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Heat exchanger capacity (condenser and evaporator)

  1. Feb 27, 2008 #1
    Window-type Aircon

    how to get this in an actual experiment?

    is it just (mass flow rate of the refrigerant X specific heat X Change in temp of the refrigerant)

    or (mass flow rate of the air passing thru the heat exchanger X specific heat X Change in temp of the air)

    or (mass flow rate of the refrigerant X change in enthalpy (outlet and inlet state of the refrigerant)

    or (mass flow rate of the air X Change in enthalpy of the air)
     
  2. jcsd
  3. Feb 27, 2008 #2
    First, think about what control volume you are doing the analysis on. Are you measuring the air or the refrigerant? Under ideal situations, the heat absorbed by the refrigerant is the same as the heat rejected in the room. But practically, you are much more likely to get good data measuring changes in the refrigerant.

    This eliminates your second and fourth equations.

    Your first equation assumes that the refrigerant is a perfect gas but because in a traditional vapor-compression refrigeration cycle the flow through a heat exchanger is typically two-phase this is a bad assumption, hence this equation does not apply.

    Your third equation will allow you to properly calculate the amount of heat absorbed.
     
  4. Feb 27, 2008 #3

    russ_watters

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    Staff: Mentor

    The first response is fine, but just a quick fyi - if the air is dry, you can use the specific heat times delta-T times mass flow for the air, but if it is moist, you'll need to add the specific heat and mass flow of condensed water. But just using enthalpy instead covers that.

    Btw, there is a recent thread about a window heat pump unit where I do this exact experiment. I'm trying to get a paper published.
     
  5. Mar 16, 2008 #4
    can i use the pyschrometric chart for 100KPa, even if the air is blown thru fan?

    the air pressure increases when blown by fan, right?
     
  6. Mar 16, 2008 #5

    russ_watters

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    Staff: Mentor

    Yes, air pressure increases when blown through a fan, but not by much. A powerful air conditioning fan might give you 1kPa of pressure rise.
     
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