| Heat storage technology can effectively solve the problem of energy waste,but also to a certain extent to solve the inherent intermittent and volatility of clean energy,and can make the combined heat and power generation unit to achieve thermoelectric decoupling,has its development space in many fields.In this paper,the enthalpy model is used to simplify the calculation process greatly,and the difficult problem of that the moving boundary of phase change heat storage is effectively improved.The effects of various parameters on the heat storage and release performance of phase change heat storage device are analyzed,and the cascade phase change heat storage device and pipe-fin phase change heat storage device are optimized by combining numerical simulation with orthogonal experiment.The main research contents are as follows:Firstly,the models of four-stage cascade casing phase change heat storage device and single-stage tubular fin phase change heat storage device were established,and the effects of inlet flow rate,inlet temperature and initial temperature of phase change material(PCM)on the heat storage and heat release process of the device were studied through numerical simulation.The results show that: with the increase of the flow rate,the temperature at the outlet of the heat transfer fluid(HTF)will increase in the process of heat storage,while it will decrease in the process of heat release.The heat storage and heat release of the device were 41.518 MJ,48.601 MJ,53.039 MJ and 55.859 MJ,respectively.39.922 MJ,45.238 MJ,48.686 MJ,50.905 MJ,it can be seen that the heat absorption and heat release of phase change materials and the inlet flow of heat exchange fluid increase with the increase of heat storage and heat release processes.Exergic efficiency of the device at the end of the whole storage and exothermic process at different flow rates was 76.157%,69.746%,48.686% and 50.905% respectively.Therefore,exergic efficiency decreased with the increase of import flow.The higher the inlet temperature of the heat transfer fluid is,the higher the outlet temperature of the device will be in the process of storage and heat release.When the inlet temperature of the heat exchange fluid is increased,the heat storage and heat release of the heat exchange fluid will increase,while the heat release and heat absorption of the heat exchange fluid will decrease.At the end of the heat storage process,exergic efficiency of the device at four different inlet temperatures decreased with the increase of inlet temperature,which were 68.793%,67.455%,66.386% and 65.485%,respectively.At the end of exothermic process,exergic efficiency of the device would increase with the increase of inlet temperature,which were 38.937%,44.579%,50.541% and 56.144%respectively.The phase change material with higher initial temperature will melt faster during heat storage and solidify slower during heat release.In the process of heat storage,the higher the initial temperature of the phase change material,the heat storage of the phase change material,heat release of the heat transfer fluid,the average heat storage rate of the phase change material,the average heat storage rate density and the exergic efficiency of the device will all decrease at the same time.In the process of heat release,the higher the initial temperature of the device,the heat release of phase change material,heat absorption of heat transfer fluid and exergic efficiency of the device will all increase.Secondly,the cascade phase change heat storage device and tube-fin phase change heat storage device were optimized respectively by the combination of orthogonal test and numerical simulation.The optimization results show that: For the cascade phase change heat storage device,the regression equation between the height of phase change material of each layer and the thermal storage and exergic efficiency was established through the quadratic regression orthogonal test of three variables.The relative errors of the two equations were both less than1.45%,which had good impassability.According to the regression equation,the heat storage reaches the maximum value when the height ratio of PCM1,PCM2,PCM3 and PCM4 is 1:3:4:4.At the process of heat storage 3600 s,heat storage was 10900 k J higher than tha the same height layout.At the same time,the exergic efficiency is the highest when the height ratio of PCM1,PCM2,PCM3 and PCM4 is 4:3:4:1 according to the regression equation.At the process of heat storage 3600 s,exergic efficiency was 3.192% higher than that the same height layout.The influence degree of fin length,inner tube radius and fin thickness on the tube fin phase change heat storage device decreases successively.The regression equation satisfies regression coefficient test,regression equation test and misfitting test.According to the regression equation,the three factors are optimized within the research scope,and the heat storage device reaches the maximum at 5000 s when the inner tube radius,fin length and fin thickness are 30 mm,20mm and20 mm respectively,which can reach 2250 kJ. |
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