Learning Forum

[Peter Woodcraft]

Im trying to model dust dispersion and then a dust gas explosion. The sphere starts in a vacuum. Methane is added at a mixture of 2%. the explosive dust is shot up through the pipe and through the nozzle into the sphere with oxygen to reach atmospheric pressure. the mixture of gas and dust is then ignited. Im trying to measure the pressure increase from the explosion and the rate of pressure increase. how would i go about this?

 

[Rob]

With caution. 

You'll need to start the calculation off at a point where the continuum assumption is valid, so not full vacuum. The reaction kinetics are an entirely different problem, how are you triggering the oxygen-methane mixture to explode, and how are you including the contribution of the powder. With ideal (or real) gas for density it's probably possible, but I am unsure what approximations you'll need to make. Time step is going to need to be very small once the reaction is triggered. 

[Peter Woodcraft]

So the sphere is evacuated to roughly 0.2 ATM and the dust injection is under a pressure of 21 bar. The ignition is cause by a 1kj chemical igniter. The dust is coal dust so it increases the explosively violence of the reaction.

[Rob]

OK. The igniter can be mimicked by using a patch of high temperature as and when you want it. 

At 0.2 atm it's not a vacuum so continuity is probably OK - you may want to read up on Knudsen Number to confirm. You've then got an O2 & CH4 reaction plus a DPM based reaction: I think there are a couple of tutorials in Help that cover the basics. My background includes some combustion chemistry from Uni, but I'm not overly familiar with the modelling side of it.