Evaporation Rate of Liquid Nitrogen: xpost from ME

porkchop-sand

Hello everyone!

I am trying to design a magnetic testing apparatus that needs to remain at -196K for 20 minutes. There is not exactly a straight foreword equation to get a calculation for the evaporation rate of liquid nitrogen. The apparatus looks like this, and I have highlighted the area where the nitrogen will be located:



The calculations that I have have been using are as follows:



Is this equation accurate? Any advice would be appreciated.
Equation source: http://en.wikipedia.org/wiki/Acciden...e_source_terms

Thank you!