Effect of the Surfactant Concentration on the Rise of Gas Bubbles in Power-Law Non-Newtonian Liquids

Abstract

The effect of the surfactant concentration on the terminal velocity, shape, and drag coefficient of freely rising bubbles in a non-Newtonian, pseudoplastic liquid was studied. It is known that surfactants affect the bubble terminal velocity by changing both the shape and surface mobility of the bubble. In this work we studied separately the effect of surfactants on the shape and surface mobility by using the recently obtained drag curves for freely rising bubbles with and without surface mobility. It was shown that, within the range of surfactant concentrations studied, the latter had no effect on the bubble shape. However, the effect on the bubble surface mobility was significant. It was shown that the transition from a bubble with an immobile surface to a bubble with a mobile one is a function of the surfactant concentration, terminal Reynolds number, and rheological properties of liquid. The values of these parameters at which transition occurs were determined.

Terminal rise velocity, size distribution and stability of microbubble suspension

“…Garabedian [52] reported that bubble rise velocity strongly depends on viscosity and decreases with increasing viscosity. A similar observation is reported by Margaritis et al [53] and Tzounakos et al [54] The increase in apparent viscosity was attributed to the main cause of the decrease in velocity. Theoretically the order of rise velocity for the gases for same concentration of SCMC in liquid is U B-Nitrogen > U B-Air > U B-carbondioxide .…”

Modelling mass transfer in an aerated 0.2m3 vessel agitated by Rushton, Phasejet and Combijet impellers

“…A bubble drag model of Tzounakos et al [19] is used. It has been originally developed for slightly viscous power-law fluids.…”

Effect of Surfactants on Gas Holdup in Shear-Thinning Fluids

“…Small bubbles have a low rise velocity and long residence time in the bubble column, thereby possibly increasing gas holdup. On the other hand, when bubbles rise in a solution containing a surfactant, the surfactant molecules will accumulate on the bubble surface and decrease the bubble velocity, and as the surfactant concentration increases, the terminal velocity decreases [10]. Moreover, surfactants can prevent bubbles from undergoing coalescence [7,22].…”

“…However, several fluids in practical processing industries exhibit shear-thinning behavior. Thus far, numerous studies reporting the effect of surfactants on bubble motion behavior in shear-thinning fluids mainly focus on the shape and velocity of single bubbles [9][10][11]. As compared to that of Newtonian fluids, significantly less is known about the effect of surfactants on the gas holdup in shear-thinning fluids because of their complicated rheological characteristics.…”