Abstract
Two classes of random waves exist on falling films at flow rates of practical interest; large waves which carry the bulk of the liquid and small waves which cover the substrate. In this paper statistics of the large waves are presented and compared with existing theory. These waves are bimodal in character at ReL > 700. The form drag of the large waves is shown to contribute negligibly the observed pressure drop in the gas phase. It is thus concluded that the small wave structure controls the fluid resistance and transfer processes in the gas while the large waves control these same processes in the liquid film.

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