Abstract
This work presents visualization and measurement of the evaporation resistance for operating flat-plate heat pipes with composite groove/mesh wicked. For comparison, experiments are also conducted for heat pipes with a groove or a mesh wick. The performances of these heat pipes are compared under different inclination angles. The parallel, U-shaped grooves with a width of 0.18 mm and a depth of 0.1 mm are sintered with a layer of 200 mesh copper screen covering the top of the grooves. With stepwise increase of heat load Q, the behavior of the working fluid in the groove/mesh wicked was visualized and the evaporator and condenser resistances were measured. Horizontally, different stages are identified with increasing heat load. For Q < 44 W, the evaporator can be fully wetted and the evaporator resistance ranges between 0.05~0.07 Kcm2/W; for 44 W < Q < 66 W, partial dryout appears in the evaporator, with the evaporator resistances jump to about 0.3 Kcm2/W; for Q > 66 W, the evaporator fully dries out with runaway evaporator resistances. At inclination angle of 45°, 60°, or 90°, Qmax could remain at about 44 W. In contrast, Qmax is 14 W for the groove wicked heat pipe and 24 W for the 2 × 200 mesh heat pipe under the horizontal orientation. The results show that the composite groove/mesh wick provides strong capillary force yet low flow resistance to yield high Qmax even for high inclination angles. In addition, no boiling is observed in all present tests.