Abstract

Multiphase plumes may result from a concentrated and continuous release of buoyancy in the form of small bubbles, droplets or particles. Here, we present an experimental and theoretical study of the behaviour of such expanding plumes. Laboratory measurements using Particle Image Velocimetry are combined with scaling and numerical results. It is found that mixing and dispersal in reactive plumes is fundamentally different to that found in plumes without reaction; this difference in behaviour is caused by buoyancy-induced changes in turbulence and fluid flowing in the opposite direction to that of the bulk plume flow. Cases are observed which result in collapsing or imploding plumes; we use our model to propose a criterion which predicts this occurrence, and verify it experimentally for a wide range of reaction rates and release conditions. Implications of our results for deep ocean CO2 plumes, volcanic eruptions and buoyancy-driven cloud formations are explored.