This is generally how your
fridge works, and also the method
KryoTech uses to
cool its
computer systems to -40
degrees Celcius in order to highly
overclock them.
Very basically it's taking advantage of the fact that phase change of a liquid to a gas consumes a lot of energy (ie. thermal heat), and since gas needs a larger volume than liquid, you compress this gas back to fluid so that it can consume heat for turning into gas again. Neato, eh?