Droplets on angled fibers: A surprising change to the Rayleigh-Plateau instability

The Rayleigh-Plateau (RP) instability on a thin viscous film flowing down on a fiber (aka droplets on a wire) is a complex phenomenon studied mostly on vertical wires. Here, we reexamine the RP instability by gradually varying the angle of the fiber and the position of the fiber within the nozzle. We observe that the different regime instabilities can stably occur by varying the angle when the flow rate is held constant. Further, for non-angled wires, the same can occur by altering the position of the fiber within the nozzle. The wavelength and velocity of the RP regime are highly sensitive to the angle and position of the fiber. Interestingly, the effect of the position of the fiber within the nozzle becomes negligible as the inclination angle is increased. One important finding is that the effective surface area of the film increases by up to 50% when the angle of the fiber is increased which could be useful in industrial applications where it would allow for more efficient heat or mass transfer.