Numerical analysis of a (MnNiSi) 0.66 (Fe 2 Ge) 0.34 alloy-based thermomagnetic generator for low-grade heat sources

Abstract

This study focuses on the performance of the thermomagnetic generator which uses pseudo-binary alloy (MnNiSi)_0.66(Fe₂Ge)_0.34 and benchmark material Gadolinium. Knowledge of temperature dependent magnetization of thermomagnetic material (TMM) is essential during the design of thermomagnetic generator. Various activities involved in the generators namely the oscillation of TMM, heat transfer between heat source, heat sink and TMM, interaction of magnetic flux density with TMM and coil and emf generated by the coil can be analysed as a coupled problem using finite element analysis of COMSOL Multiphysics. As the voltage induced in the coil is variable intermittent, it can be rectified and stored in capacitor and utilized for further use. The results indicate that (MnNiSi)_0.66(Fe₂Ge)_0.34 exhibits a smaller magnetic flux density interaction (0.15 T) with a permanent magnet compared to Gd (0.5 T), due to its lower magnetization value. Consequently, the voltage generated per cycle is approximately 0.38 V for the Mn-Fe alloy and 0.6 V for Gd. Due to its higher thermal conductivity, the Mn-Fe alloy achieves a greater number of thermomagnetic cycles per unit time compared to Gadolinium. The overall output leads to higher voltage and power output, with improvements of 20.18% in voltage and 22.55% in power compared to Gadolinium. To achieve superior generator performance, a parametric study was conducted on the distance between the heat source and heat sink, the temperature of the heat source, and the thickness of the TMM.