Liquid Nitrogen?

Question

Liquid Nitrogen is a liquid at 77 deg. Kelvin. To prevent it from warming and expanding to a gaseous state, at what temperature would I have to set a thermostat to keep it cryogenically cooled to 77deg Kelvin. In other words, does it take a lot of energy to keep it at that temperature?

I need to seal a superconducting magnet (with an induced current) in liquid nitrogen indefinitely. The current is supposed to "persist" forever in a superconducting state when super cooled. Space application.

Answer 1

Your answer is 77 Kelvin. But nobody actually keeps it that cool because of the high cost of doing so. It is cheaper to put it under pressure. If you know the Ideal gas law then you know that PV=nRT and that this can be made even simplier by assuming that you are talking about a set amount of N2, or moles of nitrogen and then you can compare the gas at different pressures, temperatures and volumes. So, (P1V1/T1)=(P2V2/T2) now to change from 1 to 2 what is cheaper, to change the pressure, temperature or the volume? Pressure is almost always the winner. That is why you can see trucks driving around carrying oxygen and nitrogen. Almost every heating and air conditioning contractor truck that you see has a steel tank of nitrogen gas on board that they use to test coolent system for leaks. I can't remember the maximum safe level for these cylinders, but I would think that they would hold at least 30 atmospheres of pressure.

Answer 2

well sweetie ,i think your answer is 77 Kelvin. But nobody actually keeps it that cool because of the high cost of doing so. It is cheaper to put it under pressure. If you know the Ideal gas law then you know that PV=nRT and that this can be made even simplier by assuming that you are talking about a set amount of N2, or moles of nitrogen and then you can compare the gas at different pressures, temperatures and volumes. So, (P1V1/T1)=(P2V2/T2) now to change from 1 to 2 what is cheaper, to change the pressure, temperature or the volume? Pressure is almost always the winner. That is why you can see trucks driving around carrying oxygen and nitrogen. Almost every heating and air conditioning contractor truck that you see has a steel tank of nitrogen gas on board that they use to test coolent system for leaks. I can't remember the maximum safe level for these cylinders, but I would think that they would hold at least 30 atmospheres of pressure. I hope this helps . good question . -B-

Answer 3

You'd have to set it at 77 K. It is a liquid at 77 K with large latent heat of vaporisation, so it will "want" to stay liquid without much trouble.

I don't really understand what do you mean by "does it take a lot of energy to keep it cold".

Liquid nitrogen is usually kept in thermally insulated vessels called dewars (by the name of the scientisct who was first to obtain one of the cryogenic liquids, I forget which one) that don't have any extra temperature controller attached to it. You can think of the as of really good quality thermos bottles. Even a regular styrofoam cup is good: it will take more than an hour for the whole cup to be gone.

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What do you people mean by noone keeps it that cool? Some research scientists do! And some hospitals use it too.

Answer 4

To find you answer convert the Kelvin temp to Fahrenheit and yo will see it take a lot of energy to keep it that cold for long periods of time.