Fog harvesting is emerging as a promising means to ease the water shortage crisis in arid regions of the world with ample fog. The current state-of-the-art for fog harvesting is mesh netting, which is accessible yet struggles from a dual constraint: a course mesh lets most microscopic fog droplets pass through it, while a fine mesh clogs. In recent years, fog harps have been gaining attention as a superior alternative to meshes, bypassing these inherent constraints. In this work, we expand upon previous fog harp research with a focus on optimization. First, we analyze wire tangling in a harp due to capillary forces, resulting in a mathematical model that is able to predict when wire tangling will occur. Second, we systematically vary three key parameters of a fog harp (wire material, center-to-center wire pitch, and wire length), arriving at an optimal combination. Finally, we develop a numerical model to describe the dynamics of a fog droplet sliding down a harp wire while coalescing with others littered along it. By applying all knowledge acquired through these studies, the next generation of fog harps will push the performance ceiling of practical fog harvesters higher than ever. / Master of Science / The human population continues to grow, and with it the demand for fresh water. This need has caused many to turn to unconventional sources of water, including fog (the suspension of microscopic liquid water droplets in the air). Fog harvesters already exist in arid regions of the world as mesh nets, but suffer dual constraints from their grid-like structure: course meshes fail to capture most fog droplets passing through, while fine meshes get clogged. To bypass these inherent limits, we turn to nature for a solution. It has been observed that California redwood trees are able to effectively collect fog on their straight leaf needles, dripping droplets to the roots below. Inspired by this, we fabricate a device called a fog harp, which removes the impeding horizontal wires of meshes to effectively capture and slide droplets down its vertical wires. In this work, we expand upon previous fog harp research by investigating ways to optimize its water collection efficiency. First, we develop a mathematical model to describe the tangling of harp wires due to merging droplets on adjacent wires pulling them together. Second, we systematically vary three key parameters of the fog harp (wire material, center-to-center wire spacing, and wire length) to arrive at the optimal combination. Finally, we develop a model to describe the dynamics of droplets sliding down harp wires while merging with others littered along it. These studies will raise the performance ceiling of fog harps and push them to real-world applications.

In this work, we were motivated to develop novel devices for water harvesting inspired by natural trees, and to understand their collection efficiency and working principles. We accomplished that with scale-model and large-scale fog harps, floating leaves, and synthetic trees. Fluids mechanics, physics, and thermodynamics were applied to solve the problems and rationalize the results. Redwood-inspired fog harps were designed with stainless steel vertical wires, using 3D-printing and laser-cutting techniques. Fog harps always harvested more water than any of the meshes, tested both under heavy fog and light fog conditions. The aerodynamic efficiency, deposition efficiency, and sliding efficiency were calculated to compare the fog harvesting performance. These findings provide insight into the new design of fog harvesters with high-efficiency fog harvesting performance, and future development of large fog harps, applied into regions even with light fog conditions, as an economically viable means. synthetic trees were fabricated with a nanoporous ceramic disk and silicone tubes. This tree system was tested in an environmental chamber (6 cm short trees) or a plant growth chamber (3m tall trees), both with controlled ambient humidities. The system pressure was calculated with Darcy's equation, Poiseuille equation and Laplace equation. The stable transpiration can happen to any scalable tree, which pumps water up an array of large tubes. Our synthetic trees, like natural trees, have the ability to lift water across a wide range of water temperatures and ambient humidities. They can be used as the large-scale evaporation-driven hydraulic pump, for example, pumped storage hydropower, filtration, underground water extraction. / Doctor of Philosophy / The purpose of this work is to investigate and characterize novel techniques for water harvesting that are inspired by natural trees. We are interested in two modes of water harvesting in particular: fog harps and synthetic trees. Fog harps were comprised of only vertical wires, inspired by the parallel structures of redwoods, which can capture and shed off fog droplets efficiently. Fog harps harvested more water than the traditional mesh nets, both under heavy fog and light fog conditions. Redwood-inspired fog harps have the high-efficient fog harvesting performance. They can be set up at coastal deserts to collect water from fog, where there is scarce rainfall but plenty of fog, like Chile, Peru and South Africa. Synthetic trees were designed with nanoporous disk (leaf) and tubes (xylem conduits), inspired by the transpiration process in natural trees. This transpiration-powered pump can lift water against the gravity at large scales, driven by the water evaporating from the nanopores. They can be used as the large-scale evaporation-driven hydraulic pump, for example, pumped storage hydropower, filtration, underground water extraction.