MASS TRANSFER IN SHEARED SUSPENSIONS OF NEUTRALLY BUOYANT PARTICLES: HYDRODYNAMIC DIFFUSION ACROSS A SUSPENSION AND INERTIAL EFFECTS ON INTERFACE MASS TRANSFER
Mass transfer rate in dispersed multiphase flows can be increased dramatically by the random fluid velocity induced by the solid particles. In this study, the effects of solid particle volume fraction, the ratio of gap thickness of the Couette cell to the particle radius (H/a) and shear rate on the mass transfer rate are investigated in neutrally buoyant particle suspensions in simple shear flow. An electrochemical method is used to measure the mass transfer rate in the cylindrical Couette cell with solid particle volume fraction at 0.1, 0.17, 0.25, 0.33 and 0.4 with H/a=22 and 44. The experimental results show that the mass transfer rate increases with the shear rate, particle volume fraction and H/a. Lattice-Boltzmann/Fluid-tracer simulations are conducted with particle volume fraction at 0.1, 0.17 and 0.25 with H/a=10, 15 and 20. Tracer concentration profiles show that there is a bulk region and boundary layers. In the bulk region, hydrodynamic diffusion is dominant and in the boundary layers, molecular diffusion is important. A simple two-parameter model with the parameters determined from simulations yields predictions that are in good agreement with the experiments. Mass transfer from neutrally buoyant freely rotating spheres to the bulk in simple shear flow with inertial effect is studied experimentally. Ion exchange beads are used for the mass transfer study. The radius of the ion exchange particle is 275?m which makes the Re up to 1.5 and Pe up to 15,000. The experimental results agree well with the recent theoretical work.
Multiphase flow; Mass transfer; Particle suspensions; Neutrally buoyant particle