Research And Optimization On Heat Transfer Performance Of Multi-Heat-Source Watertank With Double Helical Coil Heat Exchangers

According to the architectural climate regionalization,most of the central and southern regions of China are cold or hot in summer and cold in winter,where decentralized heating is increasing needed.Based on the previous studies on the residential multi-energy complementary heating system,a "2+2" household combined heating system in which air-source heat pump and solar collector are combined as heat sources was proposed in this paper,providing heating in winter and domestic hot water.The content and purpose of the paper is to analyze and optimize the heat transfer performance of the multi-heat-source watertank with helical coil heat exchangers,which is a core part of the whole system.Firstly,based on convective heat transfer theory,a mathematical model of heat transfer was established for a household multi-heat-source water tank with helical coil heat exchanger.The three-dimensional geometric model of the tank was established by using ANSYS ICEM CFD.The relevant theory of CFD numerical simulation method was introduced and the CFD heat transfer simulation model was established.The heat transfer characteristics of the tank under different conditions were measured through experiment after combining the tank,the heat source and the ends of the load into the "2+2" household combined heating system.Datas of the four cycles of the experimental conditions were used to verify the correctness of the numerical model for the heat transfer of the multi-heat-source watertank with helical coil heat exchangers.Finally,by adjusting four controllable variables: the spiral flow direction,the position and direction of the inlet pipe,the diameter of the inlet pipe as well as the ratio of height to diameter of the tank,the heat transfer efficiency in multiple heat sources(loads)circulation was improved in the watertank.The results showed that under the premise that the temperature and flow parameters of the four inlet heat exchangers of the system were kept constant,it is conducive to heat exchanging to adjust the flow direction of the refrigerant in the spiral tube heat exchanger to the counter current.By adjusting the inflow direction of the inlet pipe,a large area concentration was formed and an extensive coverage of the spiral heat exchanger was reached.The total heat transferred of the tank with different height-to-diameter ratio varied with the diameter of the inlet pipe.The total heat transferred of the tank with the height-to-diameter ratio of n=3.5:1 had the peak value with the increase of the inlet diameter,and the combination of the optimum height-diameter ratio and the inlet pipe diameter is n= 3.5: 1 and φ= DN25.