Bubble motion and mass transfer in non-Newtonian fluids: Part I. Single bubble in power law and Bingham fluids

Abstract

The Sherwood number and drag coefficient for a single gas bubble moving in a power law fluid and a Bingham plastic fluid are obtained using perturbation methods. The perturbation parameters for power law and Bingham plastic fluids are m (= n - ½) and E (= τ₀R/Uμ₀), respectively. It is found that in the case of power law fluid, mass transfer and drag increase with increasing pseudoplasticity. These theoretical results are found to be in good agreement with the available experimental data and the data obtained in the present study. In the case of Bingham plastic fluid, mass transfer and drag are found to increase with increase in the Bingham number N_B (= 2_ε). Contours of plug flow regions, where local stresses are less than the yield stress, are obtained as a function of the Bingham number N_B. These results qualitatively predict the zero terminal velocity observed for bubble motion in liquids with very high yield stress. They are also in good agreement with the trends of the results obtained previously for solid sphere motion in Bingham plastic fluids.