Modeling and simulation of oil-free liquid-injected screw compressors using ammonia-water mixture as working fluid

Abstract

This study investigates the compression process of an oil-free screw compressor with liquid injection for an absorption-compression heat pump (ACHP) with an ammonia-water mixture as working fluid. In recent years, several studies stated that the temperature limitation of the compressor during the compression process is a critical parameter when achieving high sink outlet temperatures. High temperature heat pumps are beneficial for the intended decarbonization, and efficiency increase in various industrial applications. With the compressor identified as a critical major component, it is an important subject for further research. However, investigations on liquid injection have so far often been limited for ammonia-water mixtures only in the context of wet compression or with pure refrigerants, such as ammonia or water. To address this existing research gap, the compression process of oil-free liquid-injected twin-screw compressors was analysed, modeled, and simulated using the MODELICA Language. The simulation includes the effects of leakage flows, heat losses and fluid injection. Based on this, modifications to an existing screw compressor for use in the ACHP system were suggested. The developed model can be used for the optimization of liquid injection of existing compressors for different operating conditions. Future research will focus on verifying the simulation results for liquid injection with ammonia-water mixture as working fluid.

Modeling and simulation of oil-free liquid-injected screw compressors using ammonia-water mixture as working fluid