Effect of gadolinium particle size on the performance of a magnetic refrigeration system

This study investigates the influence of gadolinium particle size on Magnetic Refrigeration (MR) system performance. Understanding how particle size of Magnetocaloric Materials (MCMs) within a fixed Active Magnetic Regenerator (AMR) volume affects cooling capacity and Coefficient of Performance (COP) is crucial for MR system design. However, research on this influence, especially using an experimental approach, has been surprisingly rare. This is despite the importance of considering various factors like total MCM mass, porosity, and pressure drop. The particles were categorized into five cases based on their sizes, which ranged from 0.50 to 2.00 mm opening sizes of the meshes. The magnetic field source produced the maximum 0.815 and 0.069 T for magnetization and demagnetization, respectively. A total four of AMRs were installed in the MR system for each case study. First, the porosity of the AMRs mostly increased as finer particles were filled up. This led to a tendency of lower mass of the MCMs in the same volume of the AMRs with smaller particles. Second, the temperature span showed the most outstanding value of 11.1 K in the 0.20 utilization factor using the finest particles (0.50-0.85 mm) in a no-load test. It also achieved a wider 8.3 K temperature span under 3.8 W of thermal load, outperforming the other sizes despite the least total mass of the MCMs. The major contribution to these results was the larger heat transfer area between the MCMs and heat transfer fluid inside the AMRs with the smaller particles. Nevertheless, the case with the second-finest particles (0.80-1.18 mm) exhibited the highest COP of 2.6, due to their favorable combination of moderately significant cooling capacity, reasonably small particle size, and elevated porosity that reduced pumping power demand and magnetic force.