Rivulet Flow In Vertical Parallel-Wall Channel

Abstract

In comparison with studies of rivulet flow over external surfaces, rivulet flow confined by two surfaces has received almost no attention. Fully-developed rivulet flow in vertical parallel-wall channels was characterized, both experimentally and analytically for flows intermediate between a lower flow limit of drop flow and an upper limit where the rivulets meander. Although this regime is the most simple rivulet flow regime, it does not appear to have been previously investigated in detail. Experiments were performed that measured rivulet widths for aperture spacing ranging from 0.152 mm to 0.914 mm. The results were compared with a simple steadystate analytical model for laminar flow. The model divides the rivulet cross-section into an inner region, which is dominated by viscous and gravitational forces and where essentially all flow is assumed to occur, and an outer region, dominated by capillary forces, where the geometry is determined by the contact angle between the fluid and the wall. Calculations using the model provided excellent agreement with data for inner rivulet widths and good agreement with measurements of outer rivulet widths.