Phase Change Material Behavior in Finite Thickness Slabs Under a Step Response Heat

Phase change materials (PCMs) can provide thermal buffering to systems that experience transient heat loads, including electronics and optoelectronics packaging. Placing the PCM in the primary path of heat rejection decreases the thermal resistance between the heat source and the PCM volume, but increases the total thermal resistance between the heat source and heat sink. In systems that operate in both steady-state and transient regimes, this introduces tradeoffs between cooling performance in these distinct regimes. Employing a conductive finite volume model, Parapower, we investigate those tradeoffs considering the impact of adding a layer of gallium (Ga), a low melting point metal, and a layer of copper (Cu) between a planar heat source and a convective boundary condition heatsink. We demonstrate: (1) side-by-side comparisons of latent (Ga) and sensible (Cu) heat storage layers must consider different layer thicknesses to account for the different thermal storage mechanisms, (2) for short periods of time, conditions exist in which a PCM outperforms a traditional heat sink for transient thermal buffering at an equivalent steady-state temperature rise, and (3) under these conditions, the Ga layer is approximately an order of magnitude thinner than the equivalent Cu, leading to significant mass and volume savings.