Thermodynamic Efficacy of Irreversible Magnetocaloric Effect Cycles
MetadataShow full item record
The discovery of the Giant Magnetocaloric Effect (GMCE) has led to a renewed interest in the prospect of magnetic refrigeration as a more environmentally friendly and efficient alternative to vapor-compression cooling. This effect is observed when certain materials with coupled thermal and magnetic properties undergo a magnetostructural first-order phase transition (FOPT). GMCE materials can exhibit large adiabatic temperature changes (ΔTad) and isothermal entropy changes (ΔSm) near 300 K, which provide a basis for refrigeration cycles near room temperature. However, the presence of thermal hysteresis associated with the FOPT has been a major obstacle to the use of GMCE materials for commercial refrigeration. In this paper, a methodology is presented for evaluating the thermodynamic efficacy of GMCE-based Brayton refrigeration cycles. This approach combines a Preisach hysteresis model with the experimentally observed thermal and magnetic properties of a Ni45Co5Mn36.6In13.4 alloy. This methodology predicts that a complete adiabatic FOPT results in a large temperature change in excess of 50 K; however, the full transition requires the application of an unreasonably large magnetic field in excess of 40 T. The model shows that Brayton refrigeration cycles are still possible with the application of a more feasible 5 T magnetic field, but with only a partial FOPT. For these Brayton cycles, we show the effect of varying amounts of rate-independent thermal hysteresis on two thermodynamic figures of merit: fractional Carnot efficiency and the amount of heat removed from a cold reservoir per cycle. We also present the operational parameters, Thot and Tcold, that optimize these figures of merit under different amounts of thermal hysteresis.
Buffington, Tyler Colby (2016). Thermodynamic Efficacy of Irreversible Magnetocaloric Effect Cycles. Undergraduate Research Scholars Program. Available electronically from