Study On The Performance Of Multi-row Helical Coil Used In Closed-loop Surface Water Source Heat Pump

With the impetus of the policy of "coal to electricity",the market of heat pump develops rapidly,and there is an abundance of surface water resources in china,so the development of surface water source heat pump will have a good prospect.But the growth trend compared to the air source heat pump,surface water heat pump development is slow,and compared to the open-loop SWHPs,due to lack of design guides of heat exchanger,the heat exchanger heat transfer performance is not clear understanding,theory research is not enough,which seriously restricts the development of closed surface water source heat pump.Therefore,it is necessary to study the performance of the closed surface water source heat pump heat exchanger.In this paper,the performance of multi row helical coil heat exchanger for closed surface water source heat pumps were investigated.For multi row spiral heat exchanger simulation experimental platform,the mathematical model was established corresponding,the heat transfer process of multi row helical coil were simulated,and the convection heat transfer of surface water,solid wall heat conduction and convection heat transfer of the fluid in the tube were considered.For the mathematical model of multi-row helical coil heat exchanger,and the heat exchange process in laboratory conditions also was simulated,the experimental data of exterior coil surface and calculated data were in a good agreement,it proved the feasibility of the mathematical model simulation of multi-row helical coil heat exchanger process.Subsequently,to simulate the endothermic process of helical coil heat exchanger through using a typical operating mode as an example,a detailed description of the heat transfer process of fluid surface water side and tube were given,in-depth analysis of the hydraulic characteristics of the heat transfer and temperature change.Secondly,it took out the heat transfer process of multi-row helical coil heat exchanger with different surface flow velocity and different temperatures,and the detailed analysis of the theory was given separately from three aspects of heat transfer which included the surface water side fluid side and tube heat transfer characteristics.The calculation results show that the flow rate will decline when the flow process of surface water is hindered by multi row helical coil heat exchanger.The flow of fluid in the pipe creates a high velocity region and enhances the heat transfer in the tube.Under the variable condition of surface water flow rate,the increase of surface water velocity promotes the enhancement of heat transfer capability at the surface water side of the pipe,and the heat transfer capacity of the pipe will increase accordingly.Changes in surface water temperature conditions,with the increase of surface water temperature,the heat exchange capacity of helical coil surface water side heat exchanger and the fluid in the tube side of the heat transfer was enhanced,per unit length heat transfer increased significantly.Finally,effect of thermal resistance on the heat transfer performance of tube wall side was analyzed,found the wall thermal resistance is generally accounted for more than 90% of the total resistance,are the main factors causing the helical coil to reduce the efficiency of the heat exchanger.The calculation of the heat transfer process of different thermal conductivity were done,with 5.6% decrease of the solid wall heating tube thermal resistance,close to 30% per unit length heat transfer can be increased.