This liquid nitrogen generator uses a Stirling-cycle cryocooler that was pulled from a cellular phone tower. It was used to cool a superconducting RF filter that aids cell communications. The cryocooler is able to pump enough heat away from its cold end that air will liquify and drip into a vacuum flask for storage. Jeri's video at Maker Faire 2010: https://www.youtube.com/watch?v=14B8LynojI4 Blog post with more construction details: http://benkrasnow.blogspot.com/2008/08/diy-liquid-nitrogen-generator.html