•A 100 K temperature span is measured with a bespoke magnetic refrigerator.•Simulations assert the importance of fluid density and field strength on efficiency.•An optimization of the material ...composition yields an efficient gas liquefier.
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.
•Entropy generation minimization was used to optimize an active magnetic regenerator.•Range of geometries studied included micro-channel and packed screens.•AMRs can be more efficient using ...alternative geometries except packed spheres.•Practical difficulties in implementing new geometries were discussed.
Room temperature magnetic refrigeration has attracted substantial attention during the past decades and continuing to increase the performance of active magnetic regenerators (AMR) is of great interest. Optimizing the regenerator geometry and related operating parameters is a practical and effective way to obtain the desired cooling performance. To investigate how to choose and optimize the AMR geometry, a quantitative study is presented by simulations based on a one-dimensional (1D) numerical model. Correlations for calculating the friction factor and heat transfer coefficient are reviewed and chosen for modeling different geometries. Moreover, the simulated impacts of various parameters on the regenerator efficiency with a constant specific cooling capacity are presented. An analysis based on entropy production minimization reveals how those parameters affect the main losses occurring inside the AMR. In addition, optimum geometry and operating parameters corresponding to the highest efficiency for different geometries are presented and compared. The results show that parallel plate and micro-channel matrices show the highest theoretical efficiency, while the packed screen and packed sphere beds are possibly more practical from the application point of view.
Magnetic/magnetocaloric refrigeration is an energy-efficient and environmentally safer cooling technology with the potential to be an alternative to conventional vapor compression systems in the ...future. Magnetocaloric effect (MCE) is a measure of relative temperature rise/drop of certain ferromagnetic materials upon the application/removal of a magnetic field. The technology uses MCE of some materials such as Gd to produce temperature difference/span relative to the ambient via a four-stage regenerative cycle known as active magnetic regenerative (AMR) cycle. Research in this area has been thriving especially during the last two decades focussing on different aspects of technology such as materials, magnetic field sources, and system design. On the system design, studies investigating the effect of different magnetic, thermal-hydraulic, and geometric parameters on the performance have been found in the literature. The present work offers a chronological review and comparison of recent advances in AMR refrigerators. Findings and results reported in the literature are compared in terms of magnetocaloric materials, geometric parameters (such as regenerator geometry); operating parameters e.g. cycle frequency, utilization, heat transfer fluid, heat rejection temperature, and cooling load, etc. Besides, performance indicators such as no-load temperature span, cooling capacity, and/or system coefficient of performance have been considered. Parametric sensitivity and performance trends have been identified and discussed. Major barriers to achieving system peak performance and hence the marketability of the technology are also highlighted.
•Magnetic field and magnetocaloric material are crucial parameters determining overall performance.•Regenerator geometry and heat transfer fluid strongly influence the regenerator temperature gradient.•Utilization and cycle frequency require optimization to meet a given cooling load requirement.
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 (AMRR) 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 span and a second-law efficiency exceeding 20% is achievable.
Magnetocaloric materials with a Curie temperature near room temperature have attracted significant interest for some time due to their possible application for high‐efficiency refrigeration devices. ...This review focuses on a number of key issues of relevance for the characterization, performance and implementation of such materials in actual devices. The phenomenology and fundamental thermodynamics of magnetocaloric materials is discussed, as well as the hysteresis behavior often found in first‐order materials. A number of theoretical and experimental approaches and their implications are reviewed. The question of how to evaluate the suitability of a given material for use in a magnetocaloric device is covered in some detail, including a critical assessment of a number of common performance metrics. Of particular interest is which non‐magnetocaloric properties need to be considered in this connection. An overview of several important materials classes is given before considering the performance of materials in actual devices. Finally, an outlook on further developments is presented.
Magnetocaloric materials attract significant interest due to their possible application for more efficient, environmentally friendly refrigeration. Recent years have seen improvements in both materials research and device design (the TOC image shows a device built at the Technical University of Denmark). This article reviews a number of key issues related to the performance and implementation of magnetocaloric materials in actual devices.
•Evaluation of parallel-plate, pin array and packed-sphere regenerative geometries.•Thermal and viscous losses were quantified with (passive) stainless steel matrices.•Magnetic losses were quantified ...with (active magnetic) gadolinium matrices.•Matrices had the same porosity, volume and interstitial area.•Packed spheres had the highest cooling capacity and pin arrays the highest COP.
The development of efficient active magnetic regenerators (AMR) is highly dependent on the regenerative matrix thermal performance. Matrix geometries should have a high thermal effectiveness and small thermal and viscous losses. In this study, we present a systematic experimental evaluation of three different regenerator geometries: parallel-plate, pin array and packed bed of spheres. All matrices were fabricated with approximately the same porosity (between 0.36 and 0.37). The cross sectional area and length of the regenerator beds are identical, resulting in the same interstitial area. Hence, any difference in performance between the matrices is due to interstitial heat transfer between the solid and the fluid and losses related to thermal, viscous and magnetic effects. As a means to quantify these losses individually, experiments were first conducted using stainless steel matrices without the application of a magnetic field (passive regenerator mode). Later, gadolinium matrices made with the same characteristics as the stainless steel ones were evaluated in an AMR test apparatus for which experimental results of cooling capacity, temperature span between the thermal reservoirs, coefficient of performance and second-law efficiency were generated as a function of utilization for different operating frequencies. Parallel plates had the poorest performance, while the packed bed of spheres presented the highest cooling capacity. On the other hand, the packed bed also had the highest viscous losses. For this reason, the pin array exhibited the highest COP and second-law efficiency.
Magnetic refrigeration is an important new refrigeration technology in the temperature range of liquid hydrogen. A multistage magnetic refrigeration system between 20 K and 80 K has been proposed, ...which includes three-stage active magnetic regenerators (AMRs). Based on the multistage system, a two-dimensional transient AMR model is established to research the cycle performance mechanism by considering the compressibility of helium, which has not been done before. Firstly, to simplify the simulation difficulty, the AMR model with ideal magnetocaloric materials (the constant isothermal entropy change of 5.4 J/(kg·K) at 1 T) are investigated in the temperature range between 60 K and 80 K. Some parameters including particle diameter, fluid flow fraction, and filling mass of magnetocaloric materials have been compared and analyzed. Based on the above simulation results, the AMR model with real magnetocaloric materials has been done. In the three-layer AMR, the maximum cooling power of 71.04 W at the cooling temperature of 60 K has been obtained, which is 80.17% larger than that of the one-layer AMR. Then, the cooling performance of the multistage magnetic refrigeration system has been studied. In the system, six magnetocaloric materials are filled in three-stage AMRs based on the filling method of adiabatic temperature change. With the optimal mass flow rates of each stage AMR, the maximum cooling power of 40.09 W has been obtained in the multistage system, and the corresponding thermodynamic second efficiency has been 28.14%.
•A 2D transient AMR model in the temperature range of liquid hydrogen has been developed.•The influence of some parameters on the cooling performance of AMR was evaluated.•Three-layer AMR has provided the better cooling performance than one-layer AMR.•Maximum cooling power of multistage magnetic refrigeration system could reach 40.09 W.
Although magnetocaloric cooling is considered a promising long-term alternative to vapor compression, recent prototype developments have not yet made this technology commercially competitive, ...primarily due to its high energy consumption and lack of cost-effective, long-term mechanically-chemically stable materials. To address the first issue and understand how the efficiency of magnetocaloric systems can be improved, dynamic models can offer valuable insights into their transient operation. This work focuses on the development of an artificial neural network with experimental data to model the dynamic operation of a magnetic refrigeration system. Through a design of experiments approach, we propose excitation signals for the identification experiment, involving five manipulated variables and one selected disturbance as inputs, with the output temperature of the cold manifold and power consumption as the target parameters. We chose a nonlinear autoregressive artificial neural network with exogenous inputs to model the transient operation of the system. The temperature model achieved R2 values of 0.995 and 0.955 for the 1-step and 90-step ahead predictions, respectively. Similarly, the power consumption model achieved R2 values of 0.988 and 0.949 for the 1-step and 90-step ahead predictions, respectively. These performance metrics were evaluated on the test sets that were not used for training the models, highlighting the robustness and accuracy of the models in both short-term and long-term predictions.
•Dynamic-model-predicted magnetic refrigerator’s temperature and power consumption.•A nonlinear autoregressive with exogenous inputs neural network modeled the system.•Experimental design methodology collected data for training and testing the model.•Model predicted system’s long-term dynamics with MSE of 0.091 °C and 70.38 W.
This work advances an integrated approach to design the components of a magnetocaloric air conditioner capable of producing a cooling capacity of 9000 BTU h−1 (2637 W) for indoor and outdoor ambient ...temperatures of 22 °C and 35 °C, respectively. Through a combination of data-driven and deep learning-based approaches, standalone models were developed for the active magnetic regenerator and magnetic circuit. The cooling system analysis was complemented by existing models for the tube-fin heat exchangers and the hydraulic management system. A multi-objective method based on genetic algorithms was proposed to optimize the system for minimal power consumption and the total assembly cost. The final design exhibited a COP of 2.57 and a second-law efficiency of 11.4%. A power consumption breakdown revealed that the most significant contributions are the magnetization of the solid refrigerant and fluid pumping. As for the capital cost and system mass, the most critical contribution is associated with the magnetic circuit’s rotor due to the volume of soft and hard magnetic materials.
•Integrated design of 2600-W magnetocaloric air conditioner is presented.•AMR and magnetic circuit are designed via data-driven and deep learning approaches.•The system is optimized via multi-objective method and genetic algorithms.•The final design exhibited a COP of 2.57 and a second-law efficiency of 11.4%.
•The cooling performance of a multi-bed AMR device with gadolinium is presented.•A cooling power of 818 W with a COP of 4.2 was achieved over a 10 K span.•The device can establish a 16.6 K span ...starting from room temperature in 25 min.•Active valve control can increase cooling power and COP by more than 70%.•A maximum second-law efficiency of 39.2% was obtained at a span of 7.3 K.
We present the experimental results for a rotary magnetocaloric prototype that uses the concept of active magnetic regeneration, presenting an alternative to conventional vapor compression cooling systems. Thirteen packed-bed regenerators subjected to a rotating two-pole permanent magnet with a maximum magnetic field of 1.44 T are implemented. It is the first performance assessment of the prototype with gadolinium spheres as the magnetocaloric refrigerant and water mixed with commercial ethylene glycol as the heat transfer fluid. The importance of various operating parameters, such as fluid flow rate, cycle frequency, cold and hot reservoir temperatures, and blow fraction on the system performance is reported. The cycle frequency and utilization factor ranged from 0.5 to 1.7 Hz and 0.25 to 0.50, respectively. Operating near room temperature and employing 3.83 kg of gadolinium, the device produced cooling powers exceeding 800 W at a coefficient of performance of 4 or higher over a temperature span of above 10 K at 1.4 Hz. It was also shown that variations in the flow resistance between the beds could significantly limit the system performance, and a method to correct those is presented. The performance metrics presented here compare well with those of currently existing magnetocaloric devices. Such a prototype could achieve efficiencies as high as conventional vapor compression systems without the use of refrigerants that have high global warming potential.
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