The Optimization Method Of Non-uniform Cellular Material As Thermal Conductivity Enhancer For Phase Change Temperature Control

Phase-change material can absorb/release a lot of heat(latent heat)when the phase changes,the process have a characteristic that the material temperature keep constant,which is of great significance for the design of temperature control system of aerospace equipment under extremely harsh thermal environment.Due to the low thermal conductivity of the phase-change material,the energy accumulation of the phase-change material near the heat source will result in a large temperature gradient,seriously limiting the effect of temperature control.Metal cellular materials with high porosity are ideal thermal conductivity enhancer because of large specific surface area,high thermal conductivity,strong mixing ability,high lightweight and large design space.In this paper,an optimization method of metal cellular material as thermal conductivity enhancer for the phase-change temperature control is proposed.There are two types of models,one is structure which has gradient porosity and the other is composite structure of metal fin and metal cellular material.Details are as follows:(1)The linear gradient optimization of metal cellular material as thermal conductivity enhancer for phase-change temperature control.In this section,the linear gradient optimization model of cellular material as thermal conductivity enhancer for the phas e-change temperature control is proposed.In the optimization model,the linear porosity is regarded as design variable,the usage of the cellular material is constant as the constraint,and the minimum temperature at the key position is the design goal.The numerical method based on the two equations model of cellular media considering phase-change is employed here.Firstly,it is proved that the optimization problem is a typical multi-peak optimization problem through a simple example,so it is necessary to use genetic algorithm(intelligent search algorithm)to solve this problem.Two special examples demonstrate that the enhanced performance of phase-change temperature control can be achieved by the gradient design of metal cellular material as thermal conductivity enhancer.(2)Shape function parameterization based on non-uniform optimization of metal cellular material as thermal conductivity enhancer for phase-change temperature control.The numerical simulation of phase change process requires a large amount of computation,besides the optimization is a multi-peak problem which needs to be solved by intelligent optimization algorithm.Therefore,the calculation is huge.In this section,a non-uniform optimization method of cellular material as thermal conductivity enhancer for the phase-change temperature control based on interpolation of shape function is proposed.Typical numerical examples show that the gradient complex structures can be well described by only a few elements(i.e.fewer design variables),and the improvement of performance is significant.By increasing the number of nodes,the performance of optimization design effect can be better.Finally,three examples are optimized to verify the effectiveness of the optimization method established in this section.(3)An effective method for improving the phase change heat transfer performance by enhancing natural convection.In the solid-liquid phase change transfer process,there are usually two mechanisms.One is the heat conduction in phase change material(PCM)and t he other is the natural convection of melted PCM.The possible way to improve the performance of phase change heat transfer is to enhance the natural convection without reducing the thermal conduction performance.In this section,an effective method of improving the phase change heat transfer performance by enhancing natural convection of melted PCM in the cellular material is proposed for the phase-change temperature controller heated at the bottom.In this method,the enhanced natural convection is achieved by rationally embedding the fins into the cellular materials.Several different fin configurations are analyzed and compared.Results indicate that the embedded fins can enhance the natural convection of liquid PCM during the melting process,accelerate the melting speed and thus improve the performance of phase change heat transfer.On the premise of constant mass of the heat conductivity enhancer,special examples illustrate that this method can improve the phase change performance by more than 20%.