Tubular Heat Exchanger Types
Welcome to this lecture where we are going to discuss the tubular connection here and the various types of tubular protection. Here do they present in the market so far we have talked about different heat exchangers, design methodology and analysis. We have seen that most of the time we are taking the heat transfer coefficient of the friction factor that is already given but in reality we will find that those at the parameters which are to be determined and first of all we will start with the geometry for children simple and gradually we’ll go into the complicated so we'll start with the tubular FedEx nearhow it look like in real life so that if you look at this is a heat exchanger double pipe heat exchanger where you can see the understand the size of the exchanges from this diagram that and you will find that the cubes are coming or the fluid is coming from morning to the other end to this bunch of tubes or if we just try to look into it schematically will find that one so it will be entering from designed and that way it will be flowing through this inner tube from design to design and it will come out from this side that’s about the other plate this is say one of the freight trains the other place we will come from this ain’t so it will end their entrance into this heat exchanger then it will flow through this any worse case if I take a cross-sectional view of this one we will find that the reason of getting this is the inner tube and this is the annular space through which the this blue colour fluid is flowing and it will come like this and finally it will move out through this and not depending on the direction of the flow itI’m finally come out during the initial phase you can understand that if the fluid is entering from this side this will be in parallel flow in combination to with respect to theconfiguration from this this this will be in parallel to the store and the green makeup parallel flow and it meant after eating it so this is the simplest possible geometry where we find we call it double pipe heat exchanger are often it is called double 5/2 in heat exchanger we know the hairpin like it looks like being like this and this is similar to that configuration so that’s why we call it so this is one of the simplest configuration what I mean is that say this is the some of the characteristics of this heat exchanger is that the this type of exchanges are in use when we need a smaller class for surface area also the this particular type of heat exchanger is suitable for high pressure 3 screams when both are one of the field strength is wearing very high pressureand we can think of using this kind of question yet on the negative side what we have is the it is bit bulky and it’s bit expensive per unit surface area typically it is having about us a 50 metre square of surface area and about this when we need in a typically of this kind of surface area and high-pressure liquid strength we go for such kind of fidget spinners and it said that it is bulky and otherwise keep it in her position will be I mean they have a single thing or it may have a bunch of pubes like this this is also possible I mean we may have depending on the contribution he may have bunch of tubes of a single too so it is not then double pipe it will have multiple multiple times and it may also have depending on the heat transfer coefficient of this annular specifically find that the heat transfer coefficient of designing spaces small then we may have to use the extended he transports substance or freeze on the this signed on the outside of the inner tube this is particularly sought the single cube are multiple tips so this extended across the surface will try to compensate that smaller heat transfer coefficient on the anniversaries depending on the process requirement we may go for an extended heat transfer service or clinical configuration we may also go for multiple tube configuration of this a double v Italy so next is at the Shell and tube type heat exchanger it is one of the most common configuration we commonly looking I mean get in the industries such as you can see that we have a Shell and we have the cube we have bunch of tubes you know this is the tube inlet through which the fluid will enter to the heat exchanger I mean this is the site and we have this is the future in the complete we have the holes through which all these tubes will pass through there is also an Alice to sit on this side so this gives it will have holes through which this deal bill passed through and in between this hold tube set on both sides will be enclosed by the shell now the sell-side fluid will enter from the sink and it will come out from the Saint or it may also have a different configuration or it may I mean the it is also allowed that the Fred Meyer enter come this side and it may come out from this side also depending on the configuration this is the tube side so it going in and coming out and locally the hillside Chloe this is a 2-3-2 configuration where they sell cyclone is coming and passing over The cubes this is the battles these are called the battles so as we have written here these battles will try to I didn’t check the fluid or dialled the fluid from one end to the other like this it it will be flowing like this from one end to the other line so if we look into ifand this will be flowing onto this side through this annular space and it will come out so it will be basically counter-current on parallel current arrangement but if you look at the same time of this rate it is very small was on this side if we have battles it is coming like this it is a cross-flow and then here this is a countercurrent tournament then again it was snowing in cross-flow again it is in the current tournament then Cross close this cross and counter-current an event will allow the freight to stay for longer time and have lunch is heat transfer time as a result what will happen will find that obviously the heat transfer will enhance but at the same time will find that the pressure drop penalty has also impact so this is what is in a nutshell about the Sheeran tickets in yet there are different kind of Sri Lanka configuration switch will be feeling later on that you can understand that if there’s another tube size and this is the sell-side cute shirts and the shell if they are welded together and if there is differential temperaturethat difference thing is very large between the shell and the pill that may result in some kind of I will expansion which is an art centre thermal stress may be generated and which if it is not designed properly that maybe disasters so we may have to design it in such a way that the thermal contraction or thermal expansion due to differential temperature between the shell and the free time and if we quit floor has can be taken care and it is not the arming and generating an Amarok generating some kind of thermal stress is which is not good for the health so now you will try to move to the third one this is spiral old heat exchanger you can look into the side of this particular exchanging it is just not in a larger than just a fingertip small finger and this kind of exchanges any news particularly encouraging like both but this example something taken from the crisis is typically a joke and state exchanges is this particularthat is having incredible pain on top of it typically this is called at cooler here this is not going to love this one at this moment we will look into the eyes have said that we will try to find out what is the heat transfer coefficient available for that if we look into this all these tubular heater configuration will find that one of the flight is passing through the tube was the other plane passing through the cell site so what we need to look into is what we need to look into is the internal floor and sometimes we also need to look into the external flow so one fluid is flowing inside the steel so when we talk about we talked about the internal heat transfer coefficient and also this is the wall most of the time will eclipse the resistance offered by the middle of this wall and we also have the extra dollar transfer coefficient so far in our analysis we have assumed that this heat transfer coefficient has already been given to us but this time we are trying to find out how this heat transfer coefficient unknown or how this has to be estimated so here for the internal floor we have some kind of correlation for the external floor depending on the type of fluid flow we will have a different type of heat transfer coefficient and for the internal floor we have different type of heat transfer coefficient of correlation sebastopol will try to look into that internal heat transfer coefficient and there are different type of correlations available in the different textbooks they will be able to follow in American follow any one of them now when we talk about the internal flow through a circular table what we need to know also how is the floor condition whether this floor is laminar or the flow is turbulent depending on that the heat transfer coefficient will change so what is the transition event how will we know the way that it is in the laminar flow or in the turbulent flow so first of all what we need to find out is the Reynolds number it is a dimensionless number we often call it re the rules number and wait if I buy CD buy milk at this stage is the hydraulic diameter it is called the hydraulic diameter and we define it as 4 * the free-flow area / wetted perimeter so this is how I define the hydraulic diameter what is G3 is known as the mass velocity this is mass flow rate per unit free flow the mass velocity and we will viscosity of the flick if the strings number is less than 2300 2300 then for the circle is small circular Dwight way and you that the floor is aluminium so if it is having a laminate floor to the circular fireside collective we will assume that it is laminar and the friction factor will be given by 64 by ari Ferrari is the rivals number and why do we need this friction factor because any heat exchanger design 14 concern is the pressure drop and we define this pressure drop as flg Square by 2 row and then the hydraulic diameter that we have defined so please if in case of laminar flow calculation through a circular file we will be using 64 pyari we have busy as soon as velocity and is the length of the tube and this row is the density of the fridge so this is how we calculate the pressure drop across the length of the cube so now let us look into the nurses number this is again and dimensionless heat transfer coefficient this is dimensionless heat transfer coefficient and we define his by HD by kvsh is the address for proficient the hydraulic diameter and Kaiser colour conductivity of this given by 3.657 flowers channel 50668 gross number ÷ 1 + 0.046 to the baths stupid that this wizard is called grosnor live and we defined it as are there in to peer and Dubai the correlation for the turbulent flow we understand that the friction factor values are like this so if the Audi range is between 3500 and 2 into 10 to the power 4 we have this kind of the friction factor and signal do we have when the army is on the site more than 280 we have PT 140 to the 4.1.2 and facts about the Asian facts about the heat transfer coefficient the heat transfer coefficient we can generally it is defined in terms of the nurses number or it is often it is defined in terms of the cold ones affected it is given by age by TCP what is the heat transfer coefficient g is the mass velocity Sikhism Stanton number this is nothing but Stanton number into tunnel number 2 The part 2 3rd schoolmoney factor so so this is what will find as .023 in to order to the power minus .2 so this will be come if we Express at this stage also guess they can also be written as the nurses number / or defer to the part one called ok so this becomes if we want to express it in terms of the nurses number then the nurses number becomes point 23 re it becomes r e to the power .8 and pier one third this is in terms of the message number or can’t answer the call when she factor this is just JH equals to as we have set .023 into r e to the power what is film average temperature is the average fridge temperature this is TF is average fridge temperature plus by temperature / to sort this is how we evaluate this film average temperature and all the fluid properties have been evaluated at this film Everest temperature while calculating the cold ones a factor of the number so this is very important so far as the estimation of this fluid properties are concerned and we should not deviate from that film average temperature for evaluating the properties otherwise we may have in a possibility that we will be calculating a long cold winter factor of the nurses number for this we have to keep it in my know if we go back to our discussion last year we will find that this is the way we talked about the internal slope of weather slime inner or turbulent we have the internal heat transfer coefficient in terms of the nurses number the affected and from there we would be able to calculate the heat transfer coefficient age that will give you the internal heat transfer coefficient know if we have a bunch of tubes and office which the fluid is flowing on top of it then we may have to I mean if we have to calculate the heat transfer coefficient on the external floor then how do you do that so depending on the configuration we may find that this this is the two possibilities I mean in French in one of the floor configuration we will find that this fluid is flowing on a Bangkok to this is a cross-sectional view and this other direction This is the internal storage and this is the external so this is how it is flowing through this over The cubes over the tube that’s this is called this distance between the Central line distance is called the transfer switch and the distance between the two consecutive tubes in the floor direction is called the longitudinal beach and the is the external diameter of theoffset the second row of pill is upset and it is just in between the perfect I will go to to use there is the third one of the second row tube is just in between these two pills this tube and this team and this is the third one so they are forming like a triangle so here they were forming of this for that for me a kind of rectangle and this is a forming a kind of triangle and depending on this angle I will we may have a different floor Avon bit and she is now I’m in the heat transfer coefficient is possible so we have the transfer speech we have the longitudinal pitch for this is the longitudinal pitch the Central line distance between two consecutive tissues in the flow direction we also have another the length this is the diagonal length called HD and this is also important in case of syllabus first try to find out what is the what is there in the in lines are confident they will find that it is important to know what is the maximum velocity because that will be used to calculate the Reynolds number and if you look at this one who’s number that if it is either in terms of the same as we have said that we will define it the Devil’s number we have defined as she stick by me and hit this DH is the external diameter of the stew and what is the GC is the mass velocity so here’s the velocity of the fluid is we and it is flowing over its bank of thieves and we need to find outas you can understand that this maximum tupelo city in this particular configuration is supposed to occur at this location when we have the minimum so the velocity of the fluid is taking place from this direction and here we had the minimum free flow area so that will constitute the maximum velocity at that point and how do you find out the maximum velocity we know that the total mass flow remains constant so if we write it in terms of the AFL AFL is just nothing but the frontal area x the velocity and the density this is just nothing but the mass flow of the incoming freight and if it is the flow rate is remaining constant so here’s this a one that is the area at this point and here you have the velocity Sophie Max and corresponding the density is rope so we have a relation for the VMAX related to the frontal area and the minimum employee area so minimum area is if you look at the entrance of the speech we have a city that is corresponding to the front area and the minimum area is just nothing what is t minus this length and this line so that will constitute DST - it is in the denominator and x see Sophie Max is previous slide this is if we have the minimum and say sorry if we have the minimum flow free flow area on the maximum velocity of hiring at this point then we have already looked into this in configuration that even if it is at a1 then we have the VMAX equals to s t y s t minus t the other possibility is as we are talking about that if we have the floor area opening at this point then this flu is getting coming here and display is coming over here so it is getting divided into two parts so it is right that same equations we now have 3 Max is equals to half of front caladium / 8 to 12 is this particular area and this is obviously related to SD and this is we will find that, they will be able to relocate with the formula. So we have here, x is equalsto half of St – tbsd – DA2 so and when will it happen. Thank you
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