Heat Transfer Analysis Of Graphite Foams Infiltrated With Phase Change Materials For Energy Storage

According to NASA’s statistics,90%failures of aerospace missions were due to someelectronic components’ failures caused by heat that cannot be unable to transfer timely. Phasechange materials (PCMs) can absorb and release energy by the way of phase change, andmaintain the temperature within the small range of the melting point. However, the PCMswith large latent heat have low thermal conductivities. When the heat loads are sharp, it mayexacerbate heat accumulation. Graphite foams infiltrated with phase change materials caneffectively unify the high thermal conductivity of graphite foam and large latent heat of PCM.It has broad application prospects for thermal management.In this paper, the heat transfer performance of graphite foam was analyzed firstly. Therandom numbers were generated by linear congruential method. Using AutocadVBA program,the2D and3D random foam geometry models were got and their effective thermalconductivities were simulated by Fluent software. The results show that,2D models only usedto qualitative research for the effective thermal conductivity of foam structure, and3D modelscan predict the effective thermal conductivity value well if stochastic factor is appropriate,besides, the effective thermal conductivity mainly depended on the porosity and uniformity,and is unrelated to pore size. The lower porosity, the better uniformity, and the effectivethermal conductivity is higher.Secondly, based on the melting/solidification module of Fluent software, the simulationsof the pure phase change material and graphite foam encapsulated phase change materialswere studied. It was observed from the results that the phase change speed was improved bygraphite foam, meanwhile the effect of natural convection for phase change process wasreduced. Then, the effect of Ra number and Da number for the composite melting process wasinvestigated. The results show that, effect of natural convection for phase change processenhanced with Ra number and Da number, and the melting speed also correspondinglyincreased. At the same time, according to the Da number expression, the effect of pore size forphase change process was known. The bigger pore size, the stronger the influence of naturalconvection, and the melting speed also increased.Finally, in the three different cases: pure PCMs, finned enhanced PCMs and graphitefoam infiltrated PCMs, storage/release heat properties were analyzed and compared. The results indicate that, graphite foam enhanced PCMs had obvious advantages at the storage andrelease process, compared with the other two cases. Especially, for the sharp heat flow, itsadvantages are more obvious. Because graphite foam can enhance effective thermalconductivity to improve the storage/release energy, at the case of aerospace that no gravity ormicrogravity, graphite foam enhanced PCMs have greater advantages.