Lattice Boltzmann Simulation Of A Vapor Bubble Along Lower Tube Surface

The boiling heat transfer has drawn greater public attention because of its high heat transfer rate and is widely used in refrigeration,nuclear power,new energy and other fields.To explore the mechanism of boiling heat transfer,bubble dynamics is developing step by step.Under the unremitting study,researchers have put forward many kinds of mathematical models with good verifications and applications,obtained a lot of experiment experience and achieved fruitful results.During the process of boiling heat transfer,the structure of heat transfer surface has an important influence on heat transfer rate.Most scholars choose to study regular surface,and the models aiming at irregular surface is rare.However,irregular surfaces such as circular tubes are very common in practical production and living.So studying the dynamic characteristics and heat and mass transfer of the vapor bubble on the surface of circular tube and has extremely important scientific significance and application value.In this paper,the basic theory of lattice Boltzmann method is introduced firstly.In this part,the standard model of lattice Boltzmann method,a coupled lattice BGK model for the Boussinesq equations and a lattice Boltzmann model for multiphase flows with large density ratio are explained in detail.It also refers to several common boundary treatment methods and the generalized form of interpolation lattice Boltzmann method.Then,the composite lattice Boltzmann model in Cartesian coordinate to simulate the bubble growth on vertical wall is introduced.The hybrid phase change LBM model proposed by Weizhong Li et al is chosen.By simulating the bubble growth on vertical wall and getting results in good agreement with theoretical result,the model is validated to be effective in non-isothermal,two-phase and arbitrary bounded flow field.At last,a bubble rising along a lower tube surface under different Jakob numbers has been simulated.Before simulating,using the grid generation techniques and interpolation-supplemented lattice Boltzmann method,a body-fitted coordinate is built to transfer the irregular area in physical plane needed to be researched into a rectangular area in calculation plane.The results show that during its moving process,at the beginning,the bubble's shape changes from a nearly-hemiciclo to a nearly-circular,and then slides over the curved surface.During the slip process,the bubble flats obviously and has a tendency to departs from the wall.The bubble grows due to heat tranfer from its underneath thin liquid film and surrounding hot liquid.Bubble movement causes the disturbance of temperature field and strengthens the heat transfer.There is a positive correlation between the parameter changes and Jakob number.