Experimental investigation of a 10 kW loop heat pipe: Effects of condenser cooling mode, fill ratio and heat leak on thermal performance

A high-capacity loop heat pipe (LHP) incorporating a flat evaporator and a bi-metallic, bi-porous Cu Ni wick is developed and experimentally evaluated using water as the working fluid. Thermal performance of the LHP is investigated under natural air condensation (NAC) and natural water condensation (NWC) modes for the filling ratios of 40%, 50% and 60%, with emphasis on the combined effects of condenser cooling mode and fluid inventory on heat transport capability and heat leak behaviour. The maximum heat load capacity of the LHP varied from 5.8 to 10 kW across the operating ranges. Although the filling ratio increases the heat transport capacity by delaying the onset of dry-out, the overall performance of the LHP is significantly affected by the condenser-cooling mode. Under NAC mode, the liquid in the compensation chamber reaches its saturation temperature due to insufficient sub-cooling, causing vapour formation and dry-out of the loop. In contrast, under NWC mode, the lower compensation chamber temperature enables stable operation of the LHP up to 10 kW at the heater-block temperature of 240 °C. Consequently, NWC mode achieves lower thermal resistance and higher evaporative heat transfer coefficient, allowing the LHP to sustain a significantly higher heat flux of 80 W/cm 2 at 60% filling ratio. A subcooling-based dry-out criterion, coupled with a global pressure-balance assessment, is employed to identify the governing mechanisms and distinguish the onset of dry-out under NAC and NWC modes. Furthermore, an experimentally validated numerical model is developed for preliminary thermal design and performance prediction of the LHP.