Numercial Research Of Pool Boiling On Suspending Plate And The Improved Lattice Boltzmann Phase Change Model

Boiling heat transfer has wide applications in both daily life and industrial production.With the widely used of high temperature in thermal equipment,enhancing the energy efficiency of heat utilization and regulating the boiling heat transfer mode have become increasingly important.Active enhanced heat transfer technology relies on external input energy,while passive enhanced heat transfer technology has weaker enhancement effects.Therefore,establishing an effective boiling heat transfer enhancement technology becomes necessary research.In previous studies of pool boiling,the bubbles were regarded as the medium for heat transfer,while the bubble dynamic during bubble growth was neglected.Our model utilizes the dynamics of bubble growth to push the heating surface,which is benefit to bubble departure.It is an efficient passive boiling heat transfer enhancement technology.However,due to the limitations of experimental techniques and theoretical research models,a complete scientific explanation system has not been established for the heat transfer modes and mechanisms of micro-scale heat transfer equipment,while the existing macroscopic numerical models are unable to reasonably study microbubble dynamics and other problems.In order to solve these problems,this paper established a boiling heat transfer model of moving surface based on the lattice Boltzmann method model of vapor-liquid phase change,which coupled with the Bounce-Back fluid-structure coupling boundary of moving surface based on momentum exchange method,and studied the boiling heat transfer bubble dynamics of moving surface.Furthermore,the vapor-liquid phase change numerical model of lattice Boltzmann method is improved,and the LBM numerical model of droplet evaporation considering radiation heat transfer is established with three distribution functions,and the influences of radiation heat transfer parameters in the process of droplet evaporation were discussion.1.Based on the vapor-liquid phase change model of lattice Boltzmann method,the boiling heat transfer model of the movable surface was constructed based on the Bounce-Back boundary,and the moving characteristics of the plate were calculated by the momentum exchange method.The correctness of this model is verified by comparing the diameter and period of bubble departure under different gravity conditions.This model can simulate the complete nucleation process of bubble on a moving heating surface.The influence of surface mobility on boiling heat transfer was studied by this model.The bubble departure diameter and bubble departure period of the moving surface were calculated by numerical simulation.The numerical results show that the boiling heat transfer phenomenon of the moving surface may have different pool boiling characteristics from that of the stationary surface.The streamline distribution on the heating surface is studied and the influence of boiling liquid replenishment on the moving surface is analyzed.2.A numerical model for the evaporation of suspended liquid droplets considering radiation heat transfer was established based on the lattice Boltzmann method.The model employs a three-distribution function model,including the density distribution function,temperature distribution function,and radiation distribution function.In the energy equation,the source terms for phase change and radiation heat transfer are added to consider the effects of phase change and radiation heat transfer on droplet evaporation.The calculation model is established to solve the multi-layered media problem when radiation energy passes through the vapor-liquid interface.The refraction,reflection,and absorption of radiation energy by the droplet surface are all considered in the calculation frame.The radiation field boundary condition at the vapor-liquid interface is treated by the energy conservation equation of heat conduction,convective heat transfer,latent heat of evaporation,and radiation energy absorption at the droplet surface.The correctness of the model was verified by comparison with the D2 law and the theories proposed by scholars considering radiation heat transfer.The results show that during the evaporation of suspended liquid droplets,the droplet diameter deviates gradually from the D2 line with time increasing,especially when the temperature is high and the droplet diameter is small.By comparing the radiation heat transfer to total heat transfer,it was found that the radiation heat transfer ratio decreases as the droplet diameter decreases,Through detailed analysis of the flow lines and temperature distribution,the influence of extinction coefficient β and scattering albedo w on the evaporation process was discussed,and the mechanism of radiation heat transfer enhancing droplet evaporation was elucidated.