Introduction

Experimental

Setup Photographs

Sample Movies 1

Sample Movies 2

Slug flow levitation

Dr. Jürg Ellenberger; Dr. Chippla Vandu; Prof. Rajamani Krishna
van 't Hoff Institute for Molecular Sciences
University of Amsterdam, The Netherlands

When a liquid in a column is subjected to vertical vibrations, an oscillating pressure field is produced in it. The oscillating pressure in the liquid mimics an acoustic field at the vibration frequency. A gas bubble injected into the liquid, experiencing these pressure oscillations, pulsates at a rate that is equivalent to the frequency of the vertical vibrations. Pulsation gives rise to a continuous distortion of the shape of the bubble.

In the absence of an oscillating pressure field, a gas bubble in a liquid rises as a result of the fact that its buoyancy force is larger than the drag force on it. However when the liquid is vibrated, additional forces tend to act on the bubble. These forces, sometimes called acoustic radiation-pressure forces, are better known as Bjerknes force after C.A. Bjerknes and his son V.F.K. Bjerknes who were the first to report on their existence in 1906.

The Bjerknes forces are generally divided into two classes: the primary Bjerknes forces (which result from an interaction of the sound field with a single bubble) and the secondary or mutual Bjerknes forces (which result from the interaction of two bubbles in the sound field). Our interest lies in the study of the primary Bjerknes forces.

The presence of the primary Bjerknes forces in a sound field affects the motion of a bubble in a liquid. By combining with the pulsating motion of the bubble, these forces are able to produce a translational motion on the bubble. Depending on the position of the bubble in the liquid, the bubble size and the vibration frequency and amplitude, the bubble may be made to move downwards in the liquid or remain trapped at an equilibrium position.

Therefore, subjecting a bubble in a liquid to vibration excitement could yield interesting and significant discoveries. Our ultimate goal is the application of these results to the improvement of the performance of multiphase reactors.

ERRATUM

Erratum to the paper Exploiting the Bjerknes force in bubble column reactors by Juerg Ellenberger, Jasper M. van Baten and Rajamani Krishna, Chemical Engineering Science 60 (2005) 5962-5970. Click here.