Re: What form of heat transfer does Liquid Air use?

Ryan,

Evaporation of liquid air (made up of liquid nitrogen and liquid oxygen, I 
presume) wiill take place due to all types of heat transfer; conduction, 
convection and radiation.  Which one dominates will depend on the exact 
situation.  Any object in contact with the liquid will heat it through 
conduction, heat will be distributed throughout the liquid  and air 
currents made to pass over the surface by convection, and a warm object 
separated from the liquid but which has a clear line of sight will heat it 
by radiation.  

Therefore, as liquid is first poured into a dewar flask, for example, 
conduction from the warm walls of the flask dominates, causing the liquid 
to boil.  Eventually the walls of the dewar cool down and then, if there is 
no lid on the flask, convection will take over, with cool air flowing out 
and warm air coming in to take its place.  If there is a lid in place to 
block convection, then radiation is the dominant mechanism, with heat 
radiating from the outer walls of the flask, through the vacuum between the 
walls to the inner walls.  This last mechanism is very slow, and the liquid 
air might last for many hours or even days in the dewar, but eventually it 
will all boil away.