Abstract:

An optimized design of the ejector was presented, which was applied to a transcritical CO₂ heat pump as an experimental water heater system. Experiments were carried out not only to investigate the effects of flow rate and outlet temperature of hot water and the high-side pressure on the system and the ejector performance, such as the heating coefficient of performance (COP_h), entrainment ratio, pressure lift and ejector efficiency, but also to reflect the ejector influence on system performance. The experimental results show that though the ejector efficiency was related to the entrainment ratio, their change with the hot water flow rate or the outlet temperature were different. In the other word, the entrainment ratio was decreased while the ejector efficiency was increased with the decrease of the cooling water flow rate or the increase of the outlet temperature. Under the experimental working conditions, pressure lift was kept constant and the COP_h reached about 3.5. With this ejector, high side optimal pressure decreased dramatically, which results in safer operation for this system. However when the COP_h reached the highest value, the ejector efficiency was not the best one. The experimental results also showed that there existed an optimal operation pressure for the transcritical CO₂ heat pump with the ejector. What should be noted was under optimal hide side pressure, hot water outlet temperature was not the highest value but still more than 55℃. Therefore stable operation in the optimal high side pressure for the heat pump system is of great significance. It can not only greatly improve system performance, but also ensure attain higher water temperature of the hot water.

Key words: ejector, optimal design, thermodynamics, CO₂, transcritical cycle, heat pump, COP_h

摘要：

在跨临界CO₂热泵热水器系统中引入优化设计的喷射器,对系统进行实验研究,分析了制热系数、引射比、升压比、喷射器效率等参数随热水体积流量和出口温度及高压侧压力的变化趋势以及优化设计的喷射器对系统的影响。实验结果表明:随着热水体积流量减小或其出口温度增加,引射比将逐渐减小,而喷射器效率逐渐升高;在测试工况范围内升压比基本保持不变,系统COP_h最高将近3.5;系统高压侧的压力因优化喷射器的引入而明显降低,有利于系统的安全运行;跨临界二氧化碳热泵喷射循环系统存在一个最优运行压力,值得注意的是在最优运行压力下,热水出水温度虽未达到最高,但依旧超过55℃。系统稳定运行在最优高压侧压力下,不仅系统性能大幅度提高,而且保证了热水的出水温度。

关键词: 喷射器, 优化设计, 热力学, CO₂, 跨临界循环, 热泵, COP_h