Effect of geometries on the heat transfer characteristics of flat-plate micro heat pipes

Abstract The geometries of wicking structure of flat-plate micro heat pipes (FPMHPs) determine the capillary force and quantity of working fluid, which remarkably affect thermal performance. In this study, flat-plate micro heat pipes (FPMHPs) with different geometries were designed and fabricated, and their heat transfer characteristics were compared. Results showed that the thermal performance of the FPMHPs was relatively weak at α = 0° because the condensate backflow can only be driven by capillary force. At α = 90°, the A-4-type FPMHP presented the best performance under the common joint effect of capillary force, gravitational force, and the quantity of working fluid. The minimum thermal resistance and the maximum thermal conductivity of this FPMHP were 0.89 K/W and 1739.98 W/(m·K), respectively. A visualization study was also conducted to validate and investigate the heat transfer process of the vapor–liquid phase–change and the heat transfer limit in the FPMHP. We found that a slug-train unit formed when the heating power was sufficiently large, causing a local dryout phenomenon. The evaporation section presented a complete dryout with the further increase in heating power. Therefore, the heat transfer limit in the mini/micro FPMHP was dependent on the dryout limit.