CFD Simulation Of Concentrated-suspension Flow And Particle Migration In A Microchannel

Micro-chemical system are increasingly become an important technique forchemical process intensification with its high heat-transfer and mass-transfer efficiency.The suspension flow and the phenomenon of particle migration in micro-scale havewide application prospect in nanoparticles preparation, micro-reaction, micro-dissectionand micro-mixing. Therefore, the research on the flow characteristics of suspension hasboth important theoretical and applied values.This paper is concerned with the CFD modeling of particle migration inconcentrated suspensions flowing in straight microchannel, T shape microchannel and Yshape microchannel based on the Diffusive Flux Model (DFM) and solved by using theFluent package. The main conclusions gained are as follows:①Microchannel model were set up, the geometry were carefully divided based onthe particle migration characteristics, reasonable boundary conditions were givenaccording to relevant experimental research results. The mass-transport equation of theparticles was set up based on the Diffusive Flux Model (DFM) and solved along withthe continuity equation and momentum equation by using the Fluent package. Thesimulation method was validated by comparing the simulation result of thenon-Brownian suspension flows in a millimeter channel with the experimental andtheoretical data in the literatures.②The suspension flow and particle migration in microchannel were studied. Thedifference between millimeter-sized channel and micron-sized were discussed, Then,the suspension flow in a microchannel was studied and the necessary modifications ofthe computation model and the relative parameters were analyzed due to the microscaleeffect, and the influence of Brownian motion is considered. The calculation resultindicates that the DFM-CFD results show good agreement with the experimentalresults.③The effect of the particle concentration, particle size, flowing velocity, andPéclet number on the particle distribution was investigated, especially the influence ofBrownian motion was clarified. The main results can be summarized as follows: Theviscosity flux increase with the initial average particle concentration and thus theparticles become more equally distributed; The particle radius has obvious effect onparticle distribution when the particle radius is less than0.1μm. At this point, the evenness extent of the particle distribution increase with the decrease of particle radius;when particle radius is greater than1μm, the influence of particle radius is notremarkable.④The effect of Péclet number on the particle distribution was investigated. WhenPe <100, the effects of Brownian motion are clear, the particles were equallydistributed. However, the effects of Brownian motion would decreases with increasingPe number. When Pe≥100, the effects of Brownian motion is negligible.⑤The separation of particle and the carrying liquid were analyzed. The resultsshowed that after the separation, the maximum particle concentration is not obtained atthe centre, but at the regions close to the wall, and more particles are moving towardsthe straight branch compared to the bent.⑥The status for the T shape and Y shape micromixer were investigated. Themixing effect of the two micromixers were compared. The results showed that theeffects of T shape micromixer is better than the Y shape micromixer, and for a mix ofsuspension system, well mixed couldn’t be achieved as the inhomogeneous sheardistribution will induce the cross stream migration of particles to the low shear regions.For Newtonian-suspension system, the micromixer will enable mixing only near thecenterline of the channel (0.2<y/H <0.8), and the effects of mixing increases slightlywith the flow developing downstream. However, well mixed still couldn’t be achieved.