Experimental study on p– V indicator diagrams of twin-screw refrigeration compressor with economizer

This paper presents the experimental investigation on the effects of the superfeed pressure together with economizer type on the performance of the twin-screw refrigeration compressor by means of the indicator diagram. With a pressure sensor embedded into the groove at the root of the female rotor on the discharge side, the pressure within the working chamber of a semi-hermetic twin-screw compressor with an economizer is recorded and then transformed into the indicator diagram. The results thus obtained are utilized to investigate the thermodynamic process of the compressor. It is shown that the compressor with an economizer has higher pressure during almost the whole compression process than without an economizer, resulting in the increase in the indicated power. Under different superfeed pressures, the pressure within the compression experiences different changes. This results in an optimal superfeed pressure for maximized compressor efficiency, which can be identified from the calculated compressor efficiency based on the indicator diagrams. It is also found that the pressure has a rapid increase at the beginning of superfeed process, and then a slow rise even a slight drop at the end of superfeed process, which is caused by the dynamic effect during superfeed process. Furthermore, if the superfeed pressure keeps the same, the pressure during compression in the compressor with the heat exchanger economizer is slightly higher than with the flash tank economizer, due to the higher temperature of superfeed refrigerant gas in the former case.