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Mass flow in Vapor Compression Cylce HELP

  1. Oct 17, 2011 #1
    Hi guys,

    I'm doing some calculations on a vapor compression cycle system for my Master Thesis.

    My question is:
    Does the mass flow change when the refrigerant flows through the (electronic) expansion valve (assuming steady state flow)?

    I assume that it doesn't but I can't seem to get the "correct value" in my mass flow equations.

    I have an artice from where I get my steady state values and the compressor mass flow equation seems to be correct.

    I have used the
    m_dot = Cv*A_orifice*sqrt(2*rho*(Pin - Pout))
    equation for the valve mass flow.

    I have the technical data document for the expansion valve and I know that the stroke is 3.2 mm. I've tried to calculate the A_orifice from that value (assuming a cicular area).
    Other values are Cv = 0.94 (found that value in another article), rho = 1141.7 kg/m^3, Pin = 1046 kPa (condenser pressure) and Pout = 348.6 kPa (evaporator pressure).

    I'm not sure what I've missed.
    Although I'm not sure that it's correct to assume a circular area for the valve and on top of that I'm not sure that the value for Cv is correct either.

    Please guys I've been struggling with this for over two weeks now and I'm in desperate need for help.

    Thanks in advance,
  2. jcsd
  3. Oct 20, 2011 #2


    User Avatar
    Science Advisor

    Based on the Conservation of Mass principle, the mass flow rate is constant for a tube with one inlet and one outlet (i.e. no mass is gained or lost). The volumetric flow rate, however, may certainly change.

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