Numerical Investigation On Vapor Bubble Growth And Moving In Subcooled Water

Due to advantages such as the high heat transfer efficiency and low required driving potential,vapor bubble condensation is widely used in industrial applications.Vapor bubble condensation is composed by three stages——formation,detachment and rising.Bubble formation is affected by various factors,such as subcooling degree,wall contact angle and so on.Bubble rising process is related to bubble detach volume.Therefore,it's difficult to predict the moving of bubble,which needs to be deeply researched.In this paper,a numerical method for condensation of water vapor bubble is established by user defined function(UDF)based on method of volume of fluid(VOF).The processes of water vapor bubble growing and detaching in subcooled water and a single vapor and vapor-air mixture bubble rising in liquid water are numerically studied.The volume of fluid(VOF)and species transport model are applied to simulate the two phase flow and species transport in the mixture,respectively.A modified phase model of vapor and vapor-air mixture condensing in liquid water is built which is based on the kinetic gas theory.The mass transfer in phase change is added to the function by the form of source.With the help of related citations and charts,the properties of parameters in our simulated condition are determined.The real gas state equation is selected to calculated density of gas mixture and the other physical parameters are calculated by empirical or polynomial fitting formula.A single bubble rising in subcooled water is numerically studied.The phase change model is firstly verified based on a one-dimensional Stefan phase change problem.The results show that bubble deformation during the condensation process is determined by Re,Eo and M,respectively.The bubble lifetime is longer and deformation is more complicated with increase the initial diameter of bubble.An accelerated condensation which is caused by bubble collapse is appeared in the end of condensation.With increase of the subcooling degree,the bubble lifetime is shorter and the bubble size decreases almost linearly.The bubble lifetime is prolonged and the bubble shapes seldom deform at higher pressure system.The bubble condensation time is prolonged and the bubble acceleration and terminal velocity decreases when there are non-condensable gas.The heat transfer coefficient of gas-liquid interface drops sharply with the increase of non-condensable gas fraction.Numerical investigation of vapor and air bubble formation and detachment at a submerged orifice is carried out with a constant flow rate.The results show that the bubble base is fixed at orifice rim when the surface contact angle is less than 90°.Conversely,the bubble base will spread outward on the horizontal surface when the surface contact angle reaches 90°.When the surface contact angle is greater than 40°,the bubble detachment time increases with contact angle.Hence,the vapor bubble detachment time augments more obviously.An increase of flow rate promotes the bubble detachment and leads the bubble regimes from a single periodic to a double periodic.With increasing of subcooling degree and orifice diameter,the bubble detachment time is prolonged and the double periodic feature is weaken.