Influence of the flow rate waveform and mass imbalance on the performance of active magnetic regenerators. Part I: Experimental analysis

This is the first part of a two-part paper on the synchronization between the applied magnetic field and fluid displacement waveforms in a gadolinium packed sphere active magnetic regenerator (AMR) apparatus. For a rectified cosine magnetic field waveform, new rotary valves were developed to assess the influence of the duration of the fluid flow steps on the AMR performance. In order to correct flow imbalance effects caused by torque oscillations in the magnetic circuit and guarantee thermodynamically consistent conditions, a new criterion based on a mass imbalance parameter has been proposed. By keeping the displaced fluid mass fixed for a given utilization, the cooling capacity increased significantly with shorter blow times due to the higher fluid velocity and larger average magnetic field change. However, because of the associated increase in power consumption, an optimal blow time fraction of 45% was identified for operating frequencies of 0.25 and 0.5 Hz. (C) 2018 Elsevier Ltd and IIR. All rights reserved.