Lattice Boltzmann Simulation Of Non-isothermal Particle & Droplet Suspension Flow

Non-isothermal particulate flow are widely found in nature and industrial applications.Thermal convection between particles and fluids will have an important influence on the interaction between particles and particles.Therefore,studying the internal mechanism of non-isothermal particulate flow is of great significance to deeply understand natural phenomena such as dust storms and guide boiler production and operation.Collision between particles and droplet also plays an important role in nature,food industry,and pharmaceutical industry.It is difficult to grasp the internal details of these complex two-phase flow by experiments,so numerical simulation is a better choice.Lattice Boltzmann method(LBM),as an increasingly mature mesoscopic simulation method,has the advantages of high computational efficiency,ability to capture internal details,and parallel efficiency,and has become an important tool for studying particulate flow and particle-droplet collision.This paper uses LBM to explore some issues of non-isothermal particulate flow and particle-droplet collision,including the following aspects:Firstly,using LBM and immersion boundary method(IBM),sedimentation of two hot particles,two cold particles and one hot and one cold particles are studied respectively,and effects of Grashof numbers on the interaction between two non-isothermal particle are analyzed.At the same time,differences of interactions between two settling particles among these three conditions are studied.Secondly,LBM-IBM is used to study effects of particle size ratio on the settling behavior of two spherical particles under thermal convection conditions.Three working conditions are studied: sedimentation of two normal-temperature particles,two hot particles,and two cold particles.The results show that the particle size ratio has an important effect on the drag,collision and tumbling(DKT)processes in the sedimentation of two unnormal-temperature particles.The larger the particle size ratio,the earlier the tumbling process of the two unnormal-temperature particles takes place.Effects of thermal convection on the critical particle size ratio of two settling particles are studied.When the small particle is initially placed above the large particle,the critical particle size ratios of the two cold particles,the two normal-temperature particles,and the two hot particles sequentially increase.As the particle size ratio increases,effects of thermal convection on the interactions between two unnormal-temperature particles decreases.Then,settling behaviors of hot and cold particle groups under gravity are studied,and influence of Grashof numbers on the settlement of non-isothermal particle groups is discussed.As a result,it is found that with the increase of Grashof numbers,average settling velocity of the hot particle group decreases,and difference in the settling velocity among the particles also decreases.With the increase of Grashof numbers,upper part of the hot particles moves upward under the impact of hot buoyancy and gradually moves away from the lower particles.After reaching a steady state,the hot particle groups are distributed in layers,and the settling velocity of particles in each layer is greatly different.With the increase of Grashof numbers,the average settling velocity of cold particle groups increases,and the difference in the settling velocity among particles also increases.Due to repulsive force among cold particles,the particle dispersion of the cold particle group is maximized when a steady state is reached.Finally,collision behavior between moving particles and droplets is studied.Based on the size of the eccentricity between the particle and the droplet,two collision mechanisms of merging and separatiton are observed.When the eccentricity is very small,the particle and droplet appear as a merging mechanism;when the eccentricity is large,the particle and droplet behave as a separation mechanism.On the basis of these two collision mechanisms,effects of particle surface wettability and particle-droplet size ratio on particle-droplet collision behavior are further analyzed.