Experimental And Theoretical Study On Heat Transfer And Flow Characteristics Of Pulsating Heat Pipes

The pulsating heat pipe is a new type of heat pipe.It has a simple structure,excellent heat transfer performance,wide adaptability to the environment,and does not require external energy supply.It is regarded as a new way to solve the heat dissipation problem at this stage.However,the extremely complicated flow,heat transfer and mass transfer behavior of vaporliquid two-phase flow inside the tube cannot explain the internal mechanism of its operation,which poses certain obstacles to its application.Therefore,the exploration of the heat transfer and flow characteristics of the pulsating heat pipe has high engineering value,as well as important scientific significance for multiphase flow,phase change heat transfer and other problems.Since the pulsating heat pipe was invented in the 1990 s,researchers at home and abroad have conducted many researches on it.However,due to the imperfect theories of turbulence model,vapor-liquid two-phase flow model and phase change heat transfer model,there are still many problems in the field of pulsating heat pipes to be explored.In order to learn the working process and mechanism of the pulsating heat pipe systematically,this paper carried out experimental and theoretical researches on the pulsating heat pipe.Firstly,in order to carry out experimental research on the pulsating heat pipe,a large amount of references are studied and based on this,a set of pulsating heat pipe experimental rigs was designed to observe the temperature characteristics of the pulsating heat pipe at its start-up and stable operation,and to explore the diathermancy under different factors.The experimental device was successfully used to carry out the experiment.Sudden temperature changes at its start-up and temperature oscillation in stable operation were observed.The thermal resistance value and evaporation temperature under different working conditions were obtained and the ways different factors work on pulsating heat pipe were also analyzed Secondly,the numerical simulation of the four-bend pulsating heat pipe model was developed,and calculation of the established model was carried out by Ansys Fluent software.On this basis the initialization process of the pulsating heat pipe was successfully simulated,and the three stages of the pulsating heat pipe in the working stage were observed,and the phenomena simulated in the three stages were analyzed and compared with the actual process.Finally,based on the "mass-spring-damping" model,the two-cylinder plug-liquid plug model in the pulsating heat pipe was established.The oscillation mechanism and heat transfer characteristics of the pulsating heat pipe during the stable operation were analyzed,and the working performance of the pulsating heat pipe under factors were analyzed such as pipe diameter,evaporator temperature and thermal properties of the working fluid.This paper completes the basic exploration of pulsating heat pipes,and studies the pulsating heat pipes from both experimental and theoretical aspects to deepen the understanding of the working mechanism of pulsating heat pipes.And shortcomings of the completed work and some improvement methods are also proposed for follow-up researches as reference.