Improvement of the bubble separation through eccentric planar cyclones: Experiments and CFD simulations

Abstract

Planar cyclones have great advantages as electrolyzers, photocatalytic reactors, and gas–liquid separators. For planar cyclones, the separation efficiency of bubbles is a key parameter. The effect of eccentricity on bubble separation efficiency in planar cyclones was studied through a combination of experiments and simulations. When eccentricity dc = 0 mm, the separation efficiency of the bubbles decreased with an increase in the liquid injection velocity. This indicates that a greater centrifugal acceleration in planar cyclones does not contribute to bubble separation. Eccentricity dc = −5 mm resulted in a higher bubble separation efficiency. Each planar cyclone was divided into 12 sub-regions with equal areas. When eccentricity dc = −5 mm, subregions 11 and 12 exhibited larger bubble sizes, and a higher bubble separation efficiency was achieved. The area weighted average sauter mean diameter ds reached 0.47 mm and 0.475 mm and area weighted average gas volume fraction εs reached 2.75 % in subregion 11 when liquid Reynolds numberRel = 20075.4 and gas Reynolds number Reg = 23.8. The maximum separation efficiency can be increased from 43 % to 60 % when Rel = 20075.4 and Reg = 6.8 when the eccentricity varies from 0 to − 5 mm. Bubble size changes due to coalescence and breakup have an important influence on bubble separation. The trajectory of bubbles exhibits helix. The gradually decreasing curvature radius of the bubble trajectory dominates the bubble separation. Eccentric swirling field provides a sudden decrease in the swirl radius which promotes the reduction of the curvature radius of the bubble trajectory. This study provides an optimization method for the structural design of cyclones.