Comparative study of linear thermomagnetic motors based on return mechanism: Spring, gravity, and purely magnetic

Thermomagnetic motors (TMMs) are solid-state devices capable of converting low-grade thermal energy into mechanical work. This paper presents the first direct numerical comparison of three linear TMMs distinguished by their return mechanisms: gravity, spring, and purely magnetic. A finite volume model was applied under identical operating conditions to ensure a fair comparison. Results show that the maximum power output reached 1.80 W for the gravity-return motor, 2.11 W for the spring-return motor, and 2.16 W for the purely magnetic motor. While gravity and spring-return motors exhibited similar behavior, the spring-return motor achieved higher performance with lower complexity. The purely magnetic motor demonstrated compactness and the possibility of scaling with multiple elements but operated within a narrower stability range. These findings provide design guidelines for future TMM development, highlighting their potential for harvesting industrial waste heat and other low-grade thermal sources.