Predicting Pressure of an Explosion

[sean001]

I'm having trouble finding an equation(s) that will help me predict the maximum pressure inside an enclosure due to an explosion. Although air and vapors can get into the enclosure, I will assume a constant volume. I've thumbed through some old thermo books but nothing jumps out at me. Does such an equation(s) exist? If so, what is it or where can I find it? Thanks.

 

[Ashereng]

I may be way out in left field here, but:

Wouldn't the maximum pressure inside an enclosure prior to explosion be the maximum pressure capability of the enclosure itself? After explosion, there is nothing to hold the pressure in the enclsoure.

Are you looking for the "force" generated by the explosion?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[jte]

Sean-

I presume you have a situation where you have a vessel with a potentially explosive environment inside it. You've been asked to determine what happens if it goes boom and presumably the vessel will be designed to withstand/contain that. I dealt with that a loooong time ago with a food product processing plant. If I recall correctly, there was an article or two, maybe even a standard, which dealt with "deflagration." Never knew the word existed, basically the difference between "combustion", "deflagration", and "explosion" is the speed of the wavefront when the stuff oxidizes. I'll poke around a bit and see if I can find the old articles; in the mean time try google'ing on "deflagration" and see what you get...

Or... on a similar note, are you designing containment for testing explosive devices?

jt

 

[sailoday28]

jte (Mechanical).........." Never knew the word existed, basically the difference between "combustion", "deflagration", and "explosion" is the speed of the wavefront when"""

Refer to the Chapman-Jouget curve. This basically represents state conditions for the resulting mixture with the added heat from the combustion. The plot is pressure vs. sp. volume. From the initial conditions of p1, v1, a line is drawn which is tanget to the p2, v2 final condition curve. Two tangents may be drawn. One is results in a pressure rise - a detonation, and the other a pressure drop--deflagration.


Good luck

 

[vzeos]

I had to do something like this a number of years ago regarding a manhole explosion. I had obtained a copy of Explosion Development in Closed Vessels – Bureau of Mines Report of Investigations/April 1971 (RI-7507) which, as it turns out, I didn’t use but I would recommend getting it if you’re going to get into the subject in any detail. The higher-ups needed a “quick and dirty” number for the incident investigation. I don’t know how good my method was but what I did was to calculate the constant volume adiabatic flame temperature and then calculate the pressure using an equation of state.

 

[sean001]

Thanks everyone. I may have misused the word "explosion". The enclosure is not that big and houses some electronics. The idea is to have it contain an explosion if any of the electronics spark and ignite the vapors inside. I will look into the references mentioned. Thanks again.

 

[JStephen]

Seems to me that if you knew the components of the reaction, and could find internal energy for products and original constituents, you could just assume constant volume adiabatic condition, and solve for the temp/pressure that matched the original conditions.

 

[stanier]

Sailoday28

Look at this site for some definitions.

http://www.blastgardintl.com/td_explosion_terminology.asp

Geoffrey D Stone FIMechE C.Eng;FIEust CP Eng

http://www.waterhammer.bigblog.com.au

 

[sailoday28]

stanier (Mechanical)Thank you for the interesting website.
My explantion of shock and detonation were oversimplified.

From a search of your recommended website, I did glean the following which might also be of interest ot others.

Regards

The ideal detonation speed, known as the Chapman-Jouguet velocity, is a function of the reactant composition, initial temperature and pressure.

Chapman-Jouguet Velocity This is the velocity that an ideal detonation travels at as determined by the Chapman-Jouguet (CJ) condition: the burned gas at the end of the reaction zone travel at sound speed relative to the detonation wave front. CJ velocities can be computed numerically by solving for thermodynamic equilibrium and satisfying mass, momentum, and energy conservation for a steadily-propagating wave terminating in a sonic point. CJ velocities in typical fuel-air mixtures are between 1400 and 1800 m/s


Sonic point The point at which the flow velocity is equal to the speed of sound. When this is applied to detonations, the velocity is computed relative to leading shock front. The elementary Chapman- Jouguet condition is that the sonic point occurs at the end of the reaction zone when the products are in equilibrium.

 

[GenB]

Try the combustion forum,
genb