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Homework Help: Thermodynamics refrigeration Problem

  1. Nov 3, 2005 #1
    Hey, I'm having a bit of trouble with a Thermo problem on a homework assignment. The problem is:

    6-138 (Thermodynamics: An Engineering Approach, 5th Edition)

    The drinking water needs of a production facility with 20 employees is to be met by a bobbler type water fountain. The refrigerated water fountain is to cool water from 22 C to 8 C and supply cold water at a rate of 0.4 L per hour per person. Heat is transferred to the reservoir from the surroundings at 25 C at a rate of 45 W. If the COP of the refrigeration system is 2.9, determine the size of the compressor, in W, that will be suitable for the refrigeration system of this water cooler.

    Using the density of water, I first determined the mass flow rate of the water to be 0.00222 kg/s.

    I know that I can use COP=(Ql)/(Qh-Ql)=(Ql)/(Win).

    I think the next step I need to take is to set up an energy balance (Sum Ein = Sum Eexit) but I'm not entirely sure how to complete this step.

    Thanks in advance for the help.
  2. jcsd
  3. Nov 3, 2005 #2


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    The rate of Ql is [itex]\dot{m}\,c_p\,\Delta{T}[/itex] ,
    and you know COP, and heat out to environment, 45 W.
    Last edited: Nov 3, 2005
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