Combustion pressure for explosion proof enclosure
Combustion pressure for explosion proof enclosure
(OP)
Hi All,
I need to find the resulting pressure of an explosion of a 50% Acetylene and 50% oxygen explosion in an enclosure. The idea is the resulting pressure as to be able to design an enclosure which will sustain such a blast.
I found the http://en.wikipedia.org/wiki/Heat_of_combustion value of acetylene and used it along with Q=mcΔt to determine the final temperature. Is this method reliable for this solution?
According to the above the temperature only raised by about 35°. Considering that acetylene burns at 3500°C I am doubtful of my conclusion here. Can anyone help me in the right direction please?
I need to find the resulting pressure of an explosion of a 50% Acetylene and 50% oxygen explosion in an enclosure. The idea is the resulting pressure as to be able to design an enclosure which will sustain such a blast.
I found the http://en.wikipedia.org/wiki/Heat_of_combustion value of acetylene and used it along with Q=mcΔt to determine the final temperature. Is this method reliable for this solution?
According to the above the temperature only raised by about 35°. Considering that acetylene burns at 3500°C I am doubtful of my conclusion here. Can anyone help me in the right direction please?





RE: Combustion pressure for explosion proof enclosure
is the pressure rise due to combustion, spontaneous ignition, electrical spark, etc.?
what type of enclosure? how big-volume? materials of construction? thicknesses of material?
dynamic pressure increase is way different than a gradual pressure increase.
not sure how else to help, but this may spur further analysis.
good luck!
-pmover
RE: Combustion pressure for explosion proof enclosure
Yes it is ex rating for an enclosure. The gas is ignited by a spark. The volume is undetermined because it will depend on the design, it will be less than a 1000 CC anyway but as there is an escape path the volume will not be constant. However I guess that initially the volume will be constant as the flow path is controlled in order to pass the heat on to the enclosure.
Thanks
RE: Combustion pressure for explosion proof enclosure
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There are several NFPA standards that may be helpful. Google "deflagration containment", "explosion containment", "compression due to combustion', etc.
Good luck,
Latexman
RE: Combustion pressure for explosion proof enclosure
RE: Combustion pressure for explosion proof enclosure
The equipment must have been tested in some way to prove to be "explosion proof". So there must be a standard you can look at. Maybe talk to Appleton. They make a ton of stuff. On that note there is not a lot of equipment rated for Acetylene. Most group B equipment is purged.
Anyway I hope this helps.
Regards
StoneCold
RE: Combustion pressure for explosion proof enclosure
B.E.
The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
RE: Combustion pressure for explosion proof enclosure
http://www.kele.com/templates/product.aspx?id=1923
If there's any way possible, make your work intrinsically safe instead. Acetylene is too scary for me.
Also, I'm not a chemical guy, but is 50/50 the ideal explosive mixture for acetylene and oxygen? (I'd like to know). The concern in the field and the standards will be percentage by volume of air, not oxygen, so you may want to factor that into your calculation. Or, it might be easier to just take a stab and start testing.
Your UL or FM test will involve igniting the ideal explosive mixture of acetylene and air inside your enclosure while it is inside another enclosure that also contains the ideal explosive mixture of acetylene and air. Yours will have to contain the explosion and cool the escaping gases enough to prevent igniting the surrounding mixture.
I bet they do this test outdoors.
Let us know how it goes!
Good on ya,
Goober Dave
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RE: Combustion pressure for explosion proof enclosure
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RE: Combustion pressure for explosion proof enclosure
DRWeig
EX enclosures I have dealt with depend on eliminating the flame path with very smooth and flat mating flanges <.002". Exhaust gasses will still be hot but not currently undergoing combustion when leaving the enclosure. Cooling is secondary as the gasses only need to fall below the auto ignition temperature of the working fluid (acetylene ~580F).
Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations
RE: Combustion pressure for explosion proof enclosure
Irstuff, That is why I ask the question. I realize that in my mixture I will have about 11 Mj of energy. How to get this energy released and absorbed in such a way that there is not too much force on the enclosure. That is the question!
Thanks anyway, I am looking at some standards now, thanks Latexman.
RE: Combustion pressure for explosion proof enclosure
In any case, the critical missing factor is either the time or the velocity. With either, you can potentially synthesize a pressure. Say the explosion front velocity is 2270 m/s for acetylene. If you use the aerodynamic drag equation:
1/2(v^2)ρ, you get a pressure of 3.3 MPa, which is comparable to the 3+ MPa shown here: http://www.gexcon.com/handbook/6_6.gif
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RE: Combustion pressure for explosion proof enclosure
Acetyene with 50% O2 has a fundamental burning vel of 1140 cm/sec. I think Pmax ( maximum pressure of a confined explosion) can be calculated.
RE: Combustion pressure for explosion proof enclosure
That's why FAE's work when dispersed over a large volume.
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RE: Combustion pressure for explosion proof enclosure