Interface inclination in partially filled metal-foam/PCM thermal buffers for solar-facing renewable-energy applications

Solar-facing thermal interfaces may experience intense transient heat loads that increase peak temperature and produce local temperature non-uniformity. Phase change materials provide passive thermal buffering, but their low thermal conductivity limits charging performance. This study investigates a passive internal-geometry strategy for partially filled copper-foam/paraffin thermal buffers without changing the external module orientation. Visualization experiments were conducted, and a local thermal non-equilibrium model was validated against melting-front evolution and infrared temperature patterns. The validated model was then used to vary the inclination of the interface between the pure-paraffin and copper-foam/paraffin regions at a fixed filling ratio and constant foam volume under a controlled heat flux. Relative to a horizontal interface, a +60° inclination reduced complete-melting time by 18.0% but increased the peak heated-wall temperature indicator by 4.0%. Redistributing a small fraction of foam to a top layer occupying one-eighth of the cavity height reduced the peak heated-wall temperature and hotspot indicators by 14.6% and 61.6%, respectively. The refined configuration retained comparable charging performance, with complete-melting time reduced by 2.8% and the time to 90% melting advanced by 8.8%. These results demonstrate that interface orientation and targeted foam redistribution can coordinate buoyancy-driven convection and foam-assisted conduction in compact solar-facing thermal buffers.