Influence of wetting conditions on bubble formation at orifice in an inviscid liquid. Transformation of bubble shape and size

This paper presents experimental results of the surface phenomena effect on bubble formation from a single orifice (1 mm diameter) submerged in water with air blowing at an extremely small flow rate (2 cm3 min−1). Bubble formation was studied for a wide range of contact angles (68°≤θ0≤110°) at liquid–orifice plate–gas interface using key geometrical parameters of a bubble: volume (V), surface area (S), radius at the tip (R0) and the dimension of bubble periphery at the base (D). The meaningful stages, termed (1) nucleation period, (2) under critical growth, (3) critical growth and (4) necking, were identified during bubble formation. It was determined that bubble volume essentially depends on wettability. It increases by more than half as wetting conditions worsen, e.g. equilibrium contact angle, θ0, increases from 68° to 110°. Bubble formation is found to be substantially controlled by hysteresis of contact angle.