Fluidised beds

When gas is forced upwards through the porous base of a particulate bed (e.g. sand, glass beads) the particles "fluidise" when the gas velocity exceeds a critical value. Such fluidisation typically results in the formation of kidney-shaped gas "bubbles" which rise through the bed. But the gas is continuously entering and leaving these bubbles, so they are quite unlike bubbles rising in champagne. The prediction of bubble shape is an interesting free boundary problem (see entry on free boundary problems). Bubble dynamics is especially important when the bubbles nucleate at the base of a stationary obstacle in the bed. This situation is relevant to medical fluidized beds, where the obstacle is the patient.

People working in this area within OCIAM are

• Dr John Ockendon