# Time to evaporate LN2 from a container

pve
TL;DR Summary
How long will it take for LN2 in a room temperature container to evaporate?
Hello,
Could someone please help me understand how to approximate how long it will take for liquid nitrogen in a room temperature container to completely evaporate.

Here's the scenario:
I have a metal container (41x13x15") filled with 5.5" of liquid nitrogen (just released from a Dewar ~ 320F). If the container is at room temperature (~70 F), how quickly will the LN2 completely evaporate.

I'm having trouble understanding where to start with this problem as thermodynamics is not my strong point.

Thanks!

File attached is the container in question.

#### Attachments

• MVE-CryoCart-Spec-Sheet.pdf
1.3 MB · Views: 6

Mentor
Welcome to PF.

But that cart isn't usually filled on top with LN2, is it? It looks like it is maybe cooled by LN2 being down inside it and that top part is for placing cryo biological samples, no?

And if you start pouring LN2 into the top open part of that while it's at room temperature, it seems like it would boil off pretty quickly while you are trying to dump the LN2 in from your dewar's hose...

pve
pve
Thank you,

The dewar hose is connected via the side of the cart and the lids are kept closed during the filling. Our team is concerned about filling the device and then moving it so we wanted a hypothetical situation where we had to wait for it all to boil off before moving.

It does boil off pretty quickly right away, it usually takes up to 30 minutes to get the full 5.5" of liquid in the cart. At that point, we'd want to know how long it would take to go from "full (5.5")" to empty.
Welcome to PF.

But that cart isn't usually filled on top with LN2, is it? It looks like it is maybe cooled by LN2 being down inside it and that top part is for placing cryo biological samples, no?

And if you start pouring LN2 into the top open part of that while it's at room temperature, it seems like it would boil off pretty quickly while you are trying to dump the LN2 in from your dewar's hose...

View attachment 321022

View attachment 321023

Mentor
The data sheet says up to 8 hrs, but it will depend on the specifics of how or if you use it. Can you test it?

pve
pve
The data sheet says up to 8 hrs, but it will depend on the specifics of how or if you use it. Can you test it?
That's a good point. I see they note about 8 hours per 39.5 L. In our fill we use 5.5" or 48L. So I suppose we could imagine the "safety" of the sample as linear and say it's:
48.77L/8hr = 39.5L/Xh or ~10 hours to mostly boil off.

pve
I've also reached out to the supplier to see if they have tested it but we may need to test it ourselves to be certain.

256bits
Gold Member
I've also reached out to the supplier to see if they have tested it but we may need to test it ourselves to be certain.
A good idea, as there is heat flow through the sides of the container would be hard come by for a precise calculation.

pve
Mentor
The dewar hose is connected via the side of the cart and the lids are kept closed during the filling. Our team is concerned about filling the device and then moving it so we wanted a hypothetical situation where we had to wait for it all to boil off before moving.

It does boil off pretty quickly right away, it usually takes up to 30 minutes to get the full 5.5" of liquid in the cart. At that point, we'd want to know how long it would take to go from "full (5.5")" to empty.
If you take the lid off the cart and the LN2 is exposed in that open cavity shown in the pictures, you can probably cut the evaporation time in half or better by directing a fan to blow room air along the long direction of the open cart top. The objective is to keep replacing the cold air just above the LN2 with warm room air. Get rid of that boundary layer of cold air, and the evaporation process should go a lot faster, IMO.

https://www.lowes.com/pd/Utilitech-...zQNfzc1XJfzYRB8GIBhoCtyIQAvD_BwE&gclsrc=aw.ds