h a l f b a k e r y
It's as much a hovercraft as a pancake is a waffle.
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
or get an account
Inflatable solar stills are often carried as survival
equipment on liferafts.
A typical such still looks like a mini circular liferaft with
conical lid. The bottom of the "raft" is dark, and the lid
transparent. You put salt water in the bottom, and
the thing to your liferaft.
Sunlight heats the salt water,
which then condenses as fresh water inside the lid, and
runs down to be collected around the edge. See link for
One problem with such stills is that, in choppy water, the
salt water in the bottom can splash up and get into the
fresh water being collected in the rim.
Another problem is that the condensation has to happen
inside the transparent lid, which will be quite warm (at
least as warm as the surrounding air).
I suggest a better version.
First, imagine an inflatable ring. Now attach two
transparent, inflatable cones to it - above and below. So
now you have a sort of spindle-shaped double cone, with
the inflatable ring running around the equator. The
can be opened up using a seal like on zip-loc bags.
Now add a string, running across the centre of this device
(ie, diametrically across the ring), and from this string
hang your saltwater container. The saltwater container
(which can also be inflatable, for packability) is almost
wide as the inside of the ring (you want a lot of surface
area), and is deep enough to stop the saltwater splashing
out if the sea is a little choppy.
We'll also add some ballast (anything will do) in the end
the bottom cone.
The whole thing floats in the sea (tethered to your
liferaft), with one of the cones sticking down into the
the other one sticking up in the air, and the saltwater
container held by the string in the middle.
It works much like a conventional solar still, with water
evaporating from the saltwater container, then
and being collected in the bottom. However, it's better
1) The saltwater reservoir is not in contact with the sea,
and will therefore get hotter than it would in a
conventional solar still.
2) As well as condensing on the inside of the upper cone
(which will be at air temperature), the water can also
condense on the inside of the bottom cone, which sits
below the waterline and will therefore, generally, be
cooler. The combination of (1) and (2) should greatly
improve the thermal efficiency of the whole thing.
3) Because the saltwater container hangs from the string
the middle of the device, it should be less liable to being
tipped and splashed into the fresh water; the fresh
on the other hand, collects in the bottom where it is less
likely to be splashed into the saltwater container.
(?) Typical solar still
Thermally inefficient, and also a rip-off at £122! [MaxwellBuchanan, Jun 01 2011]
||"First, imagine an inflatable ring"
||Would it not be easier just to be rescued ?
||It might but, with limited payload capacity on a
helicopter, would you be able to bring your twelve
discs and complete works of Shakespeare?
||With appropriate use of MP3 files and the Compleat PDF's of Williame Shaikspere, we do not anticipate a problem. But the leather upholstered wing armchair, the Aubusson carpet, the polished oak bookcases, the Sheraton escritoire, the Ming vases, the collection of Etruscan ceramics in their glazed display cabinet, the life size bust of Palmerston in Carrera marble, the elephant's-foot umbrella stand, the Rembrandts, the Adam fireplace, the cellar of vintage Port, Madeira and Sherry, four footmen, six maids, the Assistant Second Bookbinder-In-Ordinary, the Coal Urchin, the Deputy Warden of the Fire Irons ... yes, you're right, it all adds up.
Good thing you're not suggesting moving one of the main Libraries. That would be quite difficult.
||Why would I need and elephant's foot umbrella
stand? Elephant's foot umbrellas are so hard to find
||Solar stills are old hat. Reverse osmosis hand pumps are where it's at.
||But I have been told that, if you hand-pump a R/O
osmosis pump, you risk losing more water in sweat
than you get back from the pump.
||//The cones can be opened up using a seal// but what if there aren't any in that part of the ocean?
||You'd manage it one way or an otter.
||A friend and I were once called upon (during an adavnced
wilderness course) to improvise a solar still, and we ended
up building something very much like this out of a few
sheets of poly, some broken tent poles, a bootlace, and a
one-gallon ziplock bag. The bottom cone was dug out of
lined with poly, and some extra tent pole segments were
arranged in the upper cone to keep rigid(ish). It worked
well but very, very slowly, and once the ziplock bag
reservoir slopped when the wind gusted, meaning we had
to clean it out and start over (we were using microbe-
contaminated bogwater and, er, urine). Still,
I can see a well-engineered and professionally-
manufactured version of this being very effective.
||Don't forget some 1/4 inch plastic tubing...you're gonna
||you'll need a better system for keeping it from
slopping, like a way to take out the fresh water as
soon as it's freshened.
||The simplest way is not to have the saltwater
sloshing around. Put a sponge in the saltwater
reservoir, so that it can be saturated with seawater
but not free to slop around.