Re: Explosive decompression - how fast?

On 2008-04-25, Brian Davis <brdavis@[EMAIL PROTECTED]
> wrote:
> She really only accelerates for the first couple seconds, after that
> the lock is at such a low pressure that the remaining 'wind' just
> doesn't have enough force to do anything.

Yes, that's about right, if the door opens outward and sticks at a
10 cm gap.  Though actually I'd be very surprised to see an airlock
with a door that opened outward at all.

If it did open outward, and was free to swing open wider, consider
that it has 100 kPa pressure acting on the inner surface.  It will
accelerate open very rapidly indeed - probably on the order of tens of
milliseconds.

Though even in that situation, I'd guess Callie would exit the airlock
with only on the order of 1-3 m/s velocity, long after the air is
gone.


> Or does Callie really fully decompress in the airlock, and gently
> drift out about 10 seconds later?

Yes.


> (if the ?breach? is one entire side of your airlock, I think I have
> to worry about the force required to accelerate the mass of air in
> addition to everything else, yes?).

Sort of.  The rarefaction front will propagate inward at the speed of
sound, with the air accelerated nearly instantaneously as the front
passes.  The temperature behind the front will be some fraction of the
starting temperature - I'd guess about 4/5 from one thermal degree of
freedom out of five being converted to kinetic energy.

The relation for adiabatic expansion then gives a pressure behind the
front of about 46% of the initial pressure, and an exit speed of about
250 m/s.

That will exert a lot of force on Callie, but only for about 20-30 ms.


- Tim