Abstract:

Zeotropic mixtures are popular alternatives to chlorofluorocarbons (CFCs）and hydrochlorofluorocarbons (HCFCs）in the high temperature heat pump system.Zeotropic mixtures exhibit two major characteristics during phase change：temperature gliding and nonlinear relationship between temperature and enthalpy.In order to reveal the distribution of temperature difference between zeotropic mixture and heat transfer fluid in heat exchangers and get clear how temperature differences affect the performance of the system, experiments were carried out with the binary mixture Z1 in the high temperature water-water heat pump system, which was composed of 17% R290 and 83% R600 (mass ratio).The experimental results showed that as the water flow rate decreased the maximum temperature difference occurred in the condenser and its location moved to the cold end of the condenser, while the minimum temperature difference occurred in the evaporator and its location moved to the cold end of the evaporator.It was found that the occurrence of maximum temperature difference decreased the coefficient of performance of the system and increased the exergy loss caused by irreversible heat transfer in the condenser, while the occurrence of pinch point increased the coefficient of performance of the system and decreased the exergy loss caused by irreversible heat transfer in the evaporator.The results demonstrate the importance and the need for pinch point analysis in the evaluation of zeotropic refrigerant mixtures applied in air-conditioner or heat pump.In addition, the change of the temperature difference between the working fluid and heat transfer media found in this study is helpful to design heat exchangers in heat pump units.

摘要：

为了探究非共沸工质与换热流体之间的相变传热温差特性，在单级蒸气压缩式水-水高温热泵系统实验台上，以R290/R600（称为Z1，质量比17%/83%）为工质进行了多工况的实验研究。实验发现，工质Z1在冷凝器中会出现最大传热温差，且最大传热温差的位置会随着冷凝器中水流量的减小而向冷凝器的冷端移动；在蒸发器中会出现最小传热温差，其位置随着蒸发器中水流量的减小而向蒸发器的冷端移动。分析结果表明，在蒸发器侧工况恒定时，冷凝器侧最大传热温差的出现会使系统的循环效率降低，冷凝器中因不可逆传热引起的可用能损失增大；在冷凝器侧工况不变时，蒸发器侧最小传热温差的出现会使系统的循环效率上升，蒸发器中因不可逆传热引起的可用能损失减小。