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For cooling of a measurement device (HPGE) i need around 30 Liters of LN2 (Liquid Nitrogen). I'm a hobbyist but, familiar with the basic rules of Ln2 (Eyeshield,Gloves, Ventilation, Pressure Danger) and also have a professional O2 sensor by hand.

My current problem is, that i own a special 30L dewar for the detector, in the region where i live, suppliers of LN2 will not fill my dewar because firstly they want to sell(rent) their storage units, and for liablity issues because my dewar is old ;)

Even if they could fill it, the dewar including Ln2 would weight over 35kg, which is kinda heavy to lift into the third floor by staircase.

My question is now, can i fill the dewar from smaller dewars? The suppliers rent out 10l Dewars. Can i "pour" the LN2 via a funnel in my dewar? Or is there any other solution that does not result in expensive devices?

Or is is possible to fill via a hose and gravity? (by placing the source dewar higher than the target dewar and let the Ln2 flow by gravity, so only one pump-action is needed to start the process)

sgt_johnny
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    Doing it by pouring seems OK. Though I have no idea of what might be special with your old dewar. Safety P issue arise whit more complicated despenser. If you get all in open dewar and your one is open as well, I don't see trouble. Just do it slowly at beginning otherwise you'll loose quite a lot. – Alchimista Apr 14 '21 at 09:47
  • I don't know as well, but all commercial suppliers said they can only fill their own, or some standard dewars, they declined to fill customer dewars with no labels etc. – sgt_johnny Apr 14 '21 at 10:02
  • that's understandable. But you can certainly pour LN, as a gesture in itself. If your dewar can be filled like this, just use the gloves and do it. Go slowly so that the bottom can cool first otherwise it take more than 35 l :) – Alchimista Apr 14 '21 at 10:04
  • This will definitely work, but make sure your old dewar's isolation is not broken (this will show by condensation forming on the outside of the dewar) and use a plastic funnel as suggested by Buttonwood. – Paul Apr 14 '21 at 17:01

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Mechanically yes, considering the weight, pouring from a smaller Dewar is easier than from a larger one. It takes some practice to aim, of course. Using an additional plastic funnel consumes some of LN2 because the funnel obviously has to be cooled before LN2 passes the bottom of the chute.

Not knowing your experimental setup: would be an other mean of cooling the detector than LN2 acceptable for you? Some of the ICCD cameras for example cool their sensor with a Peltier element, which in turn is cooled with water of a liquid thermostate. This reliably allows temperatures around $\pu{-20 ^\circ{}C}$ of the detector. Or, as a less expensive approach, why not backing your sensor with a trough made of metal, and fill the trough with a mixture of of dry ice and isopropanol?

Re pumping LN2: The larger mobile Dewars I've seen deliver LN2 by their own pressure like a spray can:

enter image description here

In the simplest form, beside a pressure indicator (I) and a safety valve (S), they have a metal tubing (H) reaching to the inner bottom of the vessel. H is removed to fill the tank, but in idle state, H is shut and there is a small, occasional hissing pressure release from the safety valve S because still some the LN2 evaporates. To obtain the LN2, you place your small Dewar below the hose H and open the valve of H. Thus, opening the valve at H allows the liquid to pass the hose toward the Dewar. There may be additional valves to eventually increase the pressure above LN2, and additional indicators to report the content of LN2, etc.; all omitted in the drawing for clarity:

enter image description here

(modified illustration, based on one here).

Buttonwood
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  • HPGE's are built for LN2, they have a long dipstick that goes into a Dewar, they need to cool down for ~6hrs before you can use them, if they go "warmer" you have to fully warm them up, and cool them down again. Some modern HPGE's bring electric cooling aggregates, but those are terrible expensive and produce a lot of heat, noise and electrical consumption. The minimum operation temperature is usually ~100K the lower, the better the resolution

    About your illustration, i think i will try this by applying a rubber foil on the and then push air in with hand pump.

     – sgt_johnny Apr 14 '21 at 12:54
  • As witnessed by a colleague working with a squid magnetometer during a humid summer day, forgetting to close the entry knobs for LN2 and He, trapped water may become a mechanical problem. But if you keep the setup all well and dry, at small scale, away from air's $\ce{CO2}$ then there is, as stated, only oxygen to have an eye on. – Buttonwood Apr 14 '21 at 16:34