General performance characteristics of an irreversible ferromagnetic Stirling refrigeration cycle

A new magnetic-refrigeration-cycle model using ferromagnetic materials as a cyclic working substance is set up, in which finite-rate heat transfer, heat leak and regeneration time are taken into account. On the basis of the thermodynamic properties of a ferromagnetic material, the general performance characteristics of the ferromagnetic Stirling refrigeration cycle are investigated and the effects of some key irreversibilities on the performance of the cycle are revealed. By usingthe optimal-control theory, the optimal relation between the coefficient of performance and thecoolingrate is derived and some important performance bounds, e.g., the maximum coolingrate, the maximum coefficient of performance, are determined. Moreover, the optimal operatingreg ions for coolingrate, coefficient of performance and the optimal operatingtemperatures of a cyclic workingsubstance in the two heat-transfer processes are obtained. Furthermore, the influences of magnetization and magnetic field on the performance characteristics of the cycle are discussed. The results obtained here have general significance and can be deduced to the related ones of the Stirling refrigeration cycle using paramagnetic salt as a cyclic working substance.