Collection and coalescence efficiencies for accretion

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Abstract
The coalescence efficiency for accretion was assumed to be governed by a collisional Weber number. This concept was used with the aid of theoretical collision efficiences to organize collection efficiency data from several sources into a unified set. The resulting collection efficiencies show a maximum of 71% for a collector drop of 115 μm and a cloud droplet of 12‐μm radius. Accretion calculations were made for a monodisperse cloud to illustrate the effects of cloud droplet sizes and collection efficiencies on drop growth. The time average collection efficiency for growth from 50 to 500 μm by accretion of 30‐μm droplets is reduced by 50% when compared to the time average collision efficiency. A maximum of 65% in the time average collection efficiency occurs for accretion of 10‐μm droplets. The contribution to accretion by cloud droplets smaller than 5 μm appears to be negligible.