Statistical characteristics of thin, wavy films: Part II. Studies of the substrate and its wave structure

Waves on falling liquid film display certain random features. At least two classes of such random waves are shown to exist; large waves which carry the bulk of the fluid and small waves which cover a substrate film that exists between large waves. It is shown that the statistics of the substrate thicknes and its wave structure can be extracted from measurements of the variation of film thickness with time. A theory is presented for calculating the mean substrate thickness and the substrate flow rate. The statistics of the wave structure is presented and compared with existing theory. The importance of the substrate in controlling transfer processes is demonstrated.