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Gas Ignition within Container

Gas Ignition within Container

(OP)
Hi All,

I'm working on an application where there's radioactive waste decomposing in an cast iron container (2.9m^3 volume). The container has a small opening (160mm^2) to diffuse the hydrogen and ideally keep it below the lower flammability limit of 4% volume in air.
Should something go wrong the max pressure created by ignition of the gas (which I am basing on a confined explosion despite the small opening) is 9 bar.

I am trying to confirm that the orifice is large enough to suitably dissipate the pressure, so I guess to do this I need to prove that the flow out of the container is greater than the mass of gas being produced due to the decaying of the material inside.

I know with the pressure difference of 9barg to 1 bara that the flow will be at sonic velocity, I've calculated the gas constant of 4% (2.8% mass) hydrogen, 96% (97.2% mass) air to be 394.34J/KgK.

What I am struggling with is what temperature the gas will be, if it initially starts at 20degC? I've read articles to suggest that a flash fire only lasts up to 3 secs? I thought if I could find the energy created by the flash then I could calculate the temperature difference using Q=mc(T2-T1) but information I've found states Hydrocarbon flash fires have an average heat flux of about 84kW/m2, this is confusing to me because it's about joule/second per m2 and I have a volume of gas.

I suspect there is a simple way of going about this and I have gone off route, so if any one can point me in the right direction it would be greatly appreciated.

Thanks

AppEng2

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