LN2 dewar in a airplane

[jonathanlavoie]

Here's my system (at the design stage):

-Two Dewar to hold each one infrared sensors.
-The Dewar are filled with liquid nitrogen
-The Dewar are inside a vacuum chamber, so we'll have LN2 feed through for refill and exhaust. Four in total.
-The vacuum chamber is inside a small plane (bigger than a Cesna, but still small)
I presume there will be around 1L or less of liquid nitrogen, spend over the course of 12 hours.

I don't know a lot about cryogenic stuff, or airplane, as a matter of fact.

Here's my questions
-Does anyone know if there can be problem if we have the pressure relief valve inside the aircraft? They can stay in flight for at least 4 hours, at an altitude of 5000m?
-Do you think that if we provide a tube with an interface to the in-line relief pressure valve and one end is outside the airplane, it can clog up to the point it is dangerous to build-up a pressure?

 

[EdStainless]

My guess is that they will want the N2 vented.
Have you thought of using TEC for the sensors? (thermo electric cooler)

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Plymouth Tube

 

[jonathanlavoie]

TEC work well in small difference of temperature. I think 240C (40C to 80 Kelvin) of difference will be too complicated and too power hungry.
Another solution is a Stirling cooler, but it produce too much vibration as we have positioning requirement for the sensor of about 3µm.

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Jonathan Lavoie
Physics engineer
Optical designer, Space photonics

 

[EdStainless]

How about a TEC with LN2 on the hot side?
Then you could just vent the exhaust through a control valve.
And the TEC would only be cooling from the LN2 temp.

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Plymouth Tube

 

[jonathanlavoie]

I think it will only make things worse, because of the heat dissipation the TEC will do.

If I have a sensors that produce X watts, a thermal conduction and loss through the Dewar of Y watts and a light-electricity conversion loss of Z watts.
I need an amount of nitrogen that is converted to gas with an energy of boiling of X+Y+Z watts.
If I have a TEC to cool my sensor down, it needs to cool it down of X+Y+Z watts, but produce T watts in the process.

If I use the system for 4 hours, I need the system to be stable, so I need an amount of nitrogen that is converted to gas with an energy of boiling of X+Y+Z+T watts.


So I use more nitrogen, but can achieve lower temperature, but I don't need that.


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Jonathan Lavoie
Physics engineer
Optical designer, Space photonics

 

[HDS]

I would vent out side the cockpit. If possible keep everything outside the cockpit in case there is a leak.

Have you considered frost build up?

How stable does you temperature need to be? Adding LN2 or venting the N2 will change the temperature.