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#11
posted to rec.boats.cruising,rec.boats.building
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Potable Water - The Third Way.
Brian Whatcott wrote:
On Sat, 22 Sep 2007 01:21:39 +0000, Larry wrote: [Brian] The boiling point of water at the top of a sealed 40 ft column of water is near ambient. My deepest apologies to the engineers who may be rolling under their desks, crushing their pocket protectors. It took me a while to stop chortling. I nearly lost my Chinese dinner! .. Larry They say if you give a fool half a chance, he will rush in. And so he did. TWICE! Chortling, at that. Brian W And your point was??? |
#12
posted to rec.boats.cruising,rec.boats.building
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Potable Water - The Third Way.
On Sat, 22 Sep 2007 01:04:55 -0500, cavelamb himself
wrote: Brian Whatcott wrote: The boiling point of water at the top of a sealed 40 ft column of water is near ambient. They say if you give a fool half a chance, he will rush in. And so he did. TWICE! Chortling, at that. Brian W And your point was??? Put this pointy hat on, and go stand in the corner with that other fellow. I'll tell you when to sit down again. Brian W |
#13
posted to rec.boats.cruising,rec.boats.building,sci.engr.mech
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Potable Water - The Third Way.
"N:dlzc D:aol T:com (dlzc)" wrote: Dear Larry: "Larry" wrote in message ... dlzc wrote in news:1190415672.506271.93890 @k79g2000hse.googlegroups.com: There are ship-board distiller units that use an engine to pull a vacuum, and the engine's waste heat to boil that water, to generate drinking water. A little shorter... http://en.wikipedia.org/wiki/Boiling_point "The boiling point of water is 100 0C (212 0F) at standard pressure. On top of Mount Everest the pressure is about 260 mbar (26 kPa) so the boiling point of water is 69 0C. (156.2 0F)." AT 40' ASL, the boiling point must be down to...to....211.95F! What Brian left to the reader's imagination, is that the head space of the tubes is at a near perfect vacuum, flooded only with water vapor. You might recall that a perfect vacuum will lift a column of water about 32 feet, on a high pressure day. Or had you not figured that out? Well no, he obviously hadn't figured that out. Nor can anybody figure out what is going to hold a column of water 40 ft high as was stated in the original post. The tubes may be 40 feet but the column of water will be considerably less. How much less will depend on how much energy is heating on the hot side and how much energy is cooling on the cool side. The total amount of energy needed is not going to be any different than any other distilling method. Unless you have the free or cheap sources of cooling and heating at specific temperatures this isn't going to work any better either. -jim David A. Smith ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#14
posted to rec.boats.cruising
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Potable Water - The Third Way.
Brian Whatcott wrote:
Briefly: Take one forty ft vertical tube filled with saline. Take one forty ft vertical tube filled with fresh water. Connect them with a little engineering help - at the top. .... The boiling point of water at the top of a sealed 40 ft column of water is near ambient. So, it doesn't take much heat to boil the brackish water, A nice idea, but unfortunately, the vast bulk of the energy used by the distiller is not used in heating the water to the boiling point, but in performing the phase change from liquid to gas. I believe this is a constant regardless of the surrounding pressure. The same principle works with ice keeping things cold. It is not so much the fact that the ice is colder than your drink that keeps it cold for so long, but rather that the energy required to accomplish the phase change from solid to liquid requires a bunch of energy. - Dan best |
#15
posted to rec.boats.cruising,rec.boats.building,sci.engr.mech
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Potable Water - The Third Way.
On Sat, 22 Sep 2007 10:15:40 -0500, jim wrote:
What Brian left to the reader's imagination, is that the head space of the tubes is at a near perfect vacuum, flooded only with water vapor. You might recall that a perfect vacuum will lift a column of water about 32 feet, on a high pressure day. Or had you not figured that out? Well no, he obviously hadn't figured that out. Nor can anybody figure out what is going to hold a column of water 40 ft high as was stated in the original post. The tubes may be 40 feet but the column of water will be considerably less. How much less will depend on how much energy is heating on the hot side and how much energy is cooling on the cool side. The total amount of energy needed is not going to be any different than any other distilling method. Unless you have the free or cheap sources of cooling and heating at specific temperatures this isn't going to work any better either. -jim Well, at least this respondent Jim, is operating at shall we say the 7th grade level of science/engineering insight. Like so many other products of the domestic school system, he seems to have a severe case of self-esteem syndrome. Still, he may be retrievable, starting with a science demonstration he may have missed. Place a beaker of water in a bell-jar and pump the air out. When 99% of the air has been pumped out, the water in the beaker is boiling vigorously, until, in the usual way, the beaker boils dry. The beaker feels cool to the touch, naturally. To quote him: "unless I have a cheap source of heating this won't work..." For the $64 prize: NOW do you get it? Brian Whatcott Altus OK |
#16
posted to rec.boats.cruising
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Potable Water - The Third Way.
On Sat, 22 Sep 2007 08:29:57 -0700, Dan Best
wrote: ...the vast bulk of the energy used by the distiller is not used in heating the water to the boiling point, but in performing the phase change from liquid to gas. I believe this is a constant regardless of the surrounding pressure.... - Dan best As it happens, you believe wrongly. But you might be surprized if you took a moment to look up enthalpy of water, or refer to steam tables, or whatever.... Brian Whatcott Altus OK |
#17
posted to rec.boats.cruising,rec.boats.building,sci.engr.mech
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Potable Water - The Third Way.
Sounds neat, haven't seen that one before.
Thanks for sharing. "Roger Long" wrote in message ... There's another neat way you can demonstrate this with minimal equipment. Take a tight fitting jar and get the water boiling vigerously in it with the cap on loose enough to let the steam out. When it is full of dense steam and about 1/3 boiling water, remove instantly from heat and tighten cap. When everything is cooled to room temperature, put an ice cube against the jar and the water will start to boil. The ice condenses the water vapor further, reducing the pressure to the point where the water will boil at room temperature. I've seen it done and it looks like the ice cube is boiling the water. My father won a science fair doing this back in the 1930's. -- Roger Long |
#18
posted to rec.boats.cruising
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Potable Water - The Third Way.
Brian Whatcott wrote:
On Sat, 22 Sep 2007 08:29:57 -0700, Dan Best wrote: ...the vast bulk of the energy used by the distiller is not used in heating the water to the boiling point, but in performing the phase change from liquid to gas. I believe this is a constant regardless of the surrounding pressure.... - Dan best As it happens, you believe wrongly. But you might be surprized if you took a moment to look up enthalpy of water, or refer to steam tables, or whatever.... Brian Whatcott Altus OK Actually, do a search on "triple point" and look at the phase diagram for water. That gives a good graphical depiction of the pressure/temperature/phase relationships. But, as to what the original poster claimed, i.e. that: Briefly: Take one forty ft vertical tube filled with saline. Take one forty ft vertical tube filled with fresh water. Connect them with a little engineering help - at the top. And that: The boiling point of water at the top of a sealed 40 ft column of water is near ambient. is simply wrong as stated. If you filled each vertical tube with water, venting the air at the u-tube connection, then sealed the u-tube *and* allowed the water to drain down about 30 feet, then you'd pull a sufficient vacuum. The water, however, would not be anywhere near the "top of a sealed 40 ft" column. So, this system will certainly work, but you need to heat the entire length of the 40' seawater column (to prevent column refluxing). You also need to cool the condenser side of the system if you want any efficiency. Bottom line, you can use a system like this to save energy, but you have to run it very, very slowly. When the seawater evaporates, the headspace pressure rises, quenching the process until the condensation on the other side reduces the headspace pressure again, and that steam has to travel 60 feet, so it's slowwwww. Diffusion is all you've got to work with here. There ain't no free lunch. You want to speed it up, you need more energy input, either on the heating side, the cooling process, or in the evacuation process. Keith Hughes |
#19
posted to rec.boats.cruising,rec.boats.building,sci.engr.marine,sci.engr.mech
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Potable Water - The Third Way.
On Fri, 21 Sep 2007 17:35:02 -0500, Brian Whatcott
wrote: The boiling point of water at the top of a sealed 40 ft column of water is near ambient. So, it doesn't take much heat to boil the brackish water, and have it pass to the fresh column where it is slightly cooled to hold the near vacuum conditions at the boiling level. Fraid not. It takes the same ammount of heat to boil water as at 212F. Approximately 1175 BTU/lb. You might save a little not heating the water all the wqy to 212. |
#20
posted to rec.boats.cruising,rec.boats.building,sci.engr.marine,sci.engr.mech
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Potable Water - The Third Way.
"Brian Whatcott" wrote in message ... You've heard all about distilling water, and you've heard all about reverse osmosis, but you haven't heard about low-cost, low energy stills: they are brand new. Briefly: Take one forty ft vertical tube filled with saline. Take one forty ft vertical tube filled with fresh water. Connect them with a little engineering help - at the top. The boiling point of water at sea level pressure is about 100 deg C The boiling point of water at the top of a sealed 40 ft column of water is near ambient. So, it doesn't take much heat to boil the brackish water, and have it pass to the fresh column where it is slightly cooled to hold the near vacuum conditions at the boiling level. [An engineering effort of a U of Utah group I think] Brian Whatcott Altus OK Lame suggestion and unworkable on most boats. Ya gotta think outta the box, man. However, there is another way. I thought it up all by my lonesome. All you need is a reverse osmosis membrane. You put it into a chamber that is vented to atmosphere on the inside and to the ocean on the outside of the membrane. You lower it into the ocean to a depth of only 500 feet and the pressure of the water is enough to push fresh water through the membrane into the chamber. When it gets full you haul it up and empty in into your tanks. Reverse osmosis without any energy used to get it. Ain't Wilbur brilliant? Wilbur Hubbard |
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