h a l f b a k e r y"More like a cross between an onion, a golf ball, and a roman multi-tiered arched aquaduct."
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Ok, I've had a bit of wine and it's late, so if I'm reading my thermodynamics tables wrong feel free to laugh at me.
Now, I was thinking about how whether it would be difficult to create a vacuum using hand power. Since atmospheric pressure is about 14.7 pounds per square inch (101.3kPa), and I
can easily lift 14.7 pounds with one hand (even after a few glasses), it should not be difficult to take a cylinder with a round cross-sectional area of 1 inch^2 (a bit larger than the size of a US quarter) and a piston with a handle and create a vacuum.
There are two ways of boiling water. You can either raise the temperature, or lower the pressure. Since water at room temperature boils at around 0.36psi (2.5kPa), it seems to me that if I put water in my cylinder it would boil. If that water were dirty (sea water, urine, or from whatever survival scenario you can imagine), it seems to me that you could use this pump to evaporate water on the upstroke, and condense it on the down stoke. Putting a reservoir that collects this clean water apart from your dirty water, you should be able to purify water fairly easily. This could be the size and weight of a bicycle pump, and would be perfect to include in any survival kit.
(?) It works!
http://www.nutriteam.com/nautilustech.htm
But someone beat you to it... [roby, Oct 06 2004, last modified Oct 17 2004]
(?) Reverse osmosis hand pump
http://www.darpa.mi...er/html/h2oros.html
Osmosed piss is no longer piss. [bungston, Oct 06 2004, last modified Oct 17 2004]
Vacuum Distillation.
http://www.severntr...cts/vacuum_dist.jsp
with diagram. [Amos Kito, Oct 06 2004, last modified Oct 17 2004]
Reverse osmosis hand pump
http://www.readymad...et=0&deep=2&cid=238
[Worldgineer, Apr 28 2005]
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You should see someone about that. Are you drinking unpurified urine? |
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No I only drink purified.
So this in effect would be like a steam engine but with a vacume boiling the water. |
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Well, kind of the reverse of a steam engine. A steam engine uses steam to increase pressure, which exerts force. This device would exert force to decrease pressure and create steam. |
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But the actual boiling of the water isn't what purifies it. The water is raised to a temperature that kills (most) of the bacteria. Simply exposing them to a brief vaccuum is unlikely to kill them. |
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It is recommended that you boil water for 3-5 minutes to purify it. So even if this were to kill the bacteria, and assuming you could make a portable piston/cylinder that could hold a vaccuum for that long, at 1 cubic inch every 3-5 minutes, you'd spend FOREVER trying to purify water to drink. |
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Note: as you have used the terms 'evaporate' and 'condense', I hope you aren't thinking this device acts as distiller. Boiled piss is still piss. |
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//Boiled piss is still piss// |
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I could argue that that anno belongs in 'Use Bizarre Metaphors', but it makes far too much sense. |
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I think [Worldgineer] is making the point that the impurities don't vaporize with the water. If the bacteria don't traverse the route from the source to receiver, who cares if they're dead? |
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[Worldgineer] is a genius born too late.
Vacuum aided boiling to distill away impurities and/or to desalinate is an invaluable concept. Intuitively I thought it didn't make sense, but I googled vacuum distill water and got the link at left, a company that makes and sells worldgineer's product.
It seems the energy consumption is a bit higher than possible with hand vacuum pumping, and entails external heat to boil at 25-65 degrees centigrade, along with coolant for condensation.
But if you're in the middle of the ocean with plenty of fuel but no drinking water, it would be a lifesaver. |
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Now its been proved that [world] wasn't just talking bollocks in the knowledge that we probably wouldn't understand anyway, he can have the sambwiches seal of approval. +. |
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This becomes useful knowledge since probably every war in the near future (after this one, obviously) will be over drinkable water,instead of being over oil. |
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In the end, I wasn't doubting that the boiling of brackish water by pressure reduction and the subsequent condensation of the vapour would make a potable fluid, I was merely stating that [World]'s idea included no mention of the method of separation of the two ingredients. If one was simply to re-squeeze the handle on this invention, the liquid and (supposed) solid would re-unite, creating undrinkable liquid again. |
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//Putting a reservoir that collects this clean water apart from your dirty water, you should be able to purify water fairly easily. //
he got it, but I have to confess, I didn't get it either, at first. He must have been drunk when he wrote this up. |
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that a clever idea, but it needs development |
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Sorry I wandered away for a few days, I was in the process of moving to Seattle. |
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[Cedar] //1 cubic inch every 3-5 minutes// How do you figure? Without testing I have no intuitive feel of how long this process would take. |
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[roby] The idea you linked look a bit large, plus fuel may not be plentiful in all situations. I'm thinking of a device you can put in a plane survival kit, in a backpack for a jaunt through the desert, etc. |
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[waffle] Reading my idea again, it seems clear to me. Please post any questions you still have. |
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Boiling is one way to get the water molecules away from impurities. Osmosis is another. Reverse osmosis hand pumps have been around for about 15 years. The advantage over boiling is that you avoid the bulk of gas (steam). The disadvantage: I am sure the filter element must be replaced - not necessarily true with the idea here. |
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I propose that the pump proposed here would be best suited not for hand pumping, but for permanent installation at a contaminated well, lake or other water source in the third world. Once set up it would require little maintenance. It could be run with a crank or by animal power. It should be larger, to be able to generate enough water for a household in a reasonable time. |
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[world] I'd be curious if it were actually feasible with a hand pump to facilitate vacuum-aided boiling and distilling.
The device in the link 88 kg for the waste-heat model. Apart from the power required to heat the water (more moderate than non-vacuum distilling), water pumps also required.
All I remember from much earlier discussions of desalination was that the energy consumption and costs were very high. |
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//Ok, I've had a bit of wine and it's late, so if I'm reading my thermodynamics tables wrong feel free to laugh at me.// |
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[worldgineer] i wouldn't presume to laugh at you if you misread a thermodynamics table, but what does make me giggle is the fact that late at night, after having a bit of wine, you would be doing anything that involves thermodynamics tables. |
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and yet, how often have i found myself in strikingly simlilar situations? |
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i suppose this is why we're halfbakers... |
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[bung] I like your thinking - I think this would be a great application. |
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[rob] I don't understand any of your arguements. Please repost using more words. |
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[urb] Ah, yes. Wine and physics - a dangerous yet all too compelling combination. I sometimes wonder if most posting ideas here are under the influence of one substance or another. |
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[world] I'm wondering if this is more conceptual than practical.
Your calculations are for a cubic inch vacuum. Pump 1 cc of water into your 1 cc vacuum, and I think your result is 1 cc of water, in liquid state. If that's true, how much volume vacuum do you need to contain the vapor/boiled state of a liquid cubic inch of water, such that it could be separated from its impurities for distilling?
And if it's a substantial volume, there's a lot more effort required to create and sustain low pressure.
But then assume you've got a suitable vacuum. You've got a few cc's o' pissy scummy water. You have to pump the water through the vacuum, perhaps cause it to boil with additional heat energy applied, then force the vapor into a condensing chamber, where it is cooled and thereby distilled. (At what pressure?)
I'm sorry to be so short-worded before, but the mechanical effort to be applied must also not be insubstantial. I R no ingineer, so I usually apply a pragmatist's Occam's razor to this type of thing--if it were easily done, it would have been done.
But the concept has such elegance to it, I was hoping you had in your more recent sobriety opportunity to fill in more details about the constraints and possible solutions. |
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Well that's easy enough to solve. Have it inject a small bubble of air into the water at the bottom of the down stroke. |
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Each up stroke could create a slight vapor, equally distributed in the vacuum. On the down stroke, you'll need to minimize the amount of vapor that condenses back into the urine (or seawater, etc.). Otherwise, you might be better off using that hand power to condense water from air. Regardless, you're gonna be pumping all day for a few drops of water.
But I do want to see you try it. + |
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Why would you think only a slight vapor? I think if you decrease the pressure to the point of boiling for water, all of it would vaporize. Then it's just a matter of funneling off the water as it condenses back. |
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The difference between the boiling pressure of water at room temperature and ambient pressure is about 14.3 psi. Considering a bicycle pump is capable of well over 60 psi differential pressure, it should be no problem. |
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Adding a bicycle-style drive, however, should get you a lot more fresh water. It's less portable, but perhaps more useful. |
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//This becomes useful knowledge since probably every war in the near future (after this one, obviously) will be over drinkable water,instead of being over oil.//
It's been over ten years since I did calculations, but I figure that the entire population of the world could live in a megalopolis bounded by the State of Alabama.
While this was based on sketches of dreams of a max 30 story increasing wave type design, I still had adequate amounts of space designated for transport, business, manufacturing, recreation, etc. & was working in how to incorporate a pseudo forest environment with void boxes as planters in the scheme before I had to give it up in order to focus on how to make enough money to eat.
The sum of all freshwater on earth would easily flood the entire city in my estimations.
Is it that the human state of being is to bicker & bargain over resources it could never use individually so as to prove dominance? |
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//Why would you think only a slight vapor? I think if you decrease the pressure to the point of boiling for water, all of it would vaporize.// |
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Enough water would vaporise to build up the pressure in the vacuum. Then it would stop. |
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The downward stroke would need to then compress the vapour quickly, before it condenses and drops back into the water, and pump it out through a check valve. The vapour could then be passed through a pipe which allows the condensing vapour to collect. |
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So, in effect, the pump needs to work in both directions. Slow up and fast down. |
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they have hand powered water filtration devices, you can buy then at any local outdoor shop. even piss filters |
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[ling] Quick isn't necesary. It needs to condense either way, the trick is seperating the condensation. If you introduce the dirty water in the center, the walls can be used to collect condensation (which generally collects on walls). |
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[10] Although 98.4% of salt removed is close to fresh water, we can get much closer using evaporation. |
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I'm a little late to this, eh? I think it's a great idea, so I'm adding my critique as well as my +. Two problems: |
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1) As [Ling] said, the pressure will change as the water vaporizes, requiring additional energy. |
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2) Water will boil in a vacuum, but (I hope I'm getting this right) the change in state requires energy, which means that as the water begins to boil, the temperature will go down. |
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I am guessing that #2 is the reason for the external heat in the aforementioned existing product. |
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This is a great idea, and I'd like to think it is feasible and practical. Anyone around here able to quantify the effects of these two energy draining issues? |
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In a past career, I worked as a Water Purification Specialist for a small city. I studied the heck out of water purification techniques. Here is the practical way. First, a common filter, much like the Britta pitcher filter is really quite adequate to remove most sediments...then you have to remove the bad chemicals (if any)...that can mostly be done with an activated charcoal filter...very much like the one you use on your fish tank (or again, get a better Britta filter)...then you must kill any and all baceriological critters...mainly of the viral and bacerial types that might escape the filter, although, there are some very nasty creatures that can survive practically most chemical sterilizers (although they are rare), like chlorine and iodine...a few drops in a quart of water and let stand for ten minutes or so...and you will have fairly safe drinking water. |
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However, if you want to use the "vacuum" evaporation system, you will need a few more bits of equipment. First, a good vacuum pup, preferrably one with an egine or an electric motor...a hand pump if you are overly energetic, will do. You will also require two chambers...the water chamber and the evaporation chamber...let the two chambers interconnect...the water chamber needs to only be slightly larger than the amount you want to evaporate...if that is a gallon, then about 1.5 gallon size pot with air tight lid will do...it must be of heavby wall stout construction, as will the "reclamation" chamber. The reclamation chamber should be as large as you can make it...but it must also be of heavy construction. Remember, although you may be able to pull one square inch of vacuum...the vessels must withstand that pressure on every squae inch of surface. A gallon sized pot may have to withstand thousands of pounds of force at full vacuum overall. I would build the reclamation pot as large as possible to imporve efficiency. |
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Now, you pull a vacuum on the system and wait...water will begin to boil and will fill the recovery vessel...stop pumping...for as soon as the interior atmosphere becomea saturated, you will begin vacuuming out water vapor. Close off the water vessel, and slowly allow air to re-enter the recovery vessl...which will then begin to condense the water vapro due to the return to normal pressure....it will help tremendously to cool the chamber as well....repeat the process amny times...soon, you will have about a half gallon of condensed evaporated moisture. The other half gallon was probably pulled off through the vacuum as you attempted to creat as much vacuum as possible....be sure to purify the recovered water...you probably will have sucked in some contaminates, especially viral products if any, with the boiling and such. They will be very viable (dangerous) since your system used little heat. |
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In other words, it will work, but only at the expense of tremendous energy and effort. The weight of a practical vacuum system would probably need to be carried around in at least a wheel barrow. |
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Better to use a commercially available hand pumped reverse osmosis device, or use a simple water purification tablet like Boy Scouts and soldiers use, or to use a well designed filter and water purification kit as is readily available in most camper and RV stores. Or, just boil the water first...filter it though a clean felt hat and drink up...after stirring and cooling, of course....unless you are making tea or coffee....drink hot ...most delightful. |
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[db] I imagine designing in a bit of thermal mass should help this. Your pump would get cold on the upstroke, but that would help condense the water on the downstroke. If this makes it too heavy, we could use environmental sources of thermal mass (example: place the base in the dirty water source). |
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[bb] Your device would be great for purifying a large quantity of water at once. I'm thinking about far smaller quantities, but running more cycles. We also wouldn't need to waste water, since we aren't starting with a volume of air. Yes, I'd design the device to handle the pressure (not as tough as you make it sound - bicycle pumps handle much higher pressures). |
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A tablet might be a good idea to handle virus contamination (I suppose a virus could tag along with a particle of water ejected during the boil-off), but a tablet wouldn't remove any contamination itself (sea water, for example). |
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Well, I was thinking in terms of smaller ..say about a gallon size. Vessels designed for pressure can be much lighter than vessels designed for vacuum. I am, of course thinking of metallic vessels ..exotic materials, such as carbon fiber and other synthetics could be lighter...but rigidity must be part of the design for vacuum containment. Also the larger the vessel the more thought has to be given to resisting the vacuum. By my assertion, the condensation portion would have to be much larger than the liquid state water portion, yet still withstand the vacuum equally well. You would not achieve full potential vacuum, say at 22 inches or so....at standard temperature and pressures you would begin filling the vacuum with water vapor rather quickly, necessitating a great many condensation cycles...otherwise, you would be expelling via the vacuum, uncondensed water vapor....also, you would have to remove the condensed water from the vessel before the next vacuum cycle. It just seems quite cumbersome and energy inefficient. Probably why such a device is not used for water purification today. |
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//Probably why such a device is not used for water purification today.// |
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I'm agreeing with [BlisterBob]. This is one of those concepts that's fairly obvious, but a bugger to build. It might be possible with a few one-way valves and a heat-exchanger, but working that out should be part of the idea. |
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I just Googled "hand pump vacuum distiller" and this very idea came up first. There's a video of a bike-powered boil-type distiller that takes about a half an hour of hard pedaling per cup of water. As we've discussed elsewhere, evaporating water by vacuum-pump saves less than a sixth of the energy needed to evaporate water with heat--and it doesn't kill the yuckies. |
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1. Strength required for a vacuum. I could run the calculations, but I highly doubt the strength required for a 14.3 psi vacuum will be close to 150 psi pressure - especially since cylindrical shapes are so good at resisting even compression.
2. I'm thinking of something the size of a bike pump, including the evaporation and condensation sections.
3. "expelling via the vacuum, uncondensed water vapor"? That's the point. We take a zero-(gas)volume cavity, make a large volume cavity to evaporate, then force down to a zero-volume to condense.
4. Removing the condensed water would be easy - the plunger would push water along the walls to the bottom, which has a one-way valve to your clean water reservoir.
5. Evaporating with heat doesn't take much more energy. Are you sure about that? As it's a full cycle, the only energy we're wasting is in friction. |
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