# Liquid Nitrogen - a question or two

Discussion in 'Physics & Math' started by Quantum Quack, Jun 4, 2004.

1. ### Quantum QuackLife's a tease...Valued Senior Member

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Another simple question.

When we take 1 litre of Liquid nitrogen and place it in a pressure vessel made of steel and seal this vessel, so that the vessel contains just Liquid Nitrogen.

Does the vessel feel cold on the outside?

Does the liquid Nitrogen remain at it's quantity even though the vessel is cold?

A sealed vessel with Liquid Nitrogen in it remains static in form but is cold on the outside for how long?

I know these are probably pretty simple questions but I ask that if the container remains fairly static in form ( liquid Nitrogen included) could it be said that the external temperature of the vessel is capable of work?

3. ### CrispGone 4everRegistered Senior Member

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Not a good idea. See below.

Yes. Steel and iron are very good heat conductors (usually good electric conductors are also very good heat conductors). This means that the steel is very good at taking energy in the form of heat from the outside and porting it to the liquid nitrogen. When you touch the vessel with your hand, energy from your fingertips is dissipated (i.e. your fingertip is cooled) and it is this sensation that makes you feel "cold".

No. The room (the environment) is at roomtemperature, let's say 20°C. This is quite a bit higher than the freezing temperature of nitrogen, which is at 77 K or -196°C. Heat from the room will dissipate through the (nicely conducting) steel to the nitrogen, heating it up and evaporating it. The result will be quite disastreous: if you sealed the steel box, it will explode after a while, because 1 liter of liquid nitrogen will expand to about 22 liters of nitrogen gas.

The total amount of nitrogen is conserved (gas + liquid).

Uhmmm.. No idea, I think it will cool pretty rapidly (judging by the nitrogen-explosion experiments that we all have done in the lab

).

Yes, you can extract work from this flow, this is what some powerplants do to generate electric power (thermocoupling). They don't use liquid nitrogen there (the energy required to cool the nitrogen is higher than you can extract from the thermocouple) but rather naturally cooled resources (e.g. rivers).

Bye!

Crisp

5. ### PeteIt's not rocket surgeryModerator

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Unless your container can contain a pressure of 300MPa (3000 atmospheres). This is the pressure required to maintain liquid nitrogen at room temperature (actually, the nitrogen is supercritical at this pressure and temperature, but that's another story).

7. ### Quantum QuackLife's a tease...Valued Senior Member

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Pete excuse me while I express my amazement....that stuff is certainly dynamic.

8. ### CrispGone 4everRegistered Senior Member

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That explains why the coca-cola bottles we used exploded quite spectacularly... appearantly they are not up to the 3000 atm challenge