高/低温环境热泵用低GWP混合工质换热机理及循环特性研究

The study of the heating capacity at low temperature and the cooling capacity at high temperature for HFO/HFC refrigerant blends with low global warming potential (GWP) will be carried out, and the main contents are as follows:.1) Based on the thermophysical properties of low GWP refrigerants, the refrigerant blends used for heat pump under high/low temperature conditions are classified, and the coupling characteristics of heat transfer and pressure drop under boiling/condensing conditions in horizontal smooth/enhanced tubes will be studied. The optimal criteria for heat exchanger structure using the refrigerant blends will be proposed based on the optimal heat transfer model adopting the coupling of heat transfer and pressure drop..2) The influence of driving temperature difference and pressure drop on the heat exchanger size will be quantitatively determined by experimental investigation, furthermore, the optimal design methods for the heat exchanger structure will be proposed..3) A new double-chamber compression heat pump system with compound throttling will be built up, and the optimal operating range of suction pressure and volume ratio under low evaporation temperature/high condensation temperature will be investigated, which can provide useful guidance for improving the heating capacity at low temperature and the cooling capacity at high temperature for heat pump using low GWP refrigerants..In this project, the heat transfer mechanism and operating characteristics of the refrigerant blends HFO/HFC used under high/low temperature conditions will be further studied, which are of significance for the applications of heat pump under extreme conditions.

对低温室效应（GWP）混合工质HFO/HFC在低温环境下的制热及高温环境下的制冷能力进行研究，包括：1）依据低GWP混合工质的热物性，提出适宜高/低温环境热泵循环的混合工质对，并对其在水平光管及不同结构的强化传热管内低温沸腾/高温冷凝传热和压降对换热性能的耦合影响进行研究，得到基于传热和压降耦合的换热优化模型，为低温沸腾传热/高温冷凝传热换热器结构优化提供理论判据；2）通过实验研究确定出低GWP混合工质高/低温工况换热时传热温差和压降与换热器几何尺寸之间的定量关系，提出换热器结构优化方法；3）构建新的适合高/低温工况的双级节流分腔压缩热泵系统，确定系统高/低温环境运行的吸气压力、容积比等关键参数优化范围，提出提高系统低温制热/高温制冷能力的有效方法。. 研究可深入了解低GWP混合工质高/低温工况的换热机理及系统运行特性，为其低温制热/高温制冷循环的实际应用提供理论与实践基础。

低GWP混合工质热泵应用中，混合工质最佳质量配比，换热器优化匹配是影响其应用的主要问题。本项目在前期研究的基础上，依据低GWP 混合工质的热物性，研究了HFO/HFC、HFO/HC等混合工质热泵工况下的最优质量配比，建立了基于熵产最小化的混合工质换热模型，探索了低GWP混合工质的换热机理，得到了混合工质饱和温度、压降、换热特性之间的变化关系，分析了换热器结构特征、不同工质及入口条件等参数对换热器传热特性的影响规律，明确了螺旋式套管换热器最优传热条件。并对低GWP混合工质最优质量配比下的热泵循环特性进行了对比实验研究。相关结果对低GWP混合工质热泵应用具有重要的科学意义与工程应用价值。