Qantas 744 Depressurisation
Just wondering - is there any significant thermal implication of discharging 1850 psi oxygen bottles ?! I gather it should provide some cool into that cargo bay, but anything that could impact the mechanical performances of the nearby structure ?!
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Just wondering - is there any significant thermal implication of discharging 1850 psi oxygen bottles ?! I gather it should provide some cool into that cargo bay, but anything that could impact the mechanical performances of the nearby structure ?!
Atakacs, this is slightly peripheral to your questions but raises a related issue that has been lingering with me for a while.
The escaped gas as it expands will absorb a lot of heat, or provide cooling, by principles familiar to anyone who understands how a refrigeration system works. In a word, when you compress a gas, the total heat energy it contains is confined to a smaller space and so it gets hotter. By the time it gets into the service bottle on the plane, it has cooled to ambient. So when you let it out of the bottle, it has less heat than before it was initially compressed, so gets cooler. So there we have cooling.
Now my lingering puzzle: Some posts back (I'm not going to search 900+ posts, can anybody link?) there were pictures of an exploded oxygen tank. They showed melted female threads where the valve had screwed in, perhaps other melted elements of the tank, but did not specify why. I think these melted from the friction created by the oxygen whizzing at high speed past the orifice. So there we have heating.
Can anybody speak authoritatively to this? And while we're at it, can anybody tell me how to make quoted text appear in blue?
Atakacs, this is slightly peripheral to your questions but raises a related issue that has been lingering with me for a while.
The escaped gas as it expands will absorb a lot of heat, or provide cooling, by principles familiar to anyone who understands how a refrigeration system works. In a word, when you compress a gas, the total heat energy it contains is confined to a smaller space and so it gets hotter. By the time it gets into the service bottle on the plane, it has cooled to ambient. So when you let it out of the bottle, it has less heat than before it was initially compressed, so gets cooler. So there we have cooling.
Now my lingering puzzle: Some posts back (I'm not going to search 900+ posts, can anybody link?) there were pictures of an exploded oxygen tank. They showed melted female threads where the valve had screwed in, perhaps other melted elements of the tank, but did not specify why. I think these melted from the friction created by the oxygen whizzing at high speed past the orifice. So there we have heating.
Can anybody speak authoritatively to this? And while we're at it, can anybody tell me how to make quoted text appear in blue?
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Re. post 922
‘Just wondering - is there any significant thermal implication of discharging 1850 psi oxygen bottles ?! I gather it should provide some cool into that cargo bay, but anything that could impact the mechanical performances of the nearby structure?!’
Not in a few milliseconds it wouldn't. This is a bang not a hiss.
Not in a few milliseconds it wouldn't. This is a bang not a hiss.
Evertonian
The video system is automatically shut down during decompression.
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"Not in a few milliseconds it wouldn't. This is a bang not a hiss."
I think that depends, how big is the orifice through which the oxygen is escaping? If the bottom suddenly falls off the tank, clearly it is a bang not a hiss. If the orifice is of a certain smaller size, like if the valve broke off, I think the gas could escape fast enough to generate a lot of friction = heat, and possibly long enough to melt some stuff locally. If the orifice is much smaller still, it could leak very little and generate only a 1"/25.4mm soap bubble a minute (a typical actual spec for gas leakage from pipes) which would generate no appreciable heat.
I happily proclaim that I haven't the knowledge to calculate this myself, though it can be done. My real questions are, A) Can somebody link the post showing the exploded O2 tank (NOT from the incident aircraft, but previous in this thread as an example) that showed melted threads, B) Why did the threads melt, C) (Excuse if I missed something, but) I have seen no information that the presumed exploded tank was steel or aluminum or composite, has this information been released? I am sure that failure modes differ according to tank type.
I hope I am not drifting the thread excessively. Answers to these questions appear to me relevant to the case.
I think that depends, how big is the orifice through which the oxygen is escaping? If the bottom suddenly falls off the tank, clearly it is a bang not a hiss. If the orifice is of a certain smaller size, like if the valve broke off, I think the gas could escape fast enough to generate a lot of friction = heat, and possibly long enough to melt some stuff locally. If the orifice is much smaller still, it could leak very little and generate only a 1"/25.4mm soap bubble a minute (a typical actual spec for gas leakage from pipes) which would generate no appreciable heat.
I happily proclaim that I haven't the knowledge to calculate this myself, though it can be done. My real questions are, A) Can somebody link the post showing the exploded O2 tank (NOT from the incident aircraft, but previous in this thread as an example) that showed melted threads, B) Why did the threads melt, C) (Excuse if I missed something, but) I have seen no information that the presumed exploded tank was steel or aluminum or composite, has this information been released? I am sure that failure modes differ according to tank type.
I hope I am not drifting the thread excessively. Answers to these questions appear to me relevant to the case.
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"Quote:
And while we're at it, can anybody tell me how to make quoted text appear in blue?
Copy it into you your reply - highlight it and press the 'quote' icon - the last on the right of the bar of them.
Took me a while to figure too !"
Thanks pasoundman, but I have nothing on my screen that looks like what you direct me to. Down below as I compose, I have three rows of "Post Icons," none of which is labelled "quote." Browser is Firefox, is it eliminating something from my view? Or am I just too ignorant?
And while we're at it, can anybody tell me how to make quoted text appear in blue?
Copy it into you your reply - highlight it and press the 'quote' icon - the last on the right of the bar of them.
Took me a while to figure too !"
Thanks pasoundman, but I have nothing on my screen that looks like what you direct me to. Down below as I compose, I have three rows of "Post Icons," none of which is labelled "quote." Browser is Firefox, is it eliminating something from my view? Or am I just too ignorant?
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The moving map was still running on this flight though... I'm assuming it is separate from the IFE then?
Interesting... Perhaps the wiring between the oxygen flow control valves and the video system was damaged.
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Originally Posted by Buster Hyman
The moving map was still running on this flight though... I'm assuming it is separate from the IFE then?
Bernd
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kansasw wrote: "Quote:
And while we're at it, can anybody tell me how to make quoted text appear in blue?
Copy it into you your reply - highlight it and press the 'quote' icon - the last on the right of the bar of them.
Took me a while to figure too !"
Thanks pasoundman, but I have nothing on my screen that looks like what you direct me to. Down below as I compose, I have three rows of "Post Icons," none of which is labelled "quote." Browser is Firefox, is it eliminating something from my view? Or am I just too ignorant?
And while we're at it, can anybody tell me how to make quoted text appear in blue?
Copy it into you your reply - highlight it and press the 'quote' icon - the last on the right of the bar of them.
Took me a while to figure too !"
Thanks pasoundman, but I have nothing on my screen that looks like what you direct me to. Down below as I compose, I have three rows of "Post Icons," none of which is labelled "quote." Browser is Firefox, is it eliminating something from my view? Or am I just too ignorant?
It's the one that looks like square box with text in it and a little pointy arrow at the bottom. I use Opera so I can't say how Firefox might render it.
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Intruder posted
The manual method is to enclose the quoted text in
[quote ... [/quote
tags. Put in the closing ] in each to make them work.
The manual method is to enclose the quoted text in
[quote ... [/quote
tags. Put in the closing ] in each to make them work.
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Has anyone seen, and can point to, video footage of the actual descent? The ones I have seen show an altitude display of ca. 10,000ft, so must have been after the descent. I have no way of telling if the IFE system was active and lit during the emergency descent.
No , it probably doesn't exist, as on an australian flight , any w@nk&r with a video camera during such a descent would have had his camera wrenched off him and thrown into the gaping hole in the fuselage. We don't have time for cowboys and jerks wanting to film their impending demise. (LOL, we're too busy putting our passports in our pockets!)
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bsieker
The clip showed the passengers still wearing their masks so it could be that the first part of the video was taken whilst the descent was still in progress.
I was interested to see a meal tray sitting firmly on a passengers tray table so the angle of descent certainly wasn't the 'death plunge' that the journo's would have you believe.
There was also the report from a pax on the flight who said, as the aircraft levelled out at 10,000 feet, his glass of beer was still where he had placed it when the masks dropped with not a drop spilled.
Further into the clip the masks are off, cabin crew are out and about and the IFE shot shows the altitude at 10,000.
The clip showed the passengers still wearing their masks so it could be that the first part of the video was taken whilst the descent was still in progress.
I was interested to see a meal tray sitting firmly on a passengers tray table so the angle of descent certainly wasn't the 'death plunge' that the journo's would have you believe.
There was also the report from a pax on the flight who said, as the aircraft levelled out at 10,000 feet, his glass of beer was still where he had placed it when the masks dropped with not a drop spilled.
Further into the clip the masks are off, cabin crew are out and about and the IFE shot shows the altitude at 10,000.
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Regarding IFE during decompression, all screens are turned OFF, PSS (Reading and call functions) still available at passenger control unit. This condition is supposed to remain unless the whole system is restarted, then, and provided no active decompression signal from Pressurisation Controller, IFE returns to normal.
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I can assure you that the doors do not get jostled open unless the pressure relief valves are opened.
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Melted gas bottle exit points?
Re post #927
I would be surprised if friction from a gas flow would raise the orifice temperature significantly. The hot connector that some of us may remember from pumping up bicycle tyres is a result of the adiabatic compression of the air in the pump body. A more likely cause of a high degree of heating is that when the pressure differential across the orifice is so high that the exit speed would be supersonic, a shock wave appears and limits the speed of the outflow. It would be the flow across the shock wave that produced the metal-melting temperature apparently observed in some cases. It's almost 50 years since I last looked at the mathematics of the situation in detail, so I'm not going to bore most of you with even further off-thread computational minutiae.
"Not in a few milliseconds it wouldn't. This is a bang not a hiss."
I think that depends, how big is the orifice through which the oxygen is escaping? If the bottom suddenly falls off the tank, clearly it is a bang not a hiss. If the orifice is of a certain smaller size, like if the valve broke off, I think the gas could escape fast enough to generate a lot of friction = heat, and possibly long enough to melt some stuff locally. If the orifice is much smaller still, it could leak very little and generate only a 1"/25.4mm soap bubble a minute (a typical actual spec for gas leakage from pipes) which would generate no appreciable heat.
I think that depends, how big is the orifice through which the oxygen is escaping? If the bottom suddenly falls off the tank, clearly it is a bang not a hiss. If the orifice is of a certain smaller size, like if the valve broke off, I think the gas could escape fast enough to generate a lot of friction = heat, and possibly long enough to melt some stuff locally. If the orifice is much smaller still, it could leak very little and generate only a 1"/25.4mm soap bubble a minute (a typical actual spec for gas leakage from pipes) which would generate no appreciable heat.
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Re-posts 923 &927- (kansasw)
The exploding cylinder was on U-tube-it appeared to be a standard medical-type aluminium cylinder.
The explosive force of a large cylinder, as fitted to the aircraft,would, IMHO, be sufficient to rupture the hull-skin....the several hundred mile an hour slipstream would take care of this distinctly un-aerodynamic intrusion into it's smooth progress.
the argument about the hull being designed as a pressure-vessel, is a bit fatuous.....it was already loaded!...at cruise altitude, pressurised internally....suddenly hit by an enormous shockwave and simultaneous over-pressure,to an already once-repaired area.
buildings where pyrotechnics,ordinance,explosives etc. are prepared/assembled,,-are designed that the roof will readily blow off in order to minimise any blast-damage in event of an "incident"- a luxury not available to the designer of a pressurised aircraft.
The exploding cylinder was on U-tube-it appeared to be a standard medical-type aluminium cylinder.
The explosive force of a large cylinder, as fitted to the aircraft,would, IMHO, be sufficient to rupture the hull-skin....the several hundred mile an hour slipstream would take care of this distinctly un-aerodynamic intrusion into it's smooth progress.
the argument about the hull being designed as a pressure-vessel, is a bit fatuous.....it was already loaded!...at cruise altitude, pressurised internally....suddenly hit by an enormous shockwave and simultaneous over-pressure,to an already once-repaired area.
buildings where pyrotechnics,ordinance,explosives etc. are prepared/assembled,,-are designed that the roof will readily blow off in order to minimise any blast-damage in event of an "incident"- a luxury not available to the designer of a pressurised aircraft.