Flow behaviour and drag coefficients of spherical bubbles in surfactant-laden Carreau model fluids

Abstract

The flow and drag phenomena of contaminated spherical bubbles in columns filled with surfactant-laden Carreau model fluids is numerically investigated using a computational fluid dynamics based commercial solver, COMSOL Multiphysics 4.3b. The effect of contaminants is incorporated in the solver by the use of the spherical stagnant cap model. The numerical solver is thoroughly benchmarked through extensive validation with the existing literature results. Further new simulations are performed over wide range of the conditions as the Reynolds number (Re) varying in the range of (0-100), the power law index (n) ranging between (0.2-0.8), the Carreau number (Λ) varying in the range of (1-100) and the degree of contamination (α) ranging between (0-180°). Briefly, the results indicate that recirculation wakes behind the bubbles are observed for all values of Carreau number ranging between 1-100 if the bubble is at least partially contaminated, i.e., for α > 30°. The total drag coefficient decreases with the increasing Carreau and/or Reynolds numbers and/or with the decreasing power-law index and/or with the decreasing cap angle.