h a l f b a k e r yI think this would be a great thing to not do.
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Jim reckons pumping fresh water out of a well is something that just cannot be simplified --- but he reckons that there is not really any need for the actual well.
Jim got a heavy bucket and covered the top with a salt water reverse osmosis membrane. Jim lowered the bucket into the sea off his mates
fishing boat and pulled out a bucket full of fresh water.
...
Jim got tired pulling up the bucket full of water so attached a little inflateable bouy the second time around and just dropped the whole lot over the side attached to some of his mates fishing line.
Supersimple reverse osmosis
Supersimple_20reverse_20osmosis
[xaviergisz, Dec 02 2009]
Zorbos bucket
Zorbo_27s_20Bucket
[+] [madness, Dec 03 2009]
[link]
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You'll need to go 8km deep (according to the calculations on 'Supersimple reverse osmosis'). |
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//You'll need to go 8km deep// |
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Actually, no. Those calculations don't apply to an empty tube, or to an empty bucket. Ling made this suggestion on the supersimple thread back in 2004: "lower a sealed pipe by rope. When it is full of fresh water, pull it back up." |
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Even so I am guessing that the bucket will not come up 'full' given there was no effort to remove any air trapped inside... |
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//I am guessing that the bucket will not come up 'full' given there was no effort to remove any air trapped inside// |
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You'll need to go down past 20-30 bar, where the air will be compressed to a fraction of its original volume by entering fresh water. The backpressure will limit how much you can fill it at a given depth, but no big deal, just make it bigger. The addition of a simple check valve will bleed off this air as you raise the bucket. This ocean bucket would be a useful backup for sailboats, or for rowboats crossing the ocean. |
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[marked-for-consideration] redundant with the linked idea. |
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The only apparent difference between that and this (apart from this one being written in the ever-annoying "Jimstyle") is that one uses a pipe, and Jim, contrary fellow that he is, has deemed to use a bucket. |
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// redundant with the linked idea//
While the idea is not the same, it's definitely in the annos:
*Alternative idea: lower a sealed pipe by rope. When it is full of fresh water, pull it back up.
*I'm with [Ling] on this one. Who needs a pump or a perpetual diffusion machine, when we could go deep-sea fresh water fishing? The cylinder could be small enough to be carried on sailboats, or on inflatable emergency rafts.
*A small cylinder...and a thousand feet of rope. |
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whyntcha make a bag out of membrane material, fill it full of water and sit on it |
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//whyntcha make a bag out of membrane material, fill it full of water and sit on it// |
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Sitting on it would work if you sat on one end of a hydraulic piston. |
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Isn't lowering a sealed section of pipe (i.e. a bucket) on a rope just a quantised alternative to sinking a long pipe? |
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1) exactly how heavy would this sealed-pipe/bucket (assume the bucket is full of air and has a volume of 1 litre) need to be in order to sink to the depths necessary for the reverse osmosis to work? |
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2) What is the maximum practical mass that Jim's mate's fishing boat can safely carry? (Assume Jim and his mate are of negligible mass) |
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3) From 1 and 2 - what is the maximum amount of fresh water that can be extracted using this method in one trip without sinking Jim's mate's boat. |
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4) How far out would Jim's mate's boat have to go in order to be deep enough for the reverse-osmosis thing to take effect? |
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5) How far from Jim is his mate's boat? |
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6) How far from Jim is the nearest well? |
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7) From 3), 4), 5) and 6) - is it easier/simpler for Jim to get the same amount of water from a well? |
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So this idea isn't an instruction? |
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Addendum to 1) How heavy is 2000 ft of rope, the winch, and the spool required to lower the bucket that far. |
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8) How much energy is required to haul the bucket back up 2000 ft (the number for an empty bucket from super simple reverse osmosis) |
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9) Given 8, Would that energy be better spent on a surface level reverse osmosis system. |
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MechE, the idea doesn't claim efficiency, so where's the bad science? As for being redundant, I'm not sure if it's redundant if it's only anticipated in an anno. |
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Yeah man --- go play with the little kids... |
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Okay, bad science Mark removed, you're right, it's just bad engineering, which is offensive but not cause for removal. |
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//As for being redundant, I'm not sure if it's redundant if it's only anticipated in an anno.// |
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It depends how far that anno extended the original idea. If there's already an idea for lollypops with 10cm sticks, and someone anno's a suggestion for a lollypop with a 12cm stick - and then Jim posts an idea about lollypops with 12cm sticks - is the second idea redundant? |
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In this case, I don't care about the length of the stick, it's plainly the lollypop that's the idea. You have to make a judgement call on how similar the ideas "get water from reverse osmosis using a tube" and "get water from reverse osmosis using a bucket" are to one another. For me, they're pretty much the same. |
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Well I know which one requires less engineering, costs less and can be carried around in the boot of a car... |
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Which, the 10 or the 12cm lollypop? |
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Or do you mean the boat? Or the rigging and equipment to send a bucket to a depth of 8km and then pull it back up again? |
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I mean, a bucket and rope (I don't need a specific winch) costs less than 1k or 8k of pipe... |
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And for the purposes of comparison I have allowed the possibility of fresh water bubbling up from the depths. But in reality the RO membrane and solid pipe will bugger the pressure differential pumping action. So in reality you will need the bucket and rope in addition to the 8k of pipe... |
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Bear in mind that a normal sized bucket should act as a fairly decent flotation device for someone of Jim's size (assuming he's normal sized) so would need to weigh at least more than Jim. Assuming Jim has normal sized muscles then he'd going to need a winch of some sort. Agreed, it's less big than a 8km pipe, but assuming Jim has a normal sized car, it still might not fit in the boot. |
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The 281 cubic feet (minimum for 2000 ft depth) of rope will also probably not fit in the trunk. That's only another 40 lbs, admittedly. If you have a winch on board that can take up that much rope, or a running winch and a drum to coil it, then no you don't need a specific winch. I'd be surprised if you do, however. |
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Yes it's cheaper than super simple reverse osmosis (which, if deep enough will allow the water to bubble up, read the full anno string to see that). It's still not cheaper or less energy intensive than a small surface RO unit. |
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// The 281 cubic feet (minimum for 2000 ft depth) of rope will also probably not fit in the trunk. // |
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281 cubic feet of rope? That's a drastic miscalculation. You only need about 30 bar for this to work, so 1000 ft should be sufficient. And 1/8 diameter nylon cord (300 lb test) would weigh only about 4 pounds. So this is quite doable if you only want a small volume of water--a quart to a gallon, say. More than that would be too tiring to pull up. |
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I went with 3/8 manilla, admittedly, and I find number closer to 50-60 bar for RO of seawater, hence 2000 feet. You're right about the volume, even 3/8" is only a couple of cubic feet, I mixed up my units. |
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If your bucket is going to be dense enough to drop to that depth while filled with air, it is going to have to be heavy. Also, not sure about the bouyancy of rope, but you may need to be able to sink that as well. In addition, the bucket is going to have to be able to withstand (300 PSI if your number is right, 735 if mine is), it will not be a simple bucket with an RO membrane taped to it. |
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300lb test might be sufficent, I upgraded from 1/4" to 3/8" because I wouldn't build it with 450lb. |
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Even at a thousand feet, have you ever hauled in that much line by hand? I've done a couple hundred, and it was tiring and hard to keep coiled even pulling it into a drum. Add in the fact that you're raising 2-300 lbs minimum that distance (even under water, if it sinks that far it will take energy to raise), you will sweat out more water than this produces. |
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//I find number closer to 50-60 bar...If your bucket is going to be dense enough to drop to that depth while filled with air, it is going to have to be heavy. // |
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The osmotic potential for seawater is around 24 bar, so you need more than that, but not a great deal more, as the speed of osmosis is not a factor here. On a lifeboat, no big deal if you have to leave it down for an hour. As for the weight of the bucket, it need only be heavy enough to overcome its empty displacement, and then some so that it doesn't take forever to sink. So lets say a twenty pound SS cylinder with a gallon and a half capacity, so a submerged weight of about seven pounds. Then, to bring up a gallon of water, that's about sixteen pounds. A lot of effort, yes, but a gallon of water should be good for a couple of days in a lifeboat. And obviously, the unit could be smaller, and therefore easier to haul up. Also, if you ran the rope through a cleat, you could use wave power to help bring it up. |
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Hmmm Jim is an adaptable fellow so he has addressed your concerns that he is not up to the job of lifting a bucket... |
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So you have a buoy that inflates at 1000 ft? That will take a compressed air cylinder or gas generating pellet. And if you're going to require such consumables, it begs the question: why not have water on board to begin with? |
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Why, thats a good point --- I suppose the bucket will work either way though. And to be honest most boaties would carry spirits in preference to h2o... |
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