Rahul Sharma, Krishnaram Karippal Kallambally, Harikrishnan Anilakkad Raman
Multiscale Multiphysics Thermo-Fluids Lab, Department of Mechanical Engineering, Birla Institute of Technology and Science Pilani, Pilani Campus, Pilani333031, Rajasthan, India.
Langmuir. 2025 Apr 22;41(15):9664-9679. doi: 10.1021/acs.langmuir.4c04928. Epub 2025 Mar 10.
Environmental fog accumulation is a sustainable source of clean water, particularly in humid and arid regions. Many organisms have evolved passive microstructures to aid in fog droplet nucleation, accumulation, and transport. Researchers have developed various fog collectors, utilizing strategies like wire mesh, conical geometries, micronano texturing, and wettability modifications to enhance water collection. Despite conical geometry being the desirable configuration for accumulating water from atmospheric fog and condensation, a uniform framework must be established to estimate, quantify, and evaluate the water collection efficiency (WCE) of a conical geometry with distinct wettabilities at varying flow rates. In the present study, we determine the WCE of multiple cones ranging from 5° to 45° with four distinct wettabilities, namely, hydrophilic (HPH), mild hydrophobic (HPB), highly hydrophobic (HHPB), and superhydrophobic (SHPB) at three different fog flow velocities. The mechanism of fog deposition and water collection for different cases is thoroughly investigated with the help of onset time. Theoretical analysis of the aerodynamic and deposition efficiencies is conducted for the conical geometry pertaining to the actual fog conditions and shows a similar variation to that observed under experimental test conditions. The flow patterns over the conical substrate are visualized using high speed imaging. The WCE of smaller cone angles (5° and 10°) is observed to be higher than the larger cone angles for all the ranges of wettabilities. SHPB wettable cones have a shorter onset time due to minimal contact angle hysteresis and, hence, have the highest water collection rate among all wettabilities. The onset time of fog collection is largely influenced by the fog velocity and the wettability of the surface material. The current study presents the basis for developing an efficient fog collector employing conical arrays.
