空气源跨临界CO_2热泵中回热器影响的研究

A Study on the Effect of the Internal Heat Exchanger in an Air-Source Transcritical CO_2 Heat Pump System

为了研究回热器对空气源跨临界CO_2热泵系统运行情况的影响,以及回热器是否适用于跨临界CO_2热泵,进行了理论和实验两方面的研究。基于热力学分析方法对不同气体冷却器出口温度、排气压力下回热器效率的影响进行了理论研究,结果表明回热器提升系统性能系数与否取决于气体冷却器出口温度,气冷出口温度较高时,回热器效率增大才能提高性能系数。实验则在跨临界CO_2热泵样机上进行,结果表明:应用回热器可降低系统最优排气压力,降低幅度随环境温度降低以及进出水温度升高而增大;采用回热器可减少最优排压下系统功耗、提高系统性能系数,但对制热量影响趋势不定,在本实验中性能系数最多提升6.65%,功耗最多降低6.22%;虽然回热器的应用能提高系统性能系数,但同时也将导致系统排气温度增大,所以不适宜在低环境温度工况下使用。对理论和实验分析结果的差异进行了讨论,同时建立了最优排压降低值与环境温度、进出水温度之间的实验关联式来数值化地体现回热器对系统排气压力的影响,对回热器在工程中实际应用具有一定的参考意义。

The impact of the internal heat exchanger(IHX) on a transcritical CO2 heat pump is investigated based on both theoretical and experimental methods. A thermodynamic analysis is conducted to study the influences of the IHX’s heat transfer efficiency at different gas cooler outlet temperatures and discharge pressures. The theoretical results show that whether the IHX improves the system performance coefficient depends on the gas cooler outlet temperature. Experiments are performed on a transcritical CO2 heat pump prototype, and the results indicate that IHX can reduce the optimal discharge pressure, and the degree of this reduction is enhanced with the decrease of ambient temperature and the increase of inlet and outlet water temperatures. Applying IHX brings an increase of 6.65% in the coefficient of performance and a decrease of 6.22% in power consumption at most, but it leads to a higher compressor discharge temperature, hence it must be restricted at lower ambient temperature. Moreover, the differences between theoretical and experimental results are analysed, and a numerical correlation of the reduced value of optimal discharge pressure with the ambient temperature, inlet and outlet water temperatures is established based on the experimental data.