A 60 mm x 33 mm x 0.8 mm micro loop heat pipe (MLHP), consisting of an evaporator, vapor line, condenser and two liquid lines, was fabricated and characterized. The wicking structure consists of parallel V-grooves with a hydraulic diameter of 47 mu m, 67 mu m and 83 mu m, and is formed by bulk silicon etching. The MLHP was realized by bonding a glass wafer onto a silicon substrate, so as to result in a transparent cover for two-phase flow visualization. Water and methanol were used as the working fluids. The test results showed that water demonstrates a wider heat load performance range (3.3 W similar to 12.96 W) than methanol (1.2 W similar to 5.85 W) for the MLHP with an evaporator area of 1 cm(2) and condenser temperature of 17 C-circle. The best thermal resistance of the MLHP was 0.106 C-circle/W, 64 times higher than that without fluid filling. The smaller diameter grooves caused the higher liquid capillarity and enhanced transfer capacity. It was observed that the presence of non-condensable gas negatively affected the reliability of the MLHP and significantly reduced the performance.
