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Homework Help: Confused on a question about vapour refrigeration cycle

  1. Mar 21, 2016 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution

    In the image linked above, I have copied and pasted 4 different slides. In the last slide, I am confused how they got the expression for T2 (the working out). I know that they did the following:

    [T2-(30+50)]/[(30+100)-(30+50)] = (5.623-5.417)/(5.75-5.417)
    (T2-80)/(130-80) = (5.623-5.417)/(5.75-5.417)
    (T2-80)/ = 50(5.623-5.417)/(5.75-5.417)
    T2 = 80+ 50(5.623-5.417)/(5.75-5.417)

    However, for the first step of the working, I am confused why the left hand side of the equation is like it is. Why do we have:

    [T2-(30+50)]/[(30+100)-(30+50)] = (5.623-5.417)/(5.75-5.417)

    I mean in terms of the vapour compression cycle, why is it -80 at the top and then 130-80 at the bottom? I know they got these values by adding the superheat temperature values but I am confused. Essentially what I want to know is what does 30+50 represent and what does 30+100 represent? If we are looking for the temperature at T2 why do we add 50 and 100 to 30 rather than to -20?

    Also for h2, I am assuming that the 1610.9 inside the brackets is a typo and is supposed to be 1610.5?
  2. jcsd
  3. Mar 26, 2016 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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