Numerical investigation of the performance and hydrodynamics of a rotating tubular membrane used for liquid–liquid separation

• Membrane rotation is employed to improve efficiency of liquid/liquid separation.
• Hydrodynamics aspects and separation efficiency of the rotating device are studied.
• Theoretical and numerical results are compared for validation.
• Rotation and crossflow sweep droplets from the membrane and reduce fouling.

The performance of a liquid–liquid separation process based on an axially rotating tubular ceramic membrane operated in a crossflow regime is studied numerically with oil–water dispersions used as a model mixture. Internal hydrodynamics are explored using computational fluid dynamics simulations to obtain the velocity field in the continuous phase (water) and predict the separation efficiency with respect to the dispersed phase (oil). A discrete phase model is used to estimate trajectories of dispersed oil droplets within the membrane channel. The separation performance of the process is evaluated in terms of the droplet cutoff size. Effects of the Reynolds and Swirl numbers on velocity and pressure fields, shear stress, droplet cutoff size, and separation efficiency are investigated. The increased shear stress on the membrane surface due to the angular and the crossflow velocities decreased the accumulation of droplets on the membrane while increasing the separation efficiency. The droplet cutoff size is observed to decrease with an increase in the Reynolds and Swirl numbers. The separation efficiency strongly depends on the Swirl and Stokes numbers but only weekly on the Reynolds number. By increasing the Swirl number of the flow, it may be possible to remove very fine droplets by centrifugal force only and avoid membrane fouling.