Time-dependent droplet detachment behaviour from wettability-engineered fibers during fog harvesting

Abstract

Water collection from natural and industrial fogs has recently been viewed as a viable freshwater source. An interesting outgrowth of the relevant research as focused on arresting of the drift losses (un-evaporated and re-condensed water droplets present in the exhaust plume from industrial cooling towers. Such exploits in fog collection have implemented metal and polyester meshes as fog water collectors (FWC). Fog droplets impinge and deposit on mesh fibers. They coalesce with previously deposited liquid to evolve as larger drops before detaching from the fibers under their own weight, an event largely dependent on the mesh fiber wettability, diameter and its arrangement relative to the fog flow. To better estimate drainage and hence collection from these fibers, the study, focuses on droplet detachment from differently wetted horizontally positioned cylindrical fibers of various diameters, placed orthogonally in the path of an oncoming fog. Droplet detachment volume is found to increase with fiber diameter and fiber surface wettability. Interestingly, in a typical fogging condition, the detachment volume is also found to exhibit a time-dependent behaviour, altering the droplet detachment criteria otherwise predicted from emulation. Our current study sheds light on this unexplored phenomenon.