Experimental Investigation On Heat Transfer Performance Of Radial Pulsating Heat Pipe Applied For High Heat-flux

As the efficient passive two-phase thermal transport device,pulsating heat pipes can be successfully applied in various high heat flow occasions.However,the critical heat flux of the flat pulsating heat pipes at present cannot effectively accommodate the local heat flow density heat dissipation requirement of small area hot spot up to 200 W/cm~2.The common flat pulsating heat pipes are no longer applicable under the background,which are prone to local boiling and drying of evaporation section and significantly reduce the heat transfer efficiency.In order to enhance the heat flux of pulsating heat pipe,the novel radial pulsating heat pipes(RPHP)was proposed and investigated in this work,which was based on the matching criterion between evaporation and condensation area of pulsating heat pipe.The fractal tree-like network was applied to the channel structure design to increase the heat and mass transfer efficiency of pulsating heat pipe.By introducing a non-azeotropic and immiscible mixture of HFE-7100 and sodium dodecylbenzenesulfonate(SDBS)aqueous solution,the radial pulsating heat pipe could achieve rapid response and stable heat dissipation,and the mechanism of enhanced oscillatory motion of the mixture in the channel was explored.Visual observation and heat transfer performance experiments of U-shaped radial pulsating heat pipe(RPHP1)and fractal tree-like radial pulsating heat pipe(RPHP2)were carried out under different filling ratios,working fluid types and heating power.The weak points including low critical heat flux,difficult start-up and low heat transfer efficiency of pulsating heat pipes were solved.The experimental results showed that a single working fluid RPHP cannot satisfy both good start-up performance and excellent heat transfer performance.The 1 wt%SDBS aqueous solution owned the best heat transfer performance,but the start-up performance was relatively poor.The HFE-7100 working fluid had good start-up performance but weak heat transfer performance.When 1 wt%SDBS aqueous solution was selected as working medium,the starting power of RPHP1 was 160W,and the critical heat flux reachable in evaporation section was 228 W/cm~2.The starting power of RPHP2 is 160W under the same fluid,and the critical heat flow density reached by evaporation section was 278 W/cm~2.The non-azeotropic and immiscible mixtures consisting of HFE-7100 and 1 wt%SDBS aqueous solution owned lower boiling point in RPHP.The oil-in-water emulsion(HFE-7100layer)absorbed heat more easily and increased the mixing fluid chaos,which accelerated the start-up of pulsating heat pipe.In the RPHP,the HFE-7100/1 wt%SDBS mixture with a mixing ratio of 1:2 could guarantee both good start-up performance and excellent heat transfer performance.In RPHP1,this mixture reduced thermal resistance by 18.9%,while the starting power was only 120 W.In RPHP2,this mixture reduced thermal resistance by 22.2%,while the starting power was only 120 W too.Therefore,HFE-7100/1 wt%SDBS mixture was an effective means to enhance the comprehensive performance of RPHP.The study showed that the heat transfer performance of RPHP2 was better than that of RPHP1 under the same conditions.Compared with RPHP1,the evaporation temperature of RPHP2 was reduced by up to 6 degrees centigrade and the thermal resistance by up to 12percent.The fractal tree-like network structure could be applied in radial RPHP stably and had better heat transfer enhancement capability.