Bubble formation at large (25.4 mm < D < 101.6 mm) submerged orifices with high
(5 litres /sec < Q < 50 litres /sec) gas flowrates has been investigated experimentally and computationally. Bubble behaviour for this range of conditions differs markedly from the large body of literature available on small bubbles. This is due to the increasing importance of buoyancy and inertial forces and the decreasing importance of viscous and surface tension forces as bubble size increases. The experimental portion of the work concentrated on a qualitative assessment of the flow and resulted in a flow regime map of bubble behaviour which consists of several distinct types of behaviour with varying degrees of bubble to bubble interaction. The boundaries between these regimes have been quantified in terms of a type of Froude number, F = Q 1? gD 5. The minimum F for which bubbles form at the pipe exit was found to be approximately one. A transition region to pairing exists for 1 < F < 2 and the pairing regime exists for 2 < F < 24. A transition to continuous interaction occurs for 24 < F < 50. Continuous interaction is present for F > 50. For F > 18 all backflooding is eliminated. The computational study was based on a finite difference, transient, twodimensional solution of the liquid velocity field and employed an Eulerian description of the gas-liquid interface based on a volume fraction specification. The model was successful in predicting bubble growth up to the point of departure. The model was also applied to the release of single cylindrical and spherical bubbles into quiescent liquids. The initial acceleration of such bubbles, g and 2g respectively, was properly predicted. In the case of a cylindrical bubble, the transition to a cylindrical cap was accurately predicted as was the transition to a toroid for spherical bubbles.
Bibliography: p. 154-162.