I Can Joule-Thomson effect freeze air?

[Malapine]

TL;DR Summary

Would air escaping thru a narrow opening into vacuum eventually clog it shut with frozen N2/O2, due to cooling from J-T effect?

Could air escaping through a narrow opening into a vacuum freeze due to cooling from Joule-Thomson expansion, and cause frozen N2/O2 to accumulate around the edges of the opening until it clogged shut ?

 

[Chestermiller]

Summary:: Would air escaping thru a narrow opening into vacuum eventually clog it shut with frozen N2/O2, due to cooling from J-T effect?

Could air escaping through a narrow opening into a vacuum freeze due to cooling from Joule-Thomson expansion, and cause frozen N2/O2 to accumulate around the edges of the opening until it clogged shut ?

Are you talking about the case of steady flow through an orifice, or the case where you have two closed chambers and you let the pressures equalize?

 

[Malapine]

Steady flow through an orifice, from an unlimited reservoir of STP air (for example an extremely large space habitat) into an unlimited vaccum.

 

[Chestermiller]

Steady flow through an orifice, from an unlimited reservoir of STP air (for example an extremely large space habitat) into an unlimited vaccum.

Are you sure you want to do it with STP air? That won't produce much of a JT effect. The JT effect is based on the deviation from ideal gas behavior, and, at STP, air behaves very close to an ideal gas.

Did you think that expansion cooling would take place? It wouldn't, because, for an ideal gas, it is offset by the viscous frictional heating in the orifice. In JT flow, the change in specific enthalpy between inlet and outlet from the orifice is zero.

 

[Malapine]

So: frictional heating of normal air flowing through the orifice will prevent it from cooling to crygenic temperatures as it expands into the vacuum, and the hull breach won't seal itself with a block of frozen air.

 

[Chestermiller]

So: frictional heating of normal air flowing through the orifice will prevent it from cooling to crygenic temperatures as it expands into the vacuum, and the hull breach won't seal itself with a block of frozen air.

No. Not if there is steady flow.

Of course, the JT effect assumes no change in kinetic energy. If the flow reaches sonic conditions and the orifice become choked, some cooling will occur by conversion of enthalpy to kinetic energy. But this would not be considered a JT effect.

 

[Malapine]

Would there be any decrease in temperature or pressure upstream from the orifice? I am assuming some sort of tornado-like vortex forms in the area above the breach, but if there is no pressure or temperature drop, then there won't be a visible condensation funnel (or no funnel at all, just inflow jets?)

 

[Chestermiller]

Well, if we are now talking about the non-JT regime, then cooling would be occurring in the approach to the orifice. But it could not cool more than where you get sonic velocity at the orifice.

 

[Chestermiller]

I think that you might find the following thread of interest: https://www.physicsforums.com/threads/unsteady-filling-of-a-vacuum-tank.971992/#post-6182728