Why Pressurize Liquid Helium?
Most recent answer: 07/01/2015
- Dean Olson (age 59)
Champaign, IL USA
The vapor pressures are very strong functions of temperature, so that comparison isn't quite the way to look at it.
I think the answer is basically economic. If you want to get say 1 L of liquid out while maintaining a constant overpressure (say 5 psi) then you need to add 1 L of gas to the dewar. Are you willing to let that much of the liquid boil off? For LN2, sure, why not? So the dewars for it are not insulated well enough to prevent a little boil-off, although sometimes you do need to augment it with some external gas. LHe2 is very expensive, and we try to recover the boil-off. So the dewars for it are made with very good insulation to keep the boil-off rate low despite its lower latent heat of evaporation.
Mike W.
(published on 07/01/2015)