Plastic KETER sheds

[JohnW2]

How do you think they cool the gasses then? Particularly Hydrogen to 30°K ...

I'm not sure that I understand your question. As I've just written, it is impossible to liquify hydrogen at a temp above its 'critical temp' (about 33 K), no matter how high the pressure - but it would (just) be possible to liquify it at 30 K with a very high pressure. At the critical temperature (about 33 K) it would require a pressure of about 1,198 psi (the 'critical pressure', about 82.7 bar) to liquify hydrogen.

I have no idea, but would suspect/presume that hydrogen is usually stored at temps well above 33 K, hence inevitably as a compressed gas, with no liquid?

[ as a pedantic point, units of absolute pressure are, strictly speaking, Kelvin ('K'), not 'degrees Kelvin' ('°K') !! ]

 

[JohnW2]

.... I recall it as using a membrane filter to separate the hydrogen and a compressor similar to a jet engine to compress it sufficiently to turn it to liquid.

As I've recently written, at its 'critical temperature' (about 33 K) it would require a pressure of about 1,198 psi (the 'critical pressure', about 82.7 bar) to liquify hydrogen - so not totally impossible. However, as said, it would be impossible to liquify it at temps above about 33 K, no matter how much pressure you coud come up with!

 

[SUNRAY]

... but I recall it as using a membrane filter to separate the hydrogen and a compressor similar to a jet engine to compress it sufficiently to turn it to liquid.

As I've recently written, at its 'critical temperature' (about 33 K) it would require a pressure of about 1,198 psi (the 'critical pressure', about 82.7 bar) to liquify hydrogen - so not totally impossible. However, as said, it would be impossible to liquify it at temps above about 33 K, no matter how much pressure you coud come up with!

and you conveniently take the post out of context

 

[JohnW2]

and you conveniently take the post out of context

Eh?

 

[fixitflav]

but would suspect/presume that hydrogen is usually stored at temps well above 33 K, hence inevitably as a compressed gas, with no liquid?

That's right, for any "permanent gas" ie one that cannot be liquefied by pressure alone at room temperature, there are 2 options - store it as a compressed gas at high pressure, or cool it, compress it (at moderate pressure), and keep it as liquid in a Dewar vessel (aka vacuum flask). Which to choose depends on the economics of the situation.

 

[plugwash]

I suspect that the same refrigerant would not be 'appropriate' (well, at least not 'ideal') for a freezer and for aircon, given that the target temps in the 'evaporator' are so different in those two scenarios.

Propane (aka R290) is quite common in commercial fridges/freezers and now seems to also be seeing use in air conditioning, while Isobutane (aka R600A) is the norm in domestic refridgeration.

CO2 has also been used for air conditioning and commercial refridgeration, it has the distinct advantage of being non-flamable while not being anywhere near as bad for the environment as flourocarbons but it's critical point is a little on the low side. I've seen a claim (which I can't verify) this is the reason for out of service freezers in UK supermarkets recently.

In a freezer, the refrigerant must be liquid at the P and T in the condenser (heat dump grid), and gas at the P and T in the freezer compartment.

Phase change is not strictly necessary for a refrigeration cycle (most aircraft use an air-based cycle to manage cabin temperatures!) but it's very helpful.