Bubble Formation in Dense Fluidised Beds

Abstract

A linear analysis of the stability of the two fluid model equations for a dense gas fluidized bed is carried out for a generalized closure relation. The classical slug forming instability is confirmed, but a new instability, leading to the formation of streamwise channels, is also found when the particle pressure is allowed to depend on the slip velocity between phases. The outcome of these instabilities is then followed using a fully nonlinear numerical code. Slugs are unstable to a secondary corrugation, which is shown to result in the formation of gas bubbles in the bed. Whether or not these bubbles coalesce into larger elongated units is shown to depend on the presence or absence of the channelling instability.