Fog fence
Encyclopedia
A fog fence or fog collector is an apparatus for collecting liquid water
from fog
, using a fine mesh
or array of parallel wires. Proposed geometries include linear, similar to a fence
and cylindrical. It has the advantage of being passive, requiring no external energy source to perform its collection. This makes it attractive for deployment in less developed areas. An ideal location for fog fences is high arid areas near cold offshore currents, where fog is common.
A related, but quite distinct, technique of obtaining atmospheric moisture is the air well
.
s of water per cubic metre, with droplets from 1 to 40 micrometre
s in diameter. It settles slowly and is carried by wind. Therefore, an efficient fog fence must be placed facing the prevailing winds
, and must be a fine mesh
, as wind would flow around a solid wall and take the fog with it.
The water droplets in the fog deposit on the mesh. A second mesh rubbing against the first causes the droplets to coalesce and run to the bottom of the meshes, where the water may be collected and led away.
). Windborne dust
can cause contamination
of the collected water. The moisture collected can promote growth of mold
and other possibly toxic microorganism
s on the mesh. Bird
s and insect
s can also be sources of contamination.
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
from fog
Fog
Fog is a collection of water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of stratus cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated...
, using a fine mesh
Mesh
Mesh consists of semi-permeable barrier made of connected strands of metal, fiber, or other flexible/ductile material. Mesh is similar to web or net in that it has many attached or woven strands.-Types of mesh:...
or array of parallel wires. Proposed geometries include linear, similar to a fence
Fence
A fence is a freestanding structure designed to restrict or prevent movement across a boundary. It is generally distinguished from a wall by the lightness of its construction: a wall is usually restricted to such barriers made from solid brick or concrete, blocking vision as well as passage .Fences...
and cylindrical. It has the advantage of being passive, requiring no external energy source to perform its collection. This makes it attractive for deployment in less developed areas. An ideal location for fog fences is high arid areas near cold offshore currents, where fog is common.
A related, but quite distinct, technique of obtaining atmospheric moisture is the air well
Air well (condenser)
An air well or aerial well is a structure or device that collects water by promoting the condensation of moisture from air. Designs for air wells are many and varied, but the simplest designs are completely passive, require no external energy source and have few, if any, moving parts.Three...
.
Principle
Fog contains about 0.05 gramGram
The gram is a metric system unit of mass....
s of water per cubic metre, with droplets from 1 to 40 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s in diameter. It settles slowly and is carried by wind. Therefore, an efficient fog fence must be placed facing the prevailing winds
Prevailing winds
Prevailing winds are winds that blow predominantly from a single general direction over a particular point on Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant winds...
, and must be a fine mesh
Mesh
Mesh consists of semi-permeable barrier made of connected strands of metal, fiber, or other flexible/ductile material. Mesh is similar to web or net in that it has many attached or woven strands.-Types of mesh:...
, as wind would flow around a solid wall and take the fog with it.
The water droplets in the fog deposit on the mesh. A second mesh rubbing against the first causes the droplets to coalesce and run to the bottom of the meshes, where the water may be collected and led away.
Limitations
Fog fences are limited by the local climate and topography. Their yield is affected by local weather and global weather fluctuations (such as El NiñoEl Niño-Southern Oscillation
El Niño/La Niña-Southern Oscillation, or ENSO, is a quasiperiodic climate pattern that occurs across the tropical Pacific Ocean roughly every five years...
). Windborne dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
can cause contamination
Contamination
Contamination is the presence of a minor and unwanted constituent in material, physical body, natural environment, at a workplace, etc.-Specifics:"Contamination" also has more specific meanings in science:...
of the collected water. The moisture collected can promote growth of mold
Mold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...
and other possibly toxic microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s on the mesh. Bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s can also be sources of contamination.
External links
- Standard Fog Collector, at USGS installation in Hawaii
- Fog Harvesting, chapter from Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean, UNEPUnited Nations Environment ProgrammeThe United Nations Environment Programme coordinates United Nations environmental activities, assisting developing countries in implementing environmentally sound policies and practices. It was founded as a result of the United Nations Conference on the Human Environment in June 1972 and has its...
International Environmental Technology Centre - The Fog Collectors: Harvesting Water From Thin Air
- FogQuest: Sustainable Water Solutions, Canadian organization, historical information on fog collection projects in developing countries
- How Peru is netting water supplies BBC News