Snowing criteria for cold traps

Criteria for the onset of fog or snow formation are established for uniform temperature water cold traps. Heterogeneous nucleation is found to begin at partial pressures of about 10 times the wall partial pressure, and homogeneous nucleation is found to begin at partial pressures on the order of 1000 times the wall partial pressure. An analogy between dimensionless temperature profiles reduces the search of local supersaturation parameter values to one space-like variable, and critical inlet water vapor partial pressures are presented as functions of surface temperature and gas inlet temperature.