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).