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Homework Help: Applied Thermodynamics - Heat Exchanger problem

  1. Sep 11, 2012 #1
    1. The problem statement, all variables and given/known data
    Refrigerant 134a enters a heat exchanger operating at steady state as a superheated vapor at 10 bars, 60C, where it is cooled and condensed to saturated liquid at 10 bars. The mass flow rate of the refrigerant is 10 kg/min. A separate stream of air enters the heat exchanger at 37C with a mass flow rate of 80 kg/min. Ignoring heat transfer from outside of the heat exchanger and neglecting kinetic and potential energy...

    2. Relevant equations
    Determine the exit air temperature in degrees C.

    3. The attempt at a solution

    I started with my conservation of mass and energy equation, and I have

    for C.O.M, since its a steady state process, I have m(in) = m(out)

    for C.O.E, I have Q-W=m(h(out)-h(in)) and..switched the change in enthalpy to cp(T2-T1) to find T2..
  2. jcsd
  3. Sep 12, 2012 #2
    Is there something in particular you are stuck on with this problem? There are two ways to go about heat exchangers by system selection. Your first option is two analyze as an entire overall system noting that the entire system is adiabatic with respect to the environment (heat transfer out to the surroundings is usually negligible in comparison to the internal workings). The second option, that I prefer is to choose a two system setup where you note a continuity condition that the heat transfer out of one system is the heat transfer in to the other system.
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