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CONCENTRATED SOLAR DISTILLATION AS A MEANS TO PURIFY SALINE/BRACKISH WATER

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Impact/Purpose:

Solar energy can be used in producing desalinated water. However, the process is slow and requires large solar collection areas to desalinate a relatively small amount of water. Currently solar distillation is viable for small-scale use generally in a batch process form. By concentrating the solar energy via a Fresnel lens we are seeking to develop a more cost effective and efficient desalination/treatment method for potable water production. We believe that by concentrating solar energy, a significant increase in efficiency can be achieved, substantially increasing production rate and reducing per unit volume cost of production.

Description:

Initial experiments focused on the ability of the lens to deliver enough energy to produce water with minimal salt content. Raw sample waters were prepared using quantities of Epsom salt (MgSO47H2O) dissolved in purchased distilled water. Three separate samples of increasing concentration were introduced batch wise into a constructed boiler unit and attached condenser. The raw samples and collected product were analyzed using a conductivity meter. The three raw samples had measured concentrations of 710, 2812, and 5526 ppm. The collected product waters all showed salt concentrations of approximately 0 ppm.

A second parameter to be tested was the use of a secondary solar collector versus direct heating of the boiler unit by the Fresnel lens. Secondary collection would allow multiple lenses to apply solar energy to a single boiler unit. In terms of scalability this would allow greater energy input with respect to the boiler unit and pumping system, which encompasses the bulk of the per unit costs. Preliminary testing of the secondary receivers showed an inability to deliver enough energy to bring the raw sample water to a boil.

The lenses also were tested with respect to degradation under exposure to direct ultraviolet radiation. The lenses under consideration were acrylic, which can discolor over time in direct sunlight. In order to simulate solar exposure, the lenses were placed in a fume hood with constant ultraviolet radiation delivered via a 15 W UV lamp. Prior to placement in the fume hood the three lenses were placed within an enclosed space and their luminosity with respect to a constant light source at a fixed distance was determined. The luminosity was determined using a lumen meter purchased from Fisher Scientific. The three lenses then were placed in the fume hood and removed once per month for 3 months. During each removal, the luminosity of each lens was once again tested and compared to the initial readings. The lenses then were replaced back into the fume hood. All readings showed approximately equal values with respect to time spent under ultraviolet radiation.

URLs/Downloads:

Final Progress Report

Record Details:

Record Type:PROJECT( ABSTRACT )
Start Date:08/15/2009
Completion Date:08/14/2010
Record ID: 248967