Research On Flow And Heat Transfer Characteristics Of Two-diameter Pulsating Heat Pipe Based On Two-phase Flow-vapor-liquid Plug Model

Pulsating heat pipe（PHP）has the advantages of simple structure,no capillary core,high thermal conductivity,high heat flux density and good adaptability,and has great research prospects in the microelectronics neighborhood.At present,the research on PHP mainly focuses on the structure of equal pipe diameter.Experimental research shows that the heat transfer performance of some variable cross-section pulsating heat pipes could be improved by improving the self-excitation of the working fluid,but lacks of relevant theoretical research at present.In order to analyze the influence of variable cross-section structure on the heat transfer performance of PHP,a two-diameter pulsating heat pipe is proposed,develops an applicable theoretical model,and analyzes the oscillation and heat transfer characteristics of the two-diameter pulsating heat pipe.The main work as follows:Firstly,based on the mass-spring-damping model,combined with the heat and mass transfer phenomenon of the working fluid,two-phase flow-vapor-liquid plug model suitable for the paper model is built.Corresponding numerical calculation method is designed,and MATLAB is used for numerical solution.The correctness of the model in this paper is proved by comparing the numerical calculation results with the experimental results.Secondly,the influence of the shape resistance on the heat transfer performance of the two-diameter pulsating heat pipe is analyzed.The result shows that the structure of the two-diameter pulsating heat pipe can effectively improve the self-excited oscillation mechanism of the pulsating heat pipe by changing the shape resistance,thereby affecting the heat transfer performance of the pulsating heat pipe.In addition,this paper accurately analyzes the evolution of the two-phase flow pattern of the working fluid in the tube and its heat transfer characteristics.The empirical formula for the heat transfer coefficient of the evaporation section of the two-diameter pulsating heat pipe is given,and it is compared with the experimental results and VOF local simulation results,which proved the accuracy of the empirical formula.Finally,the two-diameter pulsating heat pipe is studied by coupling the two-phase flow pattern and the shape resistance,and the heat transfer characteristics of the two-diameter pulsating heat pipe are analyzed.The result shows that the oscillation characteristics and heat transfer characteristics of the two-diameter pulsating heat pipe are affected by the cross-sectional ratio（β）and the base diameter(d_eff).The smaller theβand the larger the d_eff,the smaller the thermal resistance and the better the heat transfer performance.The research results show that:adopting a reasonable two-diameter pulsating heat pipe structure can improve the heat transfer performance of the working fluid by improving the self-excitation of the working fluid.The two-phase flow-vapor-liquid plug model proposed in this paper can provide good theoretical guidance for the two-diameter pulsating heat pipe,and has certain reference significance for the design of other variable cross-section pulsating heat pipes.