Collapsing bubble induced pumping in a viscous fluid

Abstract

An experimental study on the effect of liquid viscosity on the pumping efficacy of a jetting bubble is presented. Solutions of different viscosities are obtained using different concentrations of glycerine in water. To study the pumping effect, a low-voltage electrical spark is used to create a bubble near a fixed horizontal plate with a hole. The bubble oscillates and collapses with a high speed jet towards the plate and pumps fluid through the hole. The bubble dynamics are recorded using a high speed camera. As the viscosity increases, the number of bubble oscillations increases even as the bubble eventually collapses with a jet. At very high viscosities, jet formation is suppressed and the bubble does not break up into smaller bubbles upon collapse. The effect of other parameters affecting pumping such as the distance of the bubble-center from the plate and the radius of the hole in the plate, is also studied. Results show that pumping is most effective below a limiting distance of the bubble-center from the plate, which in turn depends on the viscosity. The estimated volumetric flux due to pumping through the hole also decreases with an increase in viscosity. The effect of viscosity on a free-field bubble is also presented in terms of the increase in the number of oscillations and the variation of bubble radius with time. © 2011 Elsevier B.V. All rights reserved.