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Topic: Explosive simulation  (Read 885 times)

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Offline krzywan901

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Explosive simulation
« on: September 16, 2019, 03:36:19 AM »
Hi everyone,

I have a problem. I need doing simulation in AnSys about explosion methane (as gas), unfortunately program has not such material and I do not know explosion parameters of methane (8.5% in air). I am enclosing picture with parameter of TNT (AnSys has material TNT), and does someone know about what parameters should has methane gas and could you share with me?

Best regards

Offline Enthalpy

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Re: Explosive simulation
« Reply #1 on: September 16, 2019, 02:27:55 PM »
The parameters shown are typical for solids, for instance the bulk compressibility. It would be surprising if the same part of software can compute a solid and a gas explosion.

TNT detonates while methane deflagrates almost always, at a much slower speed. TNT creates a detonation wave in air that destroys objects by impact, while methane raises slowly the pressure. The consequences are completely different, for instance TNT can destroy a nearby object in open air, while methane is destructive essentially to closed volumes.

Offline krzywan901

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Re: Explosive simulation
« Reply #2 on: September 17, 2019, 05:41:35 AM »
Thanks for response.

Yes you right, after your answer, I saw other option in program. Do you know such parameters of methane gas:
1. Adiabatic exponent γ (without unit),
2. Pressure schift (kPa),
3. Specific internal energy (J/kg)
4. Velocity explosive (mm/s)
5. Time of explosion (s)
For temperature - 293K
I am trying looking for, but for me this is not readable.

Regards

Offline Enthalpy

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Re: Explosive simulation
« Reply #3 on: September 17, 2019, 08:09:54 AM »
These are not the usual names. After interpretation:
  • γ=1.306 for methane alone
  • ??
  • Could be the heat capacity at constant volume. Cv=1708J/kg/K. Or the heat of formation, -4.65MJ/kg, but this is an enthalpy, not an internal energy. Or a heat of combustion for the gas+air mix.
  • 420mm/s for a stoechimetric premix with air without detonation, depends on proportions, pressure, temperature. Your mix is a bit fuel-rich, so 470mm/s looks better.
  • I suppose the time of explosion is not intrinsic to the explosive.
Are you aware that your chances of getting meaningful results are slim? If the consequences are important, ask a specialist. Or just use the overpressure known for such explosions, it will be more direct and reliable.

Offline krzywan901

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Re: Explosive simulation
« Reply #4 on: September 18, 2019, 03:47:05 AM »
I am very well aware of this. I told everyone, that perform this correct is imposible, but my boss knew better. My company get old KWS (electrical box for mines) and they wanted doing simulation explosive in AnSys, then perform real research through specialist and compare results. I know that results will be diffrent, but I have to perform duties receive from boss. If I had to do for real use, I would refuse. It is cool, that you give a such advise, however I was realised of this. Thank you very very much for help.
Regards

Offline Enthalpy

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Re: Explosive simulation
« Reply #5 on: September 30, 2019, 08:35:14 PM »
The overpressure of a gas explosion depends much on the container's shape. The pressure can easily double at a reflecting wall. So a simulation without shape isn't the whole picture.

Without reflections, you can get half-sensible results by computing the produced heat, temperature at constant volume, and deduce the pressure. That would be for a deflagration fast enough that the combustion happens prior to gas movement. In air, the composition of the products is predictable by hand. Methane tends to burn more slowly and would achieve that pressure only in a closed sturdy container.

Or you find existing deflagration data. Most reliable path.

Or you tinker with that software... I understand. Condolences.

Offline krzywan901

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Re: Explosive simulation
« Reply #6 on: October 10, 2019, 07:47:20 AM »
Once more thank you very much. Although I own incorrect results, you very me helped. I did not realise that there is two type explosion. In the moment I know less than I knowed. Additionally we have incomplete AnSys softwere and I can not do simulation in correct modul, so all went in .. . However interesting things I learned thanks to you. Thanks, best regards.

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