A number of magnetic refrigeration prototypes have been developed in recent years. Nevertheless, their optimization remains a challenging process. This paper presents an efficient approach based on ...artificial intelligence for optimizing the cooling performance of multi-layer active magnetic regenerators. To this end, a validated numerical model was used to predict the temperature difference between the hot and cold sources of a four-layer active magnetic regenerator. By using a nanofluid as a heat transfer fluid, the maximum temperature span of the device can be increased by approximately 20%. More importantly, by simultaneously optimizing a set of 10 key parameters, including the geometric parameters and the working conditions, the thermodynamic performance of the four-layer active magnetic regenerator prototype can be markedly enhanced by almost 40%. The newly established approach will be of considerable practical importance to both scientists and engineers since it will enable them to avoid costly experimental trials by optimizing a wide number of parameters.
•A validated numerical model of a multilayer active magnetic regenerator is developed.•Thermodynamic performance optimization using artificial intelligence is performed.•A set of 10 geometric parameters and working conditions are optimized.•An enhancement of roughly 20% in cooling performance is achieved using a nanofluid.•An optimal set of parameters yields a nearly 40% improvement in cooling performance.
This paper provides an update on alternative cooling technologies in the context of a report by Fischer et al. 2, which contains an extensive assessment of “not-in-kind” technologies including their ...state-of-the-art, development issues, and potentials to replace vapor compression equipment. After nearly 20 years, it is now of interest to update the status of alternative technologies considering regulatory actions aimed at refrigerants with high global warming potential. Several technologies are considered with sorption cooling, desiccant cooling, magnetic cooling, thermoacoustic cooling, thermoelectric cooling, and transcritical CO2 being discussed in some detail. For each technology we present its physical principle, a brief summary of the findings of Fischer et al., the technological advancements since their study leading to the current state-of-the-art, and our assessment as to the potential of each technology to enter the market as a supplement to or replacement of vapor compression equipment in the next 20 year period.
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•We reviewed the state-of-the-art of alternative cooling technologies.•Progress in developments has been lower than predicted in 1994.•Likely to find increased niche market applications in the future.•Unlikely to widely displace vapor compression technology in the near-term future.
The detailed procedure for constructing the recently proposed phenomenological universal curve for the magnetic entropy change is presented, together with the exponents which control the field ...dependence of the different magnetocaloric-related magnitudes. Practical applications of the universal curve are also outlined: as a simple screening procedure of the performance of materials, as a method for making extrapolations to temperatures or fields not available in the laboratory, for the reduction of the experimental noise, for correcting the influence of non-saturating conditions, or as a way to eliminate the contribution of minority magnetic phases, among others.
Magnetic refrigeration, heating and power conversion technologies are interesting alternatives to the conventional refrigeration, heat pumping and different conventional energy conversion ...technologies. At present they all show a realistic potential to enter conventional markets, respectively to be applied in a few years. In this review paper, mainly magnetic refrigeration and magnetic heating are addressed and from these two technologies the main part is dedicated to magnetic refrigeration at room temperature. This article covers the demand of giving a complete list and description of existing magnetic heating and cooling prototypes up to the year 2010. Forty-one machines, their components and operation principles are presented in detail.
A second-generation room-temperature permanent magnet active magnetic regenerator test apparatus using Halbach arrays is described. The magnet arrays consist of three concentric cylinders. Each ...cylinder is constructed using 12 permanent magnet segments. The inner magnet array is stationary while the intermediate and outer arrays are designed to rotate in opposite directions so as to create a sinusoidal magnetic field waveform with a stationary field direction. The fluid flow system utilizes a novel check valve configuration so that fluid dead volumes are minimized. The system construction is modular to allow for quick replacement of material or system components. Fringing fields near the outer and inner diameters of the arrays are found to create large forces between arrays leading to large torques. Test results using 650 g of gadolinium spheres produce a no-load temperature span of 33 K at 0.8 Hz.
•A second generation permanent magnet AMR test apparatus is described in detail.•A unique triple nested Halbach configuration is explained.•Torque issues regarding the magnets are discussed.•A novel hydraulic flow control method using check valves is explained.•A no-load temperature span of 33 K is achieved using 650 g of gadolinium at 0.8 Hz.
Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magneto-caloric effect (MCE). The reference cycle for magnetic ...refrigeration is AMR (Active Magnetic Regenerative refrigeration).
In order to demonstrate the potential of magnetic refrigeration to provide useful cooling in the near room temperature range, a novel Rotary Permanent Magnet Magnetic Refrigerator (RPMMR) is described in this paper. Gadolinium has been selected as magnetic refrigerant and demineralized water has been employed as regenerating fluid. The total mass of gadolinium (1.20 kg), shaped as packed bed spheres, is housed in 8 regenerators. A magnetic system, based on a double U configuration of permanent magnets, provides a magnetic flux density of 1.25 T with an air gap of 43 mm. A rotary vane pump forces the regenerating fluid through the regenerators. The operational principle of the magnetic refrigerator and initial experimental results are reported and analyzed.
Through strain‐mediated magnetoelectric coupling, it is demonstrated that the magnetocaloric effect of a ferromagnetic shape‐memory alloy can be controlled by an electric field. Large hysteresis and ...the limited operating temperature region are effectively overcome by applying an electric field on a laminate comprising a piezoelectric and the alloy. Accordingly, a model for an active magnetic refrigerator with high efficiency is proposed in principle.
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.
•The temperature relaxation time of a copper–copper contact pair was studied depending on temperature from 15 to 300 K;•Thermal interface made of indium foil reduces the time until thermal ...equilibrium of a copper–copper contact pair;•A magnetic field of 3 T does not affect the thermal equilibrium time of the contact pair with the indium thermal interface.
The main aim of this work is to study heat transfer in mechanical thermal switch under conditions close to a real magnetic refrigeration. This study examines the thermal behavior of a mechanical thermal switch which comprise a detachable pair of copper–copper contact bulks, incorporating an indium foil thermal interface with a 100 µm thickness. We investigated the time it took to reach thermal equilibrium from initial temperature span of 3 K, 5 K, and 10 K and explored the influence of the indium foil thermal interface within a temperature range of 15 to 300 K. The experimental data provided the heat dissipation values required to maintain the specified temperature of the object being cooled. As the results showed, the use an indium thermal interface significantly reduces the time until thermal equilibrium occurs.
The seminal study by Brown in 1976 showed that it was possible to use the magnetocaloric effect to produce a substantial cooling effect near room temperature. About 15 years later Green et al. built ...a device which actually cooled a load other than the magnetocaloric material itself and the heat exchange fluid. The major breakthrough, however, occurred in 1997 when the Ames Laboratory/Astronautics proof-of-principle refrigerator showed that magnetic refrigeration was competitive with conventional gas compression cooling. Since then, over 25 magnetic cooling units have been built and tested throughout the world. The current status of near room temperature magnetic cooling is reviewed, including a discussion of the major problems facing commercialization and potential solutions thereof. The future outlook for this revolutionary technology is discussed.
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