Melting behavior and heat transfer performance of gallium for spacecraft thermal energy storage application

Highlights: • Gallium is proposed as phase change material for spacecraft thermal energy storage. • Dynamic melting behavior and heat transfer under microgravity are investigated. • Role of thermocapillary convection in melting under microgravity is disclosed. • The utilization of gallium under microgravity significantly reduces melting time. A typical low melting point metal (LMPM), gallium, is proposed for spacecraft thermal energy storage due to its superior thermal transport properties, and its dynamic melting behavior and heat transfer performance under microgravity are investigated. The role of thermocapillary convection in melting is analyzed, and the dimensionless equations for predicting liquid fraction as well as Nusselt number are developed. The results show that compared with conventional phase change materials including ice and n-octadecane, the utilization of gallium under microgravity can reduce the melting time by 88.3% and 96.4% respectively, while increase the total energy storage capacity by 20.7% and 123.3% respectively. The thermocapillary convection promotes the melting under microgravity, and the promotion effect for gallium is much weaker than that for ice or n-octadecane due to its smaller Marangoni number. The melting time of gallium, ice and n-octadecane under normal gravity are 65.8%, 39.4% and 69.2% less than those under microgravity respectively. The deviations of liquid fraction and Nusselt number predicted by dimensionless equations from numerical results are within ±10%. The results indicate that the thermal energy storage using gallium is effective for temperature control of spacecraft electronic devices under high and periodic heat flux.