On Monday 02 August 2010 06:01:13 [email protected] wrote: > > I can use help on a system I'm developing to take water out of the > > air using a deliquescent salt that is subsequently boiled off where > > the salt stays behind and the water is re-condensed and saved. I'm > > using CaCl2 as the deliquescent salt and everything works > > fine on getting water out of the air.
Interesting project, how do you pass the humid air over the salt? Is the salt there to provide surface area as well as absorption? How would the deliquescence ompare with using an absorption chille to directly bring the air below its dewpoint? > > > > Water takes on the order of 2.2 Mega Joules/liter to boil at 100 > > degrees Celsius and more with the salt present. Plus the specific heat to bring the salt solution to the boil, some of the water will be weakly bound to the calcium chloride molecule too. Conservation of energy applies so that with a decent amount of heat recycling the external heat source only needs to make good losses and boost temperature. > > This mixture can take > > up to 130 0C to boil and the options available to me as I > > see them are: 1. rocket stove, 2. gasification stove, 3. charcoal > > stove, 4. solar thermal concentrator, etc. The 130 0C is > > no problem for the stoves, but I'm curious about what the maximum > > efficiency of any of these is. It seems to me that the rocket or > > gasification would have about the same efficiency, but perhaps I'm > > wrong. A charcoal stove may be useful in some situations, but > > probably not in most. And I suppose reverses osmosis and flash > > boiling etc. are also possible, but seem pretty sophisticated for > > local people? My guess would be reverse osmosis is the most energy efficient but it normally means discharging some brackish water rather than getting all the water out, i'.e. the concentration of the solute will affect performance. Cascaded flash next to cut heat losses and direct boiling a poor third. If you go for boiling and condensing then there will be little difference in the combustion technology, it's the heat exchanges where savings could be made. The difficulty I see is that normally you would have lots of cold salty water to act as a cold reservoir, in the absence of that you have only an air blasted condenser of some sort which means fans. > > > > Solar thermal concentrators would be the only way to go in a > > desert, What insolation do you have? If you have a bit of height available then gravity may assist in lowering the pressure and hence the boiling point of water if you can stuff the salt solution in through a valve. I'd be more inclined to look at a solar trough with an inflated platic bubble around it, the reflector just tracking the height of the sun and the liqui boiled off in a steel pipe forming the axis. I've been dismantling computer hard drives and the platters seem ideal for a solar project but I suspect you are looking at large scale. _______________________________________________ Stoves mailing list [email protected] http://listserv.repp.org/mailman/listinfo/stoves_listserv.repp.org http://stoves.bioenergylists.org http://info.bioenergylists.org
