Fig 1: Dew collection off of a roof in Croatia

Introduction

As the world’s population increases, fresh water supplies are being tapped out. Desalinization has become a necessary means of acquiring water; however current methods are usually quite costly and use fossil fuels. This is inappropriate for the developing world, where there is a serious need for increased fresh water availability. Atmospheric or atmospheric water vapor processing (AWVP) is an emerging technology in which the atmospheric water vapor is condensed and collected [1, 2, 9]. AWVP is a relatively new technology.

Advantages

  • It is at an early stage in development, but has the potential to provide environmentally acceptable alternatives [12, 13] to standard water supplies.
  • Many AWVP designs favor decentralization of water distribution and avoidance of huge capital costs for infrastructure [13].
  • AWVP can be made appropriate, community-managed and community-maintained for developing countries [review].
  • AWVP methods are competitive with desalination plants and simpler and less expensive to operate and maintain.
  • The amount of water produced would vary according to installation size, and be suitable to provide potable water to individuals or even thousands of people.
  • AWVP production can take place in a wide variety of locations. Thus, expensive water distribution infrastructure can be reduced or avoided.


Disadvantages

Background information

Dew Formation

Fig 2: Dew on a flower

Interestingly, many desert and costal plants and animals depend on this source [4]. Naturally, the phenomenon of dew formation takes place due to night sky radiation cooling. On a clear night, heat energy is radiated away from the earth’s surface into the sky. As the surface temperature drops below the dew point, water vapor will condense into droplets. Dew is formed both from water vapor in the atmosphere in the form of dewfall, as well as from water in the soil in the form of dewrise.
The amount of dewfall can be approximated from a complex turbulent fluid analysis; however it is far simpler to consider it as an energy balance problem [5]. The process of condensation releases heat, and thus raises the surface temperature.
http://en.wikipedia.org/wiki/File:Dew_on_a_flower.jpg

Failed to parse (syntax error): {\displaystyle R + G + C + λF + M = Q \frac{\partial T}{\partial t} } [5]

Where

R = net incoming radiation flux (a negative term)
G = flux of total heat from soil to surface
C = flux of sensible heat from air to surface
F = flux of water vapor from air to surface
λ = latent heat of vaporization
Q = heat capacity of the air-grass layer per cm2
T = mean temperature of layer
M = heat released by vegetable metablism per cm2


Furthermore, it follows that the maximum possible condensation rate for combined dewfall and dew-rise during nighttime is [10, 11, 7, 8]:

Where

Df = rate of dewfall (kg m−2 s−1)
Dr = rate of dew rise (kg m−2 s−1)
s = slope saturation curve (Pa K−1)
Q* = net radiation (W m−2)
γ = psychrometric constant (66 Pa K−1)
λ = latent energy for vaporization (J kg−1)


Studies have demonstrated that the above modle can accurately and reliably predict dew rates [11].
The maximum amount of dewfall possible on a given night is limited by the amount of radiative cooling possible, and is estimated to be approximately 1mm [6, 7]. In actuality, this number is usually much lower, ranging from 0.17 – 0.45 mm per night [8].


3). What engineering principle(s) underlie the function of the device – include equations and explanations of variables and design features. 8). Skills and knowledge necessary to make the device – link to relevant wikipedia or wikiversity articles/courses -literature review

   using passive solar heating to power the ___, is used to cool the dew collection surface. Dew will form on a surface, if the temperature is below the dew point. 
the daily dew collection time to be 

A significant amount of research into passive dew collectors has occured, resulting in devices able to harvest as much as 0.22 L/m2 of fresh water per night. The proposed device, namely a solar powered dew collector, aims to increase the usefulness of a dew collector by making it function meet this need through condensing water in the ambient atmosphere.


Dew collectors

Solar absorption refridgeration

-regional considerations

Design

Materials and tools

6). Materials needed for fabrication of device and alternative materials if they are not available 7). Tools needed for fabrication of the device and alternative tools if they are not available 11). Estimated costs

Technical specifications

9). Technical specifications including drawings or pictures of the device at minimum. Ideally full CAD files would be provided along with detailed fabrication instructions. You can scan any of your own drawings or schematics and paste them in your document. If you use pictures from other sources be sure to have proper permissions. You can upload files (e.g. pictures, images, etc.) here: http://www.appropedia.org/Special:Upload and then link back to them in your article 10). If it is a device design be detailed enough in your “how to” to ensure that someone could construct the device from your description. Consider the elegance of IKEA like instructions.

References

13). The sources of information (e.g. engineering handbooks, journal articles, government documents, webpages, books, magazine articles etc.). References should use the Cite error: Invalid <ref> tag; refs with no name must have content and tags and can be in any format but should include all the information necessary for someone else to find the same information you did. For example: web page: Department of Energy (DOE) Landscaping and Energy Efficiency, DOE/GO-10095 (1995) Available: www.eren.doe.gov/erec/factsheets/landscape.html [Accessed Date] book: Innovations and Materials for Green Engineering Vol 3, eds. A. Lakhtakia and C.E. Bakis, Department of Engineering Science and Mechanics, PSU, June 2001. journal article: Joshua Pearce, “Photovoltaics – A Path to Sustainable Futures”, Futures 34(7), 663-674, 2002.


5). Based on the developmental needs addressed (e.g. food, heat, electricity, clean water, health care, etc.) be sure to label your device in the proper categories e.g. use. Be sure to categorize your device so that it will be easy to find – for example “Low voltage connection basics” is categorized in,,. Finally you will want to link to your article by in other Appropedia articles that mention your articles name and you may wish to put your article in a portal (e.g. http://www.appropedia.org/Portal:Energy )

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