mechanical vapor recompression, mulit-effect evaporation, twin screw water vapor compressor, water injection, mathematical model
The heat pump system of mechanical vapor compression/recompression (MVC/MVR) combined with evaporation is a high efficiency, energy-saving solution for energy intensive processes. However, a suitable compressor with high pressure ratio and low discharge temperature is not available in engineering practice. In this paper a water-injected twin screw compressor recognized as a promising type for water vapor compression is presented by detailed descriptions of the rotor profile development and structure design. Then the calculation of water quantity and its influence on the steam flow rate are presented. Moreover, the effects of injected water on the working process and performance of the compressor are discussed. Finally, it is found that the volume flow rate increases a lot because of the water evaporation during the compressing process which is originally aims to guarantee saturate discharge temperature. And the temperature difference of the MVC system is a main parameter that affects the performance of the compressor.