Balance on Evaporator

Unlike the overall system, the evaporator is an open system. That is, there is a flow past the system boundaries. From a simple mass balance and since there is no accumulation, we find that the mass flow into the evaporator is equal to the mass flow out of the evaporator. While this does not help us solve for the mass flow, it does simplify calculations in the energy balance.

Energy Balance:

 (Kinetic and potential energy terms are negligible)

 The evaporator is at steady state, so the energy accumulation (dU/dt) is equal to zero.

 Neither shaft nor boundary work is being done in an evaporator.
0=Qc-0-0+mH4-mH1
0=Qc+m(H4-H1)

 m=Qc/(H1-H4)

This equation will be used later when other equations are obtained.
 
 

  1. Overall
  2. Evaporator
  3. Compressor
  4. Valve

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