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Homework Help: Thermo Question - Fridge cycles

  1. Jan 30, 2007 #1
    Consider a 300 kJ/min refrigeration system that operates on an ideal vapor-compression cycle with refrigerant-134a as the working fluid. The refrigerant enters the compressor as saturated vapor at 140 kPa and is compressed to 800 kPa. Determine the (a) quality of the refrigerant at the end of the throttling process, (b) the coefficient of performance, and (c) the power input into the compressor.


    2. Relevant equations
    In a refigeration cycle I am considering state 1 after the evaporator, 2 after the compressor, 3 after the condenser and 4 before the evaporator.

    P1=140 kPa, x (quality)=1 since its a saturated vapor.
    P2=800 kPa, x=1

    W=m(h2-h1)

    3. The attempt at a solution
    300 kJ/min = 5KW

    In an ideal refigeration cycle isn't the only work considered the work for the compressor, so isn't the answer to (c) 5KW?

    I'm having the most problems with (a) because I am unsure to begin. I can find other states such as enthalpies with the pressure I have been given, is that the correct approach?
     
  2. jcsd
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