Magnetic Refrigeration Prototype Research Articles

Development and experimental analysis of a multi-bed active magnetic regenerator

Room temperature magnetic refrigeration technology is a potentially efficient and environmentally friendly refrigeration technology. A magnetic refrigeration prototype with two high/low magnetic field regions was designed and built. The device consists of eight beds, using gadolinium particles as the magnetocaloric material, with a total filling mass of 1.35 kg. The hydraulic system consists mainly of a magnetic centrifugal pump, solenoid valves, and check valves. The flow of the heat transfer fluid through the regenerators is controlled by controlling the opening and closing of the solenoid valves. The no-load temperature span, cooling capacity, power consumption, and COP of the regenerators were investigated separately. The maximum no-load temperature span of 17.5 K was obtained at an AMR frequency of 0.5 Hz and flow rate of 1.15 L/min. The total power consumption and the magnetic power and pumping power were analyzed for different operating conditions.

New horizons in magnetic refrigeration using artificial intelligence

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.

Performance investigation and optimization of the magnetic refrigeration cycle with two-stage magnetization and demagnetization

Recently, room-temperature magnetic refrigeration (MR) has attracted immense attention as a prospective substitute for vapor-compression refrigeration. The greatest obstacles faced by existing room-temperature MR prototypes are their inadequate cooling capacity, small temperature span, and low efficiency. A potential solution to these issues could include constructing new MR cycles based on regeneration. Therefore, in this paper, we constructed a few potentially efficient two-stage MR thermodynamic cycles. The thermodynamic model of the two-stage MR cycle was established to evaluate its cyclic performance. The performances of different two-stage MR cycles were investigated, and compared with that of the basic MR cycle. The results revealed that the two-stage MR cycles always performed better than the basic MR cycle, on account of the increased cooling capacity, and the reduced magnetic work. Moreover, it was found that the two-stage MR cycle with two-stage magnetization and demagnetization was the optimal configuration. Therefore, further investigation was conducted on the performance of the optimal two-stage MR cycle. The effects of certain key parameters (such as, the intermediate magnetic field, and the cold- and hot-end operating temperatures) on the cyclic performance were carefully analyzed. It was observed that when the operating temperature was between 280 K and 310 K, a magnetic field ratio between 0.371 and 0.492 was optimal for achieving the best cyclic performance. Maximum thermodynamic perfection of approximately 0.635 was obtained, which was 27.55% greater than that of the basic MR cycle. Furthermore, we investigated the influence of adiabatic irreversibility on the cyclic performance. The results demonstrated that when adiabatic irreversibility factors ranged between 0.9 and 1, the two-stage MR cycle consistently performed better than the basic MR cycle. Thus, this paper can provide a theoretical direction for the design and optimization of efficient room-temperature magnetic refrigerators employing new thermodynamic cycles.

Performance comparison of Ga and Ga/La alloy layered active magnetic regeneration beds in a rotary magnetic refrigeration prototype

A magnetocaloric material (MCE) is a material whose temperature changes under varying magnetic field. It has been used as a solid-state refrigerant in a magnetic refrigeration prototype. This work reported the design and development of a rotary active magnetic regeneration (AMR) prototype with a magnetic field amplitude of 0.625 T. The purpose of this study is to compare the performances between two different magnetocaloric AMR beds: Gadolinium (Gd) AMR bed and Gd/Lanthanum (La)-alloy layered AMR bed. The Gd/La alloy layered AMR bed is composed of 5 segments of MCE materials with different Curie temperature (Tc). All Gd and La-alloy materials used in this study were irregular-shape particles with particle sizes smaller than 200 µm. The MCE materials were packed in an AMR bed. The cooling performance of the 40 mm Gd/La layered AMR bed, 80 mm Gd/La layered AMR bed, 80 mm Gd AMR bed were tested and compared by adjusting the heat-exchange fluid flow rate and the frequency of magnetization. At zero thermal load, the 40 mm Gd/La layered bed resulted in the temperature span of 2 °C, which is relatively similar to that of the 80 mm Gd/La layered AMR (1.8 °C). The 4-cm AMR bed resulted in relatively similar temperature span to the 80 mm AMR bed span, even though the amount of active MCE materials is lower. The 40 mm AMR bed exhibited much lower pressure drop than the 80 mm AMR bed. As a result, higher flow rate of the heat-exchange fluid could be applied for the 40 mm AMR bed under higher magnetization frequency.

Numerical simulation of a fully solid-state micro-unit regeneration magnetic refrigerator with micro Peltier elements

As an alternative to the vapor-compression technology, magnetic refrigeration has been an active area of research in recent years. A serious obstacle faced by existing magnetic refrigeration prototypes is the use of a heat-transfer fluid, which may result in high irreversible losses, large pressure drops and complex fluid circuits. Solid-state magnetic refrigeration has been investigated as a potential solution. For our previously proposed solid-state micro-unit regeneration magnetic refrigerator, the special three-dimensional structure design allows the heat to be regenerated at a small temperature difference. It is note-worthy that a three-dimensional numerical simulation is necessary for analysing the internal heat transfer characteristic and revealing the operation parameters matching rule of micro-unit regeneration cycle. Therefore, in this work a three-dimensional solid-state magnetic refrigerator based on micro-unit regeneration cycle and Peltier elements is modelled in detail. Multiple micro Peltier (9506-063-022M) modules are coupled with a system to enhance the heat regeneration between the magnetocaloric material lattices. The reliability of the model, in parts and in whole, is verified by experimental data. The heat transfer process and performance characteristics are carefully compared and discussed for several configurations, including the system with/without Peltier elements, two types of lattice heat-transfer structures, different Peltier’s input voltages, and different required times for rotation per lattice. The results show that a larger temperature span and higher frequency are obtained when coupled with Peltier elements. Meanwhile, the parallel-plate heat transfer structure of the magnetocaloric material lattice further improves the performance of the system. The optimal system performance is simultaneously determined by the input voltage and rotating speed. Using gadolinium as a magnetocaloric material and in the case of a 0.7 T applied magnetic field, a maximum temperature span of 32 K, an optimal coefficient of performance of 5.45, and a maximum specific cooling power of 252.5 W/kg can be achieved in such a fully solid-state micro-unit regeneration magnetic refrigeration system. The simulation results can serve as guidelines for solid-state magnetic refrigerator design and optimisation.

A 15kW magnetocaloric proof-of-concept unit: Initial development and first experimental results

Abstract As any innovative development program, magnetic refrigeration still faces many challenges before being widely accepted as an actual replacement technology for cooling. In the last years, more than 50 different types of prototypes of magnetocaloric refrigerators have been presented in literature, with limited cooling power values and/or limited temperature span. This paper presents several assembly details and experimental results of a new proof-of-concept magnetic refrigeration prototype having both a temperature span of more than 20 K and a cooling capacity designed for around 15 kW. It has been made as a part of a pilot project for a large industrial partner to be used for an industrial process. The obtained experimental results have been measured and validated by an exterior independent body. This performance achievement, that we believe to be as the largest rotary magnetic refrigerator ever created, could be a milestone for the future of magnetocaloric chillers.

A successful process to prevent corrosion of rich Gd-based room temperature magnetocaloric material during ageing

When the heat transport processes occur in a magnetic refrigeration device, there is possibility of corrosion thereforth, insight on the magnetocaloric regenerator corrosion could be shed in light. Our work mimicks this phenomenon by subjecting the magnetocaloric material Gd6Co1.67Si3 to controlled water flow. The corrosion is first explained based on the elemental electrochemical oxidation thereby allowing a new test by the exposing material in passive fluid (KOH) up to 1 year. The neglected degradation of the material was justified by X-Ray photoelectron spectroscopy (XPS) and depth profile Auger spectroscopy, and thus the control of its corrosion is reported. The effective control of the corrosion when material is exposed to KOH could be a universal procedure in magnetic refrigeration prototype.

Comparative study on the series, parallel and cascade cycles of a multi-mode room temperature magnetic refrigeration system

Abstract Magnetic refrigeration has been investigated as an appropriate alternative for vapor-compression refrigeration to reduce the greenhouse effect. However, the commercialization process of MR is obstructed by the inadequate cooling condition. In this paper, a multi-mode MR system with series, parallel and cascade cycle modes is constructed. The optimal utilization factors, internal cycle mechanisms and refrigeration characteristics of three modes are compared. The magnetocaloric material used is 277.4 g of gadolinium, and two NbFeB permanent magnets are assembled to provide a maximum magnetic field intensity of 1.5 T. The results show that different modes affect the MR system performance. The series mode increases the temperature span by increasing the length of the regeneration zone. The parallel mode improves the cooling power owing to the simultaneous output of double regenerators. The novel cascade cycle constructs the higher- and lower- temperature regeneration stages, which are effectively utilized to provide a large temperature span and suitable cooling power. The obtained no-load temperature spans are 5.66 K, 4.16 K and 7.35 K in the series, parallel and cascade cycles, respectively, and the corresponding maximum specific cooling powers are 29.02, 39.47 and 34.79 W/kg. Compared with the parallel mode, the cycle characteristics of the series and cascade modes receive a greater degree of investigation. The series mode shows a larger potential for large-temperature-span output system, and the cascade cycle is most likely to meet both the temperature span and cooling power output requirements simultaneously. The results provide some guidelines for the design of magnetic refrigeration prototypes.

Looking for Energy Losses of a Rotary Permanent Magnet Magnetic Refrigerator to Optimize Its Performances

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.

Design and development of rotary magnetic refrigeration prototype with active magnetic regeneration system

In the field of cooling system, a traditional vapor compression (VC) technology has been used over long time. The VC cooling is simple and cost effective, however, it raises global warming concern due to its relatively low energy efficiency and usage of ozone depletion substances. Magnetic refrigeration (MR) has been proposed as a potential cooling technology that can replace the VC cooling. MR can potentially be operated with efficiency closer to the theoretical efficiency, without using environmentally-harmful refrigerants. In the MR system, a magnetocaloric material (MCM) with magnetocaloric effect (MCE) is used as a refrigerant. The temperature of MCM can be increased and decreased under adiabatic magnetization and demagnetization, respectively. Water/ethylene glycol can be used as heat-exchanging fluid. In this work, a rotary MR prototype was designed and built. The prototype consists of the following main systems: 1. Flow distribution system, 2. Rotary magnetic field generator 3. Mechanic system, and 4. Temperature and pressure sensor system. Four beds of magnetocaloric gadolinium (Gd) particulates were used as an active magnetic regenerative cooling media. Fluid flow was controlled by pneumatic pump and solenoid valves. Rotary magnetic field generator was designed and built with maximum and minimum fields of 0.65 and 0 T, respectively. The overall setup and preliminary study showed that the pressure drop across the system was 2 bar when the flow rate was only 0.5 L/min. Increasing flow rate further resulted in too high pressure drop causing the MCM bed to swell. Therefore, the flow rate was limited to 0.5 L/min resulting in insufficient heat transfer rate by the slow heat exchange fluid flow. Consequently, the maximum temperature span was measured to be 0.5 K. The prototype must be improved to drive flow rate higher and to reduce the pressure drop of the system.

Development of an experimental rotary magnetic refrigerator prototype

A rotary active magnetic regeneration refrigerator prototype named FAME Cooler was developed for studying the performance of different magnetocaloric materials in a realistic practical environment. The rotary magnetic field source generates an average magnetic field of 0.875 T within a volume of 0.71 l The regenerator is designed asymmetrically and holds in total 1.18 kg of gadolinium spheres for a first performance test. Combined with a real-time controlled programmable solenoid-valves system, different working parameters or thermodynamic cycles can be applied. In the performance test, while the temperature of system hot side was fixed at 295 K, under a utilization condition of 0.25, this prototype achieved a maximum zero-span cooling power of 162.4 W, and a zero-power temperature span of 11.6 K. Under a utilization condition of 0.15, a maximum COP of 1.85 was reached. These performance metrics are comparable with existing magnetic heat pump devices of the same scale.

Enhancing the Magnetocaloric Effect of a Paramagnet to above Liquid Hydrogen Temperature

Liquid hydrogen (LH2) is one of the most efficient ways for storing and transporting the H2 energy in hydrogen economy. Magnetic refrigeration using the magnetocaloric effect (MCE) is the preferable means to liquify H2 since the adiabatic demagnetization process can approach 100% of carnot efficiency. In practice, mainly due to the lack of single material that covers enough temperature span, the efficiencies of the prototypes of magnetic refrigerators are still far below the economic viable threshold (50%). Based on a theoretical analysis on the single ion anisotropy of Tb3+‐containing materials, it is found experimentally that MCE can be 100% enhanced for a model crystal LiCaTb5(BO3)6 (LCTB) at 20.2 K over the practical magnetic cooling medium Gd3Ga5O13 (GGG) for the cryogenic temperatures, and more importantly the enhancement covers a range of at least 15–40 K in a typical field change of 6 T.

Effect of Cycle Frequency of a Reciprocating Magnetic Refrigerator Prototype on the Temperature Span and Cooling Capacity

Magnetic refrigeration is an environment-friendly cooling technology and an interesting potential replacement for the vapor compression refrigeration system. This paper presents a linear reciprocating magnetic refrigerator prototype that operates at room temperature by using gadolinium parallel plates under a maximum magnetic field intensity of 0.94[Formula: see text]T. The design, installation and preliminary results are reported. The temperature span and cooling capacity are studied in a function of cycle frequency, and the results show the cycle frequency effects on temperature span and cooling capacity. The maximum temperature span and cooling capacity for cycle frequency of 0.16[Formula: see text]Hz are 1.3[Formula: see text]K and 4.68[Formula: see text]W, respectively. The results from the experiment will be a guideline to determine the maximum performance of the magnetic refrigerator prototype.

Performance investigation of a high-field active magnetic regenerator

Regenerative magnetic cycles are of interest for small-scale, high-efficiency cryogen liquefiers; however, commercially relevant performance has yet to be demonstrated. To develop improved engineering prototypes, an efficient modeling tool is required to screen the multi-parameter design space. In this work, we describe an active magnetic regenerative refrigerator prototype using a high-field superconducting magnet that produces a 100 K temperature span. Using the experimental data, a semi-analytic AMR element model is validated and enhanced system performance is simulated using liquid propane as a heat transfer fluid. In addition, the regenerator composition and fluid flow are simultaneously optimized using a differential evolution algorithm. Simulation results indicate that a natural gas liquefier with a 160 K temperature span and a second-law efficiency exceeding 20% is achievable.

Design and development of magnetic refrigeration prototype for the performance analysis of magnetocaloric materials

Magnetic refrigeration (MR) has been receiving an attention as an alternative system to conventional refrigeration based on vapor compression. Normally, the vapor compression uses hydrofluorocarbons (HFC) and Chlorofluorocarbons (CFC) as refrigerant fluids which damage ozone layers causing global warming. Consequently, the magnetic system has been developed to replace the traditional system to reduce global warming potential (GWP). The alternative cooling technology is based on the magnetocaloric effect (MCE) of magnetocaloric materials (MCM) which are able to change their temperature following magnetic flux density under magnetic field generator. The refrigeration is operated via an active magnetic regeneration (AMR) cycle with rotating magnets. In this work, the magnet assembly has been designed and studied with the aspiration for compact and efficiency. Based on extensive reviews, the magnet assembly model of Okamura et al. provides the conceptual design with optimal compactness and efficiency. Hence, in this study, the magnet assembly design has been developed based on the model by Okamura et al. The magnetic system consists of a soft magnetic composite stator and four neodymium (NdFeB) permanent magnets rotated by motor. The magnetic field performance of the assembly is analyzed using the COMSOL Multiphysics software. The generated magnetic flux density is 0.65 T provided by only 0.9 L of permanent magnets. In addition, the efficiency of the magnet design is represented by a figure of merit parameter, Λcool. Among others, the proposed design exhibit a high Λcool value of 0.17, which is as high as five times better than the magnet assembly designs by prior work.

Plastically deformed Gd-X (X = Y, In, Zr, Ga, B) solid solutions for magnetocaloric regenerator of parallel plate geometry

Despite significant progress in the study of materials undergoing first-order magnetic phase transitions accompanied by the so-called giant magnetocaloric effect (MCE), Gd metal still remains the most widely used material in prototypes of magnetic refrigerators due to its significant MCE, good machinability and reasonable mechanical and chemical stabilities. Alloying of Gd enables fine-tuning the Curie temperature of Gd-based solid solutions (all show second-order phase transitions), for graded magnetocaloric materials. Commonly, Gd packed spheres are used as a magnetocaloric working substance in the active magnetic regenerator (AMR) cycle. In this work, we show that the optimized stacking parallel-plate geometry of AMR bed made of Gd is more effective for application at frequencies 1–10 Hz then the packed spheres. We also give a short review on magnetocaloric properties of cold-rolled Gd-X (X = Y, In, Zr, Ga, B) solid solutions. These materials can be produced in the form of thin (∼100 μm) foils/plates to ensure rapid heat exchange between to the heat transfer fluid. Although the magnetocaloric effect decreases in the as-rolled foils, it can be recovered by thermal treatment of the final stacked-plates regenerators. Gd-Y, Gd-In and Gd-Zr solid solutions have magnetocaloric properties, comparable to the MCE of pure Gd in a wide temperature working span up to 37 K, 36 K, and 16 K respectively, which makes them suitable magnetocaloric material systems for testing the fundamental heat exchangers geometries at ambient temperature and in frequencies of 1–10 Hz.

Influence of magnetization on the applied magnetic field in various AMR regenerators

The aim of this work is to assess the influence of a magnetic sample on the applied magnetic field inside the air gap of a magnetic circuit. Different magnetic sources including an electromagnet, a permanent magnet in a soft ferromagnetic toroidal yoke, as well as 2D and 3D Halbach cylinders are considered, using a numerical model. Gadolinium is chosen as magnetic material for the sample, due to its strong magnetocaloric properties and its wide use in magnetic refrigeration prototypes. We find that using uniform theoretical demagnetizing factors for cylinders or spheres results in a deviation of less than 2% in the calculation of internal magnetic fields at temperatures above the Curie point of gadolinium. Below the Curie point, a stronger magnetization of the cylinders and spheres leads to a larger deviation which can reach 8% when using uniform demagnetizing factors for internal magnetic field calculations.

Review of magnetic refrigeration system as alternative to conventional refrigeration system

The refrigeration system is one of the most important systems in industry. Developers are constantly seeking for how to avoid the damage to the environment. Magnetic refrigeration is an emerging, environment-friendly technology based on a magnetic solid that acts as a refrigerant by magneto-caloric effect (MCE). In the case of ferromagnetic materials, MCE warms as the magnetic moments of the atom are aligned by the application of a magnetic field. There are two types of magnetic phase changes that may occur at the Curie point: first order magnetic transition (FOMT) and second order magnetic transition (SOMT). The reference cycle for magnetic refrigeration is AMR (Active Magnetic Regenerative cycle), where the magnetic material matrix works both as a refrigerating medium and as a heat regenerating medium, while the fluid flowing in the porous matrix works as a heat transfer medium. Regeneration can be accomplished by blowing a heat transfer fluid in a reciprocating fashion through the regenerator made of magnetocaloric material that is alternately magnetized and demagnetized. Many magnetic refrigeration prototypes with different designs and software models have been built in different parts of the world. In this paper, the authors try to shed light on the magnetic refrigeration and show its effectiveness compared with conventional refrigeration methods.

Mastering hysteresis in magnetocaloric materials.

Hysteresis is more than just an interesting oddity that occurs in materials with a first-order transition. It is a real obstacle on the path from existing laboratory-scale prototypes of magnetic refrigerators towards commercialization of this potentially disruptive cooling technology. Indeed, the reversibility of the magnetocaloric effect, being essential for magnetic heat pumps, strongly depends on the width of the thermal hysteresis and, therefore, it is necessary to understand the mechanisms causing hysteresis and to find solutions to minimize losses associated with thermal hysteresis in order to maximize the efficiency of magnetic cooling devices. In this work, we discuss the fundamental aspects that can contribute to thermal hysteresis and the strategies that we are developing to at least partially overcome the hysteresis problem in some selected classes of magnetocaloric materials with large application potential. In doing so, we refer to the most relevant classes of magnetic refrigerants La-Fe-Si-, Heusler- and Fe2P-type compounds.This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

Design and performance of a novel magnetocaloric heat pump

The design and preliminary results of an active magnetic refrigeration prototype for room temperature cooling applications are investigated. The physical prototype along with its operational and measurement envelopes are described. General design goals included: A wide range of cycle parameter control, independent fluid and magnetic circuits, extensive measurement capability, and compact overall design. An initial set of measurements has been made with Gadolinium particulate of an industrial purity. The maximum no-load span recorded was 21 K and the maximum power recorded was 26 W at a span of 1 K. Additionally, three different cyclical parameters have been varied to help determine the optimal cycle for such a machine. The unique modularity and control of this system will allow for a detailed understanding of the operation of commercial active magnetic regeneration designs.