Steady-state mushy layers: experiments and theory

A new facility has been developed to investigate the directional solidification of transparent aqueous solutions forming mushy layers in a quasi-two-dimensional system. Experiments have been conducted on NaCl–H 2 O solutions by translating a Hele-Shaw cell at prescribed rates between fixed heat exchangers providing a temperature gradient of approximately 1°C mm −1 . The mush–liquid interface remained planar at all freezing velocities larger than 8 μm s −1 , while steepling occurred at lower velocities. No significant undercooling of the mush–liquid interface was detected at freezing velocities up to 12 μm s −1 . Mathematical predictions of the steady-state temperature profile and mushy-layer thickness as functions of freezing rate are in excellent agreement with experimental measurements.