Double effect floating solar still comprising a submerged condensing system

The double effect floating solar still uses a partly immersed corrugated metal plate to heat the upper layer of a body of water in order to establish a temperature difference between the upper and lower sections of the still. The difference in temperature creates a difference in vapor pressures, forcing the vapor produced in the hot section of the still to flow into a submerged condenser, giving up the heat of condensation to the surrounding water, preheating it before it reaches the stage of evaporation.

BACKGROUND OF THE INVENTION 
Most solar stills, and particularly those of the greenhouse type, are of a 
low thermal efficiency because of a loss of heat. In such systems, the 
vapor produced in the still is condensed on the surface of glass panels, 
giving up the heat of condensation to the atmosphere, causing thereby a 
loss of energy. The purpose of the present invention is to improve the 
thermal efficiency of solar stills by using the heat of condensation for 
preheating the distilland before evaporating it. 
SUMMARY OF THE INVENTION 
In the double effect floating solar still a corrugated metal plate is used 
as a heat absorbing element. The corrugated plate, covered by glass, is 
immersed in the distilland in such a manner as to enable the non-immersed 
part of the corrugations to be used as ducts to carry the hot vapors into 
the cold submerged condenser. 
When heated by solar radiation, the partly immersed corrugated metal plate 
brings about a rise in temperature in the upper section of the still, 
resulting in a higher vapor pressure. The higher pressure in the upper 
section of the still forces the vapor to flow into the submerged 
condenser, giving up the heat of condensation to the surrounding water, 
preheating it before it reaches the stage of evaporation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the system shown in FIG. 1, a floating frame 2 has its top covered by a 
transparent glass 4, and its bottom closed by an insulating material such 
as plastic foam or wooden planks 11. 
The transparent glass 4 is held in place by rubber flaps 7 which are either 
glued or nailed to the floating frame 2. Beneath the transparent glass, 
attached to the floating frame 2, is a corrugated metal plate 3 which 
covers the whole of the inner surface of the floating frame. The 
corrugated plate 3 has spacers 10 attached to it and adjusted so as to 
hold the submerged condenser 6 at a suitable distance from the bottom 
planks 11, to enable water to freely flow under the condenser. 
The corrugated plate is preferably made of sheet metal the external surface 
of which is treated with a suitable black paint in order to enhance the 
absorption of heat. When heated by solar radiation, the black-painted 
corrugated metal plate transmits the heat to the water which is in contact 
with the underside of the corrugations, establishing a temperature 
difference between the condenser and the upper layer of water in the 
still. 
The difference in temperature between the condenser and the upper layer of 
water in the still corresponds, as those who are skilled in the art know, 
to difference in vapor pressures. Therefore, as soon as the temperature of 
the water which is in contact with the underside of the corrugated plate 3 
rises above the temperature of the submerged condenser 6, a difference in 
pressure is established in the system, forcing the vapor of the hot 
section to flow through the vertical pipes 5 into the submerged condenser 
6, giving up the heat of condensation to the water which surrounds the 
condenser. Being lighter than the colder water which surrounds the 
floating still, the water preheated by the submerged condenser 6 has a 
natural tendency to reach the upper level of the still and to come in 
contact with the corrugated heat absorbing meatal plate 3. There, the 
water is evaporated, allowing new cold water to enter into the confine of 
the still through inlets 9, provided at the sides of the still, near the 
bottom, and to maintain a continuous cycle of preheating the distilland, 
evaporating it and condensing the vapor to be taken out as fresh potable 
water from outlet 8 which is connected to a reservoir on the shore. 
It is understood that minor variations from the form of the invention 
disclosed herein may be made without departure from the spirit and scope 
of the invention. The corrugations of the metal heat absorbing plate, for 
example, may have a different form from that shown in the drawing, and 
instead of transparent glass, a suitable transparent plastic plate may be 
used to cover the top of the double effect floating still. It is therefore 
quite obvious that the drawing and specifications of the disclosure are to 
be considered as merely illustrative rather than limiting in any way.