Being a potential alternative to the traditional vapour compression refrigeration technology, active magnetic regenerator (AMR) has been paid an increasing attention as the core of magnetic cooling systems at room temperature. An AMR makes use of the magnetocaloric effect of the ferromagnetic materials, such as alloys of gadolinium or lanthanum, to produce temperature difference. However, the temperature change of the magnetocaloric materials realized in magnetization and demagnetization cycle is within a few degrees, so the thermal-fluid cycle in the AMR is of crucial importance to generate enough temperature span as well as to improve the operation performance of the whole system. Numerical simulation is expected to be an effective way to quantify the hydro and thermal dynamics in the AMR duct, which can be then used to optimize the design and operation of AMRs.
In this talk, we present a practice to directly simulate the thermal fluid dynamics in a 3D AMR duct packed with tens of thousands spheres of magnetic material, which has been used in a prototype magnetic refrigeration system. In order to compute the internal flow in the densely packed duct, we use an accurate and robust fluid solver for unstructured grid, so-called Volume integrated average and Point value based Multi-moment (VPM) method, in which the VIA moment is computed by a finite volume formulation of flux form, and thus exactly conservative, while the PV moment is updated by point-wise Riemann solver that can be computed very efficiently in unstructured grids. In comparison with the conventional finite volume method, VPM shows significant improvements in numerical accuracy and robustness to the quality of unstructured mesh.
Systematic numerical experiments were carried out to optimize the packing configuration of the spherical porous magnetic material so as to enhance heat transfer and reduce pressure loss. It is observed that the pressure loss is quite sensitive to the shape of flow path and the porous structure, which drastically varies among the configurations examined. Numerical simulations were also conducted to investigate the real-case operation of magnetization-demagnetization cycle and flow circulation. To our knowledge, there is no work reported so far on three dimensional CFD simulation of a real AMR. This study manifests the great potential of the proposed approach as a CAE tool for AMR design and operation.
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