[AR] Re: BLEVE Concerns
- From: Peter Fairbrother <peter@xxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Thu, 14 Jan 2021 22:21:57 +0000
On 14/01/2021 15:00, Brett Coles wrote:
Hi all!
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
Any 1,500 psi rupture disk rupturing is going to be a violent event.
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.
If the oxygen is in the tank is at 1,500 psi it will be supercritical -
this prevents the liquid being (somehow) forced out of the tank then
BLEVE-ing in the open air, as there is no liquid to BLEVE.
This is not much of a blessing, as supercritical oxygen at 1500 psi can
have a fairly high density, can be similar to liquid density depending
on tank fill.
However, in a disk rupture you have a limited opening to the outside -
keep the opening small and the rate of escape is small.
"Small" here means only big enough to cope with any further increase in
pressure due to eg heating or internal reactions which might rupture the
tank. This also has the advantage of less rapid pressure change on the tank.
Note that once the pressure falls to ~750 psi then liquid will form - if
the vent is above the liquid surface this will further slow the escape,
if the vent is below the surface it could increase the mass flow rate.
(the above is theory not experience - perhaps Henry or someone will
correct my errors)
Peter Fairbrother
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