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• We develop a program capable of multi-threading and automatically running REGEN 3.3 software to generate 181,440 regenerator performance data. • We use a simple and novel one-dimensional convolutional neural network model to predict regenerator performance. • This model exhibits excellent performance and high reliability in both fitting and generalization. • This model computes diverse ruleless regenerator parameters, reducing compute time from 2500 min for 1000 data with REGEN 3.3 software to 130 ms. The regenerator is the core component of the regenerative cryogenic refrigerator, for its structure sizes, operating parameters and phase characteristics at the cold and hot ends co-determine the power and efficiency of the refrigerator, and the design parameters of other coupled components. Efficiently predicting the regenerator performance can reduce the design period of cryogenic refrigerators. Addressing the long computational time constraints in the traditional numerical simulation methods, a novel approach based on a one-dimensional convolutional neural network (1D-CNN) was proposed. Initially, a program capable of multi-threading and automatically running the specialized regenerator calculation software REGEN 3.3 was developed. The performance of the regenerators with various parameter combinations at the cold end temperature of 60–120 K were calculated and 181,440 pieces of data were obtained. Subsequently, the architecture and hyperparameters of the model were determined. The trained model exhibits an average relative error of 3.83% for predicting regenerator power, 0.13% for predicting pressure ratio at the hot end, and 1.55% for predicting the coefficient of performance (COP). The model's generalization ability was confirmed by generating data points beyond the original dataset. Additionally, the model allows for the simultaneous calculation of multiple sets of irregular regenerator parameters, and reduces the calculation time from 2500 min for 1000 pieces using REGEN 3.3 software to just 130 ms, representing a decrease by nearly six orders of magnitude. This approach effectively resolves the long computation time associated with traditional numerical simulation methods, and will present a new solution for the rapid and precise design of regenerators. [ABSTRACT FROM AUTHOR]

• A parametric convective heat transfer term is used to assess t span & cooling power. • Four major magnetocaloric materials are screened. • Optimal fluid velocity depends on the magnetic transition temperature. A 2-dimensional numerical model of a room temperature operating Active Magnetic Regenerator (AMR) that comprises of a regenerator, hot and cold heat exchangers, heat transfer fluid is developed. The regenerator is made of a magnetocaloric material (MCM) which heats up upon applying a magnetic field, H, and cools down when the field is removed; thus, making it the most essential part of an AMR. The model takes experimentally measured ∆T ad (H,T) and the C p (H,T) data as input and provides quantitative performance metrics of the magnetic cooling system, such as ∆T span and the cooling load, as output. With this model, it is possible to assess a wide range of MCMs in an AMR. 4 different MCMs were investigated using this model in terms of their ∆T span and the cooling loads—LaFe 10.96 Co 0.97 Si 1.07 , MnFeP (1-x) As (x) and AlFe 2 B 2 and Gd. During the screening of MCMs, all the important operating conditions of the device were fixed such as the fluid flow rate, ambient temperature, cycle duration, magnetic field strength. Our results indicate that Gd exhibits the maximum ∆T span with respectable cooling load, while AlFe 2 B 2 generates the lowest ∆T span. Even though LaFeCoSi compound did not perform as well as Gd, it could be the MCM choice for the realization of magnetic refrigeration on a global scale due to its much lower cost. [ABSTRACT FROM AUTHOR]

• Step displacer two-stage pulse tube refrigerator is analyzed by an ideal model. • Power distribution ratio proportional to step ratio and refrigeration temperature ratio. • Dead volume at the hot end of the pulse tube can avoid over phase shifter effect of displacer. • It is investigated by an updated numerical method which includes the pressure drop in the regenerator. Compared with double inlet type two-stage pulse tube refrigerator, step displacer type has higher efficiency. The step displacer has two functions, input power distribution function and phase shifting function, which are fundamental issues of this type refrigerator. The two functions are discussed by an ideal model, and are investigated by a numerical simulation. Theoretically, the exergy flow ratio to the first stage over the second stage depends on the refrigeration temperature ratio and step ratio, the dead volume at the hot end of the pulse tube can be an additional parameter for adjusting the phase angle difference at the cold end of the regenerator. [ABSTRACT FROM AUTHOR]

• A series of experiments for a cross-flow regenerator with a lithium chloride desiccant solution was conducted. • The regeneration effectiveness and energy performance were measured in a laboratory. • The optimal regeneration temperature of the desiccant solution was 65°C. Recently, a package unit of liquid desiccant and an indirect and a direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS) has been proposed. In this system, the amount of heating energy consumed to regenerate the desiccant solution is significant and should be reduced to achieve better energy conservation than that of a conventional air handling unit. The purpose of this research is to empirically investigate the optimum regeneration temperature of a lithium chloride (LiCl) desiccant solution, balancing the regeneration performance and solution heating energy consumption in the LD-IDECOAS package unit. The adiabatic cross-flow regenerator was tested in a test facility at desiccant solution temperatures of 50–90°C. The measurement results were compared with the predicted data in the regenerator to assess the reliability of the experimental results. By balancing the regeneration performance with the solution heating energy consumption, the recommended temperature to regenerate the desiccant solution was 65°C. [ABSTRACT FROM AUTHOR]

A rotary multi-bed active magnetic regenerator (AMR) device was modified to allow testing different fluid flow waveforms, with different blow fractions (i.e., the fraction of the AMR cycle when there is fluid flow in the regenerators). The different values of blow fraction were generated using different cam rings that actuate the poppet valves at the inlet and outlet of the regenerators, controlling how long the valves stay open and the number of valves open at the same time. Results showed that smaller blow fractions yield higher values of temperature span for fixed flow rate and cooling capacity, but lower values of coefficient of performance for the same conditions. An analysis of the shaft and pumping powers showed that shorter blow fractions cause higher pressure drop and higher torque oscillations and mechanical vibrations. The highest value of second-law efficiency of 19.1% was obtained for the largest blow fraction tested (80%). Designs for magnetic refrigerators where the fluid flow waveform can change during operation are also discussed in this paper. [ABSTRACT FROM AUTHOR]

Bonded plates made by hot pressing La 0.85 Ce 0.15 Fe 11.25 Mn 0.25 Si 1.5 H y particles and resin have been tested as active magnetic regenerators in a small scale magnetocaloric device. Firstly, the plates were carefully characterised magnetically and thermally. The plates were prepared with 5 wt% resin, and from density measurements it was found that the volume ratio of the magnetocaloric material in the plates was 0.53, due to the resin and porosity. The best operating conditions for the plate regenerator were determined at which a temperature span of 6.4 K was measured along the plates. [ABSTRACT FROM AUTHOR]

La nécessité de réduire les émissions de dioxyde de carbone (CO2) a conduit à revaloriser les moteurs à combustion externe fonctionnant selon le cycle de Stirling. Les moteurs Stirling connaissent depuis peu une vogue nouvelle, car ils sont silencieux, non polluants, acceptent tout type de chaleur externe et demandent peu de maintenance. Ce moteur a été utilisé avec succès pour la conversion de l’énergie solaire en électricité par la technologie dite ‘Dish Stirling System’ qui utilise un moteur Stirling placé au foyer d’un concentrateur parabolique. Dans cette étude, une modélisation dynamique d’un moteur Stirling de type gamma basée une approche quasi stationnaire a été présentée. Ce modèle, qui prend en compte les différentes pertes thermiques et mécaniques dont le moteur Stirling est le siège, a conduit à l’écriture d’important système d’équation algébro différentielles. Le programme de calcul développé sous Matlab a permis, dans le but d’améliorer les performances du moteur Stirling, d’optimiser les paramètres géométriques et physiques, tels que la géométrie des échangeurs, la température du réchauffeur et du refroidisseur, les volumes morts et la vitesse de rotation.

A novel rotary magnetic refrigerator was designed and built at the Federal University of Santa Catarina (UFSC). The optimized magnetic circuit is a two-pole system in a rotor-stator configuration with high flux density regions of approximately 1 T. Eight pairs of stationary regenerator beds filled with approximately 1.7 kg of gadolinium spheres (425–600 µm diameter) were placed in the magnetic gap. Two low-friction rotary valves were developed to synchronize the hydraulic and magnetic cycles. The valves were positioned at the hot end to avoid heat generation in the cold end. In this work, experimental results are presented as a function of the operating frequency, fluid flow rate, hot reservoir temperature and thermal load. The performance of the device was evaluated in terms of the coefficient of performance (COP) and overall second-law efficiency ( η 2 nd ). The maximum no-load temperature span was 12 K at 1.5 Hz and 150 L h −1 , and the maximum zero-span cooling power was 150 W at 0.8 Hz and 200 L h −1 . For a thermal load of 80.4 W, at 0.8 Hz and 200 L h −1 , the device generated a temperature span of 7.1 K, with a COP of 0.54 and η 2 nd of 1.16%. [ABSTRACT FROM AUTHOR]

The interest of the scientific community regarding magnetic refrigeration at room temperature is constantly growing. In recent years, there has been an increase in the experimental work relating to both new prototypes and new magnetocaloric materials. The magnetic refrigerators built to date still have some limitations that make them uncompetitive when compared with conventional vapour compression systems. However, among the different configurations realized, one can recognize that rotary devices, having rotating magnets and static regenerators, are of particular interest because of their good energy performances. In this paper, we report an experimental investigation on the identification of the energy performances of a Rotary Permanent Magnet Magnetic Refrigerator. Employing 1.20 kg of gadolinium and operating at a temperature of heat rejection equal to 296 K, the system was subjected to different operating conditions obtained by varying the thermal load, volumetric flow rate of the regenerating fluid and cycle frequency. [ABSTRACT FROM AUTHOR]

Les problèmes énergétiques et d’environnement et l’abondance d’énergie solaire gratuite en Tunisie, incitent à développer l’étude du moteur Stirling à piston libre à énergie solaire ‘FPSE’. C’est un moteur à cogénération. Cette étude nécessite plusieurs étapes de modélisations et de simulation numérique. Les équations thermodynamiques et thermiques du moteur sont introduites dans le modèle dynamique, qui forme un système d’équations non linéaires. L’étude de stabilité du moteur examine les zones de travail stable et instable. Une programmation contrôlée permet de définir un moteur performant.

Magnetic refrigeration has played an important role in the scientific landscape in recent years and could potentially be an alternative to vapour compression technology. Although new prototypes have recently been developed and new material refrigerants have been tested, there is still no equipment that can be used in the refrigeration industry. In the present work, we demonstrate how magnetic refrigeration can be applied to climate system environments by combining the technology of magnetic refrigeration with that of low temperature geothermal energy. Thus, we introduce the concept of GeoThermag. After describing the GeoThermag system in detail, we report experimental results that demonstrate the validity of this application. These experimental tests were obtained by using a magnetic refrigerator that was connected to a geothermal probe. Using 1.20 kg of gadolinium, we found that the GeoThermag system configured in this manner is capable of providing cold water to feed a radiating panel and to develop a cooling capacity of 190 W with a COP of 2.20. [ABSTRACT FROM AUTHOR]

A one-dimensional model of a parallel-plate active magnetic regenerator (AMR) is presented in this work. The model is based on an efficient numerical scheme which has been developed after analysing the heat transfer mechanisms in the regenerator bed. The new finite difference scheme optimally combines explicit and implicit techniques in order to solve the one-dimensional conjugate heat transfer problem in an accurate and fast manner while ensuring energy conservation. The present model has been thoroughly validated against passive regenerator cases with an analytical solution. Compared to the fully implicit scheme, the proposed scheme achieves more accurate results, prevents numerical errors and requires less computational effort. In AMR simulations the new scheme can reduce the computational time by 89%. [ABSTRACT FROM AUTHOR]

Abstract: A thermodynamic analysis is performed on open, regenerated, inverse air-cycles, focussing on low temperature refrigeration, in order to provide general optimization criteria, support for a rational configuration choice and potential performance improvement for this specific application. The effect of high regenerator effectiveness (0.95) is explored, showing that it may double the air cycle COP in the case at hand. Low and high pressure configurations (i.e. featuring only one heat exchanger on the cold or hot cycle side) are compared. High pressure configuration, normally preferred in the field of low temperature refrigeration, has a lower efficiency, but the gap reduces as regenerator effectiveness increases. Avoidance of a cold heat exchanger eliminates frosting problems and power input for the circulation fan, so that the small COP decrease suffered by the high pressure cycle can easily be compensated for and eventually yield higher average plant efficiency. The feasibility of such a highly effective regenerator, already reported in the literature, is demonstrated using classic Kays and London (1964) data. [Copyright &y& Elsevier]

Abstract: In this paper, the development of the tandem reciprocating room-temperature active magnetic regenerative refrigerator and the numerical simulation for the effect of the dead volume are presented. The dead volume effect is analyzed by establishing a one-dimensional time-dependent model for the active magnetic regenerator (AMR). The cooling power at the mass flow rate of 5 g s−1 water and a temperature span of 20 K is reduced from 4 W to 2 W when the length of the dead volume (D DV = 12 mm) is increased from 15 mm to 30 mm. The numerical results indicate that the minimization of dead volume facilitates the improvement of the AMR performance. In particular, the components and the parameters of AMR system are demonstrated. The printed circuit heat exchangers (PCHEs) are employed as the warm end heat exchangers in order to minimize the dead volume of the system. The experimental apparatus includes two active magnetic regenerators containing 186 g of Gd spheres. The maximum no-load temperature span of 26.8 K and a maximum cooling power of 33 W at a zero temperature span were obtained with the frequency of 0.5 Hz under the maximum field of 1.4 T. [Copyright &y& Elsevier]

Abstract: The paper presents the numerical optimization of a packed-bed and a parallel-plate AMR with gadolinium as the magnetocaloric material. The diameter of the spheres and the length of the packed-bed AMR, and the plate thickness, the spacing between the plates (porosity) and the length of the parallel-plate AMR, were varied and optimized. The results reveal that for the considered conditions the optimum length of the packed-bed AMR should be 20 mm or less at higher operating frequency (3 Hz) and 40 mm at lower operating frequency (0.5 Hz) and the corresponding optimum sphere diameter should be between 0.07 mm (with regard to the cooling load) and 0.17 mm (with regard to the COP). The parallel-plate AMR should consist of plates that are as thin as possible, with a spacing between the plates of 0.035 mm (with regard to the cooling load) and 0.075 mm (with regard to the COP). [Copyright &y& Elsevier]

Abstract: The behavior of active magnetic regenerators (AMR) can be described by means of a one-dimensional set of equations. A lot of geometrical, thermo-physical and magnetic parameters influence the behavior and performance of an AMR, together with external controls and operating parameters. Literature data on AMR performances, both experimental and numerical, are given in different conditions and configurations, so that a consistent comparison among different results is not straightforward, and sometimes even not possible. In this paper the most relevant parameters are outlined, by means of a derivation of the dimensionless 1-D AMR equations. The resulting reduced number of key parameters simplifies the performance optimization procedure. Moreover, if the proposed dimensionless set of parameters is reported each time in corresponding scientific work, a comparison of experimental or/and numerical results would become much more feasible and easy to be performed. [Copyright &y& Elsevier]

Abstract: In this paper the field equations of compressible oscillating flow in the regenerator of Pulse Tube Refrigerators (PTRs) are solved. To obtain an analytical solution, successive approximation technique is applied to continuity, momentum, gas and matrix energy equations and ideal gas equation of state. In this respect, the flow field variables are expanded to second-order unsteady terms. To introduce the influence of consecutive terms in the expansions, a comparative study is conducted on first unsteady, second steady and second unsteady terms. The proposed model presents a powerful analytical tool, applicable to oscillating flow analysis in porous media and rapid optimization of the pulse tube cycle. Results proved that expanding the terms to second-order ones can enhance the solution precision considerably. Friction factor and Nusselt number for different meshes are proposed based on the second-order analytical solution. [Copyright &y& Elsevier]

Abstract: Active magnetic regenerator (AMR) refrigerators represent an alternative to vapor compression technology and have great potential in realizing cooling devices with high efficiency, which are highly desirable for a broad range of applications. The technology relies on the magnetocaloric effect in a solid refrigerant rather than the temperature change that occurs when a gas is compressed/expanded. This paper presents the general considerations for the design and construction of a high frequency rotary AMR device. Experimental results are presented at various cooling powers for a range of operating conditions near room temperature. The device exhibited a no-load temperature span of over 25 K and can absorb a 100 W cooling load at a 20.5 K temperature span. [Copyright &y& Elsevier]

Abstract: The primary objective of this paper is to quantify the impact of the internal magnetic field and reversibility of the magnetocaloric effect on the numerical evaluation of the thermal performance of a parallel-plate active magnetic regenerator. To this end, direct measurements of the adiabatic temperature change of commercial-grade gadolinium samples were carried out for an applied field change of 1.65 ± 0.03 T (for both magnetization and demagnetization) and temperatures between 283 and 303 K. The tests were carried out in a specially constructed apparatus and the results were in good agreement with the literature. The data were incorporated into a mathematical model for solving the fluid flow and conjugated heat transfer in the parallel-plate regenerator. It was found that if demagnetization phenomena (i.e., the demagnetization factor and the reversibility of the magnetocaloric effect) are not take properly into account, the thermal performance of the regenerator can be severely over-predicted. [Copyright &y& Elsevier]

Abstract: Magnetic refrigeration promises to be a breakthrough technology in the field of refrigeration at room temperature. Several magnetic refrigerator prototypes have been developed by research groups, with different embodiments and process thermodynamics. This short paper follows an idealized line connecting, from a conceptual rather than historical point of view, the different geometries, and proposes a classification based essentially on the type of magnetic source, the type of magnetocaloric material, and the relative motion of the active elements of the device. The proposed taxonomy is then applied to some prototype presented in literature, showing its potential to give a comprehensive description of magnetic refrigeration devices by means of a twelve digit string. [Copyright &y& Elsevier]

Abstract: This paper evaluates the thermal behavior of a magnetic-Brayton-based parallel plate reciprocating active magnetic regenerator (AMR). A time-dependent, 2D model of the fluid flow and the coupled heat transfer between the working fluid and the solid refrigerant (gadolinium) is proposed. A hybrid calculation method which consists of an analytical solution for the flow and a numerical solution for the thermal field has been adopted. Results for the cooling capacity as a function of the temperature span and mass flow rate agree well with trends observed in experimental data and other theoretical models available in the literature. The volume of fluid displaced through the channels during the isofield processes influences significantly the AMR performance. For a cycle frequency of 1 Hz, the cycle-averaged cooling capacity reaches a maximum when the utilization factor is 0.1 and the displaced fluid volume equals 62% of the fluid volume of the AMR. [Copyright &y& Elsevier]

Abstract: Active magnetic regenerative (AMR) systems are being investigated because they represent a potentially attractive alternative to vapor compression technology. The performance of these systems is dependent on the heat transfer and pressure drop performance of the regenerator geometry. Therefore this article studies the effects of regenerator geometry on performance for flat plate regenerators. This paper investigates methods of improving the performance of flat plate regenerators for use in AMR systems and studies how manufacturing variation affects regenerator performance. In order to eliminate experimental uncertainty associated with magnetocaloric material properties, all regenerators are made of aluminum. The performance of corrugated plates and dimpled plates are compared to traditional flat plate regenerators for a range of cycle times and utilizations. Each regenerator is built using 18 aluminum plates with a 0.4 mm thickness, which allows their performance to be compared directly. [Copyright &y& Elsevier]

Abstract: An expression is determined for the mass of the magnet and magnetocaloric material needed for a magnetic refrigerator and these are determined using numerical modeling for both parallel plate and packed sphere bed regenerators as function of temperature span and cooling power. As magnetocaloric material Gd or a model material with a constant adiabatic temperature change, representing an infinitely linearly graded refrigeration device, is used. For the magnet a maximum figure of merit magnet or a Halbach cylinder is used. For a cost of $40 and $20 per kg for the magnet and magnetocaloric material, respectively, the cheapest 100W parallel plate refrigerator with a temperature span of 20K using Gd and a Halbach magnet has 0.8kg of magnet, 0.3kg of Gd and a cost of $35. Using the constant material reduces this cost to $25. A packed sphere bed refrigerator with the constant material costs $7. It is also shown that increasing the operation frequency reduces the cost. Finally, the lowest cost is also found as a function of the cost of the magnet and magnetocaloric material. [Copyright &y& Elsevier]

Abstract: The present paper describes the design, operation and preliminary results of an active magnetic regenerator test machine. The regenerator consists of twenty eight 0.85 mm thick parallel gadolinium (Gd) plates that form 0.1 mm thick parallel channels with an effective length of 126 mm. The working fluid is water and the magnetic field source is a Halbach array with a maximum flux density of 1.65 T. A maximum temperature span between the hot and cold ends of the regenerator (∆T REG) of 4.45 K and a maximum cooling capacity of 3.9 W were measured in tests without and with a thermal load, respectively. The behavior of ∆T REG as a function of the utilization factor and of the temperature of the hot source is explored in the manuscript. The experimental results are discussed in the light of the fluid flow and heat transfer phenomena taking place in the regenerator. [Copyright &y& Elsevier]

Abstract: A new, fast and flexible, time-dependent, one-dimensional numerical model was developed in order to study in detail the operation of an active magnetic regenerator (AMR). The model is based on a coupled system of equations (for the magnetocaloric material and the heat-transfer fluid) that have been solved simultaneously with the software package MATLAB. The model can be employed to analyze a wide range of different operating conditions (mass-flow rate, operating frequency, magnetic field change), different AMR geometries, different magnetocaloric materials and heat-transfer fluids, layered and single-bed AMRs, etc. This paper also presents an optimization of the AMR’s geometry, where the AMR consists of a packed-bed of grains (spheres) of gadolinium (Gd). The optimization of the mass-flow rate and the operating frequency of the AMR were performed by studying five different diameters of Gd spheres. [Copyright &y& Elsevier]

Abstract: Magnetic refrigeration is a potentially environmentally-friendly alternative to vapor compression technology because it has a potentially higher coefficient of performance and does not use a gaseous refrigerant. The active magnetic regenerator refrigerator is currently the most common magnetic refrigeration device for near room temperature applications, and it is driven by the magnetocaloric effect in the regenerator material. Several magnetocaloric materials with potential magnetic refrigeration applications have recently been developed and characterized; however, few of them have been tested in an experimental device. This paper compares the performance of three magnetocaloric material candidates for AMRs, La(Fe,Co,Si)13, (La,Ca,Sr)MnO3 and Gd, in an experimental active magnetic regenerator with a parallel plate geometry. The performance of single-material regenerators of each magnetocaloric material family were compared. In an attempt to improve system performance, graded two-material regenerators were made from two different combinations of La(Fe,Co,Si)13 compounds having different magnetic transition temperatures. One combination of the La(Fe,Co,Si)13 materials yielded a higher performance, while the performance of the other combination was lower than the single-material regenerator. The highest no-load temperature span was achieved by the Gd regenerator. [Copyright &y& Elsevier]

Abstract: A traveling wave thermoacoustic refrigerator was designed, constructed, and tested. This refrigerator was composed of a linear motor, a branched tube, and a looped tube. A regenerator, composed of many screen meshes, was installed inside the looped tube. When the linear motor delivers an acoustic wave to the branched and looped tubes, heat pumping occurs along the regenerator. In this work, the regenerator radius and position were numerically optimized and the performance of the optimized refrigerator was measured. At the optimized values of regenerator radius and position, the refrigerator achieves a minimum cold temperature of 232 K and about 20% of the Carnot coefficient of performance at 265 K. [Copyright &y& Elsevier]

Abstract: Magnetic refrigeration (MR) using permanent magnets is being investigated for near-room temperature applications. An MR prototype is described and results using gadolinium as refrigerant are presented. Important design features are simple sealing, compactness, high operating frequencies, and ease of use. Using a total of 110 g of refrigerant, the device produces a maximum temperature span under no thermal load of 29 °C, and 10 °C under 50 W. The overall COP determined by using the power to the drive motor is between 0.3 and 0.8 under most operating conditions and temperature spans. The maximum COP measured is 1.6 with a span of 2.5 °C when operating at 1.4 Hz and utilization of 1.28. If the inefficiency of the motor is removed the maximum COP is 2.2, and, when the magnet drive losses are excluded, the maximum COP becomes 10. The peak specific exergetic cooling power is 0.085 W T−1 cm−3. [Copyright &y& Elsevier]

Abstract: In order to obtain a better reliability, consistency and accuracy of results obtained with a numerical simulation of an AMRR (active magnetic regenerator refrigerator), a dimensionless numerical model was developed, which can equally be used for determination of regenerator’s heat transfer coefficient and simulation of passive heat regenerators or AMRR operation. Regenerator’s heat transfer coefficient α f, is a crucial input parameter in the simulation of AMRR operation and has a primal effect on the outcome of a solution. This paper deals with a derived dimensionless model and discusses errors involved when using different models for heat transfer coefficient and AMRR operation simulation. [Copyright &y& Elsevier]

Abstract: A two-dimensional numerical heat transfer model is used to investigate an active magnetic regenerator (AMR) based on parallel plates of magnetocaloric material. A large range of parameter variations are performed to study the optimal AMR. The parameters varied are the plate and channel thicknesses, cycle frequency and fluid movement. These are cast into the non-dimensional units utilization, porosity and number of transfer units (NTU). The cooling capacity vs. temperature span is mapped as a function of these parameters and each configuration is evaluated through the maximum temperature span and exergy. The results show that the optimal AMR should have a utilization in the range 0.2–1 and an NTU higher than 10 and not necessarily more than 30. It is concluded that parallel plate-based regenerators face significant challenges in terms of manufacturability. However, the benefit of parallel plate regenerators is a very low pressure drop, which is needed for high performance. [Copyright &y& Elsevier]

Abstract: Active Magnetic Regeneration (AMR) is a configuration that allows magnetic refrigeration to be suitable also for room temperature applications. This work is intended to detect, by means of a 1-D numerical model, the influence on the regenerator performances of the working condition ambient temperature (T CURIE ±20K) and of the operating parameters fluid mass flow rate (utilization factor 0.5÷3.5) and cycle frequency (0.1÷0.6Hz). Simulations show that, tuning the fluid mass flow rate, a gadolinium AMR (395g, f =0.25Hz, ΔB =1.7T) can reach a maximum cooling capacity of 130W and a 40W cooling power over a temperature span of 30K. A COP of 5 can also be achieved with a temperature span of 30K and a cooling power of 35W. Frequency has a weak influence on the AMR''s COP, while the ambient temperature is crucial. The system loses the 60% of cooling capacity if the ambient temperature is 20K away from the material Curie temperature. [Copyright &y& Elsevier]

Abstract: For providing good performance of dehumidifier and regenerator with certain dimensions, a new type of internally cooled/heated dehumidifier/regenerator based on the plate–fin heat exchanger (PFHE) was designed. To investigate the behavior of the new equipment, an experimental setup was established in an environment chamber with regulable temperature and humidity air. By the internally cooled dehumidification testing, effects of the cooling water temperature, the air flow rate and the desiccant temperature on the dehumidification performance and the cooling efficiency were presented. The behavior of internally cooled dehumidification process was compared with that of the adiabatic dehumidification process. The results suggested that the cooling efficiency decreased with the increasing of the cooling water temperature and desiccant with low temperature could bring more mass transfer coefficients. There is an optimal air flow rate to achieve the maximum absolute humidity decrease of the air. By the internally heated regeneration testing, effects of the air flow rate and the desiccant inlet temperature on the regeneration performance and air outlet parameters were discussed and also compared with those of the adiabatic regeneration process. It was concluded that the regeneration efficiency of internally heated regeneration was more than that of the adiabatic regeneration, and the internally heated regenerator could offer better thermal performance. [Copyright &y& Elsevier]

Abstract: A time-dependent, two-dimensional mathematical model of a reciprocating Active Magnetic Regenerator (AMR) operating at room-temperature has been developed. The model geometry comprises a regenerator made of parallel plates separated by channels of a heat transfer fluid and a hot as well as a cold heat exchanger. The model simulates the different steps of the AMR refrigeration cycle and evaluates the performance in terms of refrigeration capacity and temperature span between the two heat exchangers. The model was used to perform an analysis of an AMR with a regenerator made of gadolinium and water as the heat transfer fluid. The results show that the AMR is able to obtain a no-load temperature span of 10.9K in a 1T magnetic field with a corresponding work input of 93.0kJm−3 of gadolinium per cycle. The model shows significant temperature differences between the regenerator and the heat transfer fluid during the AMR cycle. This indicates that it is necessary to use two-dimensional models when a parallel-plate regenerator geometry is used. [Copyright &y& Elsevier]

Abstract: There has been a demand for developments of the ejector refrigeration systems using low grade thermal energy, such as solar energy and waste heat. In this paper, a novel regenerative ejector refrigeration cycle was described, which uses an auxiliary jet pump and a conventional regenerator to enhance the performance of the novel cycle. The theoretical analysis on the performance characteristics was carried out for the novel cycle with the refrigerant R141b. Compared with the conventional cycle, the simulation results show that the coefficient of performance (COP) of the novel cycle increases, respectively, by from 9.3 to 12.1% when generating temperature is in a range of 80–160°C, the condensing temperature is in a range of 35–45°C and the evaporating temperature is fixed at 10°C. Especially due to the enhanced regeneration with increasing the pump outlet pressure, the improvement of COP of the novel cycle is approached to 17.8% compared with that in the conventional cycle under the operating condition that generating temperature is 100°C, condensing temperature is 40°C and evaporating temperature is 10°C. Therefore, the characteristics of the novel cycle performance show its promise in using low grade thermal energy for the ejector refrigeration system. [Copyright &y& Elsevier]

Abstract: The operation behaviour of an active magnetic regenerator (AMR) with a wavy-structure, or a honeycomb-like regenerator bed was numerically investigated. The thermodynamic model was applied to a static regenerator and – in a generalized version – to a rotary type. The models take two-dimensional unsteady heat conduction in the magnetic material during the four basic processes of the AMR cycle into account. The numerical results were used to determine optimal arrangements of different magnetic materials in order to obtain larger temperature spans between both ends of the porous beds. Furthermore, a first study of magnetic flux lines in a porous rotary heat exchanger was performed. [Copyright &y& Elsevier]

Linear thermoacoustic theory is applied to study the regenerator of a Stirling machine or a Pulsed gas refrigerator regenerator filled with a stack of beds in a cylindrical envelope. Pressure, velocity and temperature amplitude are calculated, and a formulation of the thermal time constant of the regenerator is proposed. A global equivalent electrical scheme of the regenerator is also deduced. The total axial energy flux expression is demonstrated and the influence of the thermal time constant and of the various impedance is discussed. Axial variations of the energy flux, which correspond to thermal exchanges with the surroundings are expressed through consideration of thermoacoustical phenomena: thermal relaxation of the acoustical energy, viscous losses, thermoacoustical source/sink. Theoretical results are analysed to comment on temperature profiles along the regenerator in a periodical regime. [Copyright &y& Elsevier]

The circular duct between the cylinder and displacer serves as a regenerator in free-piston Stirling engines. The cylinder wall is fixed and the displacer wall is in reciprocating motion during the steady operation of the engine. The basic equations of the working fluid and regenerative duct are derived using the Lagrangian method in terms of the displacement of the displacer, so that time does not appear in the equations. A relation is derived between the cylinder and displacer wall temperatures to obtain the initial wall temperature distributions. A computer program is written in fortran and the governing equations, which include the pressure fluctuations due to the flow reversals, are solved numerically using a finite difference method. The results and discussion are presented. [Copyright &y& Elsevier]

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