Abstract
Two principal areas of study were selected in this work: 1) The measurement of the local area presented by the gas-liquid interface of the falling film. 2) The extension of present knowledge in order to explain the presence and form of the wave motion on the surface of the film. The fulfilment of the former of these objectives commenced with a fundamental study of the area of random surfaces, and an experimental method of measuring this area was systematically developed. The method was based on the photography of a dyed falling film by transmitted light. The resulting specially prepared negatives, for a wide range of flow conditions were scanned by a microdensitometer, and the output was converted into digital form suitable for processing by an Elliot 503 computer. The computer was used to calculate the surface area of the film over which mass and heat transfer occur, as a function of the flow rate and distance below the distributor, during cocurrent, countercurrent, and zero air velocity conditions. The results were compared with the predictions of the Portalski equation which has generally been used outside its range of validity, and it was shown that such general use produces gross errors. In the second part of this work, a unit was. designed and built which was able to sample the instantaneous film thickness and to punch the data onto 8 channel computer tape. A method of constructing the original wave profiles from the statistical information thereby obtained is described. The results of, this work also enabled measurement of 1) the mean film thickness at varying distances below the distributor, 2) the residual film thickness and maximum wave peak displacement from the mean film thickness at varying distances below the distributor, 3) the ratio of the mean positive wave slopes to mean negative wave slopes at varying distances below the distributor. This information lead to a modified view of the flow of films based on an extension theory. A study of the developing wave motion was also carried out, based on the clear wave profiles produced in the photographic part of this work.