Free convection about a rectangular prismatic crystal growing from a solution

Abstract

Sodium chlorate crystals growing from unstirred aqueous solutions were observed by schlieren techniques. Growth rate data were best correlated by Sh = 0.48 Ra 0.25 with finite interface kinetics and a characteristic length L equal to the crystal height plus the inverse reciprocal sum of the horizontal dimensions. The growth rate was slightly higher when the plume was laminar than when it was irregular. The horizontal growth rate was greater than the vertical growth rate, with the ratio tending to decrease with increasing plume instability. The threshold Grashof number for plume instability was greatly decreased with decreasing height for crystals with the same horizontal dimensions. The frequency of eddy emission was proportional to L −2 Ra 0.8. The velocity of the eddies approached a constant value with increasing distance above the crystal surface, the terminal value being roughly proportional to Ra 1 2 /L .