The main goal of this study was an experimental comparison of six different active magnetic regenerators (AMRs) with gadolinium as the magnetocaloric material. The analysis was carried out for three different parallel-plate AMRs (with different porosities and different orientations of the plates in the magnetic field) and three different packed-bed AMRs (filled with spheres, powders and cylinders). Since the operation of an AMR is strongly affected by the operating conditions, the experiments were performed at different mass-flow rates and at different operating frequencies. These were required in order to define the optimum corresponding operating conditions for the analyzed AMRs. As comparative criteria the maximum temperature span, the cooling capacity and the experimentally predicted COP were taken into consideration. The experimental analysis was performed on a new prototype of magnetic refrigerator designed as an experimental device. Its operation is based on the linear movement of a permanent-magnet assembly over a static AMR. The magnet assembly provides a measured magnetic field of about 1.15 T. The results reveal that the geometry of the AMR (the form of the magnetocaloric material) has a crucial impact on the performance of the magnetic refrigerator. The best overall cooling characteristics (temperature span, cooling capacity and COP) were obtained for the parallel-plate AMR with the smallest porosity (25%) and the orientation of the plates parallel to the magnetic field. This particular AMR generated a temperature span of 20 K, which is also the largest, so-far measured and published temperature span with a parallel-plate AMR for a given magnetic field change generated by permanent magnets. With respect to the comparison of the experimentally predicted COP values, the parallel-plate AMRs show higher efficiencies than the packed-bed AMRs.
COBISS.SI-ID: 12647707
This paper describes passive heat regenerators appropriate for active magnetic refrigerators (AMR) and evaluates them from the point of view of thermo-hydraulic characteristics and magnetic properties. A dimensionless numerical model for the determination of the heat transfer coefficient is used together with experimental data for the evaluation of six different regenerator geometries using heat transfer, pressure drop and thermal efficiency as evaluation criteria. An existing numerical model was upgraded with magnetic properties and employed in the computer programme for an active magnetic regenerator in which the magnetic properties are obtained using molecular field approximation. The model was tested for thermodynamic consistency and verified using available experimental data.
COBISS.SI-ID: 12192283
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 AMRA news 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.
COBISS.SI-ID: 11935003
A team of researchers have developed and built a prototype of a rotary magnetic refrigerator (MR). The principle of the operation of the presented magnetic refrigerator is based on the rotary movement of active magnetic regenerators (AMRs) with a magnetocaloric material and on the magnetic field generated by permanent magnets NdFeB. The first part of the paper presents the development and analysis of the structure for generating the magnetic field and the basic operational principle of the magnetic refrigerator concerned, and the second part gives a description of the development process for certain key elements of the complete magnetic refrigeration system.
COBISS.SI-ID: 11191067
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.
COBISS.SI-ID: 11767323