Coupling Effects in Parallel Thermomagnetic Generators Based on Resonant Self-Actuation

We investigate the cross coupling between parallel operating thermo-magnetic generators (TMGs) on their dynamic performance and power output. TMGs are an emerging technology for waste heat recovery. Here, TMG operation relies on the abrupt drop of magnetization at the Curie temperature of a magnetic shape memory (MSMA) film of Ni-Mn-Ga mounted at the front of a cantilever and on rapid heat transfer due to the film's large surface-to-volume ratio. Parallel designs are highly demanded to increase power output. When exposed to heat source temperatures Ts of 110-170 °C, resonant self-oscillation of each cantilever is excited in the range of 50-70 Hz resulting in a power output up to $30\ \text{mW}/\text{cm}^{3}$ for each TMG. At low Ts, oscillations remain stable even for a small distance $D$ of 0.4 mm between cantilevers, while at $\text{Ts}\ \geq\ 150^{\circ}\mathrm{C}$, instabilities occur below $D=1$ mm affecting power output.