The influence of demagnetizing effects on the performance of active magnetic regenerators

Nielsen, Kaspar Kirstein; Smith, Anders; Bahl, Christian; Olsen, Ulrik Lund

doi:10.1063/1.4764039

Cited by 21 publications

(8 citation statements)

References 18 publications

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“…They also conducted a parametric study to investigate the influence of various operating parameter on the performance of the AMR [54]. Nielsen et al [55] have numerically investigated the performance dependence on demagnetizing fields for parallel-plate regenerators. Legait et al [56] developed a 2D model using a commercial software Fluent.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigation of room temperature magnetic refrigerator using microchannel regenerators

Kamran

Sun

Tang

et al. 2016

Applied Thermal Engineering

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The paper reports numerical investigation of room temperature, active magnetocaloric regeneration (AMR) refrigerators/heat pumps using microchannel regenerator. The microchannel regenerators are made of a magnetocaloric material (MCM), Gd, with diameter of the circular channels ranging from 0.7 mm to 2.0 mm. Water, the working fluid, oscillates in the regenerator loop driven by two piston-cylinder displacers operating in a range of mass flow rates. Three dimensional conjugated fluid convection and conduction heat transfer in the microchannel regenerator was modeled and numerically simulated using ANSYS Fluent. The magnetocaloric effect (MCE) was incorporated into conservation of energy using a discrete method to simulate the magnetization and demagnetization of the MCM. The hot and cold end heat exchangers were treated with the ε-NTU method. Effects of utilization and porosity of the microchannel regenerator and cycle frequency on the cooling capacity and temperature span were examined. When the utilization, porosity and cycle frequency are 0.2, 0.5 and 5.0 Hz, respectively, the predicted maximum cooling capacity was about 22 W for a 0.8 T variation in intensity of magnetic field. The effects of magnetic field intensity, reservoir temperature span and flow rate profile on the refrigeration performance were also investigated. The performance of the microchannel regenerator is compared with that of the parallel plate regenerator for the no-load temperature span, cooling capacity and pumping power. Under specific geometric and operating conditions, the microchannel regenerator shows better performance than the parallel-plate one.

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Section: Introductionmentioning

confidence: 99%

Numerical investigation of room temperature magnetic refrigerator using microchannel regenerators

Kamran

Sun

Tang

et al. 2016

Applied Thermal Engineering

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“…[113][114][115][116][117] Considering the case of the depolarizing field in ferroelectrics, its influence on electrocaloric properties is ignored in most studies. This is because for strongly polar materials, such as ferroelectrics,…”

Section: G Depolarizing Fieldmentioning

confidence: 99%

Direct and indirect measurements on electrocaloric effect: Recent developments and perspectives

Liu

Scott

Dkhil

2016

Applied Physics Reviews

244

150

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It has been ten years since the discovery of the giant electrocaloric effect in ferroelectric materials showed that it is possible to employ this effect for substantial cooling applications. This last decade has been marked by increasing research interest, especially in characterizing and measuring the electrocaloric effect using both the so-called indirect and direct approaches. In this context, a comprehensive summary and careful reexamination of these approaches are very timely and of great importance to justify the assumptions used in different measurement techniques. This review is therefore dedicated to cover recent important and rapid advances from both the indirect and direct measurements and provides critical insights relevant for quantifying the electrocaloric effect. It involves electrocaloric materials from normal ferroelectrics, antiferroelectrics, and relaxors, and it fundamentally focuses on how the electrocaloric entropy changes in response to electric field in these typical electrocalorics. The article addresses recent developments, especially during the past three years, such as technical selection of proper polarization-electric field loops, negative electrocaloric effect in antiferroelectrics and relaxors, the controversial debate on the indirect method in relaxors, the important role of field dependence of specific heat, kinetic factors, and so on. Moreover, this review also is concerned with extracting reliable data by direct measurements. Four typical techniques and devices used recently, such as thermocouples, differential scanning calorimeters, specifically designed calorimeters, and scanning thermal microscopy, are briefly reviewed, while infrared cameras are emphasized. We hope that our review will not only provide a useful background to understand fundamentally the electrocaloric effect and what one really measures but also may act as a practical guide to exploit and develop electrocalorics towards the design of suitable devices. Published by AIP Publishing. [http://dx

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“…In the case of a typical AMR with a porosity of about 30 % subjected to a magnetic field of 1 T the internal magnetic field, in the two extreme cases (parallel-plate AMR with the plate's distribution parallel to the applied magnetic field and perpendicular to it) can be reduced from 10 % (paralleldistribution) and up to 70 % (perpendicular distribution) [96,100]. It was also shown numerically as well as experimentally that a parallel-plate AMR with the plate's distribution parallel to the magnetic field can generate significantly higher cooling characteristics compared to the perpendicular distribution [92,99,101].…”

Section: The Demagnetization Fieldmentioning

confidence: 91%

“…a packed-bed AMR). Furthermore, a coupled AMR model with the demagnetization model can be found in [92,98,99].…”

Section: The Demagnetization Fieldmentioning

confidence: 99%

Active Magnetic Regeneration

Kitanovski

Tušek

Tomc

et al. 2014

Green Energy and Technology

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It is well known that the magnetocaloric effect of most magnetocaloric materials at moderate magnetic fields (up to 1.5 T) is limited to a maximum adiabatic temperature change of 5 K [1,2]. This value is not sufficient for such materials to be directly implemented into a practical cooling or heating device where temperature span over 30 K is required. Therefore, in order to increase the temperature span, one and so far the best option is for a heat regenerator to be included in the magnetic thermodynamic cycle.A heat regenerator is a type of indirect heat exchanger where the heat is periodically stored and transferred from/to a thermal storage medium (regenerative material) by a working (heat-transfer) fluid. The regenerative material usually has a porous structure, through which a working fluid is pumped in an oscillatory, counter-flow manner (which is more efficient than a parallel flow system). During the 'hot period', a warmer fluid flows through the regenerative material, which cools down, while the material heats up. As a result, heat is stored in the material. During the 'cold period', a cooler fluid flows through previously heated regenerative material, so the fluid heats up, while the material cools down. The heat is therefore transferred back to the fluid (the same fluid or a different one) at a different phase of the thermodynamic cycle. After a certain number of such steps, a periodic steady state is reached and, as a result, a temperature profile can be established along the length of the regenerator [3].The need to apply heat regenerators in a magnetic refrigerator was already realized by Brown [4] in the first prototype of a magnetic refrigerator, built in 1976. He applied a regenerative Stirling-like thermodynamic cycle (very similar to AMR), which significantly increased the temperature span of the device [4,5]. A few years later Steyert [6] and Barclay and Steyert [7] presented and explained the active magnetic regenerator, which remains the most applied method for the exploitation of the magnetocaloric effect at room temperature. Furthermore, all prototypes of magnetic refrigerators built since then have been based on the AMR process [5]. An AMR, unlike a passive (regular) heat regenerator, contains a magnetocaloric material as the regenerative material. It has a double function in a magnetic regenerator, i.e. it works as a regenerator and enables an increase in the temperature span as well as working as a coolant and generating/absorbing heat between the particular phases of the

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The influence of demagnetizing effects on the performance of active magnetic regenerators

Cited by 21 publications

References 18 publications

Numerical investigation of room temperature magnetic refrigerator using microchannel regenerators

Numerical investigation of room temperature magnetic refrigerator using microchannel regenerators

Direct and indirect measurements on electrocaloric effect: Recent developments and perspectives

Active Magnetic Regeneration

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