EXPERIMENTAL-STUDY OF DENDRITIC GROWTH WITH AN EXTERNAL FLOW

In this paper, we report new experimental results on dendritic growth in the presence of an imposed flow; we also summarise the theoretical approaches to the problem, and discuss previous results obtained on the subject. In a first part, we describe the available theoretical descriptions of the flow around a paraboloid of revolution, performed under various approximations: potential, uniform or Oseen flow. Each of these leads to an expression for the temperature or concentration field, and relates the supercooling or supersaturation to the Peclet number of the dendrite. Several predictions on the selected growth constant are also presented. The experiments themselves are performed on the growth of ammonium bromide with an external flow; we measure the concentration field around the crystal during the growth process. We also characterise the velocity field. We find supersaturations in good agreement with predictions based on potential or uniform flows. The growth constant is also determined in this system. We finally suggest that the available experimental results on dendritic growth in the presence of a flow can be interpreted within a unique theoretical framework.