The cycle of bubble production from a gas cavity in a supersaturated solution

Bubble nucleation, classified according to the review by Jones et al. (Adv. Colloid Interface Sci. 80 (1999) 27-50) as type IV non-classical, was exam ined in this study. Trains of bubbles were produced in carbonated water sol utions at low levels of supersaturation, typically less than about 2, at sp ecific sites on the surface of the vessel in contact with the liquid. Close r examination at a given site revealed a cycle of bubble formation, growth and detachment, defined by the growth time, t(g), required for the bubble t o grow to its detachment diameter, and the nucleation time, t(n), required for a new bubble to appear following detachment. A relationship, representi ng the cycle of bubble production, was obtained by combining the bubble gro wth time, calculated using Scriven's model (Scriven, Chem. Eng. Sci. 10(1/2 ) (1959) 1-13), with the bubble nucleation time. That is, 1/t(g) = N/t(n) + 1/t(g)* where N is a dimensionless number characterising the bubble nucleation time , and t(g)* is the growth time of the last possible bubble. Experiments con ducted at a number of sites, and at different temperatures, produced result s consistent with the above relationship. Most of the experiments were cond ucted with the contact angle at 65 degrees, and these generally resulted in a bubble detachment diameter of about 600 mu m, and a value of N similar t o 0.3. It was concluded that the nucleation time was dependent on the diame ter of the detaching bubble. This dependence was explained by considering t he volume of liquid, partially depleted of carbon dioxide, in the boundary layer of the bubble. Some of this partially depleted liquid should leave wi th the departing bubble, and the rest should remain above the gas cavity, t hus slowing down the rate of bubble growth in the cavity. A consideration o f the critical condition for bubble detachment indicated that the bubble re mained rooted at the cavity mouth during its growth, It was shown, using th e growth time of the last possible bubble, that the critical radius of curv ature of the meniscus in the cavity was about 3.3 mu m at 16 degrees C. The radius was also found to increase significantly with temperature, suggesti ng that the position of the meniscus inside the cavity moved when the syste m temperature was changed, and that the cavity was essentially conical. (C) 1999 Elsevier Science B.V. All rights reserved.