Deep Sea Gas Venting ?
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From: Timo Nieminen on 2 May 2010 17:10 On May 3, 4:58 am, "Ken S. Tucker" <dynam...(a)vianet.on.ca> wrote: > Hi Timo and guys. > > > > To compress air to the density of water needs 800 atmospheric > > > pressures, or 800 x 33' = 26,400 ft of depth. > > > If I understand correctly, at that point the bouyancy of the air in > > > the balloon with go negative and want to sink. > > > > That's why I'm curious about gas expulsions, such as O2, N2, > > > below 26,400' from undersea vents. > > > Well past the point where the ideal gas law is at all accurate, so > > don't trust numbers from PV = const. Vapour pressure of nitrogen at > > 300K is about 650 atmospheres, so your balloon won't have gas inside. > > Still, could have gas at that depth if hot enough. If not, it just > > isn't gas. Liquid N2 is less dense than water, so it would float up > > anyway, and turn to gas when sufficiently shallow. > > Right, (thanks that's helpful) I had to look up the density of N2, > but then I went to O2http://en.wikipedia.org/wiki/Liquid_oxygen > and LOX is more dense than H2O. > > If I understand correctly, dropping a balloon of O2 into the Mariana, > at some deep depth the O2 liquifies, (as N2 would do), but the O2, > being denser than H2O would sink down. > Is that waht you all think? I wouldn't expect to see significant amounts of O2, it being so reactive, but your basic point is sound - if a glob of liquid O2 was burped out down there, it should sink. (One should check the density at room temperature (and 800 atm), and compare with the density of seawater at 800 atm (seawater is only a few % denser than pure water).) If it comes out hot, and less dense enough to rise, then a large glob will rise and form a bubble, and a small glob will rise too slowly and cool down to quickly. If it sinks, what then? If soluble, it will dissolve. If soluble, I'd expect it to already be dissolved when expelled, so instead of O2, you'd get O2-rich hot water (or CO2-rich water, or SO2, or whatever). Without solubility, you get stratification (as we already do, with the ocean being below the atmosphere). With solubility, you still get concentration gradients, but this is continuous so not really stratification. E.g., concentration gradients in the atmosphere (we need to get above the convective mixing to see this).
From: Darwin123 on 2 May 2010 17:16 On May 2, 2:47 am, "Ken S. Tucker" <dynam...(a)vianet.on.ca> wrote: > To compress air to the density of water needs 800 atmospheric > pressures, or 800 x 33' = 26,400 ft of depth. > If I understand correctly, at that point the bouyancy of the air in > the balloon with go negative and want to sink. I think the oxygen-water patches rose because they were hotter than the surrounding sea water, not that the patches were heavier. Water expelled from a volcano would be hotter, and thus less dense, than the water already in the ocean. The turbulence caused by the sudden release of underground pressure would also hurl patches of oxygen rich fluid upward. The buoyancy had nothing to do with the fact that oxygen was there. Thus, you calculation would be erroneous. There is another factor that makes me think that the density of gases is not an issue with these expulsions. The critical point of water is at 218 atm pressure and 374 centigrade. Now the temperature of the water in the black smokers can exceed 600 C. You just pointed out that the pressure in the black smokers must be greater than 800 atm. So I don't think you can separate the gas phases from the liquid phases at the bottom of the vents. Above the critical point of water, water is still a fluid. However, there is no difference between a gas fluid and a liquid fluid. Thus, any other gas would be fully soluble in super-critical water. There could be no "bubbles" as you understand them. If a patch of material rises, it would be mostly due to the relative temperature between a patch and its surroundings. or maybe because of the average molecular weight inside the patch (it would work for hydrogen). At these pressures, there is no such thing as a true liquid. > > That's why I'm curious about gas expulsions, such as O2, N2, > below 26,400' from undersea vents. > Thanks for responses. How was the gas detected in these expulsions? My conjecture is that the scientist did not actually look at "bubbles." Maybe the scientists was using Raman scattering, or some other nonvisual means of detecting concentrations of these substances. Instead of bubbles, there could have been "patches" of dissolved oxygen without a well defined surface. I am sure they didn't see a bright mass of bubbles rising to the surface. They used some method that determined the chemical nature of these patches. A bubble has a well-defined surface, and a surface tension. However, there is no well defined surface past the critical point. Therefore, surface tension disappears at temperatures and pressures past the critical point. There are no bubbles past the critical point. What may have been rising is patches of oxygen-nitrogen-carbon dioxide- water solution, without a clear phase identity. The fact that the scientists identified the chemical identity of these gases makes me think we are not talking about a visual identification. Maybe they sunk oxygen sensors to travel with the vehicle. The chemical sensor could have used an oxidation-reduction reaction. Or maybe they used Raman scattering, or a pH measurement. The sensor sensed the oxygen well enough. However, it didn't and couldn't distinguish between oxygen dissolved in the water and oxygen that was rising as a free gas. I dont think bubbles can exist past the critical point of water. In order to have a bubble, you need a separation between the vapor phase and the liquid phase of water. This makes it interesting to contemplate how the critical point of water affects organisms deep undersea. Here is a link concerning critical points. http://en.wikipedia.org/wiki/Critical_point_%28thermodynamics%29 In physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions (temperature, pressure and sometimes composition) at which a phase boundary ceases to exist. There are multiple types of critical points such as vapor-liquid critical points and liquid-liquid critical points. http://wiki.answers.com/Q/What_is_the_critical_point_of_water the values for water are 218 atm pressure and 374 centigrade.
From: tadchem on 2 May 2010 19:10 On May 2, 2:58 pm, "Ken S. Tucker" <dynam...(a)vianet.on.ca> wrote: > Hi Timo and guys. > > On May 2, 4:31 am, Timo Nieminen <t...(a)physics.uq.edu.au> wrote: > > > > > > > On May 2, 4:47 pm, "Ken S. Tucker" <dynam...(a)vianet.on.ca> wrote: > > > Let me ask you Edward or anyone to opine on a problem I have, > > > (I'm studying 'Undersea Venting of Gases). > > > > Allow me to attach a good quality balloon to a brick so it sinks into > > > the Mariana Trench,http://en.wikipedia.org/wiki/Mariana_Trench > > > enabling > 35000' depth. > > > > Air is compressible, so doubling the pressure, 1/2's the volume, > > > and doubles the air density (I think that's right?). > > > 1 atmosphere of pressure is added every ~ 33' of water depth. > > > I use water density = 800x sea level air density. > > > > To compress air to the density of water needs 800 atmospheric > > > pressures, or 800 x 33' = 26,400 ft of depth. > > > If I understand correctly, at that point the bouyancy of the air in > > > the balloon with go negative and want to sink. > > > > That's why I'm curious about gas expulsions, such as O2, N2, > > > below 26,400' from undersea vents. > > > Well past the point where the ideal gas law is at all accurate, so > > don't trust numbers from PV = const. Vapour pressure of nitrogen at > > 300K is about 650 atmospheres, so your balloon won't have gas inside. > > Still, could have gas at that depth if hot enough. If not, it just > > isn't gas. Liquid N2 is less dense than water, so it would float up > > anyway, and turn to gas when sufficiently shallow. > > Right, (thanks that's helpful) I had to look up the density of N2, > but then I went to O2http://en.wikipedia.org/wiki/Liquid_oxygen > and LOX is more dense than H2O. > > If I understand correctly, dropping a balloon of O2 into the Mariana, > at some deep depth the O2 liquifies, (as N2 would do), but the O2, > being denser than H2O would sink down. > Is that waht you all think? > > > Similar thing with water - stuff coming out of volcanic vents that > > would be (mostly) water vapour if one the surface is just (mostly) hot > > water at depth (e.g., 300C, about 600K). > > Understood. > > > Also similar thing with bubbles - high pressure is high pressure, > > whether the pressure is due to the weight of overlying water or the > > surface tension of a bubble. We melted toner (so for this toner, > > T>180C iirc) suspended in water with no boiling - small scale, we'd > > have needed micron-sized bubbles, and that's a lot of pressure there. > > Thanks > Ken- Hide quoted text - > > - Show quoted text - The critical temperature of O2, above which it CANNOT be a liquid, is -118.6 °C http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=48 ....awful cold for liquid water. Chill O2 to that temperature at 1 atm pressure and it will liquefy. "Accuracy" is relative: the Ideal gas law is accurate to +/- 10% over a much wider range than the range for which it is accurate to +/- 1%. Generally, the closer you get to the critical point (staying above the critical temperature and below the critical pressure) the less accurate the Ideal Gas Law is for any gas. The 'gas' expelled from undersea vents is superheated steam - water at a temperature above its critical temperature of about 374 °C. The steam bubbles collapse as they cool down. Some gases are also released, but they are not air. Methane, H2S, and ammonia are seen. http://www.noaaworld.noaa.gov/scitech/images/nov2009_scitech_1_1_550.jpg http://www.noaaworld.noaa.gov/scitech/nov2009_scitech_1.html http://www.terrapub.co.jp/journals/GJ/pdf/2605/26050291.PDF http://www.greateryellowstonescience.org/files/pdf/6thConf_Cuhel_et_al.pdf Tom Davidson Richmond, VA
From: Ken S. Tucker on 4 May 2010 03:50 On May 2, 4:10 pm, tadchem <tadc...(a)comcast.net> wrote: > On May 2, 2:58 pm, "Ken S. Tucker" <dynam...(a)vianet.on.ca> wrote: > > > > > Hi Timo and guys. > > > On May 2, 4:31 am, Timo Nieminen <t...(a)physics.uq.edu.au> wrote: > > > > On May 2, 4:47 pm, "Ken S. Tucker" <dynam...(a)vianet.on.ca> wrote: > > > > Let me ask you Edward or anyone to opine on a problem I have, > > > > (I'm studying 'Undersea Venting of Gases). > > > > > Allow me to attach a good quality balloon to a brick so it sinks into > > > > the Mariana Trench,http://en.wikipedia.org/wiki/Mariana_Trench > > > > enabling > 35000' depth. > > > > > Air is compressible, so doubling the pressure, 1/2's the volume, > > > > and doubles the air density (I think that's right?). > > > > 1 atmosphere of pressure is added every ~ 33' of water depth. > > > > I use water density = 800x sea level air density. > > > > > To compress air to the density of water needs 800 atmospheric > > > > pressures, or 800 x 33' = 26,400 ft of depth. > > > > If I understand correctly, at that point the bouyancy of the air in > > > > the balloon with go negative and want to sink. > > > > > That's why I'm curious about gas expulsions, such as O2, N2, > > > > below 26,400' from undersea vents. > > > > Well past the point where the ideal gas law is at all accurate, so > > > don't trust numbers from PV = const. Vapour pressure of nitrogen at > > > 300K is about 650 atmospheres, so your balloon won't have gas inside. > > > Still, could have gas at that depth if hot enough. If not, it just > > > isn't gas. Liquid N2 is less dense than water, so it would float up > > > anyway, and turn to gas when sufficiently shallow. > > > Right, (thanks that's helpful) I had to look up the density of N2, > > but then I went to O2http://en.wikipedia.org/wiki/Liquid_oxygen > > and LOX is more dense than H2O. > > > If I understand correctly, dropping a balloon of O2 into the Mariana, > > at some deep depth the O2 liquifies, (as N2 would do), but the O2, > > being denser than H2O would sink down. > > Is that waht you all think? > > > > Similar thing with water - stuff coming out of volcanic vents that > > > would be (mostly) water vapour if one the surface is just (mostly) hot > > > water at depth (e.g., 300C, about 600K). > > > Understood. > > > > Also similar thing with bubbles - high pressure is high pressure, > > > whether the pressure is due to the weight of overlying water or the > > > surface tension of a bubble. We melted toner (so for this toner, > > > T>180C iirc) suspended in water with no boiling - small scale, we'd > > > have needed micron-sized bubbles, and that's a lot of pressure there. > > > Thanks > > Ken- Hide quoted text - > > > - Show quoted text - > > The critical temperature of O2, above which it CANNOT be a liquid, is > -118.6 °Chttp://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=48 > ...awful cold for liquid water. Chill O2 to that temperature at 1 atm > pressure and it will liquefy. > > "Accuracy" is relative: the Ideal gas law is accurate to +/- 10% over > a much wider range than the range for which it is accurate to +/- 1%. > > Generally, the closer you get to the critical point (staying above the > critical temperature and below the critical pressure) the less > accurate the Ideal Gas Law is for any gas. > > The 'gas' expelled from undersea vents is superheated steam - water at > a temperature above its critical temperature of about 374 °C. The > steam bubbles collapse as they cool down. > > Some gases are also released, but they are not air. Methane, H2S, and > ammonia are seen.http://www.noaaworld.noaa.gov/scitech/images/nov2009_scitech_1_1_550.jpghttp://www.noaaworld.noaa.gov/scitech/nov2009_scitech_1.htmlhttp://www.terrapub.co.jp/journals/GJ/pdf/2605/26050291.PDFhttp://www.greateryellowstonescience.org/files/pdf/6thConf_Cuhel_et_a... > > Tom Davidson > Richmond, VA Thank you for your replies guys, Most of us are interested about Earth, so a look at venting at Mariana Trench pressure is of interest. Here's my picture, the vented O2 sinks, the vented N2 floats, and the vented H2O just becomes water. Now, from the standpoint of deep ocean biology, the said O2 can saturate the lower ocean depths, via pressure while N2 is expelled. So at the 'Bottom of the Sea' O2 based life could thrive. When fish swim they use gills to collect O2, so I calculated the figure 26,400' at which point O2 will sink (+/- some), then O2 based life can thrive on sinking sediment, dead whales imploding and stuff like that. That provides a bit more insight into how deep sea fish live, based on the carbon cycle. Best Regards and Thanks Ken S. Tucker
From: tadchem on 4 May 2010 19:16
On May 4, 3:50 am, "Ken S. Tucker" <dynam...(a)vianet.on.ca> wrote: <snip repost> > Thank you for your replies guys, > Most of us are interested about Earth, so a look at venting at > Mariana Trench pressure is of interest. > > Here's my picture, the vented O2 sinks, the vented N2 floats, > and the vented H2O just becomes water. > Now, from the standpoint of deep ocean biology, the said O2 > can saturate the lower ocean depths, via pressure while N2 > is expelled. > So at the 'Bottom of the Sea' O2 based life could thrive. > When fish swim they use gills to collect O2, so I calculated > the figure 26,400' at which point O2 will sink (+/- some), > then O2 based life can thrive on sinking sediment, dead > whales imploding and stuff like that. > > That provides a bit more insight into how deep sea fish live, > based on the carbon cycle. > Best Regards and Thanks > Ken S. Tucker- Hide quoted text - > > - Show quoted text - Pressure at the bottom of the Mariana trench is 108.6 megapascals. Assume a temperature of 4° C for the 'best-case' scenario, as any higher temperature will only expand the gas, making it more buoyant. Calculate (if you can) the density of oxygen using a suitable equation of state. Peng-Robinson or BWR should be good enough. The Ideal Gas Law is NOT acceptable at these pressures. Will O2 bubbles sink at the bottom of the trench? Bonus question: if fish use O2 for metabolism (and they do, converting it to CO2) what is the mechanism that regenerates O2 in the deep trenches? Tom Davidson Richmond, VA |