Study on shrinkage characteristics of heated falling liquid films

A liquid film, flowing down along a heated solid surface may be substantially influenced by the Marangoni effect, which arises from the existence of a surface tension gradient that is induced by the variations of surface temperature in the transverse direction of the film, causing appreciable contraction of the film. In this work, the governing equations for laminar falling liquid films over a heated plate with constant surface temperature were solved and the surface temperature profile of the film was obtained. By considering the surface tension gradient and shrinkage characteristics in the brim of the heated film, a shrinkage model that gives the film interfacial area was derived based on the experimental infrared images. A comparison of the model with experimental data shows that the model can satisfactorily describe the flow characteristics of falling heated films. The model is expected to be useful for the design and operation of falling film equipments. (c) 2005 American Institute of Chemical Engineers.