Numerical Simulation Of Multiphase Turbulent Flow In Pipe At Different Temperature

With the continuous development of industrial production,the problem of air pollution has been highlighted.The airborne respirable particulate matter poses a huge potential threat to human health.Hence,in order to explore the reduction and control of respirable particulate matter emissions in industrial production processes,clarify the flow pattern of particulate matter under the influence of temperature,this thesis applies numerical simulation to study the motion characteristics of multiphase flow in pipes at different temperatures.In this thesis,the turbulent flow field is calculated based on the RSM model,and the Lagrangian particle tracking method is applied to track the particle trajectories,the effects of the Reynolds number of the flow field,temperature difference and particle size on the particle distribution in the circular tube are investigated.Firstly,the flow fields with three Reynolds numbers of Re=44000,Re=36700 and Re=24580 were simulated numerically,verified with the experimental results,and the calculated results were good.In addition,the effect of three temperature fields(tube wall and inlet fluid temperature difference of 0K,380 K and-70K)on the characteristics of the flow field was studied,and it was found that the lower the Reynolds number of the flow field,the greater the temperature gradient,and the greater the thermal swimming force.When the fluid is heated,volume velocity increases.The volume velocity decreases as the fluid cools;the average flow velocity of the viscous bottom and buffer layers under the former condition is lower,compared with that under the latter condition,but the opposite is true for the logarithmic layer.Based on the above work,this thesis proceeds to study the distribution characteristics of particles of different particle sizes(0.2μm,2μm,10μm,50μm,250μm)in pipes with different Reynolds numbers and temperature differences.It is found that all particles have the tendency to gather to the pipe wall,regardless of particle size;small particles follow the fluid flow well and are easy to gather to form a band structure,while large particles have high inertia and tend to gather to the pipe wall;What’s more,the higher the Reynolds number,the more the particles tend to gather to the pipe wall.In the presence of temperature difference,small particles are susceptible to thermophoretic forces,resulting in significant changes in their distribution in the pipe;when the fluid is heated,the thermophoretic effect suppresses the turbulent effect;while the fluid is cooled,the thermophoretic effect promotes the turbulent effect.In addition,it was found that the larger the particle size,the smaller the longitudinal diffusion of the particles;heating decreases the longitudinal diffusion of the particles,and cooling increases the longitudinal diffusion of the particles.Besides,the higher the Reynolds number,the greater the degree of longitudinal diffusion of particles.In summary,the results obtained in this paper provide a theoretical basis for reducing and controlling the emission of inhalable particles in practice.