Separation Characteristics of Oil Droplets in a Shallow-Layer Countercurrent Flow Field with a Conical Disc-Stack Structure

Shallow-layer separation technology is an effective approach to enhance the separation performance of produced water treatment systems. However, the separation characteristics in the shallow-layer countercurrent flow field with conical disc-stack structure remain poorly understood. In this study, Computational Fluid Dynamics (CFD) simulations combined with experimental validation were employed to investigate oil droplet transport and separation mechanisms in multilayer shallow-layer channels. Studies have shown that within the shallow-layer countercurrent flow field formed by the conical disc-stacks, the internal flow field exhibits a velocity gradient that varies with the radial distance. A theoretical plate length calculation formula was established, and given α = 60°, h = 30 mm, V = 0.01 m/s, the theoretical plate length for 50 μm oil droplets was determined to be 112.1 mm, which is in close agreement with the numerical simulation result of 112 mm. The oil–water separation process in the shallow-layer countercurrent flow field can be divided into three regions: the chaotic region, the separation region, and the clarification region. The chaotic region accounted for more than 51% of the total plate length. Numerical simulations and experimental tests further revealed that the anisotropic stratified flow characteristics and back-mixing phenomena within the channels adversely affect the separation process. These findings demonstrate that optimizing the uniformity of flow distribution, controlling the slip distance, and suppressing back-mixing are critical to improving the separation efficiency.