A Study of Droplet Spectra in Fogs

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  • 1 Advanced Technology Laboratories, Inc., Westbury, N. Y. 11590
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Abstract

The possible phenomena leading to the observed droplet spectral distributions in stationary fogs are discussed and the relationships between these distributions and the expected conditions of supersaturation and turbulence are developed. It is postulated that condensation nuclei enter the fog layer from above and are activated by the prevailing conditions of supersaturation existing within the layer. The droplets grow in the supersaturated environment and fall under the influence of gravity. The description of such a system in which particles of all sizes are present requires a statistical formulation, as is provided by the spray equation. Solutions of the spray equation are shown to be unrealistic when droplet diffusion is disregarded. A spray equation which incorporates droplet diffusion is then developed together with the requisite boundary and initial conditions and it is shown to provide realistic quantitative estimates of droplet size and number density.

Abstract

The possible phenomena leading to the observed droplet spectral distributions in stationary fogs are discussed and the relationships between these distributions and the expected conditions of supersaturation and turbulence are developed. It is postulated that condensation nuclei enter the fog layer from above and are activated by the prevailing conditions of supersaturation existing within the layer. The droplets grow in the supersaturated environment and fall under the influence of gravity. The description of such a system in which particles of all sizes are present requires a statistical formulation, as is provided by the spray equation. Solutions of the spray equation are shown to be unrealistic when droplet diffusion is disregarded. A spray equation which incorporates droplet diffusion is then developed together with the requisite boundary and initial conditions and it is shown to provide realistic quantitative estimates of droplet size and number density.

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