Introduction to Heat Exchangers
Hello everyone welcome to the course heat exchangers fundamental and design analysis I am Professor Kumar Das I am from the department of mechanical engineering IIT Kharagpur. I am one of the instructorS of this particular course. Today in the first lecture I will try to give some background of heat exchangers and some aims and goals of this particular course. Because you will be taken jointly by two instructors I am one of them and professor… from the Cragganwick engineering centre of iit-kharagpur who will join me after one or two lectures and in-between we will swap some lectures will be taken by me and some lectures will be taken by professor Indonekosh there will be three teaching assistants who will be assisting us. The participants they will form a forum the in forum you can raise your queries you can raise some questions related to the course and those forum will be conducted by our TAs. These will help you in understanding certain things which you could cannot pick up with you you are unable to pick up from the lecture there will be some sort of a liaison between the participants and the instructors. We are also trying that if we can have some sort of interactive classes between the participants when the participants will be present on the on one side and on the other side the instructor. The course has been divided more or less 50/50 between two instructors. I will start with it and as I have told personnel who will take over after one of two lectures. So we are going to the introduction to the course the course name as has been already told it is heat exchangers fundamental and design analysis. So what we’re trying to do that we will first make you familiar with different kind of heat exchangers we assume that students or participants will be from different background and they might have some basic knowledge of heat exchanger, some might not have a good perception regarding so we will try to provide that kind of perception or appreciation for heat exchangers. So after that we would like to, so the topics to be covered if we see, so first is introduction which I have just explained that I we will try to give you some sort of appreciation generate in you some sort of interest regarding heat exchangers then basic thermal and hydraulic design or analysis rather it is basic thermal and hydraulic analysis. Heat transfer is the key phenomena which occur in a heat exchanger and it may occur in any any mode of heat transfer that is conduction convection and radiation but we will see that conviction dominance that means in most of the cases convection plays a very key role. So when convection is there so obviously there is free through involved and we have got many hydraulic issues. So along with heat transfer we have to have some consideration for the hydraulics of the heat exchanger and in general how the heat transfer and hydraulics is to be considered in a heat exchanger that we will try to make you understand once we give basic introduction to heat exchanger. Heat exchangers we will repeat this point time and again that heat exchangers have got just right probably it is very difficult to name and industry name and industry where we will not find heat exchangers and if heat exchangers are everpresent and in other field of human activity then we will find that there are a large number of varieties and one of the main variety of heat exchanger is tubular heat exchanger where the main construction geometry is tubular check so we would like to spend some time on the tubular heat exchanger. Then heat exchanger is an industrial device we want to get best out of it that means spending small amount of time spending more small amount of power spending small amount of space we want to have more capacity from the heat exchanger and as I have told that the heat transfer is the key mechanism of key information occurring in a heat exchanger so heat transfer should be very very effective and we should have heat transfer at a very high rate or enhanced rate in heat exchangers so that’s why enhancement of heat transfer that becomes very important in the discussion and design of heat exchangers. So when we are talking about heat transfer we have a whole class of heat exchangers which have been made over the years very very compact for that within a small volume or giving a very small temperature difference we are capable of transferring heat at a very high rate. So those heat exchangers are called compact heat exchangers, they are very important and they are replacing the conventional heat exchanger very rapidly. Newer applications are coming and newer and competitive changes are being designed so we will spend some time on competitive. Then been among the compact exchanger there is plate-fin heat exchanger which is very important because of its flexibility, I do not want to tell what are the what are the merits of plate fin heat exchanger over other heat exchanger in general and other compact heat exchanger in particular. When we will discuss plate fin heat exchanger we will discuss that but plate fin heat exchanger is so important that we like to spend some time on plate fin heat exchanger and this is one of the one of the important topics of the course which we are going to offer. And then in plate fin heat exchanger there is a capability of taking number of strings, this is one thing I like to spend some time or my colleague will spend some time. Then direct contact heat exchanger what is the direct contact with heat exchanger we will discuss what is a heat exchanger and we will give some idea but it is like this sometimes the fluid streams they can mix together in a heat exchanger so this is called direct contact heat exchanger, though direct contact heat exchangers are not many in number but they again occupy a very key position in the family of heat exchangers and again we would like to discuss direct contact heat exchangers especially because they are slightly different from indirect contact heat exchangers, the regenerators are heat exchangers for recovering or energy conservation regarding the importance of regenerators important and we thought that we should spend some time on regenerators. The heat pipes it can be considered to be a device for energy conservation they are special type of heat exchanger and they are very efficient they have got unique use and we will find that in many demand they play a very key role so we will try to explain the principle of heat pipes separately. Microscale heat exchangers with the advancement of industry particularly with the advancement of electronic industry, the miniaturization that has taken the centre-stage .So as we go for very high scale of integration of the electronic component then on a small surface we have to dissipate more amount but at the same time the the components should be small enough so we should have heat exchangers which are very efficient but at the same time which are of miniature size this is not only there for electronic there other places miniaturization has shown its benefits. So micro scale heat exchangers it needs a special mention and some attention from us we are going to give it. Phase change heat exchanger generally talks about about phase change between liquids and particles so basically these are evaporators, boilers, condensors etc their design principle are again slightly different compared to conventional heat exchangers so we are going to give due importance to this kind of heat exchangers then heat exchanger testing we can manufacture a new heat exchanger so probably following the best design practice we can manufacture a new heat exchanger but we are not sure whether what we have manufactured according to some specification that will depart person not sure what is needed we need to test the heat exchanger for its performance. That could be one requirement or in the industry we have got already manufactured and installed heat exchanger yet we are not very sure regarding its performance so we need to test it. So these are the requirements of heat exchanger testing, itself is a very elaborate and complex topic but within the purview of this course we are trying to touch up on this topic and give some sort of basic idea how heat exchangers are tested and then in an industry not a single heat exchanger is used. Heat exchangers are used in numbers very large in numbers. If we consider the petroleum refinery there will be very large number of heat exchangers and this heat exchangers do not operate as an individual unit. The whole plant is to be designed by integrating, integrating different strains of fluid through heat exchanger and this integration is heat integration or integration from the point of thermal energy. So then what we get in a plant in a network is a network of heat exchangers. How we can synthesise, synthesize this kind of figured that that is a different topic the fundamentals of heat exchanger is needed but heat exchanger network synthesis needs certain other kind that we are going to spend some time. Secondly we have not mentioned categorically because we have got limitation of the time and how much one can give in a course but obviously there are certain things which we are going to it is not appearing in this list like howling of heat exchangers is a very important aspect of heat exchanger design and maintenance then some aspects of the mechanical design that will be covered when we are telling regarding the other aspects of design let’s equally important hard manufacturing techniques of heat exchanger that itself can create another course but obviously when unique features that there’s something we have to tell regarding the uniqueness of the manufacturing of heat exchanger we are going to mention this is more or less is the cost structure and we will go in the sequence it has been mentioned there will be numerical examples etc equations and obviously there will be description for different extension once we have got some idea what we’re going to do in this particular course let us have some definition of heat exchanger this definition I have picked up from the book of Acacia and securities references been given for this particular course should the definition goes like this heat exchanger is a device used to transfer thermal energy between two or more fluids or is solid surface and a fluid or particulate solids and if so when we are giving definition we like to be generalized definition but after that we try to create the impression so that we can have a proper proper perspective regarding heat exchanger
So now I like to tell what are the common features and we take which are not so common in heat exchanger according to this this particular definition heat exchangers wide variety of applications there will be substantial variation in their design it is still there could be very small it could be gigantic in size of the heat exchangers are used most commonly most comprehensive it is used by some of the heat exchanger is not that common core principle of heat exchanger operation we like to explain at the very beginning of the course taking some commentators changes to let us see what is the principle of operation of heat exchanger many of you may be aware of the principle of operation but for the benefit of others and for this EK of completeness please bear with me latest AP most basic construction of heat exchanger and try to understand how does a heat exchanger operate most commonly heat exchanger Tamil exchange between two fruits do we have given a general description of heat exchanger definition of heat exchanger that it can be heat exchange between number of fluids or there could be heat exchange between a fluid and solid but most of the heat exchanger will have only two sweets and probably we are having probably we are having the most basic most basic construction of heat exchanger shown in this particular slide which is called do sweet tube in tube indirectly texted sometime in allergies are to be explained so let us give some time so let’s say there are let us let us appreciate that they are not to see the one sweet that is sweet one and it’s my spirit is in dock one that is entering the central team and then it is going out there is no change in mass flow rate the same 3 is coming out very sweet to which has got a mass flow rate 22 this is entering here and it is occupying in some sort of it’s between these two weeks then there will be exchange of thermal energy the temperature difference transport of thermal energy and the exchange of thermal energy is the temperature here one that is higher compared to the temperature of two at that point then what we will find that one it is coming with a higher temperature it’s temperature will fall down when it goes out 32 it is coming at you are comparatively lower temperature it’s temperature will go up as it passes through this annular sale and goes out this is the basic principle of heat transfer or other basic principle of operation in heat exchanger they are exchanging hit due to why it is called indirect heat exchanger is a solid wall this Central tube wall of the Central to is the solid wall which separates these two sweets so that’s why it is and it is an indirect heat exchanger and most of the heat exchangers we will find that they are indirectly most of the heat exchanger there may be different geometry different construction they are too sweetie text but indirect type heat exchanger is not the not the sole kind of it extended there could be other time so let us see in this heat exchanger gas can be cold here of course there could be two mechanism of cooling first thing due to the temperature difference between the hot gas and the cold liquid droplets there could be sensible heat transfer and the liquid evaporate also why you have pretty they may take this liquid meeting certain amount of latent heat from the hot gas so that ultimately cost temperature at me but please find that to Sweet screams that is liquid and gas they are intermingling with each other they are not separated by another solid surface so that’s why these kind of heat exchangers are called direct contact with extension through this is one main variety of heat exchanger do this type of heat exchangers are not as many as we can find the as we can find very large Ibrahim variety of heat exchanger in some application 1 intermediate medium is used for transferring energy from one form to another what does it mean it means that there will be an intermediate medium once we will transfer him to the intermediate medium for temporarily thermal energy will get stored in that intermediate medium this is basically a storage type it exchange show from one free thermal energy or he will gain store in summit immediate Media this inter medium medium would be a solid me a circulating fluid and again this morning could be stationary or moving salad depending upon design and away again we can have some sort of a phase change medium for the inter medium as the intermediate medium or for some substances is changing its face as the intermediate media as I have told that the BD 1st spring Lake Court fruits team will transfer it to the intermediate medium intermediate medium temporarily West Orient and it will then transfer it to the Good food store here I have shown as schematically one arrangement which is very portal very common and we will liberate we will discuss more deliberately this particular type of heat exchanger in later-stage of this particular course here you see there is a rotating let’s say we are thinking of a pot plant for hot product of combustion is to be sent to the atmosphere so what we are doing that what product of combustion we are sending you this message but in between there is a way which is rotating at a slower speed so as the hill is rotating and the gas is passing through it the portion of the Hill which is in contact with hot guys that will get and then this will is coming to the other side I wish we could have dumped to the atmosphere or wasted so that is the advantage and obviously gives us protection of the environment so this is called a rotating wheel drive storage heat exchanger this is another classification of it we can prepare we can see three quantities which we have 40 cubic is equal to zero that means the envelope off the heat exchanger that is insulated w.w. is equal to zero that means within the heat exchanger there is no work done or no work is being transferred from the outside and keep that Jane is equal to zero show his generation within the heat exchanger this is a very common type of representation of the heater exception only in some cases of direct contact m is equal to 8 in most of the cases only in some cases of direct contact between these teams and is not equal to otherwise it in direct contact and m is equal to ideally there is no get out of work input because there is some sort of education created in different the principle of heat exchangers it back from when people started heartland the art of cooking show you see initially be cooking pots particularly which male organ pot and metallic 4000 not there for cooking what they used to do they used to use the principle of storage heat transfer stones well-fitted and then the Stones were placed in water so that the water will be heated and all boiling and then that could be used for cooking so that was the principle used by the Vikings for cooking meat the similar kind of storage heat in was used for room heating in cold countries in Egypt for hours they deployed large number of people so they are dwelling will be covered by stone which will be cold during night and early in the morning go school cold stone will be placed in the room and again during night does thrones will be taken back to the desert to get cold then in ancient Rome we can see central home heating and that was by hitting the floor panel of the door side of the room where hot gas used to be sent to a chamber below the show we can see in the next slide how it is this is this is a bath Roman baths public Bath which was very common in Rome and you see below this below this there is this is firebox he had heat is generated show the hot gas that passes through this and at the top there is liquid so you see this is it transferred between two liquids and this is the early concept of heat exchanger the physical construction was something like this year you can see below this there are these stone structure through which the hot product of combustion will pass and at the top of this there could be a room or there could be a bath which will be kept secret and this structure is called hypocaust and this extra architecture some people say it is also common in your indus Valley civilization but it has not been authenticated by the Roman structure Roman and Seth architecture this is invented in sorry this is discovered in any number of places so you can see the reputation of this concept in in Korea and in Korea this this particular concept is still used in a different form by electrical heating for your room air condition this is the earliest use of heat exchanger what one can say next we will go for the different classification of heat exchangers but in this lecture I have tried to give you some idea regarding the heat exchanger and what could be the vastness of heat exchanger and how did ancient people knew the use of heat exchanger the way we know it the design construction was slightly different thank you and if you have got any query please interact with the TAs in the forum.