Volume change effect on the salt-finger stability of directionally solidifying ammonium chloride solution

Abstract

The effect of the volume change due to phase transformation on the stability of salt-finger convection of directionally solidifying NH 4Cl aqueous solution cooling from below is investigated. The basic flow, induced by the volume change, not only changes the morphology and the depth of the dendritic mushy layer, but also influences the stability of salt-finger convection. A new mathematical model is proposed, which differs from the previous one mainly on the dynamical condition at the melt/mush interface. This difference not only leads to a less stable state, but can also be crucial to the dynamical behavior of the oscillatory instability mode since the convection cells of this mode are coupled viscously through the interface. In the discussion, special emphasis is placed on the volume change effect on the instability mode competition, which may be influential to the stability characteristics of the subsequent plume convection.