Studies on Multi Branch Heat Pipe

Abstract

The concept of conventional heat pipe is known for more than a half century and a huge amount of work has already been done. Conventional heat pipes are widely used in applications like electronics cooling, space crafts, heat recovery etc. Conventional single evaporator-single condenser heat pipes are used in the transport of heat from a single source to single sink. In an electronics circuit, it is a normal practice to locate multiple heat sources in available small space. The concept of multi-branch heat pipes is the solution for multiple heat loads in case of electronics cooling. Multi-branch heat pipe with two evaporators and single condenser has already been designed and fabricated. Sintered powders with mesh sizes of 200-270 (dia.: 50-75 μm), 140-200 (dia.: 75-100 μm) and 120-140 (dia.: 100-125 μm) have been selected as a wick material in the heat pipe. Primary sintering experiments have been conducted in the muffle furnace in the steps of 400 °C, 600 °C, 800 ° C, 850 °C and 900 °C. It has been concluded from the sintering experiments that the brazed portion of T-section in heat pipe possess sufficient strength against sintering temperature of 900 °C. Further, a layer of sintered powder with approximate 1.5 mm thickness has been observed inside of the heat pipe at the temperature of 900 °C maintained for 1 hour. In the present work, the experimental setup has been developed to study the effect of filling ratios, start-up characteristics, thermal resistance analysis, heat transfer coefficient analysis, dynamic characteristics and temperature distributions of wickless multi-branch heat pipe. The experiments have also been performed on wicked MBHP having copper powder sizes of 50-75 μm, 75-100 μm and 100-125 μm for the filling ratio of 60%. The experimental results obtained are as following: (1) the optimum filling ratio of wickless MBHP is 60% (2) start-up temperature rise of MBHP (filling ratio 60%) is 56.4 °C and start-up time is 13.5 min for the heat load of 180 W (3) MBHP can dissipate upto maximum heat load of 200 W with minimum thermal resistance of 0.31 °C/W and maximum temperature rise of both the evaporators are 105 °C for the filling ratio of 60% (4) maximum heat transfer coefficient is 600 W/ m 2 K and maximum heat flux is 314.46 W/cm 2.