Effect of spheroid bubble interface contamination on gas-liquid mass transfer at intermediate Reynolds numbers: From DNS to Sherwood numbers

Gas-liquid mass transfer from spherical bubbles is studied by DNS for various Reynolds numbers (1 <= Re <= 300), Schmidt numbers (1 <= Sc <= 500) and bubble surface contamination degrees (0 degrees <= theta(cap) <= 180 degrees). Computed separation angles, drag coefficients and average Sherwood numbers for both clean and fully contaminated bubbles are favorably compared to literature. For partially contaminated bubbles, a correlation giving the separation angle versus Re and Ocap is proposed. Local Sherwood numbers along the bubble interface shows a transition between clean and contaminated zones closed to the separation angle. At low Re, for theta(cap) < 40 degrees, mass transfer of the contaminated bubble can be estimated by correlations for spherical solid particles, meanwhile for theta(cap) > 160 degrees, bubbles can be assimilated to clean bubbles. For intermediate contamination levels, a normalized Sherwood number Sh* from the drag Sadhal(1983) model can be used. For intermediate Re and high Sc; Sh* converges to a function well correlated to the normalized drag coefficient C*(D) bySh*(lower) = 1- (1-(C*(D))(2))(0:5). (C) 2021 Elsevier Ltd. All rights reserved.