HIGH PERFORMANCE TRANSCRITICAL HEAT PUMP CYCLE USING CARBON DIOXIDE AS A REFRIGERANT

研究开发了一种名为喷射器的膨胀功率回收装置，有望提高二氧化碳热泵的COP。在超声速喷管研究成果的基础上，实际设计了整个喷管系统，制造了包含该系统的实际喷管式热泵，进行了性能测试，并对实验结果进行了分析。这些研究结果澄清了以下几点。首先，喷射器在一个喷射器循环中的性能是由混合部分和扩散器处产生的激波引起的压力增加和覆盖整个吸流通道的压力损失特性的平衡来确定的，从喷射器出口到喷射器的吸入部分，经过气液分离器、膨胀阀和蒸发器。阐明了安装在吸气管路上的膨胀阀的控制方法，使COP达到最优。根据上述平衡可以解释混合部分尺寸的影响，并可以从理论上预测混合部分的最佳尺寸。适当地假设喷嘴效率和扩散器效率，可以较准确地解释实验结果。二氧化碳的低粘度表明混合部分的长度对效率的影响不大。为了提高以二氧化碳为操作介质的换热器的效率，采用1 ~ 6mm内径的换热管对蒸发换热性能进行了研究。研究了含润滑油情况下的传热特性。由实验结果得到以下实验相关性：干燥发生前的预干燥换热，干燥发生时的质量换热，干燥发生后的后干燥换热。

Research and development of the expansion power recovery mechanism called an ejector, which is expected to improve the COP of carbon dioxide heat pumps, were performed. Based on the research result to a supersonic nozzle, the whole ejector system was actually designed, the actual ejector type heat pump incorporating it was manufactured, the performance test was performed, and analysis to the experimental result was performed. The following things were clarified by these research results. First, the performance of ejector in an ejector cycle is determined from the balance of the pressure increase due to the shock wave, which is produced at the mixing part and the diffuser, and the pressure loss characteristics covering the whole passage of the suction flow, from an ejector exit to the suction part of ejector through a gas-liquid separator, an expansion valve, and an evaporator. Moreover, the method of controlling the expansion valve, which is installed in suction line, for making COP optimal was clarified. The effect of the size of mixing part can be explained based on the above-mentioned balance, and the optimum size of the mixing part can also be predicted theoretically. Experimental results can be explained with sufficient accuracy by assuming nozzle efficiency and diffuser efficiency appropriately. The low viscosity of carbon dioxide showed that the length of mixing part did not have large effect on the efficiency.About the improvement in efficiency of the heat exchanger, which uses carbon dioxide as an operation medium, the performance of evaporation heat transfer was investigated using heat transfer tubes with 1-6mm ID. Heat transfer characteristics in case lubricant oil was included were also investigated. Following experimental correlations were obtained from the experimental results ; the pre-dry out heat transfer before dry out occurs, the quality when dry out generates, and the post dry out heat transfer after dry out generating.