Suitaiology (3)

Keynote I: Fog naturally has a situation as water resource for creatures.  
Keynote II: Fog's situation as water resource is generated and transformed into dew or rainwater under the comprehensive conditions of temperature, pressure, humidity, wind and action object.  
Keynote III: Creatures naturally get water from fog.  

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      Fog in mountains is a frequent phenomenon. Fog often occurs in the night and morning with low temperature and high humidity. When the temperature increases and the humidity decreases, the fog rises into clouds and even disappears completely.

      Fog is ethereal and unpredictable with the wind, which can be so beautiful. And more, it has a natural situation as water resource for the eco-system and human. This situation is generated and transformed into dew or rainwater under the comprehensive conditions of temperature, pressure, humidity, wind and action object.

      Under natural conditions, leaves that face the night sky are radiating and losing energy, and can become cooler than the ambient air temperature. Thus they are prone to become surfaces that support condensation. Fog transforms to dew first on the coolest surfaces as air cools and approaches the dew point.

      Dew lowers evaporates, reduces transpiration, provide some species a direct source of hydration. Dew is extremely beneficial to the growth of plants. In agriculture, the most typical examples are tea and coffee gardens. Fog helps the plants thrive and improve their quality.

      Interestingly, in southern Africa, Namib beetles collect fog on their hardened wings, which coalesces into droplets that roll into their mouths.

      If no wind blowing fog away, fog eventually just falls to the ground. But winds can take most of the fog out of its chances as a water resource.

Keynote I:  Nature is the mother of invention.  
Keynote II:  Dew water collection from radiative passive collectors.

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      Fog is fleeting. The natural transformation of fog into water resources is extremely weak and unstable. However, as the saying goes, no matter how small a mosquito is, it is also meat. In areas of the world where water is scarce but fog is present, fog collection can be a possible long-term means of revitalizing the arid area.

      Some people have long started biomimetic fog collection to make dew available as an alternative source of water, such as high-mass air wells used in the early 20th century, but the approach failed.

      In the early 1960s, dew condensers made from sheets of polyethylene supported on a simple frame resembling a ridge tent were used in Israel to irrigate plants.

      After the set up of the International Organisation for Dew Utilization (OPUR) in the late 20th century, more low-mass, radiative collectors have been developed, proved to be pretty successful.

      Sharan and his team went on to develop radiative condensers for use in the arid coastal region of Kutch, India. Active commercialization of their inventions began in 2006. A typical radiative collector presents a condensing surface at an angle of 30° from the horizontal. The condensing surface is backed by a thick layer of insulating material such as polystyrene foam and located 2–3 meters above ground level.

      Other types of fog catchers are being developed, such as FogQuest invented by FogQuest, a Canadian non-profit and CloudFisher designed by WasserStiftung, a German nonprofit. Both use giant mesh nettings to catch fog. Vapor from fog turns into droplets on the specially-designed nets and rolls down into pipes that are connected to water collection tanks. They are vertically standing up in deserts and other arid areas over our planet.

      Virginia Tech (2018) has tested its fog harp technology. Fog harp uses tightly-parallelly-placed vertical wires to replace the generally used criss-crossed mesh.

      In a high-tech world, fog collection using radiative condensers is a brilliant low-tech solution for clean water, uses no energy to operate, is easy to assemble, and mimics Mother Nature. 

Keynote I: The fog collection capacity can be further increased by enhancing the situation of fog to dew or rainwater.  
Keynote II: No dew, no water resource situation of fog.  
Keynote III: Only the mist layer close to the condensation surface condenses into dew.  
Keynote IV: The condensation situation of fog flowing through the cross section orthogonal to the flow direction is the best.  

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      The fog collection capacity can be further increased by optimizing the conditions for enhancing the situation of fog to dew or rainwater.

      From a micro perspective, the water droplets in the fog surround every plant or protruding object in all directions. If there is no surface which temperature is below the dew point, fog has no water resource situation but keeps floating or is dispersed eventually.

      When there is a surface which temperature is below the dew point, it becomes the surface supporting condensation. The mist layer close to this surface tends to condense into dew, but most of floating water droplets in other layers of fog still remain idle and no significance of water resources.

      Dimension of situation: — The situation of floating fog is three-dimensional,  
— The fog situation to dew is relatively two-dimensional (such as wide leaf surface) or one-dimensional (such as California redwood needle leafs or spider webs) or even punctate (such as needle tips).

      Fog flux & situation: When wind blows, fog flows with the wind. The fog flux of the cross section orthogonal to the fog flow direction is the largest. According to the situation formula, p = mv, the condensation situation is positively correlated with the fog flux.

Keynote: The fog situation as water resource can be created, stimulated and improved by adjusting the conditions.

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3.4.1. Increase the intersection angle between fog catchers and fog flows  

      As the condensation situation is positively correlated with the fog flux which reaches the largest at the cross section orthogonal to the fog flow direction, the condensation situation can be enhanced by increasing the intersection angle between fog collector and fog flows.

      While Sharan’s fog catcher intersects fog flows at an angle, fog nets and fog harps stand up vertically, almost orthogonal to fog flows. Therefore, fog net and fog harp should be more conducive than Sharan’s fog catcher.

3.4.2. Adjust the intersection pattern between fog catchers and fog flows  

      To be harvested, water droplets must be caught on the mesh or harp as fog passes through, traveling downward into collection points by gravity.

      The standard fog nets have criss-crossed mesh construction. Fog may get stuck if the mesh holes are too small, or get lost by passing through mesh holes that are too big.

      By contrast, fog harps use only tightly-parallelly-placed vertical wires, creating an unimpeded path for mobile drops.

      In field tests, mesh collectors routinely required droplets reaching a size roughly 100 times larger than those on harps before descending. Water that never drops will simply evaporate and cannot be collected as a water resource.

      According to Virginia Tech, fog harps can get at least two times more water than mesh nets in heavy fog, and up to 20 times more water on average in a moderate fog. Fog harps harvest water even in the lightest fog.

3.4.3. Adjust speed of fog flow  

      Scientists from MIT discovered that blasting fog with a beam of electrically-charged particles propels droplets toward the mesh, greatly increasing its ability to capture fog.

      It can be understand that the condensation situation is positively correlated with the fog moving speed. We can adjust the fog flow speed to the best for higher fog collection..

3.4.4. Multiple capture of fog in multi-rows  

      The water production of a single row of fog traps is limited, especially when the amount of a fog mass is limited.

      It may be helpful to design and build an array of multi-row fog catchers, based on the studies on the aerodynamic effects of fog catcher system and the terrain of the site. As the wind speed and wind direction can be controlled as perfectly as possible, the fog catcher array can capture the fog flow multiple times, and effectively multiplies the ability of water creation from fog..

3.4.5. Adjust the material of fog catcher  

      Material is always matter. Current radiative condensers tested a wide range of materials and some special plastics, such as polyester, worked even better than the metal materials and were less expensive.

      The further development of technology and the selection of materials need to comprehensively consider work efficiency, service objectives, use environment, production costs, cost efficiency, technical possibilities, etc.

      It maybe helpful that a possible new technology and material controls the stability and time-extension of condensation situation by actively reducing the temperature of the fog catcher and prolonging the time below the dew point. Then, it can produce more dew with fewer restrictions from regional climate and terrain.

      Such a kind of technology should belong to active.

Keynote: The fog situation as water resource can be created, stimulated and improved by adjusting the conditions.  

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      The ways in which the creatures naturally use water from fog and the current fog collection technologies are passive.

      Passive technologies have too many restrictions from regional climate and terrain. So, we also need to develop some cheap, efficient and green active technologies.

3.5.1. Atmospheric water generators (AWG)  

      There are a number of commercially available atmospheric water generators (AWG). Such a kind of technology is usually based on refrigeration cycles that cool the air to below the dew point to form condensation, thus, it is energy intensive and is limited to specific temperature and relative humidity ranges for optimum results.

      For example, in cold climates or areas with low humidity, its performance significantly decreases, producing less water and therefore increasing the production costs.

3.5.2. UC Berkeley’s MOF device  

      A team of researchers from the University of California Berkeley (2018) had created a device that can extract water from dry desert air, without using an external fuel source.

      The new device used an aluminium-based powder called meta-organic framework 303 (MOF-303). The key to the water-capturing capacity of the design is the massive surface-area-to-mass ratio of the MOF powder.

      The device is opened at night when desert air is at its most saturated, allowing water to be absorbed by the MOF powder. During the day when relative humidity can drop to 10 per cent or less, the insulated case is closed and an aerogel is placed over the top of the MOF powder, which absorbs heat from the sun. When water vapor released from the heated powder comes in contact with a condenser which has been cooled overnight, it cools and condenses the vapor, allowing the liquid to be collected.

      Lab testing has shown the MOF-303 design was able to yield around 400 ml of water per kilogram of powder.

      The issue is that the system needs large volumes of dry air to come in contact with the MOF, but without a fan it is reliant on passive airflow. Then, where to get the energy to bring moist air into the material?

3.5.3. Newcastle's Hydro Harvester  

      Similar to the Berkeley model but more active, the University of Newcastle's system, called Hydro Harvester, absorbs water from the air at night into silica desiccant, then uses solar energy during the day to produce hot. Warming air can increase the moisture content of air. The hyper-saturated air is then pushed by fan through a condenser where it is cooled and releases the water for collection.

      Hydro Harvester's modular system is capable of producing about 20 liters of water per module per day, may higher than the Berkeley design.

      Unlike commercially available AWGs, the Hydro Harvester works by heating air instead of cooling it.

3.5.4. Artificial rainfall  

      Artificial rainfall is a traditional active technology to create water from clouds. In this case, the clouds have a beneficial situation of "reservoirs in the sky”.

      Fog is just a cloud that is formed at surface level. The basics are not so different and just require the wind to be blowing the damp air in a direction other than upwards.

      Artificial rainfall technology may also be used to create water from fog, but it needs to avoid any possible side effects that can harm the environment.