Design Optimization of a Rotary Thermomagnetic Motor for More Efficient Heat Energy Harvesting

Abstract

A rotary thermomagnetic motor that is designed for heat energy harvesting is presented in this paper. The power output, power density, and efficiency of the device is estimated using a mathematical model coupling the heat transfer, magnetic interactions, and rotor dynamics. The design analysis shows that the efficiency of the device is maximized, when there is a balance between the volume of thermomagnetic material used against the rate of heating and cooling of the material. On the other hand, the power output is determined largely by the size of the rotor, while the power density tends to peak at a particular aspect (length to diameter) ratio of the rotor. It is also observed that a higher rate of cooling leads to more output, especially when this is matched to a similar rate of heat supplied to the thermomagnetic motor. The result from the design optimization points to an ‘optimal’ design configuration and corresponding operating conditions that results in the largest power output, highest power density and best efficiency. After the optimization, it is estimated that the rotary thermomagnetic motor is able to produce up to 88 W of power with a power density of approximately 27 kW/m3 of thermomagnetic material used, while a maximum thermal-to-mechanical energy conversion efficiency of 2.1% is achievable. The results obtained from this design analysis and optimization shows the potential for such a rotary thermomagnetic motor to be implemented at a larger scale for heat energy harvesting application.