【作者】 魏晋；

【导师】 唐黎明； 陈琪；

【作者基本信息】 浙江大学 ， 供热、供燃气、通风及空调工程， 2016， 硕士

【摘要】 由于臭氧层破坏与温室效应,CFCs(氯氟烃)、HCFCs(含氢氯氟烃)和HFCs(氢氟烃)等人工制冷/热泵工质正逐渐被淘汰或面临淘汰。在工质的替代物中,由于环境友好性与良好的传热性能,CO2正在成为热泵领域的研究热点与主要制冷剂之一。跨临界CO2热泵系统在一定程度上克服了CO2在亚临界循环时性能系数较低的缺点,但较大的节流损失阻止了其性能系数的进一步提高。喷射器的经济性使其成为在小型跨临界CO2系统中回收这部分节流损失的首选元件。以前的研究发现,喷射器的加入对跨临界CO2热泵系统的贡献随着实验工况不同而改变。甚至在某些工况下,喷射器的加入反而降低了系统COP,即两系统对变工况的适应性也不尽相同。本文在前人研究的基础上,从理论和实验的两个角度对带喷射器的跨临界CO2热泵系统进行变工况适应性的进一步研究。主要研究内容如下：1)通过实验,研究变频压缩机转速对跨临界CO2热泵系统(TCHS)与带喷射器的跨临界CO2热泵系统(TCHSE)最佳充注量的影响。结论表明TCHS最佳充注量受压缩机转速影响较大,而TCHSE几乎不受影响。2)实验研究在热水出口温度与蒸发压力变化时,TCHS与TCHSE的性能变化规律。TCHSE对较为恶劣的换热条件有更好的适应性,但在热水出口温度较低、蒸发压力较高的工况,TCHSE的制热系数小于TCHS。3)模拟研究CO2气冷器出口温度对TCHS与TCHSE系统最优排气压力的影响,同时理论研究负面影响TCHSE制热系数的因素。结果表明喷射器等熵效率较低或是气液分离器气相出口带液均会降低TCHSE的制热系数,但只有气液分离器气相出口带液才会使TCHSE在相同系统高低压时制热系数低于TCHS。更多还原

【Abstract】 Majorities of the synthetic refrigerants, such as CFCs, HCFCs, HFCs, are being or will be phased out due to their ozone depletion effect and impact on global warming. As one of the alternatives, for its environmental-friendliness and favorable heat transfer performance, the natural refrigerant CO2 has become a hot spot among global researches and maybe a common refrigerant in heat pump area. The transcritical CO2 heat pump system somehow overcomes the low performance of subcritical CO2 cycle. However, the large throttling loss limits the system to getting a higher coefficient of performance (COP). The ejector is considered one of the most promising item to recover some of this throttling loss in small-sized transcritical CO2 system owing to its low-cost. It was found in previous studies that the superiority of introducing an ejector in transcritical CO2 heat pump system varies in different operating conditions. The system with ejector even inferior to the conventional system in COP under some operating conditions, which means the two systems might have different applicability in off-design conditions. Focusing on these concerns, further theoretical and experimental investigations were carried out in this paper to investigate the applicability of transcritical CO2 heat pump systems in off-design conditions.The main researches are as follows:1) Impact of compressor rotation rate on refrigerant charge of the conventional transcritical CO2 heat pump systems (TCHS) and the transcritical CO2 heat pump systems with ejector (TCHSE) were experimentally investigated. TCHS showed a large variation of optimal charge amount under the changing compressor rotation rate whereas TCHSE did not shows much variation.2) In order to analyze the system applicability in off-design conditions, experiments were carried out on TCHS and TCHSE when both hot water outlet temperature and CO2 evaporating pressure were varied. TCHSE showed better applicability in stricter working conditions. However, the COP of TCHSE was lower than TCHS when hot water outlet temperature was relatively low or evaporating pressure was relatively high.3) Thermodynamic models of TCHS and TCHSE were built up to investigate the impact of CO2 gas cooler out let temperature on the optimal heat rejection pressure as well as the factors that led TCHSE had a lower COP than TCHS. Both low isentropic efficiency of ejector and liquid comes out from the gas outlet of separator have a negative effect on system performance. Whereas, only liquid CO2 comes out from the gas outlet of separator leads that THCSE inferior to TCHS in COP when they at the same high-side and low-side pressure.更多还原