Even so, it’s absurd to say that helium initially in a cooled, liquid state cannot be constrained from expanding as it warms.
[QUOTE=Dag Otto]
The ideal gas law is only valid under some conditions.
[/QUOTE]
You want to toss in virial coefficients? Go for it! Maybe even stick in something to cover quantum tunneling at the container walls.
Ideal gas law makes for a darn good first pressure estimate.
At these densities, I wouldn’t trust it very much. The van der Waals terms and anything else dependant on the size of the atoms would be highly significant.
But still, the pressure would surely be finite, and it would surely be possible to construct a container capable of handling the pressure. It probably wouldn’t be practical, though.
[QUOTE=Mangetout]
It must be theoretically possible to make a container capable of containing the helium, even if you have to make it the size of a planet and use gravity to counteract the pressure (I doubt this is actually necessary). The pressure is finite, isn’t it?
[/QUOTE]
looks at the sun Yeh, but then you might not have helium anymore 
At least not for long… Relatively speaking.
My understanding is that at those pressures, the definitions of “liquid” and “gas” become meaningless. So, yes, you probably could confine liquid helium and then warm the container to room temperature (and I don’t think it would take a planet-sized container), but whether what was in the container was a liquid would be debatable.
[QUOTE=beowulff]
at those pressures…
[/QUOTE]
With helium, we’re talking 10,000 psi or so, +/- deviations from the gas law.
10,000 psi is nothing. Paint sprayers work at 3,000 psi, and you can buy them at Home Depot…
[QUOTE=Zerc]
My understanding is that when a liquified gas expands back into a gas it cools down because energy is need for the expansion and this energy is supplied by the available heat in the nearby area, thereby causing cooling.
If this is the the case then I would assume that a tightly enclosed container holding liquid helium will not be cold but rather at the ambient temperature. The helium may be exerting a lot of pressure on the wall of the container but so long as no helium escapes the container will not be cold.
If my assumptions so far are correct how does immersing something like the infrared detectors used on telescopes in liquid helium cause them to be cooled unless there is a deliberate venting of the helium?
Am I missing something or are my assumptions correct?
Thanks
[/QUOTE]
Everyone here has over-complicated the answer as to make it impossible to understand. Ignoring Helium, as the OP indicated later, the simple answer is that, e.g., liquid Nitrogen in a strong enough sealed container will assume room temperature after a period of time. I haven’t looked at a phase diagram of Nitrogen lately, but I suspect it would remain liquid. In order to cool an infrared detector the Nitrogen must be returned to 1 atm, and assuming there is enough of it, a large portion would vent off with the remainding liquid then assuming a temperature of 77K, until it all boils away.
[QUOTE=flex727]
In order to cool an infrared detector the Nitrogen must be returned to 1 atm
[/QUOTE]
Just to be nitpicky, you could cool an IR detector by letting your N[sub]2[/sub] boil at 2 atm, or 0.573 atm too. The heat of vaporization of the liquid is what drives the cooling process.
At 2 atm the boiling point of N2 will be higher. You will not be able to cool the detector below the boiling point of the N2.
[QUOTE=Squink]
Just to be nitpicky, you could cool an IR detector by letting your N[sub]2[/sub] boil at 2 atm, or 0.573 atm too.
[/QUOTE]
I considered this to be obvious, and it’s not normal practice, but nit-picks are always welcome on this board. 
As I mentioned in post #12 (though without the handy link). 
[QUOTE=flex727]
Everyone here has over-complicated the answer as to make it impossible to understand. Ignoring Helium, as the OP indicated later, the simple answer is that, e.g., liquid Nitrogen in a strong enough sealed container will assume room temperature after a period of time.
[/QUOTE]
Everyone? I said the same as this in post #16.
[QUOTE=Mangetout]
Everyone? I said the same as this in post #16.
[/QUOTE]
You missed the part about how to cool the IR detector.