Influence of wetting conditions on bubble formation at orifice in an inviscid liquid - Mechanism of bubble evolution

This paper presents some aspects of bubble formation under extremely low air flow rates (from 1 to 5 cm(3)/min) through a single orifice (from 0.4 to 1.0 mm in diameter) submerged in water and in a water-soap solution. Experiments were carried out at a wide range of contact angles (15degrees less than or equal to theta(0) less than or equal to 110degrees). The mechanism distinctive for bubble formation was clarified over the evolution of force balance conditions and interface equilibrium occurred periodically at the critical points, which take place at the transitions between meaningful stages called the nucleation period, under critical growth period, critical growth period and necking period. Influence of operating variables on bubble formation under various wetting conditions at the orifice plate were revealed and discussed. As a rough guide to practical purposes the empirical correlation between the volume of the bubble formed at the end of its critical growth V-b in cm(3), and flow rate Q in cm(3)/s, multiplied by the maximum diameter of bubble periphery at the base D in cm, was found for inviscid liquids to be V-b = 0.5DQ(0.4). To express the correlation between the bubble volume V and flow rate Q in general form, the equation V = K0Dn(Q(2)g - 1)(m), was developed assuming indices m and n to be varied, and 0 less than or equal to n less than or equal to 1 while 3/5 greater than or equal to m greater than or equal to 1/5, referring to certain ranges of gas flows. (C) 2003 Elsevier B.V. All rights reserved.