Mass transfer from oscillating bubbles in bioreactors

In bioreactors, the purpose of aeration is to transfer oxygen from air bubb les into the liquid phase where the biological reactions occur. In some cas es, aeration is also used as a mixing tool. In all aeration devices there i s a continuous liquid phase and, generally, a dispersed gas phase in the fo rm of bubbles. The most common aeration devices are stirred tank reactors, bubble columns and sieve plate reactor-towers. Bubble shape, bubble volume, and associated liquid flow patterns are key aspects of bubble dynamics in sieve plates. The most prevalent bubble shapes are spherical, oscillating ( wobbling), ellipsoidal, spherical-cap, and skirted. Bubble volume and bubbl e shapes determine the surface to volume ratios, a very important parameter in determining overall mass transfer rates. Mass transfer in sieve plate r eactors takes place, predominantly, within the oscillating bubble regime. M ass transfer rates from oscillating bubbles can be orders of magnitude larg er than mass transfer rates from spherical bubbles. A fundamental correlati on for mass transfer from single, oscillating bubbles was developed based o n a solution of the mass transfer equations following the domain perturbati on technique first outlined by Joseph (1973) and the hydrodynamics results of Tsamopoulos and Brown (1983) The correlation derived here entirely from hydrodynamics and mass transfer concepts, introduces the effect of interfac ial tension in bubble mass transfer from fundamental concepts, has no adjus table parameters, and agrees very well with experimental data. (C) 1999 Els evier Science Ltd. All rights reserved.