 Alright, in the last segment what we did is we derived the equation for the log mean temperature difference and so what we're going to do now we're going to take a look at how the temperature is actually within the exchanger and remember we're looking at parallel flow double pipe exchanger how the temperature is mapped to LMTD and just to write out the expression that we had so that's the expression now one thing to note and this is a bit of a shortcut or not a shortcut but it makes it a little easier to remember and notice that this expression here th2 minus TC2 is the one that is in the numerator and then th1 minus TC1 is in the denominator so that is always the way that we have it configured for the LMTD temperature and and so it's useful if you remember those makes it a little easier when you're doing your calculations but what we're now going to do is we're going to go back and and really that this was in the derivation but I'm going to summarize it again and figure out what these temperatures are and how they map to where we are in the exchanger and so if we're dealing with a parallel flow heat exchanger what we have is this is T hot 1 and this is T hot 2 and this is T cold 1 and T cold 2 so that is the way that we designate the temperatures for a parallel flow double pipe now looking at counter flow so if we're looking at a counter flow heat exchanger and then we would have TH1 here TH2 there and T cold 1 here and T cold 2 there so you can see that what we're doing we're putting this as being location 1 and this is location 2 again here that is location 1 location 2 and then the the temperatures would either be hot or cold and they would correspond and so that's how you can get the temperatures that you would use within the LMTD expression as shown above now this was derived for a double pipe heat exchanger and so we do have to make a minor correction if we want to apply it to heat exchangers other than double pipe okay so if we're trying to apply LMTD to something other than a double pipe configuration then what we would do we would write out our heat transfer overall heat transfer coefficient the area that the overall heat transfer coefficient is computed for this correction factor F and then delta T and F is a correction factor and delta TM is the log mean temperature difference for counter flow double pipe so essentially what we're doing is we're mapping one to the other now where do you get F from F is from figures I'm not going to give you any of them you would find those in any textbook but you would have them for cross flow heat exchangers so radiators things like that you'd also have them for shell and two heat exchangers you can find the value of that and those would be tabulated in these figures and you would look up the value from that so what we're going to do in the next segment we're going to solve some problems using the LMTD and we'll see how it works so that's where we're going