Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
/snip/
FWIW, the membrane is an ultrathin polymer window that allows x-rays
in the 100eV range to pass. /snip/
Normally, venting to atmosphere is done slowly, but there are
instances of window breakage during catastrophic venting. The physics
question is whether it is plausible that catastrophic venting alone
can break the window, which is designed to withstand a 1 atm
differential under steady state conditions
Let's do back of the envelope, zeroth approximation. Force due to a
fluid cylinder of cross-sectional area A moving at velocity v,
density rho, that impinges on a flat surface, and assuming worst case
elastic collision, is 2.A.rho.v^2. Normalize A to get pressure,
assume rho is atmospheric density at RT (the in-rushing air is from
the atmosphere, approx 1 gram per 1000 cc). What is a reasonable v?
Not large, intuition tells me 10cm/sec into a vacuum is a reasonable
guess. My calculation of collision pressure is 2e-6 N/cm^2, or 3e-6
psig. The more likely inelastic collision (cf wind against a sail),
and compression effects make this even smaller (right?). Even if I
increased v by 3 orders of magnitude, I'm still relatively small at
0.3 psig. Please check my math and try not to embarrass me too much
if you find a mistake :-)
Stefan Jeglinski