# Airflow speed into vacuum

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1. Jan 19, 2017

### Carlos PdL SdT

I have a weird question here. At what speed does air flow from a pressurized container at one atm into vacuum (rupture in ISS for example).
I was watching the Martian and I wanted to see how much deltaV Mark Wattney can get by puncturing his suit, so I did my homework and saw that the spacesuit held two liters of liquid nitrogen and one liter of liquid oxigen (about 2.6kg total propellant mass). The mass of a person with a spacesuit is 100kg as estimated by NASA in the bok, so I only needed to know the specific impulse, or the exit velocity. I applied Bernoulli and came to an answer of about 400m/s which is way more than Mach 0.3 so Bernoulli doesn't work.
How do I get the air escape speed if it is above Mach 0.3?

2. Jan 19, 2017

It depends on what the internal pressure and temperature are. In most cases, the flow will also be choked (it will always be choked if the external pressure is vacuum), so it will be moving exactly Mach 1.

Are you at all familiar with compressible flows?

3. Jan 19, 2017

### Carlos PdL SdT

Not much. Till now I've only seen incompressible flow in class. But then I guess I'd only have to plug in sqrt(1'4*R*T) and make a relation between T and the amount of air that remains within the suit. Or assume it's always the same which is easier to do.

4. Jan 19, 2017