Research On The Methods To Decrease Discharge Temperature Of R32 Scroll Compressor

Ozone depletion and global worming are two major environmental issues faced by the world with serious implication for the development of refrigerant. The transition from HCFCs is underway for environmental protection pursuant to the Montreal Protocol, and the increasingly stringent global restriction of greenhouse gas emission accelerates the schedule. R32 has advantages such zero ODP, low global warming potential, favorable thermal properties, reduced refrigerant charge and low cost, and has been considered as an important alternative for application in refrigeration and heat pumping. However, the increased discharge temperature of the R32 compressor, compared with other refrigerants, is the main barrier affecting the wide and quick adoption. In this work, three promising methods, namely, two-phase suction, liquid injection and two-phase injection, have been investigated to decrease the discharge temperature of R32 scroll compressor.First of all, a comprehensive dynamic distributed parameter scroll model with special consideration of scroll wall temperature distribution is established. By the time scale analysis, the heat conduction process in scroll wall is simplified as a one-dimensional heat conduction with moving boundary conditions. The differential equation of heat conduction is developed and numerically solved. The model is validated by experimental data and has proven to be of high accuracy.Secondly, based on the validated model, the effectiveness in decreasing discharge temperature and influences on performance and operating envelope of the three methods are discussed. It is concluded that all the three methods show excellent potential in decreasing the discharge temperature of R32 scroll compressor, but two-phase injection outperforms the other two methods in cooling capacity and COP. Besides, one-tube injection and two-tube injection for two-phase injection system are proposed.Thirdly, an experimental apparatus is built to study the three methods. The result shows that a lower limit of suction refrigerant quality exits in two-phase suction in low-side scroll compressor, and confirms the advantages of two-phase injection in performance. It is also found that the evaporation temperature and condensing temperature varies when the three method are adopt in the system.Finally, the design and control of one-tube two-phase injection system is discussed. The ideal injection point is proposed from the perspective of compressor. The optimization of heat transfer capability of internal heat exchanger and intermediate pressure in the system shows that the heat transfer capability of internal heat exchanger has a proper range and the intermediate pressure can be optimized according to discharge temperature.