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Conference unifix::sailing

Title:	SAILING
Notice:	Please read Note 2.* before participating in this conference
Moderator:	UNIFIX::BERENS

Created:	Wed Jul 01 1992
Last Modified:	Mon Jun 02 1997
Last Successful Update:	Fri Jun 06 1997
Number of topics:	2299
Total number of notes:	20724

422.0. "Desalinators" by EUREKA::REG_B (Bicycle break-dancer) Wed Oct 15 1986 11:48

    
    	A question of idle curiosity;  
    
    	How do desalinaters (desalinatOrs ?) work ? 
	[other than, "poorly", or, "quite well"]
    
    	The ads don't help, they just list maintenance kits and filtres.
    Since salt water is a solution of (mostly) sodium chloride in water,
    there has to be something other than filtration, i.e. a reaction to
    precipitate a solid that can be filtered. 
    
    	Reg
    
    P.S.  I know I'm going to feel foolish when I see the reply,  bound
    to be something I should have remembered from high school chem'.

T.R	Title	User	Personal Name	Date	Lines
422.1	some possibilities.	CASAD3::THOMAS		`Wed Oct 15 1986 12:16`	17
	THer eare several possibilities. Distillation which converts thw water to a gas, leaving the NaCl and other things behind. Chemical additive that would react with the NaCl to cause it to precipitate out. Osmosis. I've no idea how this would work,i.e., what fluid you would keep on the "good " side of the membrane or how water would be separated but I thought I'd stick it in because I've always wanted to talk about osmotic (love that word!!!!)reactions. Interesting topic. Ed
422.2		GRAMPS::WCLARK	Walt Clark	`Wed Oct 15 1986 14:18`	10
	I dont know exactly how the osmosis systems work, but I understand they use a Gor-Tex type material as the membrane. I have heard that, although salt cannot cross the barrier membrane, some impurities do make it thru, so the water cannot be detoxed with this system. Maybe it has something to do with the size of the crystals disolved in a solution vs. the pore size of the membrane. Walt
422.3	under pressure	MAXWEL::HAYS	Phil Hays	`Wed Oct 15 1986 15:33`	9
	Osmosis systems work by having a membrane with a pore size small enough to not pass (much) NaCl ions, and large enough to pass H2O. The system forces salt water at high pressure against one side of the membrane, and mostly H20 passes through the membrane. The pressures are ~2000 lbs/in2. Phil
422.4	more information	PULSAR::BERENS	Alan Berens	`Wed Oct 15 1986 15:33`	17
	The reverse osmosis desalinators use a membrane (not Gore Tex) with fresh water on one side and sea water on the other. A pump maintains the sea water side at a very high pressure. Water passes through the membrane from the sea water side to the fresh water side, producing drinkable water. The systems are relatively expensive -- a hand pumped liferaft model is $695. One large enough to provide all of the fresh water needs for a crew of 2 to 4 is on the order of $2500. The membranes last for at least 2000 gallons, as I recall. SeaGold makes the ones I am familiar with. Some of these systems will make thousands of gallons per day. The Gore Tex folks make a solar still that uses Gore Tex material. According to reports, this is a good still. Still not cheap ($300 or so) and usable only on relatively calm, sunny days. In an emergency, sea water could be distilled on the galley stove.