Numerical Investigations on Melting of Phase Change Material (PCM) with Different Arrangements of Heat Source-sink Pairs Under Microgravity

Designing effective thermal control modules in spacecraft is one of the prime concerns for space missions. 2D numerical simulations are carried out for investigating the melting process of paraffin wax as a phase change material (PCM) in microgravity conditions. Divided into three categories, a total of twelve different arrangements of heat source-sink pairs in a square cavity are considered to obtain the stored energy, liquid fraction, and as well as heat transfer characteristics. The differences in the arrangements of the heat sinks and sources affect the performance of these thermal storage devices greatly. Moreover, the discrete and continuous arrangements of the heat sources influence the propagation of the melting front in the PCM, and the spacing in between the discrete heat sources should be optimized considering the duration of the charging cycle. The melting fronts, along with Isotherm lines, are depicted to show the symmetric progression of melting of the PCM in the square cavity for the optimized cases. It is also found that the melting rate can be as high as 60% lower than that observed under Earth's gravity due to the lack of natural convection heat transfer. In addition, the Nusselt number decreases rapidly early in the melting process and tends toward a constant value. The simulation results are validated with available literature with good agreement for both the Earth-bound and the microgravity conditions.