  Fog harvesting relies on intercepting atmospheric or industrial fog by
placing a porous obstacle, e.g., a mesh and collecting the deposited water. In
the face of global water scarcity, such fog harvesting has emerged as a viable
alternative source of potable water. Typical fog harvesting meshes suffer from
poor collection efficiency due to aerodynamic bypassing of the oncoming fog
stream and poor collection of the deposited water from the mesh. One pestering
challenge in this context is the frequent clogging up of mesh pores by the
deposited fog water, which not only yields low drainage efficiency but also
generates high aerodynamic resistance to the oncoming fog stream, thereby
negatively impacting the fog collection efficiency. Minimizing the clogging is
possible by rendering the mesh fiber superhydrophobic, but that entails other
detrimental effects like premature dripping and flow-induced re-entrainment of
water droplets into the fog stream from the mesh fiber. Herein, we improvise on
the traditional interweaved metal mesh designs by defining critical parameters,
viz., mesh pitch, shade coefficient, and fiber wettability, and deduce their
optimal values from numerically and experimentally observed morphology of
collected fog-water droplets under various operating scenarios. We extend our
investigations over a varying range of mesh-wettability, including
superhydrophilic and hydrophobic fibers, and go on to find optimal shade
coefficients which would theoretically render clog-proof fog harvesting meshes.
The aerodynamic, deposition, and overall collection efficiencies are
characterized. Hydrophobic meshes with square pores, having fiber diameters
smaller than the capillary length scale of water, and an optimal shade
coefficient, are found to be the most effective design of such clog-proof
meshes.
