Thin film flow between fibers: inertial sheets and liquid bridge patterns

Thin film flows down fibers have been widely studied due to their complex behavior and practical applications. In contrast, flow between fibers has received less attention despite its relevance to closely packed fiber arrays where narrow inter-fiber spacings are optimal for mass transfer processes. Here, we perform experiments on liquid flow between fibers for a range of liquid properties, fiber diameters D_f, flow rates Q, and inter-fiber spacings w. We observe two possible behaviors: 1) periodic liquid bridges and 2) a uniform column (or sheet). Liquid bridge patterns appear for low flow rates Q, large D_f, and large w and result in a series of isolated bridges with equal speed and separation length, forming a unique “liquid ladder” pattern. Alternatively, for flows with higher Q, smaller D_f, and smaller w, a thin liquid column can form that spans the length of the fibers. Liquid columns can span significant widths () for flow rates common in typical bead-on-fiber applications—a result of the flow replenishing the thin column. Furthermore, we show how liquid properties and fiber diameter D_f can be optimized to sustain a liquid column at minimal flow rate Q. We conclude by illustrating the unique patterns and shapes these flows form with curved fibers.