Numerical Simulation Of Helium-based Cryogenic Pulsating Heat Pipe

In recent years,the cryogenic pulsating heat pipe has received increased attention from researchers as an efficient two-phase cooling heat transfer unit.Especially in the cooling of cryogenic superconducting magnets,it enjoys huge advantages—simple structure and strong heat transfer ability.However,a huge amount of research is required due to its complicated internal flow and that it involves gas-liquid two-phase flow and phase change heat and mass transfer.To this end,numerical simulation therefore becomes an indispensable study means as the cryogenic experiment is costly and its experiment period is long.In this paper,based on the CFD software fluent,the numerical simulation of the helium-based cryogenic pulsating heat pipe is carried out.The establishment of its numerical model,the flow characteristics at different stages in the pipe,the law of temperature and pressure changes and the heat transfer capacity are mainly studied.The numerical model for a two-dimensional single-loop cryogenic pulsating heat pipe is established using helium as the working medium,and a VOF multiphase flow model,a CSF surface tension model and a heat and mass transfer Lee model.The model is solved numerically.The result of calculation shows that with the input power at 0.1W and the liquid filling rate at 60%,the working medium in the heat pipe forms a reciprocating flow that alternates clockwise and counterclockwise.There are intermittent pauses after each cycle of flow.After the heat pipe is started and the first circulating flow is completed,the operation of the heat pipe gradually stabilizes,and a stable gas plug liquid column flow is formed in the pipe.Then,a numerical model of the two-dimensional multi-loop cryogenic pulsating heat pipe is established to study its operational similarities and differences from the two-dimensional single-loop cryogenic pulsating heat pipe so as better understand the operating characteristics of the helium-based cryogenic pulsating heat pipe.The simulation results show that with the input power at 0.4W and liquid filling rate at 57%,the flow and temperature distribution of the working medium in each tube are different and regular.After the heat pipe is successfully started and stabilized,the working medium in the tube forms a pulsating flow that alternates between counterclockwise and clockwise,and the pressure in the tube and the temperature oscillations of each section gradually stabilize.At last,a numerical model for a complete three-dimensional cryogenic pulsating heat pipe with actual dimensions is established.The numerical simulation is carried out with reference to the experimental conditions in the literature,and the flow and mass and heat transfer mechanisms of the cryogenic pulsating heat pipe are further analyzed.The initial calculation of the liquid filling rate is completed,and the random distribution of the gas plug and liquid column in the tube after the initial liquid filling is successfully simulated.The numerical simulation is carried out with the input power at 200 m W,400 m W and 600 m W respectively,and the liquid filling rate at 54%.The simulated value of the effective thermal conductivity of the heat pipe is obtained,compared with the experimental value in the literature,and analyzed for difference comparison.The results show that there is a certain error between the simulated value and the experimental value,but the accuracy of the numerical model is verified to a certain extent.