Speaker
Description
Tandem active magnetic regenerator (AMR) configurations, in which two AMR beds are magnetized and demagnetized in antiphase, are attractive because the magnetic forces acting on the beds largely cancel each other and the mechanical work required to drive the beds is reduced. In our previous force-based evaluation, however, the achieved reduction of the magnetic work was smaller than that expected from ideal cancellation. The work that remains consists of a reversible contribution associated with the temperature difference between the upper and lower beds and a dissipative contribution that cannot be recovered. This study focuses on the latter, hereafter referred to as the dissipative work, and identifies the factors that govern it. Under the idealized assumptions of isothermal magnetization and a spatially uniform bed temperature, the dissipative work is governed by the asymmetry of the axial magnetic field gradient experienced by the two beds over one stroke. We show that it becomes essentially zero if the field gradient varies linearly along the axial coordinate and its average over the entire bed length vanishes at both stroke ends. This condition is no longer sufficient once adiabatic magnetization and a realistic bed temperature gradient are taken into account. When the temperature gradient is parallel to the direction of bed motion, a substantial fraction of the input work remains dissipative. We hypothesize that this arises from the asymmetry of the magnetization caused by the local temperature distribution during the field change. To examine this, the temperature gradient was reoriented along the radial direction of the bed, so that the cross-sectionally averaged temperature becomes uniform over the whole bed length. The calculated dissipative work fraction then decreased substantially, supporting the proposed mechanism and indicating that the orientation of the temperature gradient relative to the field-gradient axis is a key design parameter for tandem AMR systems.
| Submitters Country | Japan |
|---|---|
| Are you a student? | Yes |
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