Quasi-equilibrium bubble formation during top-submerged gas injection

Abstract

The size of a bubble formed by top-submerged gas injection at very low air flow rates into water was studied and shown not to be related to the size of an equilibrium bubble at 180° contact with the lance. The growth of the bubble was initially governed by the inner lance diameter but after the maximum bubble pressure had been exceeded, the bubble size was governed by intermediate diameters between the inner and outer lance diameters. The bubble became unstable when the water–air–solid contact line moved up the outside of the lance and detachment followed quickly. For the formation of argon bubbles in pig iron, the bubble volume was determined by the outer lance diameter when the contact angle between the bubble and lance surface is at 90°. Application of the results to the maximum bubble pressure method for determining surface tension of non-wetting liquids showed that for large-diameter lances, two pressure peaks can be obtained if the chamber volume behind the lance tip is small. The first peak is related to the maximum equilibrium bubble at the inner lance diameter and the second peak is related to the outer lance diameter, both peaks can be used to determine the surface tension.