Experimental And Numerical Simulation Of Phase Change Heat Exchanger

HVAC consumes a lot of fossil energy in the process of use,which also causes serious air pollution problems.In order to realize the harmonious coexistence of ecological environment and energy utilization,energy conservation has become an essential and important link.Among many measures to save energy,heat pump has the advantages of high utilization efficiency of fossil energy and large end heating capacity.It has developed rapidly in the field of HVAC in recent years.Using heat pump technology to extract the phase change potential in cold water can solve the problem of limited heat source of heat pump system and alleviate the problems of energy consumption and environmental pollution caused by HVAC.However,there are still two major problems to be solved in the cold water phase change heat pump system.One is the heat transfer performance of the heat pump system during operation,and the other is the ice distribution in the phase change heat exchanger.Phase change heat exchanger is the core part of phase change energy heat pump system,which determines the operation efficiency of the whole heat pump system.This paper focuses on the factors affecting the efficiency of phase change heat exchanger,that is,to study the effects of cold water temperature and flow,intermediate medium flow and temperature on the efficiency of heat exchanger and ice distribution.The influencing factors of icing heat transfer of phase change heat exchanger are studied from three aspects:theoretical analysis,experimental verification and numerical simulation.The main research contents and results are as follows:（1）The factors affecting the freezing heat transfer effect of phase change heat exchanger include intermediate medium and low-temperature water flow parameters,ice thickness,material of heat exchange tube bank and so on.In this paper,the energy conservation equation of the flow solid interface is established from the perspective of theory.The equation is derived based on the energy conservation equation.According to the equation,the position of the flow solid interface and the growth rate of the flow solid interface can be obtained.The analysis shows that the position of the phase interface of the phase change heat exchanger,that is,the thickness of the ice layer,is mainly related to the flow rate and temperature of low-temperature cold water,the flow rate and temperature of the intermediate medium and the texture of the ice layer.（2）The experimental research is carried out by using the running heating system in a project.The theoretical analysis of the ice growth process is carried out according to the actual observation.During the experiment,it is found that the experimental system is easy to control the intermediate medium temperature and flow,cold water temperature and flow of the phase change heat exchanger,while it is difficult to control the ice texture.Therefore,the experimental part of this paper designs a variety of working conditions from the two aspects of changing fluid temperature and flow,analyzes in detail the effects of intermediate medium flow,cold water temperature and flow on the heat transfer efficiency and ice thickness of phase change heat exchanger,and focuses on calculating the ice thickness and heat transfer coefficient under different working conditions.Finally,the optimum working condition of phase change heat exchanger in a certain parameter range is determined.（3）The icing process of phase change heat exchanger is simulated and analyzed by numerical simulation method.Based on the structural parameters of the phase change heat exchanger used in the experiment,the physical model is established and the grid is drawn.Through numerical simulation,it is concluded that when the operating parameters are changed,the influence of cold water flow on the icing thickness outside the heat exchange tube row is more severe than that of cold water temperature and intermediate medium temperature,and the unique distribution law of ice on the heat exchange tube row is affected by the flow of intermediate medium in the tube.In this paper,the variation law of the heat transfer coefficient of the phase change heat exchanger under various working conditions obtained through theoretical and experimental analysis can be used to adjust the heat pump system in time when the phase change heat pump system is facing complex working conditions,so as to make the system run efficiently.At the same time,the ice distribution in the phase change heat exchanger is obtained through numerical simulation,which lays a theoretical foundation for the optimal design and energy-saving operation of the deicing device in the phase change heat exchanger.