LARGE BUBBLES IN DOWNWARD 2-PHASE FLOW

The formation of large standing bubbles in the sparged downcomers of U -tube fermenters is undesirable. The behaviour of such bubbles has bee n investigated experimentally in a verticle pipe of diameter 5.7 cm. T he rate of entrainment of air from the bubble base by the liquid falli ng around it is found to determine the length of the bubble. If air is injected. through holes placed around a diameter of the downcomer wal l, as opposed to through a sparger placed horizontally across a diamet er or vertically along the downcomer centre line, the bubble length is reduced. A decrease in the surface tension of the liquid being used a lso decreases the length of the bubble. An increase in viscosity incre ases the length of a bubble formed. Power law fluids also increase the length of bubble produced