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Homework Help: Heat Transfer question regarding counterflow heat exchange.

  1. Mar 6, 2013 #1
    1. The problem statement, all variables and given/known data

    A counterflow, concentric tube heat exchanger is used to cool the lubricating oil for large industrial gas turbine engine. The flow rate of cooling water through the inner tube (Di = 25 mm) is 0.2 kg/s, while the flow rate of oil through the outer annulus (Do = 45 mm) is 0.1 kg/s. The oil and water enter at temperatures of 100 and 300 C, respectively. How long must the tube be made if the outlet temperature of oil is to be 600C ?

    2. Relevant equations

    Not sure

    3. The attempt at a solution[/b

    Not sure again, sorry
  2. jcsd
  3. Mar 6, 2013 #2


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    Staff Emeritus
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    Your question is confusing. Oil enters the exchanger at 100 C and you want cool it so that it exits at 600 C, by using 'cool' water that starts at 300 C. Notice something funny about this setup?
  4. Mar 6, 2013 #3
    Sorry, I meant 30*C, and at the end also 60*C
  5. Mar 6, 2013 #4
    You are given enough information to calculate the outlet temperature of the water. To do this, you need to assume a typical heat capacity for the oil (you already know the heat capacity of water, I presume). Use the information you have to get the outlet temperature of the water. You also already have enough information to calculate the heat load of the heat exchanger. Calculate the heat load. Then show us your results. We'll help you figure out what to do next.


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