Abstract
In this paper, an extensive study on the energy losses of a magnetic refrigerator prototype developed at University of Salerno, named ‘8MAG’, is carried out with the aim to improve the performance of such a system. The design details of ‘8MAG’ evidences both mechanical and thermal losses, which are mainly attributed to the eddy currents generation into the support of the regenerators (magnetocaloric wheel) and the parasitic heat load of the rotary valve. The latter component is fundamental since it imparts the direction of the heat transfer fluid distribution through the regenerators and it serves as a drive shaft for the magnetic assembly. The energy losses concerning eddy currents and parasitic heat load are evaluated by two uncoupled models, which are validated by experimental data obtained with different operating conditions. Then, the achievable coefficient of performance (COP) improvements of ‘8MAG’ are estimated, showing that reducing eddy currents generation (by changing the material of the magnetocaloric wheel) and the parasitic heat load (enhancing the insulation of the rotary valve) can lead to increase the COP from 2.5 to 2.8 (+12.0%) and 3.0 (+20%), respectively, and to 3.3 (+32%), combining both improvements, with an hot source temperature of 22 °C and 2 K of temperature span.
Highlights
Magnetic refrigeration is an emerging and environmental-friendly technology that uses a solid refrigerant exploiting the magneto-caloric effect (MCE), which is represented by a temperature change of the material when it is subjected to a change of an external magnetic field
The models developed in this work can help to quantify main energy losses and to evaluate the performance which the prototype canthe achieve reducing at of the‘8MAG’, minimum to evaluate the performance which the prototype can achieve reducing at the minimum these losses
It was possible to calculate the reference performance of the system, that is the coefficient of performance (COP), defined as performance of the system, that is the coefficient of performance (COP), defined as
Summary
Magnetic refrigeration is an emerging and environmental-friendly technology that uses a solid refrigerant exploiting the magneto-caloric effect (MCE), which is represented by a temperature change of the material when it is subjected to a change of an external magnetic field Studies showed that this technology could lead to 20–30% energy savings compared to vapor compression refrigeration because of magnetization work recovery and lower entropy generation [1,2,3,4], as well as a reduction of the environmental impact of the refrigeration system [5,6]. ‘8MAG’ showed a maximum second-law efficiency of 2.4% at TH = 22 ◦ C and a temperature span of 3.3 K These results are comparable to the performance of the magnetic refrigerator prototype presented by Capovilla et al [42]. To reduce the experimental efforts and generalize the results, the characterization of this kind of energy losses was performed by mathematical models, properly defined and validated
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