Investigation on Axially Grooved Multi Branch Heat Pipe

Abstract

The conventional heat pipes are widely used in applications like electronics cooling, space crafts, heat recovery etc. The conventional heat pipes have one evaporator and one condenser which are used in the transport of heat from a single source to a single sink. The concept of multi-branch heat pipes could be the solution for multiple heat loads in case of electronics cooling. Multi-branch heat pipe with two evaporators and a single condenser has been designed, fabricated and tested in gravity assisted mode. In the present thesis, a T-shaped axially grooved heat pipe (AGHP) is proposed with two evaporators and one condenser connected by liquid and vapour lines. It is observed that with the same operating conditions, the temperature difference between evaporator section and condenser section increases with increasing the heat load due to practically non-zero thermal resistance. The maximum and minimum temperatures of the multi branch axially grooved heat pipe (MBAGHP) are at the end of the heating section and at the end of the condensing section respectively. An experimental setup was developed to study the effect of different filling ratios of 75%, 100%, 125%, 150%, 175% and 200% for a heat pipe with 20 grooves. For the above filling ratios, investigation has been carried out for start-up characteristics, thermal resistance analysis, heat transfer coefficient analysis, variable load characteristics, maximum heat load capacity, and temperature difference at evaporator and temperature distributions along the length. The experiments were performed with heat load ranging from 0 W to 240 W. The experimental results obtained are as following: (1) The optimum filling ratio of MBAGHP is 150% (2) MBAGHP can dissipate up to maximum heat load of 240 W with minimum thermal resistance of 0.2 ˚C/W and maximum temperature rise of both the evaporators are near to 100 ˚C for the filling ratio of 150% (3) Start-up temperature rise of MBAGHP (for optimum filling ratio 150%) is 70 ˚C and start-up time is 27.5 minutes for the heat load of 240W (4) Maximum heat transfer coefficient obtained is 720 W/m2.K at 150% filling ratio and 240 W (5) For all different heat loads the temperature variation in adiabatic section is very small for 150% filling ratio justifies the ideal condition of heat pipe.