A closed-cycle, regenerative form of this device that has an ideal theoretical efficiency uses a compressor piston and a displacer, as well as an inert gas, and is based on the Stirling cycle. Another type of this device uses phase separation between a concentrated helium-3-rich phase floating on top of a dilute helium-4-rich phase for operation. The coefficient of performance for these devices is equal to Q-sub-C over quant. Q-sub-H plus Q-sub-C. Szilard and Einstein designed an absorption type of these devices with no moving parts. Most modern types of these devices 
A closed-cycle, regenerative form of this device that has an ideal theoretical efficiency uses a compressor piston and a displacer, as well as an inert gas, and is based on the Stirling cycle. Another type of this device uses phase separation between a concentrated helium-3-rich phase floating on top of a dilute helium-4-rich phase for operation. The coefficient of performance for these devices is equal to Q-sub-C over quant. Q-sub-H plus Q-sub-C. Szilard and Einstein designed an absorption type of these devices with no moving parts. Most modern types of these devices use a vapor-compression cycle and a circulating fluid, being essentially a heat pump that transfer heats from objects to the surrounding. For 10 points, name these devices that keep their contents cool.
A closed-cycle, regenerative form of this device that has an ideal theoretical efficiency uses a compressor piston and a displacer, as well as an inert gas, and is based on the Stirling cycle.
cryorefrigerator [or cryogenic freezer; or air conditioner; or cryocooler until "cool" is read; or obvious equivalents; prompt on heat pump or heat engine]