Linear thermomagnetic energy harvester for low-grade thermal energy harvesting

Abstract

Low-grade thermal energy, either from waste heat or from natural resources, constitutes an enormous energy reserve that remains to be fully harvested. Harvesting low-grade heat is challenging because of the low Carnot efficiency. Among various thermal energy harvesting mechanisms available for capturing low-grade heat (temperature less than 100 °C), the thermomagnetic effect has been found to be quite promising. In this study, we demonstrate a scalable thermomagnetic energy harvester architecture that exhibits 140% higher power density compared to the previously published spring–mass designs. The alternating force required to oscillate the thermomagnetic mass is generated through the interaction between two magnetic forces in opposite directions. We employed numerical modeling to illustrate the behavior of a thermomagnetic device under different operating conditions and to obtain the optimal hot-side and cold-side temperatures for continuous mode operations. A miniaturized thermomagnetic harvester was fabricated and experiments were conducted to systematically evaluate the performance. The prototype was found to exhibit an oscillation frequency of 0.33 Hz, a work output of 0.6 J/kg/cycle, and a power density of 0.2 W/kg of gadolinium under the temperature difference of 60 K.

Optimization of a cylindrical thermomagnetic engine for power generation from low‐temperature heat sources

“…When gadolinium acts as a ferromagnetic material due to a temperature change, the transient equation of the magnetic field in the gadolinium blocks is illustrated as 16 :…”

“…An efficient thermomagnetic energy harvester was demonstrated using gadolinium to scavenge low-grade thermal energy. 16 The prototype generated an oscillation frequency of 0.33 Hz, a power density of 0.2 W/kg, and work output of 0.6 J/kg/cycle under a temperature difference between a hot-and cold-side of 60 K. A low-grade energy-harvesting device was proposed using two different generators; one was an electromagnetic generator, and the other one was a nanogenerator. 17,18 To fabricate the TME, 16 gadolinium blocks, one permanent magnet, and three water inlets (two hot and one cold) were used.…”

Thermomagnetic Generation Performance of Gd and La(Fe, Si)13Hy/In Material for Low‐Grade Waste Heat Recovery

“…Therefore, the research of TMG based on a few MCE materials, such as Gd, (Mn,Fe) 2 (P,As), NiMn‐based Heusler alloys, and MM′X (M, M′ = transition metals, X = carbon or boron group elements) compounds, starts to attract a surge of interest in very recent years. [ 17–36 ] However, except the benchmark Gd, most of these materials undergo a first‐order phase transition that inevitably accompanies with distinct thermal hysteresis. Large thermal hysteresis would cause the discrepancy of working temperatures during the heating and cooling cycles, which is undesirable for the practical application.…”

Lumped Element Model for Thermomagnetic Generators Based on Magnetic SMA Films

“…The device performance strongly depends on the magnetic material used for energy conversion that should exhibit, among others, a large change of magnetization Δ M at small temperature difference Δ T and a large thermal conductivity. A number of TMG devices make use of ferromagnetic materials, in particular gadolinium (Gd), showing a pronounced second-order ferromagnetic transition near the Curie point close to room temperature [ 9 , 10 ]. An interesting alternative are La-Fe-Si-based materials [ 11 , 12 ].…”

“…In recent years several TMG concepts have been introduced that involve energy generation either indirectly via periodic mechanical motion such as rotation and oscillation or directly via thermal-to-magnetic energy conversion. Macroscale TMG demonstrator designs include thermomagnetic oscillators and linear harvesters showing oscillation cycles at a frequency of typically below 1 Hz [ 9 , 23 ]. Millimeter-scale TMG devices have the potential to operate at substantially higher frequencies due to the increased surface-to-volume ratio and, thus, allow for higher power output [ 10 , 19 ].…”