| The synthetic refrigerants CFC and HCFC are the main factors of global warming. Looking for high efficiency and environment-friendly refrigerant has been an important issue of great concern to the international community. Natural refrigerant CO2 is not only environment friendly but also has good performance. Transcritical CO2 cycle has predominance in heat pump system for water heating applications due to its large temperature glide during rejecting heat and better matching with the water, but there is significant throttling loss in conventional basic transcritical CO2 cycle that limits the performance improvement. This thesis investigates the performance of a transcritical CO2 cycle with an ejector or an internal heat exchanger in basic. The theoretical and experimental investigations on the system performance are carried out. The main contents are as following:Firstly, the thermodynamic models for basic transcritical CO2 cycle (BTC), basic transcritical CO2 cycle with an internal heat exchanger (BTC-IHX) and ejector expansion transcritical CO2 cycle (ETC) are established to conduct a theoretical research on the system performance.Secondly, the effects of the external parameters on the internal parameters are investigated. From this basis of the research, the effects of internal parameters on system performance are analyzed.Based on the internal parameters, the experimental research on a comparison of the BTC and BTC-IHX is investigated under different evaporation temperatures.Thirdly, the performance study on the transcritical CO2 heat pump system with ejector is carried out. Compared to that of BTC, the experimental results prove that the ejector can improve the system performance effectively.Finally, based on the initial research, a prototype of transcritical CO2 air source heat pump water heater is built. It found a good basis in driving the development of CO2 heat pump water heater. |
