摘要
Visualization experiments are performed on flat-plate heat pipes with a sintered composite copper mesh-groove wick at different tilt angles. Deionized water is used as the working fluid. The composite wick consists of a layer of 200-mesh copper screen sintered over parallel semi-circular grooves with a width of 0.18 mm and depth of 0.09 mm. Also investigated are a groove wick with the same groove size and a sintered double-layer 200-mesh (2 × 200 mesh) wick. The effective length of the heat pipes is 101 mm. The heat pipe performance of the composite mesh-groove wick excels the other two wicks in the maximum heat load (Q max ) under the horizontal orientation and in the anti-gravity ability. Visualization reveals two evaporation stages for the horizontal orientation before full dryout in the heated zone of the composite wick. In the first stage with Q up to about 40 W, the wick at the heated zone is filled with water; in the second stage, partial dryout in the grooves occurs and expands with increasing heat load. Up to about 60 W, the heated zone becomes fully dried. In contrast, the Q max of the 2 × 200 mesh wick is 21–25 W, and full dryout prevails at 14 W for the groove wick. When the tilt angle is between 30° and 90° the Q max for the composite wick may reach 39–49 W, followed by drastic increase in the evaporator resistance. The 2 × 200 mesh wick suffers serious dryout at Q = 14 W under α = 45°; the groove wick cannot operate under α ≥ 30°. No nucleate boiling is observed in all the tests for water.