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Homework Help: Thermodynamic question: first law

  1. Apr 3, 2015 #1
    Estimate the kilowatt pump you would need to pump 450 L/min of liquid water at 20c through a rise in elevation of 100m. Assume the water is pumped adiabatically and with negligible changes changes in temperature and kinetic energy.

    answer given to us is -7.35kw..

    Question.. what formula should i use?.. im lost in this one.. please be specific guys.. i've used all i know and still cant get the answer..
  2. jcsd
  3. Apr 3, 2015 #2


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    How much energy would it take to raise 1L (=1kg) up by 100m?
    What is the equation that relates power, energy and time?
  4. Apr 3, 2015 #3
    You are supposed to use the open system steady flow version of the first law:


    where Ws is the rate of doing shaft work, m is the mass flow rate, and h is the specific enthalpy.

  5. Apr 3, 2015 #4
    weew thanks!!!
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