Effect of natural convection on growth velocity and morphology of dendritic ice crystals

Quantitative measurements were made of the growth rate and dimensions of ice crystals growing in pure water unencumbered by container walls. The structures which were photographed changed sequentially from disks, to perturbed disks, to disk-dendrites, to partially developed dendrites, and finally to fully developed dendrites. Therefore, the morphology of ice crystals depends on the subcooling and time elapsed from the start of free growth. Fully developed dendrites were shown by double exposure photographs to grow in a shape preserving manner with the tip propagating at constant velocity. The shape of a fully developed ice dendrite was determined by photographing it from its various planes. An elliptic paraboloid with an aspect ratio 30<R₂/R₁<100 most closely approximates the shape in the vicinity of the tip region. The growth velocity of the tip is invariant with time, but side branches constantly adjust their growth directions. Natural convection was found to affect the growth velocity, the overall morphology, and morphological stability.