Thermal Management Research Studies. Volume 1: High Performance Miniature Heat Pipes

摘要

High performance miniature heat pipes are developed for the cooling of high heat flux electronics using new capillary structures which rely on the use of a folded copper sheet fin and a folded copper screen. Using the folded sheet fin, capillary fins with fully opened grooves and folded sheet fins with notches at the fin top are made through a brazing process and the electric- discharge-machining technique. The use of the folded screen simplifies the heat pipe fabrication process. It is easy to make the capillary grooves as dense as desired through the present fabrication techniques. Heat pipes with different capillary structures and fill amounts are tested in the horizontal orientation. Three different heating areas in the heat pipe evaporator are arranged by activating different numbers of chip resistors. Thermal performances of the heat pipes are compared. The heat pipe with notched fins has the lowest internal thermal resistance at similar operating temperatures. In general, the heat pipes with notched fins, capillary fins and a folded screen demonstrated their favorable thermal performance. Compared with the capillary fins, the use of the folded sheet fins with notches resulted in a significant increase in the condenser heat transfer coefficient by 120 percent or greater at an operating temperature of 110 deg C. Heat fluxes higher than 140 W/sq cm are achieved using one-chip and two-chip heating modes.