Cold Model Experiments on the Dynamic Behavior of Bubbles Rising in Highly Viscous Liquid

Abstract

Water and aqueous glycerol solutions were used to examine the effects of the viscosity of liquids on the bubble dispersion in a vertical bubbling jet. Bubble frequency, gas holdup, and bubble rising velocity were measured with two kinds of electro-resistivity probes. Observation of bubbles was made by means of a Schlieren method and a high speed video camera, and mean bubble diameter and bubble rising velocity were determined. With increasing the viscosity, bubbles became to flock together around the centerline of the vessel and to rise after the foregoing bubble. This phenomenon was termed "channeling of bubbles". Variations in the radial distributions of gas holdup with respect to the axial distance from the nozzle were classified into four types as functions of gas flow rate and the viscosity of liquid. The limits between the four types were determined.Correlations for gas holdup proposed so far for air-water bubbling jet were applicable to bubbling jet formed in aqueous glycerol solutions with viscosity up to about 20 mPa·s. In other words, if the bubble Reynolds number is greater than about 400 and hence the flow behind the bubble is turbulent, the correlations for gas holdup are valid.