water in system for a man-made system was defective whatever we designed our economypoints we have to pull out of that at least the first three points that means I inhaled a temperature difference and Lisa Lisa volume or weight of that we can have with a very good or very effective way of entrance and we can also transfer process is very effective very good very if you see it then also we’ll end up with a design exhibition this comesI have recommendation of heat transfer primary if serving of material and dinner whenever we are talking about advanced detection Deere compact heat exchanger obviously one of the main goal is to reduce the size of the information about temperatureyou will be late at w – TF in this equation we want to maximize lipsy we want to maximize our cw&t fr60 then we have got this 28th is the transfer coefficient and a circle going we are going for augmentation of the transfer particularly we are having single phase 3 and the mode of heat transfer is conviction conviction from the between the wall and the free stream then we have to concentrate on HK either separately or as a competition augmentation next slide sorry sorryis there an age difference on various that depends on the course on the property and then because we have a label on this so many ways of increasing or there are many ways of enhancing and there are ways of enhancing area or tails can be improved that means andokay some of the Legacy we will have a look and we'll have some appreciation of some of these devices before that little see this small illustration here we have a corrugated surface which is an incoming I have shown an exaggerated view so in this we have got this is the directionwe went 4-1 in their speeches I have thrown in an exaggerated manner so basically there is not much change in the surface area but due to the placement of this feature there will be change in the velocity field very near the walls and we will have some increase in h this is where we are increasing without increasing dear I have 11 extended subway surfing so basically it is increasing the surface area and here there are upset strip thing so it is likely that small small Fields are placed in the staggered manner of the fluffy or in the path of the floor so only feel there will be boundary layer development but everything’s a small rebounder India cannot develop in finitely and cannot reduce the rate of heat transfer back side of the field there will be put exformation show boundary-layer we get some sort of an obstacle for further growth heat transfer coefficient will start increasing and at the same time the small things they are giving any reason I would like to show you some other examples here we have some techniques for transfersome sort of microfilm over the over the scene inside the two different kind of small small things inside and these things as they are small they are not only with their not only and I am particularly when they’re inside so they are not only increasing the surface they are also giving a rise in the transfer fee that we have got wearing certain side you will get betterscrapping many chemical reactor exchange is also integrated with the reactor we have got these adjectives for discuss we have got scratched surface 16 July they have mentioned in some of the lectures are near then there's all these things to the boundaryelectrostatically so if there is a dielectric then we can provide some sort of a list of electrostatic and we prove that we can have we can have a good kind of transport of the particles and that will give her to transfer these particles which microscope article the molecules of different picnic and compounds like two techniques probably in our discussion think ofa hearty which is shown by this thing so now you can understand that these are showing the direction to reach your stomach with passing surrounding with you we have got played in Play which will act as an extended service dolphin this will give of mentation of heat transfer and this is a passive augmentation this is the basic design and this is what I have done here we have provided rectangular or alternative behind this and behind this weekhow we can combine two different augmentation together give some photo of concluding note 4we have not to provide any kind of auxiliary device auxiliary arrangement for power supply new power supply obviously but the fluid pumping power that generally this is one point people had to be careful when we are selecting a particular augmentation sex that is one thing second thing generally augmentation techniques when you adopt augmentation technique show you have increasing initial cost increase in weight and volume of the volume of the heat exchanger on a transfer device to this is also one point which needs to be considered here again I like to mention one thing that first what I have informed that either we have to use auxiliary power or if we are giving passing technique then what we have to do then what we have to do that we have to go for excessive pressure drop that patient of penalty we have to admit if we are admitting excess pressure drop then what is happening we are spending some more amount so hear some reference from thermodynamics maybe that we want to enhance the rate of heat transfer or that we have to spend some amount when we are trying to have more heat transfer we are dealing with delivery but we are spending pumping power we are dealing with this it is like this that we have to be very careful our transfer should be much more or from the energy point of view magnitude of energy transfer enhancement compared to the amount of work we are spending for the change in me evolution of what we can see that reduction of keeping them and this could be one that supposed we are keeping you and tell tateum constant that is the total amount of transfer and the and the mean temperature difference betweennow I will do I will have the same amount of it runs but I will have the same area are other terms of the text but I have gone for picnic so happy also and it may be possibleI would say that this delta stupid because that means basically we are we are reducing the effective temperature difference between the surface and the generation of nucleation site we need to have more evaporation or more information from many more places there increasing the range of boiling. We will revisit and see closely some of them when we learn about the phase change heat exchangers. So with this I will like to come to an end of this lecture and let us see some augmentation technique in detail in our next lecture. Thank you