Direct Numerical Simulation Of Bubble Flow In A Part Of Heat Pipe

Bubble flow,as a common and important flow pattern,widely exists in aerospace,energy and chemical industry,electronic equipment and other fields.The research on the dynamic characteristics of bubble flow is beneficial for improving the performance and production efficiency of the equipment,so the relevant research results will be of great practical significance applicative value of project.The Front Tracking Method(FTM)is a very effective and mature method for numerical simulation of bubble flow,and it can maintain high conservation of mass and energy.The dynamic characteristics of bubble flow in a local heat pipe were studied by means of the FTM.The researches and main conclusions are detailed as follows:In the start-up phase of the heat pipe,the rising process of bubble under the liquid surface and the coalescent process with the liquid surface are common phenomena,which affect the speed of start-up and work efficiency of the heat pipe.Therefore,the rising process of bubble under the liquid surface is studied by the FTM.The results of simulation show:when the relative distance δ(the distance between the centroid of bubble and the liquid surface)reaches a certain value,the resistant effect of liquid surface has no effect on the bubble,before the centroid velocity of bubble reaches the terminal velocity(reaches the stable velocity or fluctuates on a certain stable velocity).When the Reynolds number(Re)increases,the time of the terminal velocity reached is shortened,and the effect of viscosity on the terminal velocity is weakened.The stronger the interaction between the bubble and the free surface,the more helpful it is to accelerate the discharge of the liquid film.It is also shown that with the decrease of Weber number,the deformation coefficient of bubble decreases gradually,which will help to reduce the resistance of bubble.The pressure difference between the evaporation and the condensation of pulsating heat pipe and between adjacent pipes makes bubble oscillation flow between the evaporation and the condensation,so as to the quantity of heat is transferred from the evaporation to the condensation.In this paper,the oscillatory coalescence phenomenon of Taylor bubble flow under the action of fluctuating pressure gradient is simulated.The results show:the smaller the frequency is,the longer the periodic time of bubble is,and it will have enough time to discharge the liquid between the bubbles to promote the coalescence of bubble.When the number of Eu is higher,the bubbles are easier to coalesce together.On the contrary,when the number of Eu is smaller,bubbles are difficult to coalesce in a short time.The coalescent time of bubbles increases with the Re increasing,and decreases with the We increasing.The coalescent time of bubbles increases with the increase of spacing distance hi0.When the spacing distance hi0 reaches a certain value,the coalescent time of bubbles will increase dramatically,it will take a long time to shorten the distance between bubbles to promote the coalescence of bubble.In this paper,the local bubble flow in the heat pipe is simulated to provide guidance and help for the design and performance optimization of the heat pipe.