Liquid Hydrogen, Nitrogen or Helium

[ScottD]

Hello All !

 

I'm new here and this is my first post. My disclaimer is that I am not

a scientist, just a very curious software developer that wishes

he was a scientist!

 

I was wondering just how super cooled elements such as Hydrogen

, Nitrogen and Oxygen are made. Are these elements placed under great pressure to achieve

the temperatures that are several hundred degrees below zero?

 

Please accept my apologies for such a rudimentary question!

 

Thanks in advance

 

Scott

[rktpro]

Yes, they are cooled by applying pressure.

[John Cuthber]

It's not just pressure, you have to cool it too.

Have a look here

http://en.wikipedia.org/wiki/Air_separation

[evern]

for really cool temperature ,you have to use lasers.There are a number lasers focused on a point....these cover all directions of motion.A particle at this point ,irrelevent of its direction of motion,collides with at least a single laser beam.Its momentum is canceled by the collision with the photon.This takes a long time but it can achieve liq He temps.

[CaptainPanic]

The compressed gas is cooled as much as possible using regular cooling equipment. After that, the pressure is released, and the expansion causes the gas to cool down further. And after it has cooled down enough, it will become a liquid. Note that this is a simplified version of the processes that are used in reality.

Why gas cools down when it expands is explained here (Joule-Thompson effect).

 

To learn some more about cooling stuff down, I think the best explanation is just the regular refrigeration cycle as used in every common fridge and freezer in every house. The evaporation/condensation causes a temperature change. And that's the essence of all cooling / refrigeration.

 

In regular fridge/freezers you also have a liquid that evaporates / expands into a gas, and this expansion cools the gas. That cold gas can then absorb heat inside the fridge (thus cooling your food/drinks). The gas, which is now warmer, is then compressed (that's the thing that makes some noise in your fridge). The compression heats it up even more. The hot gas then goes through the condenser (all those little tubes at the back of the fridge) where the outside air cools and condenses the liquid. The cooler liquid is then evaporated again, which cools it down further, and it can go back into the inside of the fridge to cool your food.

http://en.wikipedia.org/wiki/File:Refrigeration.png

[Cap'n Refsmmat]

for really cool temperature ,you have to use lasers.There are a number lasers focused on a point....these cover all directions of motion.A particle at this point ,irrelevent of its direction of motion,collides with at least a single laser beam.Its momentum is canceled by the collision with the photon.This takes a long time but it can achieve liq He temps.

As far as I know, this works only for small collections of atoms. To produce liquid helium or liquid hydrogen you need something a little more practical, like what CaptainPanic described.