Experimental research on the heat performance of a flat copper-water loop heat pipe with different inventories

The heat performance of a flat copper-water LHP, including the start-up property, operation capacity and evaporator thermal resistance, with three inventories (charging ratio ranged from 40 to 60%) was experimentally investigated. In order to observe the flow in the compensation chamber and the evaporating zone, a flat evaporator with a transparent cover (56 mm in diameter and 30 mm in total thickness) was manufactured. The porosity of the sintered copper wick was 47.26%, and the averaged pore radius was 22.65 μm. Severe heat leak, namely bubbles attaching on the wick during the start-up and heat pipe effect during the operation at a high heat load of 120 W, was observed. In addition, intermittent backflow from the condenser, which resulted in strong temperature oscillations, was also shown at low heat loads. It was experimentally found that high inventory was an effective method to address heat leak in spite of strong temperature oscillations at low heat loads. The optimal inventory of the proposed LHP was 10.0 ml (charging ratio of 50%), it could start smoothly in no more than 250 s and operate steadily at least at a heat load of 120 W (heat flux of 16.97 W/cm2) with the allowable evaporator wall temperature of 90 °C.