Effect of inventory on the heat performance of copper–water loop heat pipe

The operating characteristics of a copper–water loop heat pipe (LHP), including start-up property, heat-transfer capacity, and heat resistance, under four different charge ratios (52.2–78.3%) were experimentally investigated. The LHP had a cylindrical evaporator (22 mm diameter and 80 mm long) with a sintered copper wick, and the clearance between the evaporator envelope and the wick surface was eliminated to attain a low heat contact resistance. The porosity of the wick was 44.54%, and the effective pore radius was 19.11 μm. The experiment showed that higher inventory is an effective method in keeping the wick saturated within the low heat-load range and in supplying adequate flow of the subcooled liquid from the condenser to cool the water in the compensation chamber within the medium heat-load range. Thus, fast start-up of 260 s (heat load: 30 W; heat flux: 8.5 × 103 W/m2), maximum heat-transfer capacity of 500 W (under allowable evaporator wall temperature of 85 °C), and minimum LHP thermal resistance of 0.075 °C/W (under 500 W heat load) were realized by the LHP charged with an optimal 69.6% volume ratio.

► High inventory is an effective method for suppressing heat leak for the LHP with a high volume ratio evaporator (>50%).
► A copper–water LHP can start fast and attain high heat-transfer capacity.
► An extremely low evaporator thermal resistance was achieved due to the new evaporator design.