A Measurement of the Efficiency for Collection between Cloud Drops

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Abstract
A chemical tracer technique was used to determine the collection efficiency of 81 µm radius drops failing at terminal velocity through a monodisperse cloud of 20 µm radius droplets. Electrical influences were minimized by controlling a charging electrode at the collector drop generator and by neutralizing the charge on the cloud droplets with an ion discharge device. The measured collection efficiency of 0.37 ± 0.05 was considerably lower than the accepted value of 0.82 based on the collision efficiency of rigid spheres. This discrepancy was attributed to a coalescence efficiency of 0.45 for water drops of these sizes. Abstract A chemical tracer technique was used to determine the collection efficiency of 81 µm radius drops failing at terminal velocity through a monodisperse cloud of 20 µm radius droplets. Electrical influences were minimized by controlling a charging electrode at the collector drop generator and by neutralizing the charge on the cloud droplets with an ion discharge device. The measured collection efficiency of 0.37 ± 0.05 was considerably lower than the accepted value of 0.82 based on the collision efficiency of rigid spheres. This discrepancy was attributed to a coalescence efficiency of 0.45 for water drops of these sizes.

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