| Structured packings are made of a variety of materials such as ceramics, metal, and plastics, and shaped to an assortment of macro- and micro-structure. Macro-structure, usually in the form of corrugations, allows for good liquid-vapor contact with low overall pressure drop. Micro-structure in the way of surface treatment, metal gauze, and surface indentations, helps to increase the stability of the liquid film by preventing breakups and dry-patch. The flow of a liquid film over micro-structure of structured packings was studied by the combined approach of theory, experiments and numerical simulations. A long-wave expansion was used to derive a free surface model of two dimensional film flow. Three parameters, Nusselt film thickness to solid characteristic length ratio, Reynolds number and Capillary number, were found to be necessary to characterize accurately liquid film flow. A series of experiments were performed in order to characterize the behavior of the liquid film over complex surfaces. Measurements were made of film thickness, free surface velocities and streamline patterns along the surface contours. The free surface profile was always found to have the same period as the wavy solid. Free surface velocities have a phase shift compared to the wavy surface. Results were obtained for many different surface geometries. A numerical method was used to solve the third order, nonlinear ordinary differential equation with a periodic boundary condition from the experiments. The simulation results showed that our model can be used to predict the behavior of liquid film flows over two-dimensional complex solid surfaces. It is clear from our experiments that micro-structure of structured packings can increase stability of non-wetting liquids on packing surfaces. Effective area and holdup of structured packing are also affected by micro-structure. |
