Predicting the thermal hysteresis behavior for a single-layer MnFeP1−xSix active magnetic regenerator

Abstract

Magnetocaloric materials with first-order magnetic (FOM) phase transitions are of interest as low-cost working materials in magnetic heat pumping cycles. Hysteresis is a property associated with first order transitions, and is undesirable as it can reduce the cycle performance. Devices using first-order materials in active magnetic refrigeration have shown performance comparable to more expensive second-order materials so some degree of hysteresis appears to be acceptable; however, the amount of hysteresis that may be tolerated is still an unanswered question. A one dimensional active magnetic regenerator (AMR) model accounting for thermal and magnetic hysteresis is developed and compared to experimental data for both a Gadolinium (Gd) and MnFeP1−xSix active magnetic regenerator. Magnetic and thermal hysteresis are quantified using measured data for magnetization and specific heat under isothermal and isofield warming and cooling processes. Numerical results for temperature span as a function of cooling power and rejection temperature show good agreement with experimental data. The irreversible work due to hysteresis has a small impact on predicted spans as compared to the deviation between experimental data and model predictions. This indicates useful cooling power is well predicted using cyclic measurements of adiabatic temperature change and disregarding hysteresis.