Drag and Mass Transfer of Bubble Swarms in Power-Law Liquids at Moderate Reynolds and Peclet Numbers

Abstract

The motion and mass transfer of swarms of mono-size non-circulating spherical bubbles (without any surface active material) in power-law liquids have been numerically investigated at moderate Reynolds and Peclet numbers. A simple sphere-in-a-sphere cell model has been used to account for hydrodynamic interactions between neighbouring bubbles. A wide range of values of gas hold-up has been considered so as to evaluate the detailed drag and mass transfer characteristics of swarms of bubbles to almost single bubble rising in power-law liquids. Extensive numerical results have been obtained to elucidate the effects of the Reynolds number (Re), power-law index (n) and gas hold-up (φ) on the drag coefficients and Sherwood numbers over the ranges of conditions: 0.6 ≤ φ ≤ 10−6, 1 ≤ Re ≤ 200, 1 ≤ Sc ≤ 1000 and 0.6 ≤ n ≤ 1.6. The total drag coefficient (CD) decreases with the decreasing values of n, whereas, the average Sherwood number (Shavg) decreases with increasing values of n. Based on the present numerical results simple predictive correlations have been proposed for CD and Shavg which can be used to estimate the free rising velocity and the rate of mass transfer in a gas-liquid system in a new gas-liquid application.