Solar desalination unit

The effectiveness of the solar desalination unit depends on the amount of solar radiation available, which in turn depends on its location on the earth s siuface and the time of year. The following example shows how to estimate the heat fluxes and the rate of water production. 

Using the specifications of Dally and Regan (1997), design a basin solar desalination unit that produces at least one ounce per hour of potable water at a location close to the Equator where the total diurnal radiant flux is 2,200 Btu/(ft -day) year-round, with a maximum flux of 260 Btu/(ft -hr) at 11 00 a.m. The entire unit should be housed in an empty box of the size used to ship 10 reams of 8.5-in. by 11-in. paper for copy machines (17 in. X 22 in. X 10 in.). The possibility of using concentrating mirrors should be considered. 

Energy balances are created to solve for the mass flux of water produced. Then, given the need to produce 1 oz/hr = 0.0625 Ib/hr, the collector area can be estimated. 

As light impinges on a surface, the firaction absorbed, a, plus the fraction transmitted, t, plus the fraction reflected, r, sum to unity that is 

In this balance, the heat accumulated equals the difference between the heat in and the heat out  

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Figure 19.7 Schematic of a basin solar desalination unit. Reprinted with permission from Daily and Regan (1997).

For the solar desalination unit in Example 19.2, consider the use of a conical mirror that multiplies the incident heat flux by a factor of three. Recompute the temperature of the glass cover, the heat flux to the glass cover, the evaporation rate of water, and die collector area. Would this area be sufficiently small to satisfy the specifications Furthermore, estimate the cost of producing one unit, as well the cost of producing 100,000 units annually. 

As the population of the Sunbelt areas of the United States increases, more demand will be placed on the limited supplies of fresh water there. One obvious source of fresh water is from the desalination of seawater. Various schemes have been suggested, including solar evaporation, reverse osmosis, and even a plan for towing icebergs from Antarctica (remember that pure... 

El-Nashar, Ali M. Multiple Effect Distillation of Seawater Using Solar Energy. New York Nova Science, 2008. Tells the story of the Abu Dhabi, United Arab Emirates, desalinization plant that uses solar energy to distill seawater. 

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