Study On Heat Storage And Release Characteristics Of Heat Pump Defrosting Phase Change Accumulator Based On Mirabilite And Copper Foam

As one of the important equipment for indoor temperature regulation,air source heat pump is widely used in people’s production and life.But in the environment of low temperature and high humidity,frost is easy to occur,resulting in the system cannot continue to heat.If defrosting is not done in time,the system may fail to run properly due to faults such as compressor liquid strike.Defrosting suppression can only delay the time of defrosting.Reverse cycle defrosting is one of the active defrosting methods in common use at present,but there are some problems such as long defrosting time and large indoor temperature fluctuation.The main reason is that there is no efficient auxiliary defrosting heat source.In order to effectively solve the problem of easy frost in winter of existing air source heat pump units,a phase change heat storage and release technology of heat pump defrosting based on mirabite and copper foam is proposed in this paper based on reverse cycle defrosting.Considering the thermal physical property parameters of phase change materials,porous medium metal copper foam was introduced to solve the problem of poor thermal conductivity of phase change materials.At the same time,a kind of phase change accumulator for heat pump defrosting based on nitro foam copper was designed for reference to the design concept of tube heat exchanger.The phase change accumulator consists of heat exchange fluid,copper tube,nitro foam copper composite phase change material and insulation layer,the innermost layer for heat exchange fluid,copper tube flow,the middle layer for nitro-copper foam composite phase change material,as one of the key components of phase change energy storage defrosting,heat storage and release rate will directly determine the efficiency of defrosting,the outermost layer for heat exchanger insulation layer,It has the function of heat preservation and insulation.Before the Fluent numerical simulation,the numerical model and solution method used in this paper were firstly simulated and verified,and the experimental results of phase change materials in references under the same conditions were compared with the simulation results of the model established in this paper,and the correctness of the simulation method and solution model used in this paper was verified by the error size.In order to study the effect of adding metal foam on the heat storage and release rate of phase change materials,this paper takes the mirabilite-copper foam phase change accumulator as the research object,and establishes the heat transfer model of the mirabilite-copper foam phase change accumulator.The heat storage and release process of pure phase change material without foam metal and the phase change material with foam metal was numerically simulated by Fluent simulation software.The length of phase change accumulator,porosity of foam metal,tube wall thickness and radius of phase change accumulator were simulated and optimized by control variable method.The results show that:(1)In the heat storage and release process,the complete liquefaction rate of phase change materials with metal foam is better than that of pure phase change materials,and the heat storage time is only 25.2% of that of pure phase change heat storage materials,which shows that metal foam has enhanced heat transfer effect.Copper foam increases the heat transfer area between hot fluid and PCM,and enhances the phase conversion heat rate of PCM.(2)The inlet temperature of the heat transfer fluid is 20℃～60℃,and the flow rate of the fluid is 0.1m/s as the optimal choice.When the heat storage and release end,the temperature of the phase change accumulator tends to be stable.(3)In the heat storage process,the average liquefaction rate of phase change material in the second condition is 168.75% higher than that in the first condition,and the time for the average temperature to reach the highest is 62.5% shorter.(4)The optimal radius of the phase change accumulator is 20 mm,and the optimal thickness of the copper tube is 2mm.For the specified phase change accumulator,the heat storage rate of the phase change material can be enhanced by adjusting the inner tube wall thickness,so as to enhance the overall performance of the phase change accumulator.