Optimization Of Reversing Valve Based On Heat Loss And Pressure Drop Analysis

For heat pump system, reversing valve is indispensable to achieve the switch between cooling and heating conditions. However, the existence of reversing valve leads to inevitable performance loss to the heat pump system. This loss does not only exist in the reversing process of valve itself, but also exist in the whole running process of system from beginning to end, and then the influence of reversing valve loss on heat pump air-conditioner performance cannot be neglected. The reversing valve loss includes three parts: refrigerant leakage loss from high-pressure side to low-pressure side, pressure loss caused by the flow resistance of irregular flow passage, and heat transfer loss from high-temperature side to low-temperature side/environment. Among the entire reversing valve loss, leakage loss accounts for less than 15%, and pressure loss is about 25%, while heat transfer loss takes the major part of 60%. Because of the relative large ratios of pressure loss and heat transfer loss, the reduction of these two losses becomes the key to decrease the reversing valve loss. Therefore, the analysis of pressure and heat transfer losses, and the corresponding optimization research of reversing valve have great meaning to improve the performance and lower the energy consumption of heat pump system.In present study, the research methods of experimental, theoretical and numerical are combined to analyze the heat transfer and pressure losses of reversing valve. Then based on the obtained analysis results, three innovative optimization methods are proposed: material optimization for heat transfer loss reduction and structure optimization for pressure loss reduction. The main research results are summarized as follows:(1) By the qualitative theoretical analysis of influence factors on heat transfer and pressure losses, the quantitative numerical analysis of influence factors composition and distribution, and the experimental verification, the heat transfer loss and pressure loss characteristics are obtained. On that basis, the material optimization idea, the structure optimization idea, and performance and cost based global optimization idea are proposed. The loss analysis indicates that: for heat transfer loss, the loss through valve body accounts for 66.5%, the loss through valve seat is about 31%, and the rest 2.5% is the loss through slider; for pressure loss, the major loss occurs at the closed volume by slider. The optimization on valve body and valve seat material could reduce the heat transfer loss, and the optimization on slider structure could reduce the pressure loss, while the material optimization combined with valve size reduction could decrease the cost on the premise of performance guarantee.(2) By the numerical and theoretical analysis of the influence of valve material on heat transfer loss and system performance, the relation curves of valve material thermal conductivity vs. heat transfer loss/system performance are obtained. Two materials with different thermal conductivities are tested, and the test results show that: after the change from brass (thermal conductivity: 109 W/(m.K)) to Z alloy(thermal conductivity: 60 W/(m.K)), the heat transfer loss decreases by 21%, and the system COP increases by 0.27%.(3) By the numerical and theoretical analysis of the influence of slide structure on pressure loss and system performance, the optimization effect of slider structure on pressure loss and system performance are obtained. After slider shape is changed from flat type to circular arc type, the pressure loss decreases by 35.6% and the system COP increases by 0.23%.(4) Based on the analysis of heat transfer and pressure losses, the global optimization scheme by comprehensively considering the performance and cost is proposed. Material optimization combined with valve size reduction could decrease the cost on the premise of performance guarantee. When thermal conductivity of reversing valve seat decreases from 110 W/(m.K) to 60 W/(m.K) and the size of reversing valve reduced by 8.7%, the capacity of heat pump system is unchanged, the COP of heat pump system increases by 0.28%, and the cost of reversing valve decreases by 16.6%.In the end, the conclusions of present study are summarized and the further research ideas are proposed.