CONVECTION IN MUSHY LAYERS

As a molten alloy or any multi-component liquid is cooled and solidifi ed the growing solid phase usually forms a porous matrix through which the residual liquid can flow. The reactive two-phase medium comprisin g the solid matrix and residual liquid is called a mushy layer. Buoyan cy forces, owing primarily to compositional depletion as one or more o f the components of the alloy are extracted to form the solid phase, c an drive convection in the layer. In this review, I present an account of various studies of buoyancy-driven convection in mushy layers, pay ing particular attention to the complex interactions between solidific ation and flow that lead to novel styles of convective behavior, inclu ding focusing of the flow to produce chimneys: narrow, vertical channe ls devoid of solid. I define an 'ideal' mushy layer and argue that chi mneys are an inevitable consequence of convection in ideal mushy layer s. The absence of chimneys in certain laboratory experiments is explai ned in terms of nonideal effects.