Monday, March 26, 2012

Creative thought (English)

Innovative designs in Homemade portable Solar Water Purifier
(Department of Physics, Sri Raaja Raajan College of Engineering and Technology,Amaravathipudur, 630 301, Tamilnadu )

Amateurs interested in harnessing solar energy, world over are continuously showing interest in constructing new designs with little modifications in the existing solar energy devices. Very few designs helped to improve the efficiency of the device to a very little extent. Miniaturizing for easy handling and operating without losing efficiency, portability for field use, reducing the material cost are certain advantages often claimed by the amateurs.
Here I give three new designs for homemade portable solar water purifier. The principle of working is well-known. The sun heats impure water causing it to evaporate. Since salt and other unsolvable corpuscular particles cannot evaporate, the vapourized water is purified. The still captures the vapours and condenses back into water
The Fig-1 gives the cross-sectional view of the device constructed under design-1. It is sufficiently a long cylindrical vessel with copper bottom to facilitate heat conduction during functioning. Its plane lid is shaped into a small cone. Just below its vertex, a small circular pan is held up with the support of little “V” shaped drain tube.
The vessel, with one third of its capacity filled with dirty or salt water, is placed on a 1x1 flat plate collector. It is covered with a glass plate to reduce IR radiation loss of the flat plate collector. In the conical lid, some cold water is taken to enhance the condensation of steam.
The “V” shaped drain tube helps to avoid escaping steam before condensation though the outlet as the condensed water, initially collected in the drain tube, closed the passage to steam. The pure water can be drained out when sufficient amount of water collected by the pan. This can be done either manually or by allowing the collected water to over-flow through the outlet gradually.

The rate of condensation can be maintained by periodically changing the water taken in the conical lid with equal amount of cold water. The condensed water collected by the pan should be removed then and there by simply tilting the vessel.
The Fig.2 gives the cross-sectional view of the device under design-2. Here the condensed water is collected by the lid itself. For water droplets to slip down towards the collector, the lid is specially designed, usually hemispherical. In order to increase the rate of condensation, wet cotton is placed on the outer surface of the lid. A small outlet tube, slightly inclined upward is fixed at the bottom of the lid. It permits pure water collected to drain out, but not the steam produced inside, as it is blocked by the condensed mass of water. In the design-2, the heating of condensed water by the steam produced inside is less than the design -1.

The design-3 is somewhat superior over the other two designs discussed here, even though it is little costlier. It has a long cylindrical vessel, made up of copper or aluminium or ever-silver. A narrow vertical tube is fused at the centre of the bottom so that a small portion is in outside. Its specially designed lid is a closed funnel like. Its limb is placed coaxially with the vertical tube without touching its wall. In order to keep the vessel on the flat plate collector, housed on a wooden box, a hole is drilled in the flat plate collector, so that the vertical tube can easily pass through it. After this arrangement, the lower end of the vertical tube is fitted with a “U” shaped bent tube. It avoids the steam to escape through the outlet, as the condensed water is collected initially at this bent and blocks the steam. It acts as volatile escape vent as well.
Capturing and then condensing the water vapour, water untainted by chemical or biological contamination is produced. The rate of vapourization can be enhanced by keeping the pressure inside lower than the normal atmospheric pressure. This is because lower the applied pressure, lower will be the boiling point. The normal boiling point of water is 100o C at standard pressure. Its boiling point decreases exponentially with the reduction in applied pressure. When the applied pressure is reduced by half, water boils at 81o C and at one fourth of the atmospheric pressure it is 52o C.

Distillation by solar energy at NTP will remove from water almost anything, even heavy metals, poisons, bacteria and viruses. But if it done under reduced pressure, as the process is carried out at lower temperature, the removal of such unwanted things will not be complete.


All the proposed designs are simple to construct. As weightless, they are portable so that they can be taken outside for field use. It is best useful to mountaineers, sailors and forest researchers. By using special coating on the flat plate collector and multiple reflectors, trapping solar energy can be improved.

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