Optimizing Fog Collector Performance through fog Droplet-Size Distribution

Abstract

Fog harvesting is a sustainable approach for potable-water supply in fog-prone coastal and elevated regions, but its fog-capture efficiency (ηcap) depends strongly on droplet-size distribution, mesh geometry, and wind speed. This study uses Eulerian-Lagrangian simulations to examine the effects of fog-mesh wire diameter (df = 0.2-1.0 mm), shade coefficient (SC = 0.3-0.7), and freestream velocity (U = 2-5 m s-1) on the capture of droplets ranging from 2 to 40 μm. To generalize the findings, droplet behavior is classified by Stokes number into three regimes: low-St droplets that follow streamlines and show weak capture, intermediate-St droplets that are highly sensitive to mesh geometry and aerodynamics, and high-St droplets dominated by inertial impaction. Large droplets generally show the highest instantaneous capture, while intermediate droplets govern the sensitivity to SC, df, and U. Fine to intermediate wires (df = 0.2-0.6 mm) with SC close to 0.6 provide the best balance between geometric interception and aerodynamic permeability. Increasing velocity enhances impaction, although wake formation and flow diversion limit further gains. The results are interpreted using a nondimensional framework based on Stokes number, mesh-fiber Reynolds number, pressure-drop coefficient, and shade coefficient. The reported ηcap values represent dry-mesh, instantaneous capture efficiencies, as wetting, liquid growth, pore clogging, and droplet re-entrainment are excluded. Overall, the study identifies a desirable design window with intermediate Stokes numbers, moderate-to-high permeability, and SC = 0.6.