Ice Nucleation in Clouds by Liquefied Propane Spray

James R. Hicks U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, N.H. 03755

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Gabor Vali Dept. of Atmospheric Resources, University of Wyoming, Laramie 82070

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Abstract

The inducement of cloud glaciation by cooling with evaporating droplets of liquefied propane was investigated in laboratory experiments and in field tests. The efficiency of ice crystal production was shown to be near 1012 crystals per gram of propane for temperatures colder than −2C; 1010 crystals were produced at supercoolings of few tenths of a degree. Observed variations of the efficiency with changes in cloud liquid water content and in wind velocity indicate that the rate of vapor supply to the cooled plume is the limiting factor in ice crystal production. Ice crystal habits and growth rates were also examined and inferences could be drawn regarding the nucleation mechanisms of the ice crystals in the cooled zone. The results indicate that liquefied propane is an effective, easy-to-use, and safe nucleating agent. The experiments helped delineate the factors which are to be considered in designing practical applications of the technique.

Abstract

The inducement of cloud glaciation by cooling with evaporating droplets of liquefied propane was investigated in laboratory experiments and in field tests. The efficiency of ice crystal production was shown to be near 1012 crystals per gram of propane for temperatures colder than −2C; 1010 crystals were produced at supercoolings of few tenths of a degree. Observed variations of the efficiency with changes in cloud liquid water content and in wind velocity indicate that the rate of vapor supply to the cooled plume is the limiting factor in ice crystal production. Ice crystal habits and growth rates were also examined and inferences could be drawn regarding the nucleation mechanisms of the ice crystals in the cooled zone. The results indicate that liquefied propane is an effective, easy-to-use, and safe nucleating agent. The experiments helped delineate the factors which are to be considered in designing practical applications of the technique.

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