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Passive Atmospheric Water Condenser and Solar Still for Production of Potable Water

IP.com Disclosure Number: IPCOM000245267D
Publication Date: 2016-Feb-24
Document File: 6 page(s) / 6M

Publishing Venue

The IP.com Prior Art Database

Related People

Calvin Rieder: AUTHOR [+2]

Abstract

Water availability and quality are universally important issues. Fresh water demands are increasing and by 2050 demand is projected to exceed supply by 40%. Attempts to develop passive technologies to supply potable water have been limited and largely unsuccessful. Current technologies are focused on desalination and purification, both of which are restricted by economic and ecological factors. This paper describes a two-part invention to passively produce fresh water. The invention comprises a novel atmospheric water condenser to extract water from air and a novel high-capacity solar still designed to convert water from non-potable to potable in volumes exceeding those of traditional basin solar stills. The systems function without electrical or mechanical assistance and do not require water infrastructure. The atmospheric water condenser is cooled to below dewpoint by enhancing its natural rate of radiative cooling, using radiating panels and parabolic reflectors, and by reducing thermal transfer into it using radiation barriers. Condensing surfaces are coated to facilitate water condensation and flow. The solar still includes evaporation basins connected to a separate, high-capacity condenser. This invention is designed to address basic human potable water requirements by increasing fresh water access to areas that are remote and where economic means are limited, as well as to more developed regions facing increasing water shortages.

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Page 01 of 6

Passive Atmospheric Water Condenser and Solar Still for Production of Potable Water

Calvin Rieder

Introduction:

The principles of this invention are condensation of water from air on passively cooled surfaces and collection of the condensed water from those surfaces, and use of solar radiation to evaporate non-­‐potable water followed by condensation of the water vapour and collection of the resulting purified water.

Natural dew forms when air cools to dewpoint and water vapour condenses.However, attempts to passively capture this water for human use have been largely unsuccessful for both technical and practical reasons. Commercial devices require electrical energy for cooling.

During nighttime, there is a net loss of longwave radiation from the earth's surface to the sky causing cooling. Furthermore, at night, passive cooling below ambient air temperature can be achieved through radiative cooling, in which a device exposed to the sky radiates heat to outer space through a window in the atmosphere between 8 and 13μm. Passive planar condensers that utilize radiative cooling exist but are restricted by their reliance on tangential airflow for exposure of the surface to water vapour. They are further constrained by a theoretical maximum of 0.8-­‐1 L/m2 of dew that can naturally form on a surface and this can only occur if wind speed is < 0.5-­‐3.0 m/s. In addition, the only way to increase yield is to increase size, resulting in very large condensers.

Finally, dew water is not generally potable and can be contaminated with microorganisms, sediment and mineralsand thus usually requires purification.

Solar stills utilize solar radiation to purify water. Passive stills utilize solar radiation exclusively as their source of energy. The majority of passive stills are single-­‐basin stills with a sloped glass cover. The sun heats the water in the basin causing evaporation and the resulting water vapour condenses on the cover and runs down into a collection trough. Climate and thermal loss factors limit their efficiencyand they are not widely used.The most important factor affecting performance is the amount of solar radiation. Other factors include temperature difference between the water and the condensing surface, water depth, and absorber area. These restrictions all limit the clean water production rate of basin stills. In addition, three other major problems with existing designs are limited feed water capacity, limited condensing surface area, and ineffective means of clean water collection resulting in some clean water re-­‐entering the basin.

Existing patents for solar still designs other than single basin stills fall into two major groups, passive which utilize solar radiation only, or those requiring an additional energy source. They are either complex and costly or have technical issues which would negatively impact their efficiency.


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The passive atmospheric water condenser and solar still descr...