Experimental investigation on melting heat transfer characteristics of a phase change material under hypergravity

Abstract

Phase change material (PCM) has great application potential in airborne equipment cooling. However, aircraft are exposed to hypergravity during maneuvering flight, and the corresponding melting heat transfer characteristics remain unknown, urgently necessitating the present research. First, an experimental system on melting heat transfer of n-docosane (C22H46) under hypergravity is established. Then, the melting characteristics under different hypergravities (0–6g) are studied, revealing a significant effect. When the heat flux is constant, an increase in hypergravity yields accelerated melting and a decrease in the heating wall temperature because hypergravity enhances the heat convection inside the liquid PCM. The maximum differences of the time required for complete melting and the corresponding heating wall temperature under hypergravity to those under normal gravity are –20.6% and –21.0%, respectively. However, with increasing hypergravity, the strengthening effect gradually weakens, indicating a limit to the influence of hypergravity on the melting characteristics. Furthermore, the melting characteristics at different heat fluxes (2.5–7.5 kW/m2) under hypergravity are investigated. Under constant hypergravity, increasing heat flux accelerates the melting rate and increases the heating wall temperature, but this effect is suppressed by the hypergravity-enhanced heat convection and weakens with increasing heat flux. Finally, the theoretical liquid level positions of the PCM in the ground and body coordinate systems are analyzed and compared with the experimental results, yielding good agreement. In addition, due to the change in liquid level position caused by hypergravity, the PCM incompletely contacts the heating wall, leading to area overheating, which should be avoided in practical applications.