Thermal conductivity enhancement for phase change storage media

Thermal energy storage can be used as either a heat source or heat sink for spacecraft energy conversion and heat rejection systems. One major issue that needed to be addressed is that most phase-change materials (PCMs) with high energy storage density have an unacceptably low thermal conductivity. Two enhancement techniques are proposed in this paper. The baseline case utilizes LiH encapsulated in a thin SS304 container. The first enhancement technique uses LiH encapsulated in smaller containers of various shapes contained in a bigger cylindrical container filled with Li. The second enhancement technique focuses on a metal/phase-change material (M/PCM) composite. Specifically, 5% Ni is added uniformly to LiH so that the mixture has the same volume as the baseline storage unit. The enhancement techniques are analyzed numerically and their effectiveness is assessed for both constant surface heat flux and constant surface temperature conditions. Results shown include the amount of PCM melted as a function of time and the maximum temperature within the storage units. The M/PCM composite gives the best enhancement in thermal conductivity.