Concept of a Magnetocaloric Generator with Latent Heat Transfer for the Conversion of Heat into Electricity

Abstract

Second-order and first-order magnetocaloric materials (MCMs) not experiencing hysteresis are characterized by a reversible temperature change when exposed to an applied magnetic field. Due to this property described by the magnetocaloric effect, MCMs are used in magnetic cooling applications. Conversely, a rapid variation of the MCM's temperature around its specific Curie temperature causes a fast change in its magnetic permeability. Cycling the MCM's temperature within a magnetic field allows the possibility of inducing voltage, which would be higher for rapid cycling rates. Herein, latent heat transfer is introduced as an approach to obtain higher heating/cooling cycle frequency in a magnetocaloric generator that converts heat to electricity. In practice, rapid condensation/evaporation cycles of the water on a first-order magnetocaloric La(Fe,Si) alloy are observed in a high vacuum system. This leads to the fast change of magnetization in an applied magnetic field from which an induced voltage is picked up. With the constructed set-up, a peak induced voltage 2.75 mVp is obtained from low-grade heat having reservoir temperature differences of △T = 56 °C. At higher temperature differences, a peak-to-peak voltage of around 3.5 mVpp at a cycle frequency of 2 Hz is achieved.