First- Versus Second-Order Magnetocaloric Material for Thermomagnetic Energy Conversion

We estimate the power and efficiency of a thermal energy harvesting thermodynamic Brayton cycle using the first- and second-order magnetocaloric materials as active substance. The thermodynamic cycle was computed using a simple thermal exchange model and an equation of the state deduced from a phenomenological Landau model. For the first- and second-order materials, narrow- and high-frequency cycles are optimum and give similar performances. Considering technological issues hindering the increase of frequency, we introduced a more detailed approach, where we take into account the time needed to switch the material between two heat reservoirs. We show that the first-order material equation of the state leads thermodynamic cycle shape keeping it closer to the optimum cycle. Conditions to improve the performance of the second-order materials are discussed. In addition, we infer key remarks for prototype design regarding the power density and efficiency reachable in different configurations.