Study On The Nonlinear Theoretical Model Of Two-phase Flow In A Single-ring Closed Pulsating Heat Pipe

Seeking efficient energy-saving methods is an effective way to deal with the increasing serious energy problems.As a new type of heat transfer element with simple structure,small volume,high efficiency and strong adaptability,pulsating heat pipe has been widely used in various fields such as heat transfer enhancement,energy saving and emission reduction.At present,the research on pulsating heat pipe is mainly focused on experiment and numerical simulation,and the relationship between the physical processes such as convection heat transfer,heat conduction and phase transition of the working fluid in the pipe and the operation mechanism of pulsating heat pipe is not thoroughly studied.In order to further study the working mechanism of pulsating heat pipe,from the perspectives of flow and heat transfer of working medium in the pipe and fluid dynamics,two types of theoretical models were established.The establishment of the two models provide a theoretical basis for the application of pulsating heat pipe in engineering practice.Firstly,based on the partial differential equations of heat convection of the pulsating heat pipe,the Lorenz-like equation model of the single-ring closed pulsating heat pipe with latent heat flow is established by using the method of separation of variables and Galerkin method.The chaos characteristic parameters of the working fluid in the pulsating heat pipe were obtained through simulation calculation,and the motion characteristics and heat transfer performance of the fluid were studied.Secondly,the spring-mass-damping hydrodynamic model of a single-ring closed pulsating heat pipe with two liquid columns is established in this paper,and the dynamic and nonlinear characteristics of the pulsating heat pipe are analyzed,during which the nonlinear and phase transformation characteristics of vapor-liquid two-phase flow in the pulsating heat pipe are considered.Finally,in order to verify the accuracy of the theoretical models of the two types of pulsating heat pipes established,the experiment and numerical simulation of the pulsating heat pipes size were also carried out.The results were compared with the conclusions obtained from the theoretical models,and it was found that the two models were in good agreement.The chaos characteristic parameters of the closed pulsating heat pipe with latent heat two-phase flow were obtained,on the basis of the two theoretical models of pulsating heat pipe,and the phase space reconfiguration of Fluent numerical simulation data and experimental data,It is found that the working fluid in the single-ring closed pulsating heat pipe is in a state of motion combining circulation and oscillation,and with the increase of heating power,the motion of the working fluid in the pulsating heat pipe gradually develops from low-dimensional chaos to high-dimensional chaos,and the heat transfer characteristics are gradually improved.At the same time,the Lorenz-like equation is used to predict the optimal structural parameters and liquid filling rate of single-ring closed pulsating heat pipe under certain conditions,which provides a theoretical basis for the further construction of the optimal heat transfer performance of the pulsating heat pipe.