Film drop production as a function of bubble size

Abstract

Film drops from air bubbles bursting in seawater and in a 3% solution of sodium chloride in distilled water were counted with a condensation nucleus counter. Bubbles of known size were released from a capillary tip at depths from 1 to 20 cm beneath the surface of the water. Film drop production did not vary significantly with depth in seawater, but it decreased by about 3 times as the depth was increased to 10 cm in the sodium chloride solution. Drop production, however, varied markedly with bubble size. Over the range of bubble sizes studied (from about 1 to over 6 mm diameter), by far the most film drops were produced in the narrow size range of about 2–2.5 mm. About 75 film drops per bubble were found for the seawater case, and about 150 for the sodium chloride solution. On either side of this peak (bubbles of 1.5 and 2.8 mm), film drop production was less than 5 per bubble. The cause of this strong peak in drop production is not known, but it appears that bubbles of 2 to 2.5 mm diameter must play a major role in the production of film drops at sea.