 In this segment what we're going to be doing is we're going to be taking a look at the ways that heat exchangers are classified. So the two ways that we classify heat exchangers, we look at the way that the flow is arranged and we'll be looking at examples of that, you can have parallel flow, you can have cross flow, you can have mixed fluid, unmixed fluid, and the type of construction and there are different types of construction we've already seen in the previous segment looking at different types of construction of heat exchangers, but these are the ways that we classify heat exchangers and it also guides our analysis depending upon which equations we would apply would depend on the type of construction or the flow arrangement. So what we're going to begin with, we're going to begin with the most simple type of design of a heat exchanger and that's where you have two pipes, one smaller diameter than the other, they're coaxial and you have fluid going either in parallel or in counter-flow with respect to one another and there's heat exchange between the pipe wall, between the two pipes. So now let's begin looking at that. Okay, so here we have two different types of flow arrangements for what we refer to as being the double pipe heat exchanger and in both of the figures, one over here that is inner tube flow as well and then on the outside we have what we refer to as being our outer tube flow. Now with these two, these are basically the same type of construction, the only difference is the direction of the fluid and we would refer to the one on the left as being the parallel flow configuration or arrangement and that is because you can see the two fluid streams are going in the same direction and that is why we call it parallel flow and then all of the heat transfer is taking place across this interface here and here so that is where our heat exchange is taking place and then the design on the right that we refer to as being the counter-flow flow arrangement. So those are two examples of the simplest which is the double pipe or concentric tube heat exchanger. Another flow arrangement and type of construction that we have is that for cross flow. So a cross flow heat exchanger, so this is a different type of construction and this is one where what we have is a tube bundle and so out of each of these tubes we would have flow coming out and then going perpendicular to that or near perpendicular we would have a cross flow and for this particular type of construction you can have fins or no fins on your tube bundle and depending upon the type of construction if you do have fins you may have a scenario where the cross flow does not mix with itself and so if you imagine if you have fins that are all connected so if you had fins that were going like this and going across all of them and then another set of fins it's kind of a poor drawing so then another set of fins going like that and then another one so if you have fins like that what's going to happen is the fluid will not be able to mix in the cross plane in terms of the cross flow and the two flow obviously the fluid there is not going to mix because they are all in individual tubes so you can have mixed and unmixed and you can have finned and unfinned different types of configurations for cross flow heat exchangers but typically this one although not exclusively but quite often this would be gas to liquid is what we're looking at for the heat exchange and when I say liquid it may not be a liquid it could be a vapor going to a liquid and that would be the case of condensation and I guess you could also be going through a phase change the other way going from liquid to vapor depending upon a particular design but anyway it typically gas to liquid that is the cross flow heat exchanger so it's another type of construction and again you can have different flow arrangements just like I said depending on if it's mixed or unmixed if you have fins or no fins and then the next type of heat exchanger that we're going to look at these are heavier units that are used in many industrial applications but these are shell and tube heat exchangers so let's take a look now the arrangement is going to depend upon how many shell and tube passes you actually have you can have two shell units sitting next to each other shell and tube and then you would be going through two shells there or the tubes you can actually have them do multi-pass and a single unit they're all different types of geometrical configurations that you can have for this but let me just show you the most basic one okay so what do we have here let's label the different things that are in here now to begin with we have fluid coming in and that is on our tube inlet and what's going to happen is that fluid is going to come into this manifold on the end and it is going to be forced to go into these tubes and then it is going to flow along the tubes like so and you'll have hundreds and hundreds of these tubes will depends on the construction but many many tubes and then it comes out and it comes into another manifold where there is some mixing but then it goes out through this exit here and that is our tube outlet now there will be another flow coming along here and this is referred to as being the shell inlet because that will be on the outside there's a shell outside of our tube bundle which is on the inside and the shell flow is forced to go normal or cross flow across our tube sheet and then it comes here and it turns direction and goes around and then it comes and it turns direction again well that's a very big section there typically they wouldn't look that way I am not an artist I apologize but you get the idea we're engineers we can figure it out okay so what what's happening is the flow is going through like that and then it's coming out in this direction shell outlet so that is the direction of the two fluid streams and we have a couple of other things in the construction here that I would like to point out first of all there are these plates here you can see two of them in my drawing these are called baffles or baffle plates and and there are different designs that they have sometimes they'll have designs where it's like a helical pattern and you get more efficient mixing that way and because what will happen if you look at the fluid mechanics here this is horrible fluid mechanically you're going to have massive separation downstream of these baffles when the flow comes around and you'll have significant pressure drop usually we're not worried about that much pressure drop at these units well you'll have a lot of pressure drop but you have a lot of you'd have a big pump circulating the fluid through so pressure drop is usually not your main concern but nonetheless you're going to have separated flow downstream of these baffles and that will minimize the heat transfer that you're having in these regions here so sometimes they'll change the baffles different types of design in order to enhance mixing the other thing that we have with the construction on this side is a tube sheet and on the other side is another tube sheet and so that is where the tubes come through and they're usually welded to that tube sheet in terms of the baffles it wouldn't be typically not welded they are free to move back and forth if they need to but you want to have the baffles there to minimize flow vibration you can have flow by vibration in these things and it also forces the flow to go around multiple times so that's kind of a poor drawing of a shell and tube heat exchanger but hopefully you get the idea in terms of what is going on so and there we have shell flow forces the flow normal to the tubes as we mentioned and we have baffles inside of the unit they support the tubes now if you look at the tube sheet and you take a look at what it looks like the tube sheet will span obviously the entire cylindrical of the shell and within the sheet itself we're going to have all these little holes drilled and that is where our tube bundle is going to come through and it'll go on so that is what the tube sheet looks like now if you look at a baffle plate it will not span the entire so it will look more like this and it'll be there'll be a cut out and that's where the fluid comes around but then you would have enough to support the tubes and you'll notice that let's see one two three four five one two three four a I did this good I did it well you actually have a couple of tubes or a number of tubes here that are free span and and so they are not confined by a baffle at that location but that is to allow the fluid to get by so if we look back at the shell and tube you have this and then you have this and you have this so the fluid is going around like that and and that's why you don't want the baffle plate to go all the way throughout the entire cross section of your shell so that is the shell and tube heat exchanger there is another design although we're not going to look at it in the lectures here but these are compact heat exchangers and so compact heat exchangers are designed in a manner where you try to maximize the contact area between the two fluid streams and and and so these are ones that have very very large contact area you could have plates connected together with gaskets and the fluid goes between those plates we won't be examining those but that is another form of heat exchanger and they're called compact because they're small and in terms of how much space they they take but they're very effective in terms of transferring thermal energy from one fluid stream to another so those are different designs or configurations types of construction as well as different flow arrangements what we'll be doing in the next segment is taking a look at temperature distributions between the fluid streams and these heat exchangers