Pressure V's Temperature 1

[salty59]

I am somewhat out of my field here (Mining Electrical Eng) and am hopeful someone can take the time to assist a layman.
An explosion of methane in a flameproof enclosure relies on escaping gases to be cooled as they cross a flamepath in order not to ignite an external explosive atmosphere. Methane explosions generate (I am led to believe)approx 600kPa 1500 deg C and sufficient temp reduction occurs to drop the temp generated in that explosion to below 537 deg C. The lengths and gaps of flamepaths, relative to enclosure volume, are critical in achieving this

Is Temperature versus pressure, as calculated from the ideal gas equation applicable

 

[zdas04]

Not really. The process is compressible flow, J-T Cooling, and transfer of fairly small-BTU mass of gas into a much larger mass of steel. None of these things are terribly conducive to analysis by the Ideal Gas Law.

David

 

[salty59]

Thanks for your response David. I will look into compressible flow and J-T cooling in an attempt to increase my understanding.

"transfer of fairly small-BTU mass of gas into a much larger mass of steel"
This is what initiated my question. It has been a long held belief in the mining industry that this is the basis of flameproofing. However, not all flamepaths are steel (or other metals). Many flamepaths are polycarbonate materials, eg Burnbrite Exd lights, which led me to the supposition that cooling by depressurisation may be the underlying principle.

Further comment appreciated.
Regards.. Rod

 

[zdas04]

It is the same thing. Say a Class 1 Div 1 junction box held 6 in^3 of air. Some natural gas gets in through external overpressure. The explosive range of methane is 5%-15% so if the pressure builds up above about 2 psig it will be above the UEL and no longer explosive. So inside the box you have something like 1.7E-4 lb of gas. The polycarbonate box weighs nearly a lb. Even a very hot, very dense pressure wave will dump its heat into a heat sink 10,000 times more massive. The box has to be strong enough to take the blast wave without shattering and massive enough to prevent its getting hot enough to ignite any explosive mixture that exists outside the box.

David

 

[salty59]

Many thanks David