Question about pressure explosions

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    Explosions Pressure
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Discussion Overview

The discussion revolves around the phenomenon of pressure explosions in closed containers, specifically focusing on liquid nitrogen in plastic bottles. Participants explore the mechanisms behind the explosive failure of the bottle, the material properties involved, and the nature of the resulting event.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the explosive failure is due to the rapid heating of liquid nitrogen, which increases pressure significantly.
  • Others propose that the material properties of the plastic, particularly its brittleness at low temperatures, contribute to the catastrophic failure rather than a gradual tear.
  • It is noted that once a crack initiates, the structural integrity of the bottle is compromised, leading to rapid propagation of the failure.
  • Some participants discuss the noise associated with the event, attributing it to the rapid tearing of the plastic and the sudden expansion of gas.
  • A distinction is made by some participants between an "explosion" and "overpressure," with the latter being likened to a balloon bursting rather than a combustion-related explosion.
  • There is a mention of high-speed photography as a means to visualize the failure process, although no images are provided.

Areas of Agreement / Disagreement

Participants express differing views on the terminology used to describe the event, with some agreeing that "overpressure" is a more accurate term than "explosion." However, there is no consensus on the exact nature of the failure mechanism or the implications of the material properties involved.

Contextual Notes

Participants reference concepts such as fracture mechanics and the behavior of brittle materials, but the discussion does not resolve the complexities surrounding these topics or the specific conditions leading to the failure.

Who May Find This Useful

This discussion may be of interest to those studying material science, engineering, or anyone curious about the behavior of gases and liquids under pressure in confined spaces.

Dracovich
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Hi, now, I've observed liquid nitrogen in a closed plastic bottle, will eventually explode pretty violently once the pressure gets high enough (that's what I'm assuming happens, the nitrogen gets warmer which increases the pressure, plus it goes from liquid to gas form). But my question is this:

Why does it end in a explosion but not a small tear/rift in the bottle? I'd expect that it does have the energy to cause a rift/tear/break in the material since it does have enough energy to make it explode.
 
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Most likely it is due to the rate at which it is being heated. Since liquid nitrogen is at such a low temperature compared to average room temperature, LN2 in an uninsulated container is being heated at a pretty substantial rate.
 
Dracovich said:
Why does it end in a explosion but not a small tear/rift in the bottle? I'd expect that it does have the energy to cause a rift/tear/break in the material since it does have enough energy to make it explode.
I would say its probably more due to the material properties. Depending on the plastic, it can get very brittle at low temperatures. Also, explosions sometimes do start as a small tear, but the tear itself weakens the surrounding material, causing a sort of cascading failure.
 
The pressures a Coke bottle can withstand are surprisingly high. Once failure initiates, the bottle is weakened significantly (almost instantly), so catastrophic failure occurs with a bit of a bang. As russ suggested, the low temperatures are likely to induce embrittlement of the polymer structure, which acts to reduce the failure stress, and causes propagation of a defect to happen much faster.
 
Polymers typically have "non-existent" leak-before break characteristics, i.e. fracture toughness, when we're considering behavior near/below crystalline temperatures etc.
 
I'm afraid i don't know much about explosions in general, but in this case is it basically just the effect of a highly compressed gas escaping and thus expanding very quickly and hurling the parts of the bottle around? And also if so what is it that causes the noise that follows the explosion?
 
Yes, pretty much. The bottle is too weak to withstand such high pressures, and once a critical pressure is reached, a crack will appear in the bottle. This greatly reduces the bottle's strength, and so a tear will form very rapidly.

The 'bang' is likely to be a combination of the plastic being torn apart rapidly, and of the sudden expansion of gas escaping from the bottle.
 
... you can try to further visualize the failure part by considering behavior of 'brittle' materials ... after reaching a critical state (which would be best evaluated using fracture mechanics) the applied loading exceeds the material resistance for crack propagation by a healthy margin, and next thing you know you've a crack propagating with speed comparable to the speed of sound. And when the material is brittle, there is nothing to arrest the crack other than complete structural failure (like hitting a window with a sledge hammer).
 
I wouldn't dare to call it an "explosion"...

the term "explosion" is more accurated for sudden combustion explosive reactions...
 
  • #10
Clausius2 said:
I wouldn't dare to call it an "explosion"...

the term "explosion" is more accurated for sudden combustion explosive reactions...
Not like I'm qualified to or anything, but I agree with that. 'Explosion' presumes the production of heat. This would more accurately be described as an 'overpressure', similar to a balloon bursting. Incidentally, if you have a chance to you should check out high-speed photography of things like this happening. You'll see that the initial activity is very similar to that which would happen in a low-pressure rupture of the same material, but it happens a lot faster. I have some nice pictures of bullets going through balloons and oranges and such. It's fascinating. (Don't ask me to post them; they're in a gun magazine and I don't know how to work my scanner.)
 
  • #11
Danger said:
Not like I'm qualified to or anything, but I agree with that. 'Explosion' presumes the production of heat. This would more accurately be described as an 'overpressure', similar to a balloon bursting.

Exactly. I agree.
 
  • #12
Clausius2 said:
Exactly. I agree.
Wait a minute! You can't agree with me; I was agreeing with you!
Maybe it's just because I'm getting into my 11th beer, but I just noticed that the word 'agreeing' looks a bit like a weenie dog. I think that I should head back down to GD now...
 
  • #13
Danger said:
Wait a minute! You can't agree with me; I was agreeing with you!
Maybe it's just because I'm getting into my 11th beer, but I just noticed that the word 'agreeing' looks a bit like a weenie dog. I think that I should head back down to GD now...

I don't know. You should try with the 12th. Maybe you see clearer the stuff. :smile:
 
  • #14
Clausius2 said:
I don't know. You should try with the 12th. Maybe you see clearer the stuff. :smile:
Aw nuts; they've worn off. Go to sleep for a couple of hours, and look what happens. Anyhow, I'm sort of getting used to some of this internet stuff now that I've had it for a couple of months, so maybe I'll see if I can find some of those pictures on line.
 

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