I need to do some work with liquid nitrogen at home. The main question is how to store it without buying huge vacuum flask specifically for liquid nitrogen.
I've tried to use usual steel household vacuum bottles, added ~1 cm of extra insulation (some foamy material, multiple layers), wrapped in plastic to protect from condensation. Cap is also made from this foamy material (I remember that I should not seal the flask) .
The problem is that liquid nitrogen evaporates in ~30 hours. I suppose the main issue is cap construction, sides of the flasks are warm, while cap is cold. Also, it seems heat loses are maximum near cap because hot and cold steel sides are touching there.
Any known tricks on how to improve heat insulation and prolong lifetime of liquid nitrogen? Is that correct that I should be wrapping it all in aluminum foil on the "hot" side of insulation?
My goal is 3 days evaporation, 7 is just perfect.