Fluidization of snow

Abstract

Fluidization experiments were performed on snow of various particle diameters and types by placing in a transparent tube through which was passed an upward air flow at various velocities and temperatures. Stable fluidization could be generated only for snow of relatively large particles of simple shape at lower temperatures. Newly fallen snow of dendritic crystals and snow of particle diameters less than about 0.3 mm could not be fluidized uniformly even at temperatures as low as −30°C. The onset of fluidization had to be initiated by an outside mechanical shock unless the temperature was very low or the snow particles large and spherical. This implies that some nuclei of fluidization must be formed within limited areas of snow before the whole of the snow is fluidized. The minimum air velocity to cause fluidization increased as the square of particle diameter, in accordance with the Kozeny-Carman equation. The overall behavior of fluidized snow is very similar to that of a liquid: the pressure within the fluidized snow equals the weight of snow in suspension above a unit area. Buoyancy was found to exist, and the volume increased linearly with air velocity, just as the volume expansion of a liquid with temperature. It was also found that the momentum and energy transfer in fluidized snow was very effective as in liquids: the apparent viscosity of fluidized snow, of particle diameter 1.25 mm, was roughly equal to that of water at 25°C and the heat transfer was three or four times larger than that in an air flow containing no ice particles.