Cryocooler

A Cryocooler is a standalone cooler, usually of table-top size. It is used to cool some particular application to cryogenic temperatures. A recent review is given by Radebaugh. The present article deals with various types of cryocoolers and is partly based on a paper by De Waele.

Ideal heat exchangers and regenerators

Heat exchangers are important components of all cryocoolers. Ideal heat exchangers have no flow resistance and the exit gas temperature is the same as the (fixed) body temperature T_X of the heat exchanger. Note that even a perfect heat exchanger will not affect the entrance temperature T_i of the gas. This leads to losses.

An important component of refrigerators, operating with oscillatory flows, is the regenerator. A regenerator consists of a matrix of a solid porous material, such as granular particles or metal sieves, through which gas flows back and forth. Periodically heat is stored and released by the material. The heat contact with the gas must be good and the flow resistance of the matrix must be low. These are conflicting requirements. The thermodynamic and hydrodynamic properties of regenerators are very complicated, so one usually makes simplifying models. In its most extreme form an ideal regenerator has the following properties: