Understanding Energy Flow and Inefficiency of a Thermomagnetic Generator by Transient Multi-Physics Modelling

TL;DR

This paper develops a validated multi-physics digital twin of a thermomagnetic generator to analyze energy flow and identify inefficiencies, aiming to improve low-grade waste heat recovery technology.

Contribution

It introduces a comprehensive 3D simulation model validated with experimental data, revealing causes of low efficiency and cycle frequency in thermomagnetic generators.

Findings

High accuracy (96% voltage, 95% power) in model validation.

Identified energy flow inefficiencies via Sankey diagram analysis.

Traced heat flow limitations affecting generator frequency.

Abstract

Waste heat recovery improves energy efficiency and reduces greenhouse gas emissions; however, much industrial and environmental heat is wasted at low temperature. Thermomagnetic recovery of waste heat has a high potential for sustainable production of electric energy, especially for low-grade waste heat where conventional technology is inefficient or infeasible. Of particular interest are thermomagnetic generators (TMG) as they require almost no mechanically moving parts, which is beneficial for high reliability. However, all existing prototypes have two remaining challenges: low efficiency and low cycle frequency. In this work, we develop a digital twin of a recent TMG with genus 3 by using multi-physics simulations. We identify shortcomings of previous simulation approaches, and describe why simulations in three dimensions are necessary, which consider coupling between magnetic, thermal, fluid flow, and electrical physics domains. We validate our model, which only uses known geometry and material parameters, by experimental data of the TMG with highest power density today, and attain 96% accuracy in open-circuit voltage and 95% accuracy in power output. This high accuracy allows us to identify the origin of both challenges for TMGs, which are not accessible by experiments. First, we uncover inefficiencies by analyzing the energy flow within a Sankey diagram. Second, we trace the transient heat flow through the generator, which identifies the factors limiting frequency. This paves the way for more efficient and faster TMGs, and their development will be accelerated by our validated digital twin.