Bubble evolution in a stirred volume of liquid closed to mass transport

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Abstract
The rate of bubble evolution, and hence the rate of mass transport across a curved liquid-gas interface, has been examined both theoretically and experimentally. A single gas bubble is contained in approximately 1.3 cc of a liquid-gas solution that is closed to mass transport. This condition provides the mechanism by which the gas bubble may be placed initially in a state of stable equilibrium, and thus allow an accurate determination of the system parameters. A stirred liquid condition is achieved by rotating a micro-stir bar within the volume, and the resultant flow pattern is characterized with laser-doppler anemometry. Through an experimental examination on the complete dissolution of nitrogen-gas bubbles in water, the mechanism of mass transport is shown to be consistent with a model comprised of two processes: (1) the primary and rate-limiting process is modelled by the diffusion of gas through an unstirred liquid-boundary layer whose thickness varies with bubble radius; and (2) a second-order limitation is due to the nonequilibrium transport of gas across the phase boundary as predicted by a statistical rate theory expression. The theoretical model is then applied to predict the evolution of a bubble towards a state of stable equilibrium.

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