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.
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Overall
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Evaporator
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Compressor
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Valve
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