# So, I bring some water back from the Marianas Trench... **URL:** \ **Category:** Factual Questions\ **Created:** [December 11, 2012, 1:00am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657 "2012-12-11T01:00:52Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [December 11, 2012, 1:00am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/1 "2012-12-11T01:00:52Z")
Well, maybe not from there exactly, but from a deep hydrothermal vent somewhere. I take an empty bathysphere to 6 miles down and fill it up with 300° C water near a black smoker. I dog down the hatch and winch it back up to the surface, still hot and pressurized. At the surface, the air temperature is 0º C, and so is the surface water. Now that I have the hot pressurized bathysphere on the deck of my ship, in practical terms how can I extract the most work from the water (which I want to keep at the surface, so dropping it back over the side isn’t an option, nice try though). Do I connect the pressure vessel to a piston or turbine and let the water flash to 300º steam and produce power that way? Can the miniscule expansion of the compressed water be harnessed before it starts to boil? How much useful energy can I actually extract from, say, 1000kg of such pressurized, heated water? Enough to recoup a significant fraction of the cost of raising it in the first place? It seems like there must be some height at which you would break even. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [December 11, 2012, 1:20am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/2 "2012-12-11T01:20:10Z")
Is there any significant compression of water at that depth? I know that it doesn’t compress at all at any of the depths we normally go to in the ocean; is the deepest part of the sea deep enough to squish, say, 1 cubic foot of water into a smaller space? ---
**Author:** ![Capt\_Kirk](https://avatars.discourse-cdn.com/v4/letter/c/779978/32.png) [@Capt\_Kirk](https://boards.straightdope.com/u/Capt_Kirk)\ **Post date:** [December 11, 2012, 1:38am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/3 "2012-12-11T01:38:15Z")
I am almost certain that you just get hot water, probably not very cost effective. AIUI there is no serious compression of the water, the pressure comes from the mass of the water column. 1000kg/2200lb of water plus vessel would have a while to cool off on the way up as you would have to dead lift it or come up with some buoyancy scheme. IANAE I am sure one will weigh in and once again show me the errors of my ways. **Capt** ---
**Author:** ![robert\_columbia](https://avatars.discourse-cdn.com/v4/letter/r/e79b87/32.png) [@robert\_columbia](https://boards.straightdope.com/u/robert_columbia)\ **Post date:** [December 11, 2012, 1:49am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/4 "2012-12-11T01:49:08Z")
> [@Capt\_Kirk](#): > > I am almost certain that you just get hot water, probably not very cost effective. AIUI there is no serious compression of the water, the pressure comes from the mass of the water column… > > **Capt** That’s what I thought too. The reason that a submarine can get crushed at great depths is not because the water is highly compressed, but because of the great weight of water that is pushing against the outside of the sub. Gases compress quite a bit - you can compress a quantity of nitrogen and get a tank of pressurized nitrogen that takes up less space but weighs the same. Liquids don’t compress nearly as much. ---
**Author:** ![Rubixcube](https://avatars.discourse-cdn.com/v4/letter/r/8e7dd6/32.png) [@Rubixcube](https://boards.straightdope.com/u/Rubixcube)\ **Post date:** [December 11, 2012, 1:56am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/5 "2012-12-11T01:56:12Z")
How hot would the water even be by the time it got to the surface? You’re pulling that bathysphere a long way up, and for most of that journey that outside water’s going to be quite cold. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [December 11, 2012, 2:00am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/6 "2012-12-11T02:00:30Z")
There was a plan I read once to use a pipe from the shore down to the depths of a trench - and exploit the heat difference to run a heat engine (Stirling Cycle?). I’m not sure how effective that would be, but due to the noncompressibility of liquid, it would not be that difficult to pump the water up, according to their calculations. ---
**Author:** ![wheresmymind](https://avatars.discourse-cdn.com/v4/letter/w/91b2a8/32.png) [@wheresmymind](https://boards.straightdope.com/u/wheresmymind)\ **Post date:** [December 11, 2012, 2:14am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/7 "2012-12-11T02:14:47Z")
The bulk modulus of water is [2.2 GPa](http://en.wikipedia.org/wiki/Bulk_modulus). The pressure at 4,000 meters (close to the average depth of the world ocean) is [.0403 GPa](http://www.calctool.org/CALC/other/games/depth_press). So water at 4,000 meters is .0403/2.2=.018. In other words, a mass of water at 4,000 meters occupies 1.8% less space than it does in a vacuum. I’m pretty sure the bulk modulus of water actually increases at high pressures, so the real difference is probably a little bit less. However, even though the water in your sealed, pressurized chamber would expand only slightly when exposed to the surface pressure, it would do so with great force. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [December 11, 2012, 2:17am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/8 "2012-12-11T02:17:33Z")
You don’t need to pull up water at the temperature of a thermal vent; OTEC and similar technologies worked on a circa 25-50 degree difference. It’s the sheer quantity of the differential heat that makes it workable. ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [December 11, 2012, 2:27am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/9 "2012-12-11T02:27:47Z")
Are you sure this isn’t an ME thermodynamics homework problem? Because the question boils down (no pun intended) to something rather simple academic in nature…which only an ME student would ask how to solve. I’ll outline the strategy only: Basically, what you are asking is simple enough. You’re equating the enthalpy of water (h-l) at Mariana Trench P,T to the percent of water (x)(h-l) + (1-x)(h-v) steam at let-down conditions, Where: h-l = enthalpy per poundmass of liquid h-v = enthalpy per poundmass of vapor x = a decimal value between 0 and 1, exclusive And, Mariana Trench water conditions can be evaluated knowing density § at depth (H) from a table of water properties. And, Mariana Trench pressure § = pgH. You can assume the mass of your sample is 1 lb-m since everything is on a per-pound basis, anyhow. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [December 11, 2012, 2:59am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/10 "2012-12-11T02:59:53Z")
This happened when an unmanned Bathysphere was raised back up from a test down to a mere 3000 feet: > [@Wikipedia](#): > > When conducting an unmanned test of the Bathysphere with the third window installed, after pulling the Bathysphere back up they found it almost entirely full of water. Realizing the immense pressure that the water must be under, Beebe ordered his crew to stand clear and began loosening the hatch’s bolts to remove the hatch himself.[2] Beebe described the experience that followed this in his book Half Mile Down: > “Suddenly, without the slightest warning, the bolt was torn from our hands, and the mass of heavy metal shot across the deck like the shell from a gun. The trajectory was almost straight, and the brass bolt hurtled into the steel winch thirty feet away across the deck and sheared a half-inch notch gouged out by the harder metal. This was followed by a solid cylinder of water, which slackened after a while into a cataract, pouring out the hole in the door, some air mingled with the water, looking like hot steam, instead of compressed air shooting through ice-cold water” ---
**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\ **Post date:** [December 11, 2012, 3:07am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/11 "2012-12-11T03:07:54Z")
> [@Capt\_Kirk](#): > > I am almost certain that you just get hot water, probably not very cost effective. Ah yes, but if it’s particularly _hot_ water, you can make particularly _hot_ tea, and, by hooking the logic circuits of a Bambelweeny 57 Sub-Meson Brain to an atomic vector plotter suspended in your particularly strong Brownian Motion producer, _and_ working out a few key improbabilities, you would, if nothing else, win the Galactic Institute’s Prize for Extreme Cleverness. I’d even by you a djinuntoonic (no Pan-Galactics though, still hung over). ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [December 11, 2012, 3:09am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/12 "2012-12-11T03:09:40Z")
> [@Lumpy](#): > > This happened when an unmanned Bathysphere was raised back up from a test down to a mere 3000 feet: But that appears to represent the compression of the air inside the pressure hull, not of the water. Much like the toy water rockets you pump up, but on a mega-scale. ---
**Author:** ![brossa](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/brossa/32/3040_2.png) [@brossa](https://boards.straightdope.com/u/brossa)\ **Post date:** [December 11, 2012, 3:56am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/13 "2012-12-11T03:56:46Z")
> [@Jinx](#): > > Are you sure this isn’t an ME thermodynamics homework problem? Because the question boils down (no pun intended) to something rather simple academic in nature…which only an ME student would ask how to solve. I’m quite sure it isn’t homework; that’s twenty years in the past. I appreciate the outline of the strategy, but I don’t know what you mean by let-down conditions. I take it that only some fraction of the water will become steam at 1 atm pressure because the heat of vaporization is so high. Plus, even if I knew how many kJ was released as heat by the water going from Marianas P,T to surface P,T based on enthalpy differences, can I really capture all that energy and turn it into mechanical work? ---
**Author:** ![ataraxy22](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ataraxy22/32/307_2.png) [@ataraxy22](https://boards.straightdope.com/u/ataraxy22)\ **Post date:** [December 11, 2012, 4:58am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/14 "2012-12-11T04:58:29Z")
> **[Ocean thermal energy conversion](https://en.wikipedia.org/wiki/OTEC)** > > Ocean Thermal Energy Conversion (OTEC) uses the ocean thermal gradient between cooler deep and warmer shallow or surface seawaters to run a heat engine and produce useful work, usually in the form of electricity. OTEC can operate with a very high capacity factor and so can operate in base load mode. > The denser cold water masses, formed by ocean surface water interaction with cold atmosphere in quite specific areas of the North Atlantic and the Southern Ocean, sink into the deep sea basins and s... ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 11, 2012, 7:35am UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/15 "2012-12-11T07:35:02Z")
> [@NitroPress](#): > > But that appears to represent the compression of the air inside the pressure hull, not of the water. Much like the toy water rockets you pump up, but on a mega-scale. Possibly also elasticity of the container itself. ---
**Author:** ![Soylent\_Juicy](https://avatars.discourse-cdn.com/v4/letter/s/82dd89/32.png) [@Soylent\_Juicy](https://boards.straightdope.com/u/Soylent_Juicy)\ **Post date:** [December 11, 2012, 3:48pm UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/16 "2012-12-11T15:48:53Z")
I brought some water back from the Marianas Trench concert - Josh Ramsay threw his water bottle into the crowd and I caught it for my friend’s kid. 🙂 ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [December 11, 2012, 10:27pm UTC](https://boards.straightdope.com/t/so-i-bring-some-water-back-from-the-marianas-trench/643657/17 "2012-12-11T22:27:52Z")
The water is pretty non-compressible, but it is likely to have a fair amount of dissolved gasses in it, especially if near a thermal vent. Those gasses will want to come out of solution when you reduce the pressure, much like when you open a warm bottle of soda pop. So you can expect a lot of foaming.