The gravitational effect on the geometric profiles of droplets on horizontal fibers

Understanding the growth or reduction of droplets on fibers during condensation or evaporation is fundamental to many applications of fibrous materials including fiber filters, water harvesting, and functional clothing. However, the effect of gravity on the geometry of droplets is still unclear. In this work, the shape change of droplets hanging from a horizontally cylindrical fiber was investigated experimentally. It was found that the relative size (as measured by the characteristic maximum height) of the NRS droplet relative to the fiber radius is inversely related to the fiber radius, meaning that (1) finer fibers can hold relatively large droplets and are therefore preferred for filtration and functional clothing, (2) the profile of the contact line between the NRS droplet and the fiber, which is crucial to understanding the gravitational effect on the shape of the droplet on the fiber, is most likely to be a spiral line in 3-D space.