Structure of air-water bubbly flow in a vertical pipe—II. Void fraction, bubble velocity and bubble size distribution

Abstract

In a companion paper (Liu and Bankoff, Int. J. Heat Mass Transfer 36, 1049–1060 (1993)) measurements were presented of liquid-phase velocity and turbulence properties in air-water bubbly upflow under a range of flow conditions. In this paper measurements of the radial profiles of void fraction, bubble velocity and bubbly size, using a miniature dual-sensor resistivity probe, under the same conditions are presented. A new digital processing method, based on threshold combinations of level and slope, was developed for phase identification by the resistivity probe. Local mean bubble sizes ranged from 2 to 4 mm. The profiles of void fraction, bubble frequency and bubble size are found to show distinct peaks near the wall, becoming flat at the core. Experimental findings and parametric trends based on the effects of superficial velocities of both phases are summarized and discussed.