Experimental analysis of the melting process in a pcm/aluminum foam composite material in hypergravity conditions

Phase change materials [(PCMs), e.g., paraffin waxes, fused silica salts, and polyethylene glycol] can be successfully used for thermal management and heat storage in ground and space applications. Open-cell metal foams embedded in the PCM material increase the overall thermal conductivity and accelerate the melting process. The literature shows that the pore size and relative density strongly affect the melting process performance. Most studies have shown that the high thermal conductivity of the open-cell metal foam dominates the melting process. The natural convection effect usually is attenuated; however, it can be relevant if it occurs. An experimental activity has been designed and carried out under the framework of the European Space Agency student program Spin Your Thesis 2017 to analyze the effect of different hypergravity levels and configurations on the melting performance of a composite aluminum foam (10 pores per inch)/paraffin wax material at two different heat fluxes. The gravity level ranges from 5g up to 20g using a large diameter centrifuge facility. The effect of gravity on the melting process has been investigated by measuring the melting time and the dynamic evolution of the melted area. The experiments show that the hypergravity condition accelerates the melting process: it is 12% faster ranging from 5g to 10 g. Infrared visualization allowed us to define the melting front dynamic evolution. A natural convection regime was observed in all of the experiments. The natural convection incipience accelerates the melting process. A critical analysis of the scaling criterion in the literature has been qualitatively done and a modified Rayleigh number is proposed to characterize the melting process.