[AR] Re: BLEVE Concerns
- From: Norman Yarvin <yarvin@xxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 14 Jan 2021 15:04:52 -0500
On Thu, Jan 14, 2021 at 08:00:00AM -0700, Brett Coles wrote:
I'm sure this has been asked before, but I was recently reminded of the
concern of having a BLEVE when working with cryo-systems. We designed the
LOX feed system for our hybrid motor to have a rupture disc so that it
would vent pressure eventually if we lost valve control. However, I did not
account for the fact that 1,500 psi LOX boils at a significantly higher
temperature than atmospheric LOX. I am concerned that the LOX would warm up
then start to boil off and cause the rupture disc to function, then all
boil off at once when the pressure drops.
That 'all boiling off at once' will be stopped by the boiling raising
the pressure, as well as by the temperature dropping due to the latent
heat of vaporization. So you're not going to get a dangerous pressure
spike from the burst disc rupturing. (There probably would be some
pressure oscillations -- pretty much anything violent produces some
oscillations -- but the first direction of pressure change would be
down, and it'd be hard for it to exceed the original pressure.)
BLEVE is usually due to a fire that supplies so much heat that the
emergency relief outlet can't pass gas fast enough to relieve the
pressure buildup. The heat also weakens the tank.
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