Most of the low temperature systems such as superconducting magnets require the efficient cooling system. The irreversible loss due to the entropy generation at the low temperature must be minimized to overcome this requirement. The concept of exergy gives a useful method to know where is the main source of this entropy generation. This paper describes the fundamentals of exergy analysis for cryocoolers or simple cryogenic systems. It includes the definition of exergy, exergy loss and thermodynamic efficiency of the system. Several examples of calculation method for the simple cryogenic system are also given.
