3.Experimental Characterization
The controllable parameters in the VCC are the compressor capacity, heat source temperature and expansion valve opening position. Changing these parameters result in different compressor and evaporator energ input, recuperator heat exchange rate and condenser
heat rejection rate. The compressor capacity has been changed from 50-100% with 10% step and
the expansion valve opening position has been changed from open number 4 into open nwnber 6.
Figure 2-a shows the effect of changing the compressor capacity on the coefficient of
performance (COP) of the cycle at different expansion valve opening positions. With increasing the compressor capacity, the length of the piston stroke in the compressor increases which leads to a higher power consumption as shown in Figure 2-d. The increase of the piston stroke length means more refrigerant mass flow rate which increases the evaporator cooling capacity as shown in Figure 2-b. However, the increase in the power consumption is higher than the increase in the evaporator cooling capacity. Therefore, the cycle COP decreases as compressor capacity increases. Figure 2-c shows the effect of changing the compressor capacity at the pressure ratio across the compressor. With increasing the compressor capacity, the compressor outlet pressure increases [11] which lead to a higher pressure ratio across the compressor at fix valve opening position