Unclogged Janus Mesh for Fog Harvesting

Abstract

Janus membranes with asymmetric surface wettability have been extensively utilized in various fields, including fog harvesting, because of their novel liquid transport properties. However, Janus membranes have an inherent disadvantage in terms of aerodynamic efficiency in harvesting fog because of the clogged water bridges caused by the small pore size. In the present work, we applied Janus wettability to mesh geometry with systematically varying hole sizes. For a clogged mesh with a small hole size, capillary water transport to the mesh back via the wettability gradient in the direction of fog flow helps harvest more fog by enhancing water drainage, similarly to the Janus membrane. The advantage of the capillary water transport extends to a clog-free mesh with larger hole sizes but more preferably to a Janus mesh with a superhydrophilic back, which presents the highest level of fog-harvesting yield because of the fast shedding frequency and short onset time. In contrast, a Janus mesh with a superhydrophobic front, which also has a wettability gradient along the fog flow, produces a lower fog-harvesting performance, particularly at slow fog speeds, because of the dropwise deposition of large water drops that locally disturb fog flow around a protruding water surface. On the other hand, the other type of Janus mesh with a superhydrophilic front is observed to minimize this disadvantage in the local fog flow by virtue of the filmwise deposition. It is also found that some Janus treatments can help protect mesh holes from clogging up by either forming a thin water meniscus or resisting water transport through the mesh holes.

Highly Durable Janus Fabrics Based on Transfer Prints for Personal Moisture Management

“…In addition, we applied the force analysis to explain the mechanism of unidirectional liquid transport, which is helpful to design and construct a Janus fabric for applications in microfluidic chips and other fields (e.g., fog harvesting and oil/water separation). [23,24] As Figure 4c showed, when the droplet was dripped onto the hydrophobic layer, it was initially subjected to two forces: the upward hydrophobic force (HF 1 ) and downward gravity (G, equals to the hydrostatic pressure (HP)). HF 1 and the positive breakthrough pressure are usually related, and G is proportional to the droplet height.…”

Gradient monolayered porous membrane for liquid manipulation: from fabrication to application

“…In addition to the morphology gradient, in recent years, many researchers have carried out further chemical modication on the porous membrane surface, and successfully prepared monolayered porous membranes with a chemical gradient or a physical-chemical compound gradient, which makes the membrane promising for a wide range of applications, such as fog collection, [39][40][41][42] sensors, 43 oil-water separation, 44,45 switchable ion transport, 46 and functional textiles. 47 Previously, Zhao's group proposed two construction strategies for a wettable anisotropic membrane.…”

Effect of Droplet-Laden Fibers on Aerodynamics of Fog Collection on Vertical Fiber Arrays

“…Often inspired by nature, such approaches are termed biomimetic surface design. They include desert beetle-inspired surfaces with heterogeneous wettability, , Janus membranes with front-to-back wettability gradient for fast water removal, − utilizing Laplace pressure gradient caused by asymmetric curvatures on conical surfaces, , or incorporating special topological features which enable unidirectional motions of droplets. − Shi et al developed fog harps, which are arrays of vertical fibers and give enhanced fog-harvesting performance due to the absence of cross fibers, which otherwise hinder droplet motion leading to pinning of droplets and clogging of mesh pores. As pointed out in a recent review by Jiang et al, fog harvesting is distinct from dew harvesting.…”