Spontaneous Droplet Nucleation in Clean, Saturated Moist Air at Atmospheric Pressure
Final rept. Jan 79-Sep 82,
CHEMICAL RESEARCH DEVELOPMENT AND ENGINEERING CENTER ABERDEEN PROVING GROUND MD
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Steaming droplet formation above the surface of liquid water that is being heated can first be observed at 50 C under normal atmospheric conditions. The droplets have been presumed by previous observers to form on condensation nuclei that are always present due to impurities in atmospheric air. But simple experiments, reported here, show that droplet nucleation apparently can occur spontaneously with warming, beginning at about 50 C, even in purified saturated air at atmospheric pressure that is free of nuclei other than water clusters. The observations suggest new ideas about structure in water vapor. A critical cluster size of about 45 molecules can explain observations over a wide range of temperatures and water vapor partial pressures.
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