A Numerical Study on Liquid Rope Coiling of a Viscous Non-Newtonian Fluid on a Static Solid Surface

Abstract Liquid rope coiling of viscous liquids (Newtonian as well as non-Newtonian) is a common phenomenon that is observed in many industrial applications. Coiling is caused by buckling instability in which liquid falling on a surface encounters compressive stress and thus becomes unstable to deformation by bending. The present work involves a numerical study of the liquid rope coiling of a non-Newtonian fluid on a static solid surface of varying wettability. The influence of the flow behavior index is also explored on the coiling appearance and characteristics. Different phenomena such as dripping, jetting, regular, irregular, and unstable coiling have been observed depending on the liquid type, fall height, nozzle diameter, and solid surface wettability. Dripping is caused by Rayleigh–Plateau instability, whereas jetting is dominated by inertial forces. Regular coiling is found to be viscous and gravity-dominated, whereas irregular coiling is caused by the combined effect of inertial, viscous, and gravity forces. Flow regimes are not affected by a change in the wettability of the solid surface but depend on the flow behavior index. On the contrary, the wettability influences the characteristics of both regular and irregular coils.