Fog Deposition and Accumulation on Smooth and Textured Hydrophobic Surfaces

Abstract

We investigated the deposition and accumulation of droplets on both smooth substrates and substrates textured with square pillars, which were tens of micrometers in size. After being coated with a hydrophobic monolayer, substrates were placed in an air flow with a sedimenting suspension of micrometer-sized water droplets (i.e., fog). We imaged the accumulation of water and measured the evolution of the mean drop size. On smooth substrates, the deposition process was qualitatively similar to condensation, but differences in length scale revealed a transient regime not reported in condensation experiments. Based on previous simulation results, we defined a time-scale characterizing the transition to steady-state behavior. On textured substrates, square pillars promoted spatial ordering of accumulated drops. Furthermore, texture regulated drop growth: first enhancing coalescence when the mean drop size was smaller than the pillar, and then inhibiting coalescence when drops were comparable to the pillar size. This inhibition led to a monodisperse drop regime, in which drop sizes varied by less than 5%. When these monodisperse drops grew sufficiently large, they coalesced and could either remain suspended on pillars (i.e., Cassie-Baxter state) or wet the substrate (i.e., Wenzel state).

Design of an environment controlled dew tracking setup to emphasize the role of the relative humidity on breath figures dynamics

“…For the theoretical second phase (phase II, Fig. 5), the measured exponent is 0.81±0.01 which is compatible with the reported values between 0.75 and 1.03 [15,27,29,30]. Phase III, the last phase described by theory, <R> is the stagnation.…”

Optimal Design of Permeable Fiber Network Structures for Fog Harvesting

“…3-8, 20, 21 Most work to date has focused on the mesh topology; the role of mesh surface wettability in fog harvesting has received little attention. 14,[20][21][22] In this study, we integrate a recent theoretical analysis 4 of the hydrodynamics near a woven mesh with physico-chemical constraints that address i) the issues of clogging of the mesh by coalesced droplets and ii) re-entrainment of collected droplets in the wind. We distill the resulting composite understanding of liquid drop impact on a fiber network structure into a design chart that predicts the overall collection efficiency for a given mesh geometry in a given 7 remains imbibed into the porous spraycoated texture after the mesh is completely withdrawn from the oil bath, resulting in a "SLIPS" surface with very low contact angle hysteresis.…”

Water harvesting from fog using building envelopes: part I

“…Work is currently being performed on the possible optimization of mesh yield through the application of lubricant coatings to the fibers, exploring the fact that hydrophobicity makes condensation phenomena more intense (Yu et al . ; Lalia et al . ; Smith et al .…”

“…In fact, building such systems with locally available products has been a key element for the sustainability of this technique in rural communities and developing countries (Olivier 2004). Work is currently being performed on the possible optimization of mesh yield through the application of lubricant coatings to the fibers, exploring the fact that hydrophobicity makes condensation phenomena more intense (Yu et al 2012;Lalia et al 2013;Smith et al 2013) or just by means of geometric optimization of the mesh fibers (Park et al 2013). However, these efforts are still undergoing laboratory development and testing, and more work needs to be performed to assess their full potential as products.…”