Study On Optimization Design Of Capillary Heat Exchanger For Surface Water Source Heat Pump

With the shortage of energy and the aggravation of environmental pollution,how to improve the efficiency of energy utilization,development and use of clean energy has become a global concern.Surface water source heat pump is a kind of equipment with high efficiency and energy saving.The development of surface water source heat pump is of great significance to energy saving and environmental protection.The design of heat exchanger is an important topic of surface water source heat pump.The recently developed capillary heat exchanger has the advantages of compact structure,large heat transfer area,small hydraulic loss,corrosion resistance and low cost,as the front heat exchanger of closed surface water source heat pump system,it has a broad application prospect.The research on the optimal design of capillary heat exchanger not only strengthens the heat transfer of heat exchanger,but also is of great significance to the popularization and development of surface water ground source heat pump and energy-saving operation.In this paper,we study closed surface water source heat pump front end of the capillary tube heat exchanger heat transfer performance and design optimization,first carries on the heat transfer and flow theory research and design,then build capillary test-bed for heat transfer performance tests,and based on the principle of minimum entropy production,establish a optimization design model of capillary tube heat exchanger,the final 3 d capillary network model is established for different pipe spacing under condition of numerical simulation,the main contents are as follows:(1)The flow and heat transfer process of capillary heat exchanger were studied and its heat transfer process was theoretically analyzed.The heat transfer capacity of capillary heat exchanger and the temperature distribution and heat transfer coefficient of capillary heat exchanger along the tube length were obtained.The flow resistance and resistance coefficient in and out of capillary heat exchanger were analyzed,and the heat transfer model and resistance model of capillary heat exchanger were established.(2)The experiment platform of a complete set of capillary front-end heat exchanger was set up to test the heat transfer performance in exothermic conditions under three different heat exchange temperature differences.The experimental data were sorted out to study and analyze the variation rules of heat transfer coefficient and heat exchange with the fluid flow rate and heat exchange temperature difference in the tube,and relevant experimental data were provided for the following study.Compared with the experimental test and capillary heat transfer coefficient are calculated by use of a heat transfer model,analysis of the available heat transfer coefficient with the change of fluid flow inside the same change trend,namely all increased with the increase of tube fluid flow,the error is within 8.0%,within the allowed error range,to verify the accuracy of the heat transfer model.(3)The optimal design model of capillary heat exchanger is established based on the principle of minimum entropy production.According to different heat transfer load and mass flow rate,the optimal tube diameter and tube length of capillary heat exchanger under exothermic and endothermic conditions were obtained,and the variation rule of the optimal tube diameter and tube length with load and flow rate was analyzed,so as to optimize the design of capillary heat exchanger.Under the same working condition,the efficiency of capillary heat exchanger optimized by entropy production model is compared with that of existing capillary heat exchanger,and the superiority of entropy production model is verified.(4)establish a three-dimensional model of capillary heat exchanger network,and conduct numerical simulation of exothermic and endothermic conditions for capillary heat exchanger network under different pipe spacing and surface water velocity.And carry out numerical simulation for a certain experimental condition.The experimental results were in good agreement with the simulated heat transfer results under the same experimental condition,which proved the feasibility of the numerical simulation of capillary heat exchanger pipe network.In exothermic conditions,under different tube spacing,the heat exchange temperature difference of capillary heat exchanger increases with the increase of surface water velocity,and the logarithmic average temperature difference decreases with the increase of surface water velocity.The best tube spacing was 10 mm,followed by 40 mm,and the worst was 20 mm.In both endothermic and exothermic conditions,the evaluation criteria have the same variation rule with the velocity of surface water,and the optimal spacing of tubes is 10 mm.Therefore,the capillary network with 10 mm spacing of tubes should be selected as far as possible when the process permits.