Numerical investigation on melting behaviour of phase change materials/metal foam composites under hypergravity conditions

With the increased number of aerospace vehicles and the associated integration of electronic devices, thermal management has become a big problem due to increased heat dissipation. To this end, thermal management of electronic devices constituting aerospace vehicles has become of great importance as one way of enhancing the operation of these devices and the overall functionality of these vehicles. Phase change materials (PCM) exhibit excellent thermal diffusivity and high thermal energy storage capacity, making them promising candidates for effective thermal management in aerospace vehicles. However, their low thermal conductivity and poor heat diffusion must be addressed to promote their application in this direction.

Embedding PCM with metal foam is a promising strategy for improving the thermal conductivity of PCM. It offers fast heat conduction paths while also increasing the heat transfer area. The heat transfer performance of PCM/metal foam under hypergravity conditions plays a fundamental role in the thermal management of space vehicles and must be considered in the design of PCM-based heat sinks. Hypergravity describes the situation when the space vehicle acceleration is greater than the gravitational acceleration, which mainly occurs during the launch or reentry of the space vehicles.

The melting behavior of PCM/metal foam under hypergravity and their corresponding thermal performance greatly differ from that obtained under normal gravity. For instance, some parameters exhibiting minimal impact on the thermal performance under normal gravity could greatly influence the melting behavior under hypergravity. Therefore, further studies on the melting behavior of PCM/metal foam under hypergravity, including the effects of different factors like the inclination angle, is necessary to provide more insights that would be useful in improving their application as thermal management materials.

Herein, Assistant Professor Chen Ding from the Beijing Institute of Technology numerically investigated the melting behavior of PCM/metal foam composites under hypergravity conditions. The numerical model considered several factors, including the flow resistance of the metal foam, nonequilibrium heat transfer, natural convection and heated wall temperature, to characterize and analyze the melting behavior. Additionally, the effects of different parameters like inclination angle, pore density and hypergravity value on the melting behavior were analyzed. Their work is currently published in the journal, Applied Thermal Engineering.

The research team showed that under hypergravity conditions, the inclination angle significantly influenced the melting interface morphology, although its effect on the average PCM liquid fraction variation was limited. An increase in the inclination angle from 0° to 180° initially decreased the heated wall temperature before increasing after reaching the lowest value at an inclination angle of 45°, which was also the optimal value for the inclination angle. The maximum heat transfer coefficient was also recorded at the inclination angle of 45°.

The hypergravity value had a negligible impact on the PCM liquid fraction. However, an increase in the hypergravity value enhanced the natural convection while reducing the heated wall temperature. For instance, a 1 g to 10 g increase in the hypergravity value increased the liquid PCM velocity by more than 10 times. Furthermore, an increase in the metal foam porosity resulted in increased heated wall temperature and natural convection, longer melting point and a decrease in the effective thermal conductivity and overall heat transfer coefficient. The converse was true when the metal foam porosity was decreased.

In summary, a validated numerical model was proposed to characterize the behavior of PCM/metal foam under hypergravity for applications in aerospace vehicles. Based on the findings, metal foam with lower pore density was recommended. In a statement to Advances in Engineering, first and corresponding author Professor Chen Ding noted that their study provided guidelines that would contribute to the optimal design of PCM-based heat sink aerospace applications.