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Aviation Forum / Country Specific / Australian Group / February 2010A new line of inquiry for JB's incident?
<http://www.dailytelegraph.com.au/news/breaking-news/oxygen-explosion-collapses-h ospital-floors/story-e6freuyi-1225820990912> If it really was an oxygen explosion. I can't see why oxygen would explode. What's the combustion product? Sylvia. > <http://www.dailytelegraph.com.au/news/breaking-news/oxygen-explosion-collapses-h ospital-floors/story-e6freuyi-1225820990912> > > If it really was an oxygen explosion. I can't see why oxygen would > explode. What's the combustion product? > > Sylvia. Very difficult to determine with so few details. Oxygen only accelerates combustion or a chemical reaction - it requires a fuel or another reagent to result in an exothermic process. It is possible that the "canisters" referred to in the article simply failed mechanically - similarly to the Qantas incident. But best to wait for more information. >> <http://www.dailytelegraph.com.au/news/breaking-news/oxygen-explosion-collapses-h ospital-floors/story-e6freuyi-1225820990912> >> [quoted text clipped - 10 lines] > mechanically - similarly to the Qantas incident. But best to wait for more > information. Were they compressed oxygen cylinders or some chemical process canister which generates oxygen. >>> <http://www.dailytelegraph.com.au/news/breaking-news/oxygen-explosion-collapses-h ospital-floors/story-e6freuyi-1225820990912> >>> [quoted text clipped - 13 lines] > Were they compressed oxygen cylinders or some chemical process canister > which generates oxygen. Not sure. Certainly the most common source for medical facilities is compressed oxygen or LOX. Generating oxygen from a chemical canister is unlikely - much more expensive. But this was in the Ukraine, so who knows? Perhaps the distinction between canister and cylinder is not so clear after translation from Russian. >>>> <http://www.dailytelegraph.com.au/news/breaking-news/oxygen-explosion-collapses-h ospital-floors/story-e6freuyi-1225820990912> >>>> [quoted text clipped - 21 lines] > Perhaps the distinction between canister and cylinder is not so clear after > translation from Russian. Emergency oxygen in airliners is typically provided by chemical generators. It was the improper carriage of these that caused the ValuJet crash in Florida. I have a feeling though that the crew emergency supply is from compressed gas in cylinders. http://en.wikipedia.org/wiki/ValuJet_Flight_592 http://en.wikipedia.org/wiki/Chemical_oxygen_generator > <http://www.dailytelegraph.com.au/news/breaking-news/oxygen-explosion-collapses-h ospital-floors/story-e6freuyi-1225820990912> > > If it really was an oxygen explosion. I can't see why oxygen would > explode. What's the combustion product? It wouldn't help if someone lubricated the cylinder thread/s. >> <http://www.dailytelegraph.com.au/news/breaking-news/oxygen-explosion-collapses-h ospital-floors/story-e6freuyi-1225820990912> >> >> If it really was an oxygen explosion. I can't see why oxygen would >> explode. What's the combustion product? > > It wouldn't help if someone lubricated the cylinder thread/s. I've certainly heard that this is a bad idea, but the energy available must be limited by the amount of lubricant. I can easily imagine it blowing the valve off, and generally being a bad thing to be near, but it's less easy to see it doing the kind of damage described in the article. Sylvia. Sylvia Else wrote... > I've certainly heard that this is a bad idea, but the energy available > must be limited by the amount of lubricant. I can easily imagine it > blowing the valve off, and generally being a bad thing to be near, but > it's less easy to see it doing the kind of damage described in the article. I watched, amazed, as an oxy bottle, one about a metre long, take off like a rocket when it fell out of a ute and the next snapped off it. Also, as any boilermaker will tell you, you never oil the fittings of an oxy bottle. The resultant super high compression can cause it to "diesel" with catasptrophic results. It's a wonder that JB's missile didn't continue its upward progress through the fuselage. >I watched, amazed, as an oxy bottle, one about a metre long, take off like a >rocket when it fell out of a ute and the next snapped off it. Yes indeed. When the Red Army Faction aka Baader-Meinhof set off a bomb at a NATO base; it did little damage but DID knock over some unsecured bottles, which then flew around punching holes in walls and destroying cars. And...{as told to me...when I arrived at the Lab..} There exists {or did..} at NASA-Lewis Research Center, a building called the Prop House. Sure it has some official name, Engine Power Research Building maybe, but don't ever bother calling it that. It was built before/during WWII to test engines (and props), for things like P-51's and P-47's. Since that much umph can make big messes, it had VERY sturdy walls and doors. Vault-type doors, for example. That way, when Things Went Wrong, not everyone suffered. As time went on, there were not many 2000 horsepower prop engines for NACA^H^H NASA to test, so other work moved in. One sunny day, Plant Protection [i.e. the fire rescue police dept] decided it was fire drill time. Now, in elementary school, the teacher pulled the alarm, and timed your exit. PP was ....more creative.... They showed up in plain clothes, and threw a few smoke grenades down the hall, and just waited to see what happened. So the erstwhile researcher was slaving away in his test cell when the Evac Alarm went off. You do not ever ignore an Evac Alarm -- even if you wanted to, you'd soon be deaf. (And, you got days off without pay if you were not out the door.) OSHA must have turned them down by now, but *^%*^& were they loud!! So, being smarter than the average PhD, our hero goes to the door, feels it carefully [not hot], undogs it and cracks it slightly. Smoke POURS in. He slams the door, redogs it and goes to the phone. He dials "17" {the emergency number on the antique PAX...} only to discover... they can't hear him and he can't hear them...that damned horn, you see is 3 ft away. The problem is, there's no other way out. The outside wall was glass block, solid. He bangs on it with a hammer, no joy. But the smoke is creeping in under the door. So he takes a K bottle [the official term for the ~5ft tall cylinder used for gases] and sets it on the counter, aimed at the glassblock. He figures he'll shear off the valve with a hammer or hatchet, the tank will punch its way out through the block, and he escapes. BUT.. he is no fool. He knows that he may well go deaf from the noise of the 3000+psi gas escaping, and the cylinder can go any way IT wants... so he delays, and attacks the glass block with the hammer and screwdriver. He finally manages to punch a small hole through... The rest of the building staff is standing across the road waiting for the building to clear of smoke when they see an arm waving.... When PP entered his cell in Scott Air Packs; and saw the cylinder and the hammer, and listened to what he'd planned..... Thereafter, they showed up and pulled the alarm, just like school; no more smoke grenades. > If it really was an oxygen explosion. I can't see why oxygen would > explode. What's the combustion product? If a pressurised vessel of any liquid cryogen develops a leak, and the gas above the liquid is escaping fast enough, the pressure inside the vessel can drop fast enough to cause the rest of the liquid to boil very quickly. If the boiling liquid moves supersonically, then an explosion is taking place, by definition. Something like that. >> If it really was an oxygen explosion. I can't see why oxygen would >> explode. What's the combustion product? [quoted text clipped - 4 lines] > quickly. If the boiling liquid moves supersonically, then an explosion > is taking place, by definition. Something like that. Doesn't seem quite right. Although the boiling point of a liquid is a function of temperature, boiling still requires an energy input. Typically what happens when you release the pressure in such a situation is that the temperature drops as the boiling liquid extracts energy from the bulk. Sylvia. >>> If it really was an oxygen explosion. I can't see why oxygen would >>> explode. What's the combustion product? [quoted text clipped - 7 lines] > Doesn't seem quite right. Although the boiling point of a liquid is a > function of temperature, boiling still requires an energy input. Correct - called the latent heat of vaporisation . The boiling point is also a function of pressure. > Typically what happens when you release the pressure in such a situation > is that the temperature drops as the boiling liquid extracts energy from > the bulk. Hence the term latent energy. When you boil a jug of water the temperature remains constant at 100 deg C, the pressure is constant, but it requires x joules of energy to convert y grams of water from liquid to steam. Now you know why a steam burn is something to avoid - when the steam contacts your skin it condenses - and so giving up this latent energy in the other direction - exothermic process. Thermodynamics is so .... dynamic Pressure -v- boiling point Best not be in the galley during a rapid decompression at altitude and don't release the pressure cap on your car cooling system until the coolant temperature has dropped to below 100 degrees. >>> If it really was an oxygen explosion. I can't see why oxygen would >>> explode. What's the combustion product? [quoted text clipped - 6 lines] > > Doesn't seem quite right. It doesn't seem right, but it happens. I invite you to research "BLEVE": Boiling liquid escaping vapour explosion, I think it stands for. > Although the boiling point of a liquid is a > function of temperature I think you mean it's a function of pressure? This is why, on high mountains, water boils before it gets hot. > , boiling still requires an energy input. The lower the pressure goes, the less energy you need. >>>> If it really was an oxygen explosion. I can't see why oxygen would >>>> explode. What's the combustion product? [quoted text clipped - 9 lines] > It doesn't seem right, but it happens. I invite you to research "BLEVE": > Boiling liquid escaping vapour explosion, I think it stands for. I'll have to think some more on the BLEVE phenomenon. It's not immediately obvious where the energy is coming from. Then again, perhaps explosions don't really involve much energy. >> Although the boiling point of a liquid is a function of temperature Yes, pressure. Don't know why I said temperature. > I think you mean it's a function of pressure? This is why, on high > mountains, water boils before it gets hot. > >> , boiling still requires an energy input. > > The lower the pressure goes, the less energy you need. Well, sort of. The latent heat of vapourisation stays the same, but the required vapour pressure is lower. Put a quantity of water into a vacuum, and it will boil, but it won't flash instantly to steam. Sylvia. >It doesn't seem right, but it happens. I invite you to research "BLEVE": Boiling liquid escaping vapour explosion, I >think it stands for. Boiling Liquid Exploding Vapour. Cheers, Paul Saccani, Perth, Western Australia >>It doesn't seem right, but it happens. I invite you to research "BLEVE": >>Boiling liquid escaping vapour explosion, I [quoted text clipped - 6 lines] > Perth, > Western Australia Actually it's Boiling Liquid Expanding Vapour Explosion. I was in the oil industry for over 30 years. cheers >>>It doesn't seem right, but it happens. I invite you to research "BLEVE": >>>Boiling liquid escaping vapour explosion, I [quoted text clipped - 3 lines] > >Actually it's Boiling Liquid Expanding Vapour Explosion. Thank you, and right you are. So much for my recollection. Cheers, Paul Saccani, Perth, Western Australia >Actually it's Boiling Liquid Expanding Vapour Explosion. >I was in the oil industry for over 30 years. I was for far less time, but even I know BLEVE is an acronym for RUN AS FAST AS YOU CAN....  SignatureA host is a host from coast to coast.................wb8foz@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 >>It doesn't seem right, but it happens. I invite you to research "BLEVE": Boiling liquid escaping vapour explosion, I >>think it stands for. [quoted text clipped - 5 lines] >Perth, >Western Australia Lefy a E out...Boiling Liquid Expanding Vapour Explosion. Most common in LPG cylinder and tank explosions where the extermal heat from a fire weakens the steel of the container. Pressure is released and the entire liquid content of the container instantly vaporises....Really Ugly!! OzOne of the three twins I welcome you to Crackerbox Palace. >>> It doesn't seem right, but it happens. I invite you to research "BLEVE": Boiling liquid escaping vapour explosion, I >>> think it stands for. [quoted text clipped - 11 lines] > Pressure is released and the entire liquid content of the container > instantly vaporises....Really Ugly!! I note, however, that the critical point for Oxygen is 154.59K, so the contents of the Oxygen bottle cannot have been part liquid anyway, and wouldn't have boiled as a result of the reduction in pressure. Sylvia. Neil Gerace wrote... > It doesn't seem right, but it happens. I invite you to research "BLEVE": Boiling liquid escaping vapour explosion, I > think it stands for. Most common with LPG storage failures. > > Although the boiling point of a liquid is a > > function of temperature > > I think you mean it's a function of pressure? This is why, on high mountains, water boils before it gets hot. Yes. For example, at around 16.4 Mpa the saturation temp (boiling temp) of water is about 360 degs C. At around 10 kpa absolute (or -90kpa) it is around 45 degs C. > > , boiling still requires an energy input. > > The lower the pressure goes, the less energy you need. And the higher you go, the more energy input. Much more, in fact, before you get into superheat regions. >> It doesn't seem right, but it happens. I invite you to research >> "BLEVE": Boiling liquid escaping vapour explosion, I think it >> stands for. >Most common with LPG storage failures. But also if you pour water atop a gasoline tank that is burning. [The multi-story several million gallon kind.] Usually, you use foam, but somtimes fog nozzles will do the trick... SignatureA host is a host from coast to coast.................wb8foz@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 >>> If it really was an oxygen explosion. I can't see why oxygen would >>> explode. What's the combustion product? [quoted text clipped - 12 lines] > >Sylvia. In general the specific heat of the liquid declines with absolute temperature. So while it takes a lot of energy to convert 1gm of water to steam, looking at it cross eyed is enought to convert 1gm of liquid helium into gas. In short it doesn't take a lot of energy to convert liquid oxygen into gaseous oxygen. The liquid may boil very rapidly, just before it solidifies...(heat of fusion also goes down with absolute temperature as well). >Doesn't seem quite right. Although the boiling point of a liquid is a >function of temperature, boiling still requires an energy input. >Typically what happens when you release the pressure in such a situation >is that the temperature drops as the boiling liquid extracts energy from >the bulk. Boiling a liquid doesn't require an energy input. All it requires is that the temperature (average kinetic energy) is above the boiling point. When a liquified gas held under pressure is depressurised rapidly, the temperature does indeed drop rapidly too. But that doesn't mean that rapid boiling doesn't happen first. An interesting real world example inolves automotive LPG tanks, typically holding a mix of propane and butane. Sometimes the automatic flow limiter/contents gauge sender is removed from the tank with about 2/3 contents, leaving a 20 mm dia. hole. The rapidly boiling liquid that escapes through the hole (because the hole is below the liquid line) boils and causes butane/propane ice to block the hole! Gas escapes, but nowhere near the amount that would escape if the hole was in vapour instead of liquid. But if the triple point can't be reached, as with, say, Oxygen in a typical environment, you can expect rapid boiling indeed, despite the cooling that the boiling produces. Cheers, Paul Saccani, Perth, Western Australia >>Doesn't seem quite right. Although the boiling point of a liquid is a >>function of temperature, boiling still requires an energy input. [quoted text clipped - 29 lines] >Perth, >Western Australia If the LOX is warm enough, and the pressure rapidly released, could it "flash off" as suggested? This might explain the explosion, perhaps? Coop >If the LOX is warm enough, and the pressure rapidly released, could it >"flash off" as suggested? This might explain the explosion, perhaps? I suspect something like that could happen, given that the boiling point for LOX is quite low compared with everyday temperature and pressures. Cheers, Paul Saccani, Perth, Western Australia >>Doesn't seem quite right. Although the boiling point of a liquid is a >>function of temperature, boiling still requires an energy input. [quoted text clipped - 3 lines] > > Boiling a liquid doesn't require an energy input. That is a misleading statement. It would however be valid to say that boiling a liquid doesn't necessarily require an external energy input. Sylvia's statement is correct. > All it requires is that the temperature (average kinetic energy) is > above the boiling point. O.K. - so the kinetic energy of the molecules in the liquid is related to its temperature, but are you saying this transformation from liquid to gas can occur without an input of energy? >>>Doesn't seem quite right. Although the boiling point of a liquid is a >>>function of temperature, boiling still requires an energy input. [quoted text clipped - 6 lines] >That is a misleading statement. It would however be valid to say that >boiling a liquid doesn't necessarily require an external energy input. Actually, it isn't misleading. Just as you have stated, it does not *require* an energy input. >Sylvia's statement is correct. It isn't, and especially so in the case of a discussion about what happens when pressure is lost. >> All it requires is that the temperature (average kinetic energy) is >> above the boiling point. > >O.K. - so the kinetic energy of the molecules in the liquid is related to >its temperature, That *is* what temperature is. > but are you saying this transformation from liquid to gas >can occur without an input of energy? Of course. If you release pressure from a pressure vessel, you aren't adding energy to it. You are in fact removing energy from the system. The liquid already has the kinetic energy to become a gas - it hasn't done so because of its confinement. Remove confinement, lowering the pressure, you don't need to add energy to boil the liquid. Cheers, Paul Saccani, Perth, Western Australia "Paul Saccani" "Sly Fox" >>> Boiling a liquid doesn't require an energy input. >> >>That is a misleading statement. It would however be valid to say that >>boiling a liquid doesn't necessarily require an external energy input. > > Actually, it isn't misleading. ** Bollocks - it is grossly wrong. > Just as you have stated, it does not > *require* an energy input. ** Wot utterly pedantic, irrational twaddle. For his next trick Paul will show us that black and white are the same. Wot a fuckwit. ... Phil <snip> > The liquid already has the kinetic energy to become a gas - it hasn't > done so because of its confinement. Remove confinement, lowering the > pressure, you don't need to add energy to boil the liquid. I was under the impression that an oxy bottle fitting ruptured and the escaping gas tore it from its mounting, drove it up through the cabin, then cabin pressure drove it back down rupturing the a/c hull ? > <snip> >> The liquid already has the kinetic energy to become a gas - it hasn't [quoted text clipped - 4 lines] > escaping gas tore it from its mounting, drove it up through the cabin, > then cabin pressure drove it back down rupturing the a/c hull ? Exactly, AFAIK civilian airliners do not carry cryogenic oxygen largely due to maintenance reasons. Since oxygen is not required on a regular basis, it makes much more sense to carry it either in chemical generators, or high pressure cylinders, both of which require little attention compared with a cryogenic system. The situation with military aircraft may be different in some circumstances. > I was under the impression that an oxy bottle fitting ruptured and the > escaping gas tore it from its mounting, drove it up through the cabin, > then cabin pressure drove it back down rupturing the a/c hull ? All very interesting reading, but none of it fits what actually happened. Hopefully the ATSB will actually be able to resolve it. I'm sure they're doing some really fun experiments. Your impression is totally incorrect. The bottles are about 30 inches high. It failed laterally, about 10 inches from the base. That instantly created two rockets, which, for a tiny instant, had thrust equal to the area of the break (the whole cross section of the bottle) times the pressure (1820 psi). In round figures, 90,000 lbs. The smaller part went down, and did all of the external damage, whilst the larger part went up and did the internal stuff. The only part of the bottle that was recovered was the regulator and fittings, which by themselves pretty much disprove most of the ideas covered in this thread. The last couple of reports cover the regulator, and its non involvement pretty well. SignatureRead the latest aviation news at www.flight.org Tongue in cheek Do you still Buy lottery tickets ? On Jan 21, 11:37 am, > > I was under the impression that an oxy bottle fitting ruptured and the > > escaping gas tore it from its mounting, drove it up through the cabin, [quoted text clipped - 21 lines] > -- > Read the latest aviation news atwww.flight.org > Tongue in cheek > > Do you still Buy lottery tickets ? If I can win at billions to one, you'd think mere millions would be easy. SignatureRead the latest aviation news at www.flight.org >> Tongue in cheek >> >> Do you still Buy lottery tickets ? > > If I can win at billions to one, you'd think mere millions would be easy. In any lottory there's always a 50/50 chance of winning. You either win it or you don't. ><snip> >> The liquid already has the kinetic energy to become a gas - it hasn't [quoted text clipped - 4 lines] >escaping gas tore it from its mounting, drove it up through the cabin, >then cabin pressure drove it back down rupturing the a/c hull ? If you mean JB's case, then yes*. But that was compressed oxygen gas, not liquid, to the best of my knowledge. *some minor issues not worth quibling over. Cheers, Paul Saccani, Perth, Western Australia >>>>Doesn't seem quite right. Although the boiling point of a liquid is a >>>>function of temperature, boiling still requires an energy input. [quoted text clipped - 9 lines] > Actually, it isn't misleading. Just as you have stated, it does not > *require* an energy input. What a wonderful misquote. Generous of you to leave out two words and so totally misrepresent what I stated. >>Sylvia's statement is correct. > [quoted text clipped - 18 lines] > done so because of its confinement. Remove confinement, lowering the > pressure, you don't need to add energy to boil the liquid. Yet more confusion: "The liquid already has the kinetic energy to become a gas" The liquid has no kinetic energy unless this mass of liquid is moving i.e. K.E. = 1/2mv*2 It is a nonsense to try and connect the absolutely miniscule kinetic energy of molecules with energy changes - such as occur in latent heat calcualtions - that are astronomical in comparison. Hint - potential energy better explains the processes involved. >>>>>Doesn't seem quite right. Although the boiling point of a liquid is a >>>>>function of temperature, boiling still requires an energy input. [quoted text clipped - 12 lines] >What a wonderful misquote. Generous of you to leave out two words and so >totally misrepresent what I stated. I'm sorry that you see it that way. No misrepresentation of your *view* was intended, rather, I intended the consequence of it to be made explicit. I'm not sure if this is a failure of language or logic. If something can be done without something else, then that something else is not a requirement of the something. That doing the something *in a particular way* requires something else, doesn't make the original something have a requirement of the something else, in order to be done. Can you not see this, and the logical effect of your statement "not neccessarily required" as to whether boiling has a requirement of adding energy? If we have sufficient heat in the liquid to boil it all when we lower the pressure, we don't require additional energy to boil it all. If we can boil it all without adding energy, then the addition of energy is not required. Even if under other circumstances, the addition of energy would be required to boil it all off, the simple fact is, the addition of energy is not required. I really can't see the difficulty with this. But again, if you still feel misrepresented, I do apologise. >>>Sylvia's statement is correct. >> [quoted text clipped - 24 lines] >The liquid has no kinetic energy unless this mass of liquid is moving i.e. >K.E. = 1/2mv*2 If you don't know that heat is kinetic energy, you might well be missing something important. I have no idea why you think your statement above has any relevence or validity. However, I do see my own very poor expression above which is a sorry one indeed. It would seem implicit in it that all of the liquid would turn into a gas, if the liquid was above boiling point. This is not, of course, the case, and how much of the liquid became a gas would be dependant on the temperature difference above boiling point. It could be a small amount, or it could be the whole amount. With LOx, it could easily be the whole quantity at temperatures likely to be encountered in the normal environment. >It is a nonsense to try and connect the absolutely miniscule kinetic energy >of molecules with energy changes - such as occur in latent heat >calcualtions - that are astronomical in comparison. >Hint - potential energy better explains the processes involved. Pray tell, in your model of physics, what happens to ice at 1,000 K if you reduce the pressure to that of a standard atmosphere? The following values are rough, I don't have any tables to look up the values - I'm sure you can do a better calcularion; Lets take, say LOx at 50° C (which is a reasonable real world temperature), with pressure suddenly reduced to standard atmospheric. The specific heat between 90 K and 323 K per kg of O2 would be around 214 kJ, whilst the latent heat required to boil a kg of O2 would be around 214 kJ. In your model, we apparently don't get to use the existing kinetic energy, and the Lox doesn't boil into gas (at low temperature) with no requirement of adding energy. In reality the energy changes are not astronomical in comparison, they are merely hundreds of times greater per K, and high temperatures can result in boil off without adding energy to the fluid. This can be unpleasant for bystanders. Cheers, Paul Saccani, Perth, Western Australia > Pray tell, in your model of physics, what happens to ice at 1,000 K if > you reduce the pressure to that of a standard atmosphere? Ice cannot exist at 1000K, because that temperature is above the triple point of water. > The following values are rough, I don't have any tables to look up the > values - I'm sure you can do a better calcularion; [quoted text clipped - 4 lines] > 214 kJ, whilst the latent heat required to boil a kg of O2 would be > around 214 kJ. LOx cannot exist at 50C because that temperature is above its triple point. Sylvia. >> Pray tell, in your model of physics, what happens to ice at 1,000 K if >> you reduce the pressure to that of a standard atmosphere? > >Ice cannot exist at 1000K, because that temperature is above the triple >point of water. At readily achievable pressures the slope of the melting point of water of P Vs T is negative in a phase diagram. That is, where the usual "laws" apply. Ice (that is to say, spatially ordered water) at 1,000 K would be at an extreme pressure and would likely be a form of degenerate matter. This exists far beyond what a phase diagram is going to show you. And remember, the triple point results from a simplification of the real thing, assuming only three states of matter. >> The following values are rough, I don't have any tables to look up the >> values - I'm sure you can do a better calcularion; [quoted text clipped - 6 lines] > >LOx cannot exist at 50C because that temperature is above its triple point. Sure - if the pressure is around 0.1% of atmospheric. It isn't in this case. By the way, using that reasoning, LOx can't exist at all at normal atmospheric pressure, where it boils at around 77 K, around 23 K above the triple point temperature. Molecular oxygen has a postive melting point slope of P Vs T, unlike water. Triple point occurs at a particular combination of temperature *and* pressure. It is *normal* for liquids to exist above the triple point. If you look at a phase diagram, you will see that the solid, liquid and gas phases all exist *above* the triple point for a typical substance. In the case of ordinary molecular oxygen, the critical point is at around 154 K and 5 MPa. LOx at 50° C would be a supercritical fluid under great pressure. In fact, because it is a real world material, it has been given the moniker of SOx for short, and it occurs far above the triple point. In fact, supercritical fluids are often used as industrial solvents, all at temperatures far above the triple point. For instance, supercritical CO2 is used in drycleaning and decaffinating coffee. Cheers, Paul Saccani, Perth, Western Australia >>> Pray tell, in your model of physics, what happens to ice at 1,000 K if >>> you reduce the pressure to that of a standard atmosphere? [quoted text clipped - 48 lines] > Perth, > Western Australia <sigh> Doesn't help when my mind is going. In both cases, I meant critical point, not triple point. I used the intended term in a previous reply to OzOne. LOx cannot exist above its critical point. The fact that it's possible to have supercritical fluids is not relevant to this dicussion. A substance in its supercritical fluid state is not a liquid, and will not boil as the pressure is reduced. Consequently the latent heat of vapourisation will not enter the discussion. Since 50C is well above the critical point for Oxygen, there will be no phase change as the pressure is reduced. Sylvia. ><sigh> Doesn't help when my mind is going. In both cases, I meant >critical point, not triple point. I used the intended term in a previous >reply to OzOne. > >LOx cannot exist above its critical point. The fact that it's possible >to have supercritical fluids is not relevant to this dicussion. Actually it is. > A >substance in its supercritical fluid state is not a liquid, A substance that is supercritical fluid *is* a liquid - it is *also* a gas. The solid state (supercritical solid) also exists above the critical point. >and will not >boil as the pressure is reduced. Only whilst it remains above the critical pressure. Clearly, a supercritical fluid such as Oxygen under pressure at 50° C will readily boil if pressure is reduced to atmospheric (superheated vapour) as the result of a pressure vessel rupturing. And it will generally flash to a gas, with all that entails. Its actually pretty common in industrial steam plant to have superheated vapour. > Consequently the latent heat of >vapourisation will not enter the discussion. Correct - I'm not sure if you see the consequence of this. >Since 50C is well above the critical point for Oxygen, there will be no >phase change as the pressure is reduced. Again, only if the pressure remains above the critical pressure. As we are talking about the case where that does not happen, there is most certainly going to be a phase change to a superheated vapour and then to a gas. Cheers, Paul Saccani, Perth, Western Australia >> <sigh> Doesn't help when my mind is going. In both cases, I meant >> critical point, not triple point. I used the intended term in a previous [quoted text clipped - 19 lines] > readily boil if pressure is reduced to atmospheric (superheated > vapour) as the result of a pressure vessel rupturing. > And it will generally flash to a gas, with all that entails. > [quoted text clipped - 5 lines] > > Correct - I'm not sure if you see the consequence of this. It means that it won't boil. If the container is ruptured, the Oxygen undergoes adiabatic expansion and cooling. But there is no BLEVE because there is no boiling. >> Since 50C is well above the critical point for Oxygen, there will be no >> phase change as the pressure is reduced. [quoted text clipped - 3 lines] > most certainly going to be a phase change to a superheated vapour and > then to a gas. I do not accept that they are phase changes. Nothing noticeable happens as a substance that's below its critical pressure drops below its critical temperature, even though it's called a superheated vapour before, and gas afterwards. Similarly, nothing noticeable happens to a substance that's above its critical temperature as the pressure drops below the critical pressure. The expanding gas might reach the point at which it starts to fog, because both its temperature and pressure have dropped below their critical values, and the pressure is sufficient to liquify it at the temperature it's reached. That would reduce any explosive effect. Sylvia. >>> <sigh> Doesn't help when my mind is going. In both cases, I meant >>> critical point, not triple point. I used the intended term in a previous [quoted text clipped - 31 lines] > >It means that it won't boil. It means that it doesn't need to increase its temperature to boil. >If the container is ruptured, the Oxygen undergoes adiabatic expansion >and cooling. You mean the expansion causes adiabatic cooling. Unless you don't know what adiabatic means. >But there is no BLEVE because there is no boiling. Who's talking about BLEVE? >>> Since 50C is well above the critical point for Oxygen, there will be no >>> phase change as the pressure is reduced. [quoted text clipped - 5 lines] > >I do not accept that they are phase changes. I suggest you seat yourself below high tide level and not accept that the tide rises. > Nothing noticeable happens >as a substance that's below its critical pressure drops below its >critical temperature, even though it's called a superheated vapour >before, and gas afterwards. But something very noticable happens when a supercritical fluid or solid drops below the critical pressure. The trees are obscuring your view of the wood. > Similarly, nothing noticeable happens to a >substance that's above its critical temperature as the pressure drops >below the critical pressure. So you don't think changing from a supercritical fluid to a superheated vapour is noticable? Pity. Supercritical fluids consist of a *mixture* of 2 phases in equilibrium, a high density liquid and a low density gas. Small changes in pressure can produce enormous changes in density. When the pressure drops below the critical pressure, a low density state is entered and gas like behavour occurs. In the superheated vapour phase, small increases in pressure can cause reversion to a supercritical state. rather than a conventional liquid state - there are thermodynamic issues involved that you might notice. >The expanding gas might reach the point at which it starts to fog, >because both its temperature and pressure have dropped below their >critical values, and the pressure is sufficient to liquify it at the >temperature it's reached. That would reduce any explosive effect. Here on earth, that isn't going to happen with Oxygen, is it? Cheers, Paul Saccani, Perth, Western Australia >>>> <sigh> Doesn't help when my mind is going. In both cases, I meant >>>> critical point, not triple point. I used the intended term in a previous [quoted text clipped - 28 lines] > > It means that it doesn't need to increase its temperature to boil. Boiling involves a phase change - from liquid to gas. If it's a supercritical fluid, then there's no distinction between liquid and gas. >> If the container is ruptured, the Oxygen undergoes adiabatic expansion >> and cooling. > > You mean the expansion causes adiabatic cooling. No, I mean that the combined expansion and cooling is adiabatic. Adiabatic means that there is no heat exchange. > Unless you don't know what adiabatic means. > [quoted text clipped - 21 lines] > solid drops below the critical pressure. The trees are obscuring your > view of the wood. Look at the pressure density phase diagram for CO2. http://en.wikipedia.org/wiki/Supercritical_fluid The lines representing temperatures above the critical temperature are continous - there are no abrupt changes, and nothing particular of note happens at the critical pressure. >> Similarly, nothing noticeable happens to a >> substance that's above its critical temperature as the pressure drops >> below the critical pressure. > > So you don't think changing from a supercritical fluid to a > superheated vapour is noticable? Pity. > Supercritical fluids consist of a *mixture* of 2 phases in > equilibrium, a high density liquid and a low density gas. That's not a supercritical fluid. Think about it - if the liquid was high density and the gas low density, they'd separate out under the effects of gravity. > Small changes in pressure can produce enormous changes in density. Only for temperatures close to the critical temperature. > When the pressure drops below the critical pressure, a low density > state is entered and gas like behavour occurs. In the superheated [quoted text clipped - 9 lines] > Here on earth, that isn't going to happen with Oxygen, is it? > Cheers, Hard to say really. The Oxygen starts off at room temperature, so it's definitely going to go below room temperature as it expands. Figuring out whether it will fog would require detailed examination of its properties. Sylvia. Paul Saccani wrote... > > Similarly, nothing noticeable happens to a > >substance that's above its critical temperature as the pressure drops [quoted text clipped - 5 lines] > Supercritical fluids consist of a *mixture* of 2 phases in > equilibrium, a high density liquid and a low density gas. Yes, and this is what happens with supercritical boilers for modern power plant. Typically the pressure is above 27 Mpa, if I remember correctly. Dunno what the figures are for oxygen in whatever form it is currently. I reckon that you two should get a room... :-] Paul Saccani wrote... > ><sigh> Doesn't help when my mind is going. In both cases, I meant > >critical point, not triple point. I used the intended term in a previous [quoted text clipped - 42 lines] > Perth, > Western Australia >I reckon that you two should get a room... One can always rely on your rapier wit. ;) I have to confess, I now know what it feels like to stop beating my head against a brick wall.... Hope all is well for you. Cheers, Paul Saccani, Perth, Western Australia ><http://www.dailytelegraph.com.au/news/breaking-news/oxygen-explosion-collapses-h ospital-floors/story-e6freuyi-1225820990912> > >If it really was an oxygen explosion. I can't see why oxygen would >explode. What's the combustion product? > >Sylvia. Only takes a little oil . OzOne of the three twins I welcome you to Crackerbox Palace. |
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