Experiment Study On Heat Transfer Performance Of Pulsating Heat Pipes With Graphene Nanofluids

With the development of the electronics industry,the integration level of electronic devices has been improved constantly,and the heat load per unit has been increasing.The high temperature of electronic devices can degrade their performance and even cause malfunction.Therefore,compact and efficient heat-dissipation devices are required to effectively cool them.Pulsating heat pipe(PHP)has excellent application prospects in the fields of heat dissipation of electronic devices,solar energy system and waste heat recovery because of its small size,simple structure and strong heat transfer capability.Exploring the new working fluids is one of the important research directions to enhance the heat transfer of PHP.At present,there are many experiments and theoretical studies of heat transfer performance of PHP with common metals or metal oxide nanofluids,but few studies have reported the results of heat transfer performance of PHP with graphene nanofluids.At present,the main obstacle to the large-scale application of graphene is the lack of industrial-scale methods to produce high-quality graphene.Firstly,the preparation of graphene by liquid-phase exfoliation is studied,which is promising scalable production of high-quality few-layer graphene.UV-Vis,Raman spectra,SEM,TEM and AFM are adopted to characterize the structure and morphology of graphene.It is proved that the exfoliated graphene has transparent sheet structure with few defects and its thickness is 3~5 layers.Ethanol,ethanol-water binary mixture and surfactant solutions are used as base liquids to prepare stable graphene nanofluids based on two-step method,and then their thermophysical properties are tested.The results show that the addition of graphene does not affect the surface tension of the base liquid,but simultaneously increases its thermal conductivity and dynamic viscosity.The addition of a small amount of surfactant has no negligible effect on the thermal conductivity of the base liquids.However,surfactant solutions with different concentrations have different surface tension and viscosity values,and the trade-off effect between surface tension and viscosity will directly affect the heat transfer performance of PHP.The experimental system of PHP is designed and built independently.The start-up and heat transfer performance of PHP with different concentration of graphene nanofluids are studied under different heat loads.The results show the heat transfer performance of PHP with liquid-phase exfoliated graphene nanofluids is slightly better than that of industrial-grade graphene nanofluids.The start-up temperature of PHP decreases and the enhancement rate is between 8.71%and14.88%for industrial-grade graphene/ethanol nanofluids,and the optimal volume concentration of graphene/ethanol nanofluids is 0.01%.The volume concentrat ion of ethanol-water binary mixture is 40%when the thermal resistance of PHP is the minimum under the heat load of 20~50W,and the enhancement rate can reach12.18~28.17%for the ethanol-water binary mixture(40%)stabilized graphene nanofluids.CTAC and Pluronic~?F127 solutions can improve start-up performance of PHP,and reduce start-up time and start-up temperature.The enhancement rate of CTAC,PVP and Pluronic~?F127 solutions are 0.38~18.72%,-13.87~11.83%and-8.11~12.89%,respectively.The proper amount of graphene can further improve the heat transfer performance of PHP with surfactant solutions,with the highest enhancement rate of 19.63%.