Theoretical And Experimental Investigation On An Improved PHP Coupling With Metal Foam

The exponential growth of nuclear industry,diode lasers and electronic devices brings a rapidly increasing demand of heat dissipation.The consequent high heat flux issue has become one of the main inhibitors of technological development,especially seeing the explosion of the big data and cloud calculation technologies in recent years.Besides,the environment with low gravity force or other harsh working conditions in aerospace device applications also needs novel heat removal solutions with light weight,good flexibility and stability.High heat flux cooling has been a very active and promising field of heat transfer research,including micro refrigeration system,spray cooling,jet impingement cooling,micro-channel cooling,porous media cooling and heat pipe cooling.Among these novel solutions,pulsating heat pipe(PHP),also known as self-excited heat pipe or oscillating heat pipe,is considered as one of the most promising heat transfer devices to address the challenge of high heat flux for its distinct advantages,e.g.,simple structure,low cost,and strong flexibility.However,the unique mechanism of PHP also brings strict limitations of its structure and dimension.The relatively small diameter would lead to larger thermal resistance and limit the heat transfer capacity.In order to improve the heat transfer performance and the maximum heat flux of PHP,the improved structure of PHP was proposed by introducing metal foam to replace the original evaporation and condensation section in this research,and theoretical and experimental study on the heat transfer and operation characteristics of this improved PHP was conducted.Theoretical models on the heat transfer performance of the evaporation section,adiabatic section and condensation section were built,and the responding heat transfer performance was analyzed.The results showed that the thermal resistance of the evaporation section was the lowest,and the thermal resistance of the adiabatic section was the main part of the whole improved PHP.By comparison with the heat transfer performance of normal PHP with the same diameter and number of turns,the thermal resistance of this improved PHP was reduced(3 8.3?42.0)%when the working fluid is water,and the thermal resistance was reduced(43.3-48.5)%when the working fluid is ethanol.The performance was obviously enhanced by introducing metal foam.An experimental setup was designed and built to investigate the heat transfer performance of the improved PHP coupling with metal foam.The experiment was conducted to investigate the effects of working fluid,heat flux,heating mode and filling ratio on the start-up and heat transfer characteristics.The experimental results were in good agreement with the theoretical results,and the conclusion of the decrease of thermal resistance by introducing metal foam in theoretical results was verified by the experimental results.The experimental results showed that,comparing with original PHP,the improved PHP could obtain lower thermal resistance,higher maximum heat flux and more even temperature distribution.The improved PHP could obtain lower thermal resistance when the working fluid was water,compared with the improved PHP with ethanol as the working fluid.For this improved PHP,the best filling ratio is 0.2.Besides,this improved PHP could show good performance under different heating modes to satisfy the requirements of heat dissipation for inhomogeneous heat source or multi-heat sources.