A La-Fe-Si Based Thermo-Magnetic Generator

Low-grade heat from industrial processes and residential buildings represents a huge and cheap energy source. Development of new technologies to convert waste heat into electricity is today considered a major objective. The new generation of magnetocaloric materials (MCM) for refrigeration applications is offering some fresh opportunities to energy harvesting technologies. In cooling applications, the magnetocaloric effect is used to pump heat through the entropy change of the MCM associated to application/removal of a field. Thermomagnetic generators (TMG) use the pyromagnetic effect, namely the variation of magnetization as a function of the temperature, to perform thermodynamic cycles under varying field and eventually convert the magnetic energy into electrical one. Several thermo-generation prototypes using MCM have been proposed relying on different conversion chains. Here we have developed a new prototype based on a three steps conversion: Thermal/Magnetic, Magnetic/Mechanical and finally Mechanical/Electrical. The geometry is similar to the one studied in [1] with three main differences: the magnetic field lines are spatially confined by the use of a Halbach array improving the magnetic force and the field inside the magnetocaloric material [2]; the active substance is a first order La(Fe,Si)13 from Vacuumschmelze; the mechanical displacement of the MCM is eventually converted to electrical energy using piezoelectric material. All the energy conversion chain steps have been studied through direct measurements performed on the working prototype. Notably the total energy efficiency of the device is worked out experimentally using the prototype as a characterization bench. [1]. Ujihara et al. Appl. Phys. Lett.91, 093508 (2007). [2]. Ahmim et al. Eur. Phys. J. Appl. Phys. 85, 10902 (2019)