Experimental investigation on a passive photovoltaic evaporative cooling system based on dual-scale capillary aluminum fins

Heat accumulation in photovoltaic modules during operation significantly degrades their efficiency and lifespan. Developing efficient passive phase-change thermal management is key to overcoming this limitation. However, existing solutions lack cooling stability under high heat fluxes and humid environments. Here, we propose and fabricate a Capillary Evaporative Finned Heat Sink (CEFHS) with a dual-scale microgroove structure. Using optical and infrared dual-modal imaging, we analyze its liquid transport and capillary performance, and evaluate its heat transfer and Photovoltaic (PV) cooling under various conditions. The dual-scale structure reduces flow resistance via large grooves while small grooves and recast layer provide capillary pressure, yielding an optimal capillary performance parameter of 1.653 × 10 −6 m. Under a 40 W high heat load and natural convection conditions, the latent heat of phase change in the CEFHS accounts for 83.6% of total heat dissipation. This high proportion of evaporative cooling lowers thermal resistance and maintains a steady-state substrate temperature of 78 °C. It also drastically shortens the time required for the system to reach thermal equilibrium. Applying a 1.5 m/s airflow further reduces the temperature by 34% under the 40 W load. Even at 99% relative humidity, the water vapor density gradient sustained by the surface temperature rise ensures efficient evaporation. Under 1.0 kW/m 2 sunlight, integrating the CEFHS onto a PV panel suppresses temperature elevation, increasing the module's output power by 22.3% and the photoelectric conversion efficiency from 7.64% to 9.36%.These findings highlight the CEFHS's potential for low-power, high-heat-density passive cooling in PV thermal management and electronic devices.