In this case, a BPHE with 50 plates has 0% oversurface. Figure 6.25 shows the performance curves of three different evaporators and a compressor curve.īelow are some examples of what happens if the heat exchanger is over- or undersurfaced. The performance and size of the evaporator influence the total cooling capacity and performance of the system, because the operating points will differ. The evaporator performance should be calculated for the same level of superheating in order to remain comparable with the compressor line. Increasing the values of these parameters will decrease the capacity of the compressor, i.e. The intersection of these two curves signifies the operating point.Ī compressor curve is defined for a certain level of superheating and a certain condensation temperature. The evaporator performance curve has a negative slope, indicating that a smaller temperature difference between the refrigerant and the secondary fluid leads to less heat transfer per area. The compressor curve in Figure 6.24 has a positive slope, indicating that the available cooling capacity increases with higher evaporation temperature. The refrigerant mass flow is determined by the compressor, and at the operating point the refrigerant is evaporated at a stable saturation temperature. The evaporator operating point is the equilibrium point at which the performance of the evaporator matches the performance of the compressor. The evaporator and condenser affect these pressure levels though their ability to transfer energy between the refrigerant and the secondary fluids. The total pressure difference between the evaporating and condensing sides also affects the required compressor power consumption. The saturation pressure of the evaporator determines the density of the refrigerant gas at the inlet of the compressor, thus affecting the refrigerant mass flow per compressor revolution. Matching the evaporator with a compressorĪs discussed in chapter 3.4, compressor performance depends on the evaporating and condensing pressures. The effect of selecting the evaporator for a chosen compressor is discussed in this section. The task of the evaporator and condenser is to utilize the available energy potential fully, thereby maximizing the efficiency and economy of the useful power that can be extracted from the system. The compressor is the "heart" of the refrigerant system, and is the component that limits the capacity of a refrigerant system.
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