Thermomagnetic energy harvesting with first order phase change materials

Abstract

Two cycles of thermomagnetic generation have been compared, one with a conventional ferromagnetic material and one using a Heusler alloy undergoing a first order phase transformation. The two have been analytically compared in terms of overall thermal-to-magnetic energy conversion efficiency. In addition, a state-space model of a thermomagnetic generator has been developed and analyzed in order to compare the performance of the two in terms of response to decreased thermal difference and changes in plate separation. Both analytical calculations and simulation indicated a large difference in operational behavior between the two materials, with the Heusler alloy's behavior being characterized by latent heat and large changes in magnetism, and the ferromagnet being characterized by a smaller heat input and more gradual magnetic change. The theoretical energy conversion efficiency of the Heusler alloy was calculated to be 0.2% under an external field of 3kOe, increasing to 0.8% under a field of 15kOe. These values corresponded to 15.9% and 63.8% of the Carnot limit, respectively, and compare favorably with the conversion efficiencies of ferromagnetic materials previously used in thermomagnetic generation.