Heat exchange with film boiling of nitrogen at the surface of solution droplets

A cryochemical method is considered for preparing nanomaterials, i.e., cryochemical synthesis of nanocrystalline powders, an important stage of which is rapid freezing of a solution droplet. A procedure is proposed for determining the heat transfer coefficient in a test unit during droplet solidification (in the period of forming a solid granule from a molten droplet or a melt with cryogenic liquid). It is noted that the central immersion angle for a droplet θ has a weak effect on heat transfer: within the limits from θ to π/2 to π the heat transfer coefficient does not change by more than 40%. It is also shown that there is no marked effect on the heat transfer coefficient of parameter β, i.e., the ratio of densities for the droplet and cooling agent (within the limits 1.24 ≤ β ≤ 2.0). © 2008 Springer Science+Business Media, Inc.