A still solar distills water, using the heat of the Sun to evaporate, cool then collect the water. There are Many Types of solar still, Including large scale Concentrated solar stills , and condensation traps (better Known As moisture traps Amongst survivalists ). In a solar still, impure water is contained outside the collector, where it is evaporated by sunlight shining through clear plastic or glass. The pure water vapor condenses on the inside and outside, where it is collected and removed.
Distillation replicates the way nature makes rain. The sun’s energy heats water to the point of evaporation. As the water evaporates, water vapor rises, condensing into water again as it cools and can then be collected. This process leaves behind impurities, such as salts and heavy metals, and eliminates microbiological organisms. The end result is pure distilled water.
History
Condensation traps have been in use since the pre- Incan peoples inhabited the Andes .
A method for gathering water in moisture traps is taught in the Argentinian Army for the purpose of conducting business in the Andean region.
Uses
Solar stills are used in cases where rain, piped, or water is impractical, such as in remote homes or during power outages. [1] In subtropical hurricane , it is possible to provide alternative sources of clean water.
Methods
Several methods of trapping condensation exist:
First method
This method was first used by the peoples of the Andes. A pit is dug into the earth, at the bottom of which is placed the receptacle that will be used to catch the condensed water. Small branches are placed on the inside of the receptacle on the edge of the pit, forming a funnel to the water. A lid is then built on this funnel, using more small branches, leaves, fat, etc. The completed trap is left overnight, and moisture can be collected from the receptacle in the morning.
This method is related to the formation of dew or frost on the receptacle, funnel, and lid. Forming dew collects on and runs down the outside of the funnel and into the receptacle. This water would typically evaporate the sun and thus vanish, but the lid traps the evaporating water and raises the humidity within the trap, reducing the amount of water that is lost. The shade produced by the lid reduces the temperature within the trap, which further reduces the rate of water loss to evaporation.
Modern method
Today, with the advent of plastic sheeting, the moisture trap has become more efficient.
The method is very similar to that described above, but a single sheet of plastic is used instead of branches and leaves. The greater efficiency of this type of trap from the waterproof nature of the plastic, which does not allow any water vapor pass through it (some water vapor escapes through the leaves and the branches of the first method). This efficiency requires a certain amount of diligence on the part of the user, in that the plastic sheet must be firmly attached to the ground on all sides; This is often done by using stones to weight the sheet and / or covering the edges of the plastic sheet with earth (such as that to make the hole in which the trap sits). Weighting the center of the plastic sheet with a stone forms the funnel via which the condensed water will run into the receptacle.
Transpiration method
Water can be obtained by placing a bag of non-poisonous tree and tightly closing the bag’s open end around the branch. [2] Any hole in the bag must be sealed to prevent the loss of water vapor.
During photosynthesis plants lose water through a process called perspiration . A clear plastic bag sealed around a branch Allows photosynthesis to continue, aim trap the water evaporating Causing the vapor pressure of water to rise to a point of Where It begins to condense on the surface area of the plastic bag. Gravity then causes the water to run to the lowest part of the bag. Water is collected by tapping the bag and then resealing it. The leaves will continue to produce water as the roots draw down and the photosynthesis occurs.
The way in which the body is exposed can not be swallowed, when using this method, the water should be drained every two hours and stored. Tests indicate that this is not done
If there are no large trees in the area, clumps of grass or small bushes can be placed inside the bag. If this is done the foliage will be reduced when the production is reduced, especially if the foliage must be uprooted to place it in the bag.
Efficiency is greatest when the bag receives maximum sunshine at all times. Exposed roots are tested for water content. Soft, pulpy roots will yield the greatest amount of liquid for the least amount of effort.
Condensation trap efficiency
Condensation traps are not in themselves a sustainable source of water; they are sources for extending or supplementing existing water sources or supplies, and should not be relied on a person’s daily requirement for water, since a trap measuring 40 cm (16 inches) in diameter by 30 cm (12 inches) deep will only yield around 100 to 150 ml per day.
One method to increase the water output is to urinate into the pit before placing the receptacle in. This increases the moisture content of the earth, reducing the amount of water that the earth can subsequently absorb.
Materials
A simple basin-type solar still can be constructed with 2-4 stones, plastic film or transparent glass , a central weight to make a point and a container for the condensate. A cubic hole in moist ground is created of about 30 cm (12 inches) on each side. Into the center of this hole, a collection container is placed. Then a sheet of plastic film is stretched over the hole. Stills can also be made from water bottles or plastic bags. [3]
Variations
Transpiration bag
An alternative method of the solar still is called the transpiration bag. [4] The bag is a simple plastic bag and it folds over a stemmed plant to a point to allow the condensate to pool. From a person can take the water by taking the bag off and pouring the water out or can make a tiny incision into the corner to drip water into a cup. Its advantage over the basin type is still in existence. It does not need to be completely transparent. A disadvantage of the perspiration bag is the requirement for a direct sunlight or heat to take the condensate.
In a study performed in 2009 [ citation needed ] , variations to the angle of plastic and increasing the internal temperature of the hole versus the outside temperature for better water production. Other methods used included with a brine to absorb water and adding dyes to the brineto change the amount of solar radiation absorbed into the system. Tilt angle experiment, the different angles used by the different researchers. In the graph, a bell curve is observed with the maximum water output being at 30 degrees angle adjustment. Each brine depth is a different amount of water and it is noted on the graph that is an inch with a decreasing trend if more is used. [5]
Wick still
The “wick” type solar is still a glass-topped box and held at an angle to allow sunlight in. [6]Salt water poured in from the top is heated by sunlight, evaporating the water. It condenses on the underside of the glass and drips to the bottom. A pool of brine in the still attached to the wicks which separates the water into banks to increase surface area for heating. The distilled water comes out of the bottom and depends on the quality of construction of the water. The more wicks, the more heat can be transferred to the salt water and more product can be made. A plastic net can also catch salt water before it falls into the container and gives it more The wick type is still vapor, but does not escape to the atmosphere. To help in absorbing more heat, some wicks are blackened to take in more heat. Glass’s absorption of heat is negligible compared to plastic at higher temperatures. A problem, depending on application, is not flexible if the solar still is not a standard shape.
Practical considerations
The pit still may be inefficient as a survival still, requiring too much construction effort for the water produced. [7] In desert environments water needs can exceed 1 US gallon (3.8 L) per day for a person at rest, while still production may average 8 US fluid ounces (240 mL) per day. [7] [8] Even with tools, digging a hole requires energy and makes a person lose water through perspiration ; This collection may not be equal to the water lost in its construction. [8]
Seawater still
In 1952 the United States military developed a portable solar still for pilots stranded on the ocean, which included an inflatable 24-inch plastic ball that floats on the ocean, with a flexible tube coming out the side. A separate plastic bag hangs from the attachment points on the outer bag. Seawater is poured into the inner bag of an opening in the ball’s neck. Fresh water is taken out by the pilot, which leads to the bottom of the inflatable ball. It was stated in the magazine that it was 2.5 US quarters (2.4 l) of fresh water could be produced. On an overcast day, 1.5 US quarters (1.4 l) was produced. [9] Similar sea water stills are included in some life raft survival kits , though reverse osmosis manualdesalinators have mostly replaced them. [10]
Distilling urine
Using a condensation trap to distill urine will remove the urea and salt, providing one with a drinkable water as a result. [11]
See also
- Concentrated solar still
- Desalination
- Freshwater
- Solar cooker
- Solar water disinfection
- watermaker
- Wikiversity: Solar Seawater Still
References
- Jump up^ Anjaneyulu, L .; Kumar, E. Arun; Sankannavar, Ravi; Rao, K. Kesava (13 June 2012). “Defluoridation of drinking water and rainwater harvesting using a solar still”. Industrial & Engineering Chemistry Research . 51 (23): 8040-8048. doi : 10.1021 / ie201692q .
- Jump up^ O’Meagher, Bert; Reid, Dennis; Harvey, Ross (2007). Aids to survival: a handbook on outback survival (PDF) (25th ed.). Maylands, WA: Western Australia Police Academy. p. 24. ISBN 0-646-36303-4 . Retrieved 7 February 2017 .
- Jump up^ [1]
- Jump up^ Munilla, R.Still Solar Practical SurvivorRetrieved April 22, 2013
- Jump up^ Abdul Jabbar N. Khalifa; Ahmad M. Hamood (30 November 2009). “Performance correlations for basin type solar stills” . Desalination . 249(1): 24-28. doi : 10.1016 / j.desal.2009.06.011 . ISSN 0011-9164 .
- Jump up^ V. Manikandan; K. Shanmugasundaram; S. Shanmugan; B. Janarthanan; J. Chandrasekaran (April 2013). “Wick type solar stills: a review” . Renewable and Sustainable Energy Reviews . 20 : 322-335. doi: 10.1016 / j.rser.2012.11.046 . ISSN 1364-0321 .
- ^ Jump up to:a b Alloway, David (2000). Desert survival skills . University of Texas Press . pp. 63-65. ISBN 978-0-292-79226-5 . Retrieved 9 May 2013 .
- ^ Jump up to:a b United States Air Force (1 April 2008). US Air Force Survival Handbook . Skyhorse Publishing . p. 285. ISBN 978-1-60239-245-8 . Retrieved 9 May 2013 .
- Jump up^ “Sea Water Still”. Popular Mechanics, February 1952, p. 113.
- Jump up^ “Manual Reverse Osmosis Desalinator – Source of Intent Sole Source, USAF” . fbo.gov . 2012 . Retrieved July 3, 2012 .
- Jump up^ Grantham, Donald F. (March 2, 2001). A Source of Wilderness Novice Survival Skills . Xlbris Corp. p. 119. ISBN 0738836826 .
