The mechanics of bubble formation

Abstract

Abstract The size of gas bubble produced from an open‐ended tube immersed in a liquid can be derived by equating surface tension and buoyancy forces. The equations do not apply, however, when the gas flow is large as in many industrial fermentations, and porous elements are therefore often used to provide many orifices and a low gas‐flow through each. Even this technique fails if a mycelial growth is formed during the fermentation because the bubbles coalesce in the fermenter. Mechanical agitation was examined by the author by measuring gas‐to‐liquid transfer rates using paper pulp to imitate the mycelium, since this was found to interfere chemically with the reaction. Without agitation, the paper pulp reduced the transfer rate by a factor of twenty. With simple paddle agitation in conjunction with a sparge ring, the effect of pulp was reduced to a factor of seven but with a high‐speed agitator used with an open tube gas inlet, the factor was reduced to two.