Modelling on space-domain surface waves of vertical low-Re falling film and the enhancement on mass transfer in halide-solution/air absorption

Vertical falling film with low Reynolds number (Re) is widely used, but the influence of surface waves on mass transfer is still unclear. This paper theoretically described the wave structure along the flow direction, and evaluating the enhancement on mass transfer during halide-solution/air absorption. The effects of flow viscosity, surface tension gradient, liquid/air convective heat transfer, film thickness and flow distance are considered. Model validation were performed by comparing with the data from literatures and our experiments. For practical use, empirical correlations of wavelength and amplitude are provided, using Re, Marangoni and Nusselt numbers as variables. Wavelength increases proportionally with liquid Re, and amplitude mainly increases with the flow distance. When Re increases from 20 to 60, wave amplitude and wavelength increase by 10% and 40%. The enhancement effect is determined by the wavelength and frequency, and is more obvious under conditions of large liquid concentration or small liquid Re.