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In this paper, a novel rotary magnetic refrigerator is described, and initial experimental results are presented. The prototype employs a two-pole magnetic system based on a double U configuration of permanent magnets with an air gap of 43 mm and 1.25 T. The magnetocaloric refrigerant is confined within eight static regenerator enclosures, which are alternatively magnetized and demagnetized with the rotation of the magnets. A rotary valve mechanically coupled with the field generator imparts the direction of heat transfer fluid through the regenerators. Using a total mass of 1.20 kg of gadolinium spheres (of 400-500 microns) as refrigerant and distilled water as regenerating fluid, the device produced a maximum temperature span of 13.5 K under zero applied thermal load with an utilization factor of 1.40 and a heat rejection temperature of 298 K. [ABSTRACT FROM AUTHOR]

Abstract: The primary objective of this paper is to quantify the impact of the internal magnetic field and reversibility of the magnetocaloric effect on the numerical evaluation of the thermal performance of a parallel-plate active magnetic regenerator. To this end, direct measurements of the adiabatic temperature change of commercial-grade gadolinium samples were carried out for an applied field change of 1.65 ± 0.03 T (for both magnetization and demagnetization) and temperatures between 283 and 303 K. The tests were carried out in a specially constructed apparatus and the results were in good agreement with the literature. The data were incorporated into a mathematical model for solving the fluid flow and conjugated heat transfer in the parallel-plate regenerator. It was found that if demagnetization phenomena (i.e., the demagnetization factor and the reversibility of the magnetocaloric effect) are not take properly into account, the thermal performance of the regenerator can be severely over-predicted. [Copyright &y& Elsevier]

Abstract: The present paper describes the design, operation and preliminary results of an active magnetic regenerator test machine. The regenerator consists of twenty eight 0.85 mm thick parallel gadolinium (Gd) plates that form 0.1 mm thick parallel channels with an effective length of 126 mm. The working fluid is water and the magnetic field source is a Halbach array with a maximum flux density of 1.65 T. A maximum temperature span between the hot and cold ends of the regenerator (∆T REG) of 4.45 K and a maximum cooling capacity of 3.9 W were measured in tests without and with a thermal load, respectively. The behavior of ∆T REG as a function of the utilization factor and of the temperature of the hot source is explored in the manuscript. The experimental results are discussed in the light of the fluid flow and heat transfer phenomena taking place in the regenerator. [Copyright &y& Elsevier]

Abstract: A new, fast and flexible, time-dependent, one-dimensional numerical model was developed in order to study in detail the operation of an active magnetic regenerator (AMR). The model is based on a coupled system of equations (for the magnetocaloric material and the heat-transfer fluid) that have been solved simultaneously with the software package MATLAB. The model can be employed to analyze a wide range of different operating conditions (mass-flow rate, operating frequency, magnetic field change), different AMR geometries, different magnetocaloric materials and heat-transfer fluids, layered and single-bed AMRs, etc. This paper also presents an optimization of the AMR’s geometry, where the AMR consists of a packed-bed of grains (spheres) of gadolinium (Gd). The optimization of the mass-flow rate and the operating frequency of the AMR were performed by studying five different diameters of Gd spheres. [Copyright &y& Elsevier]

Abstract: The active magnetic regenerator (AMR) is an alternative refrigeration cycle with a potential gain of energy efficiency compared to conventional refrigeration techniques. The AMR poses a complex problem of heat transfer, fluid dynamics and magnetic field, which requires detailed and robust modeling. This paper reviews the existing numerical modeling of room temperature AMR to date. The governing equations, implementation of the magnetocaloric effect (MCE), fluid flow and magnetic field profiles, thermal conduction etc. are discussed in detail as is their impact on the AMR cycle. Flow channeling effects, hysteresis, thermal losses and demagnetizing fields are discussed and it is concluded that more detailed modeling of these phenomena is required to obtain a better understanding of the AMR cycle. [Copyright &y& Elsevier]