I have tried several methods to desalinate water many which appear on the energy21 collection of web sites.
The methods I have tried so far tend to work but are not very efficient unfortunately. Mostly I had to complete against pressure as the closed container heated up the water vapor ceased to be produced at a point where the pressure inside the vessel could not be increased and the vaporizing and condensation reaches a standstill.
It seems water under pressure takes a lot more heat to allow it to boil,(such as case in super heated steam in most power generators.
However the opposite is true when the pressure on the water is reduced such as in a partial vacuum.
This method below although not yet tried by me may provide a better result.
The idea for this design came to me after seeing a science demonstration on Australian channel seven afternoon television childrens program called The Big Arvo.
If you wish to reproduce the experiment for yourself ,here are some brief details.
The science demonstration explained of how to produce a cloud.
It consist of a coke cola plastic 2 litre bottle.
The bottle had some hot water added to it ,probably about 1/2 litre or less in volume.
A match was lit and some ash was added from the burning match to the plastic bottle.
The bottle was again resealed and then plastic bottle was squeezed to compressed the contents (air) water can not be compressed.
When the coke bottle was re opened water vapor came out the bottle in the form of a small water cloud.
I have tried to think of a method where this means could be used to produce clean water using solar energy and have come up with idea that may work although I have not tried it yet myself.`
If you look at the drawing above you will see three large plastic ( or metal cylinders) ,I see them as being 6 inch plastic PVC tube of a suitable length and fitted with end caps
One Tube has one end cap with a brass fitting at bottom and this then is used as a water replacement container and allows feed water (saline) into the second tube and into a spiral enclosed within the second cylinder,the pathway is shown in red.
All cylinders are made airtight apart from the water storage section and the spiral coil must be wound into PVC tube to enter at the bottom and exit at the top and the reverse is true for the third cylinder as per diagram above.
I expect the water level to be maintained so that water in second tubing to be at a level somewhere near the top area as shown in red spiral path in diagram.
The saline water feed tube starts at the bottom and works it way to the exit at top of cylinder and pushes vapor into the next third cylinder.
This second 6 inch tube must be made air tight painted black to allow maximum heating of outer tube by solar energy and has some water or some other fluid also added in it.
A value is also fitted to allow a vacuum pump to reduce the pressure in the second six inch PVC tubing and then when exhausted closed ,so that a low pressure area is maintained whin the tube.
But the difference is that this tube is pressurized and wrapped in aluminium foil to reflect any heat from the sun.
I think that by inserting a bike value in the end cap at top position and by using a bicycle pump to pressurized this third cylinder.
An idea, also occurs to me that this third cylinder could also be submerged in a water bath( a 44 gallon drum perhaps ) as well,this bath would completely cover this cooling vessel and normal evaporation from this bath would also help to keep this cooling tube area cool as well.
Both cylinders would need a small amount water placed in them, but separate from that which is flowing through the two spiral tubes from the water storage area and into the distilled water collection point as show in diagram above.
Saline Water is fed by means of gravity and through the plastic spiral where it is heated from the heat gathered from the environment and because of the vacuum means a lower boiling point heat will be transferred to flowing saline water and allows it to vaporize at top of the tube.
This vapor is then pushed through the spiral plastic tube and then enters into the pressurized region of the third tube where it condenses and flows in to a collection area below the tube.
With previous experiments when inserting brass fittings I found it impossible to get a good air tight seal ,then I tried adding some fibre glass resin in the end caps and then letting it set around the brass fittings, I found the fibre glass has a tendency to close around metal objects and this makes it an excellent means for making air tight seals especially in slight pressurized applications as described here.
Then Plastic PVC cement is applied to the end caps and the 6 inch PVC cylinders walls and pressed fitted together and let dry.
I am unsure how it would work in a slightly low pressure area as is the case for the third cylinder as describe here within.
I have suggested using plastic tube (1/4") for the two spiral coils in the cylinder ,but however I feel copper piping would allow better heating and cooling transfers to the liquid within.
I see the unit as a stand up affair with the each PVC pipe standing or angled to make the maximum use of the solar heating in the area especially the second tube.
The third section cooling section could be placed in the shade or in a cooler location.
I see some flaws on your design. One. The vacuum on the middle cilinder will not get through the spiral tube, and if it goes (making the tube from some kind of plastic) it will be there as long as there are not water vapor presure inside it. As a matter of fact, the cooling on the last cilinder could be more effective on lowering the presure on the Tube as the vapour condenses. Two. As the water evaporates from the coil it will leave salt on the tube and increase the concentration on the remaining water which also increases the boiling point making it difficult to evaporate more. You need to change this water and loose the heat it gained or put so much of it that the increase in salt will not be a problem.
I still prefere the oldest method. A pan not to deep (12 inch diam. 4 inch deep) painted in black with a tube in the middle going through the bottom of the pan. Put a funnel on the tube and cover the pan with some clear plastic like the one of fruit bags and tie it to the sides of the pan. Put a little stone on the plastic just in top of the funnel and put it all to the sun and fill with salt water.
As the water evaporates it will condensate on the plastic and flow to the lower part (the stone) and drip on the funnel out of the pan.You can change the water in the morning as it will be the coldest to keep the salt level down. You can put leaves insted of salt water or chppoed cactus in the desert and they all will evaporate and give clean water.
PD. I am mexican so please forgive my english. Regards, Armando.
