🚀 go-pugleaf

>What is a good way to transport liquid nitrogen (inexpensively) ,
>about 20 miles.  It has to be taken from our laboratory to a 
>High School classroom.  Remember it is very hot and humid in 
>Alabama this time of year. 

You don't say how much....  if the amount is small (say only a litre or 
less at the receiving end), then the simplest and cheapest way is to use a 
couple of small evacuated thermos flasks..... they type kids use to take 
drinks to school.  They usually have small knecks, are evacuated in the 
same way as the larger "research dewars" that we have in our labs, and are 
very cheap.  I got one recently at K-Mart for a couple of dollars.

HOWEVER!  do NOT screw on the top of the flask after you put LN 
in.....simply leave the flask open to the air.

The temperature in your region is of little significance compared to the 
temperature of LN.  However, the number of "bumps in the road" might!  
Agitation is the only cause of increased boiling in the system I describe;  
without agitation, the LN will not all boil off over a period of many 
hours.