Numerical Study On Heat Storage And Release Performance Of PCMs Embedded In Gradient Foam Metals

Heat storage technology is widely used in photothermal generator sets to solve the volatility of solar power generation through the heat storage and release logic of "storage during the day and release at night;storage in sunny days and release in cloudy days".Compared with sensible heat storage and chemical heat storage,phase change heat storage can store more heat at a smaller temperature difference.At the same time,it has better stability than chemical heat storage and great development potential.However,the thermal conductivity of most phase change heat storage materials is low,which seriously affects the heat storage and release rate and the popularization and application of phase change heat storage technology.The enhancement of heat storage and release characteristics of phase change heat storage materials is one of the hot scientific issues at present.The methods to enhance the thermal properties of phase change materials include adding fins,adding nanomaterials and foam metal filling.Compared with the other two intensification methods,foam metal has the advantages of small size,light weight,low cost,high specific surface area and high thermal conductivity,and has great potential in the field of phase change heat transfer.A large number of random,multi directional holes can be distributed inside the foam metal,which can be used to fill phase change materials.The thermal conductivity of foam metal depends not only on its physical properties,but also on its geometric shape.Porosity and pore size are two important indicators for measuring the geometrical shape of foam metal.The existing research shows that through the gradient arrangement of foam metal with different porosity or pore diameter,the enhanced heat transfer effect is better than that of homogeneous foam metal.In this paper,the heat release characteristics of gradient hole foam metal phase change thermal storage materials are analyzed by numerical simulation.In this paper,based on the plate phase change heat storage device,a region is selected on the contact surface of the hot fluid and phase change material,and the heat storage unit is abstracted.Based on this,the corresponding gradient structure and numerical model are constructed.Through the numerical simulation of the heat storage unit,the thermal charging characteristics of different foam metal gradient strengthening phase change materials are analyzed.The numerical simulation adopts ANSYS FLUENT software to analyze and study the heat storage unit from multiple angles and working conditions.The heat transfer enhancement effect of composite phase change materials was analyzed through the comparison of several groups of different structure and different kinds of foam metal skeleton composite phase change materials.Through qualitative and quantitative analysis of the average temperature of heating surface and relative surface and the average liquid phase rate of heat storage unit,the results show that under the condition of certain heat storage capacity,heat storage density and total metal foam quality,the foam metal with larger porosity is used in the heating side,and the heat transfer rate can be effectively improved by using relatively small foam metal on the opposite side.When the maximum and minimum values of the porosity and porosity of the foam metal are certain,the gradient hole foam metal with more layers has better heat transfer enhancement capability.The larger the gradient metal foam is,the better the performance of heat transfer enhancement.However,this optimization effect will decrease gradually with the increase of gradient,but it will still greatly improve compared with the homogeneous pore structure.Finally,through the simulation of heat charging and heat release process,it can be seen that the above enhanced heat transfer effect is applicable in heat charging and heat release engineering.Gradient hole foam metal can play a great role in the design of heat storage device of photothermal power station.By proper design,the charge and heat release rate can be substantially increased without affecting the overall heat storage capacity of the heat storage device.In this paper,a plate type gradient hole foam metal phase change material heat storage device is designed.Through the simulation of the heat storage device,the enhancement effect of gradient porous medium on the heat transfer characteristics of phase change material is proved.Moreover,in practical application,the heat storage and release rate of the plate phase change heat storage device can be further improved by changing the external parameters such as the inlet temperature level and inlet velocity of the heat transfer fluid.