Ideal magnetocaloric effect for active magnetic regenerators (original) (raw)
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Thermodynamic investigations of optimum active magnetic regenerators
Cryogenics, 1998
The performance of an active magnetic regenerator refrigerator (AMRR) cycle depends strongly on the behaviour of the adiabatic magnetization temperature change (⌬T) as a function of material temperature (T) in the flow direction of the regenerator. In this study, we consider regenerators which satisfy the condition: ⌬T = T H (T/T H) for = 0 to 3, being a constant, and T H being the hot source temperature. The refrigeration capacities and the thermal efficiencies of this family of regenerators were evaluated through a numerical simulation of a complete thermodynamic AMR cycle. The Gd-Dy alloys have been chosen as constituent materials for the regenerators operating over the temperature range 300 K to 200 K. The regenerators' compositions were determined numerically and their thermomagnetic properties were calculated using the molecular field theory and the Debye approximation. Based on the simulation results, it was concluded that no unique ideal ⌬T(T) profile is required for the reversible case, but any monotonically increasing profile (i.e. Ն 0.5) seems adequate. For the irreversible case, quasi-linear profiles (i.e. 1 Յ Յ 2) were found to be the ones most suitable.
Thermodynamic Study of the Active Magnetic Regenerative Refrigeration in Transitional Regime
2015
Magnetic refrigeration is an emerging technology based on the magnetocaloric effect. In this paper, the magnetocaloric effect is remembered. The components of magnetic refrigeration system are described. An analogy between magnetic refrigeration and conventional refrigeration is done concerning the steps and the original work received by the system. A regenerator positioned between the hot source and the cold source increases the efficiency of the refrigeration system, from which the active magnetic regenerative refrigeration (AMRR) is studied. Thus a thermodynamic study is developed and thermal regenerator study transitional regime is done. From the results obtained by the numerical calculation, the difference of temperature between hot and cold sides reaches a limit after a certain number of cycles. This number of cycles (Nc) necessary to wait for the permanent regime depends on the difference in temperature hot side and cold side (∆T), the flow regime and the magnetocaloric effec...
Evaluation of fundamental performance on magnetocaloric cooling with active magnetic regenerator
Applied Thermal Engineering, 2011
This paper deals with the cooling characteristics of a magnetocaloric cooling technique refrigerator an active magnetic regenerator (AMR). The AMR-based refrigeration cycle, which has a thermal storage process and a regeneration process, realizes a practical magnetic refrigerator running near room temperature. The AMR cycle has four sequential processes: adiabatic magnetization, fluid flow, adiabatic demagnetization, and fluid flow. We devise an appropriate simulation model of the cyclic heat transfer process inside the particle bed as the target AMR. Then, the temperature profile inside the AMR particle bed and the cooling characteristics of the room-temperature magnetic regenerator are studied analytically. In addition, the validity of the analytical model by molecular field approximation theory is verified by comparing the experimental results with the analytical results. The results show that, when a higher magnetic field is applied to the magnetocaloric material, a greater temperature difference is obtained.
Cryogenics, 2011
AMRR cycle Layered bed Gd Àx Tb 1Àx alloys Gd Àx Dy 1Àx alloys a b s t r a c t Magnetic refrigeration is an emerging technology based on the magnetocaloric effect in solid-state refrigerants. The active magnetic regenerative refrigeration (AMRR) cycle is a special kind of regenerator for the magnetic refrigerator, in which 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. The performance of an AMRR cycle depends strongly on the behaviour of the adiabatic magnetization temperature change as a function of material temperature in the flow direction of the regenerator. In the present paper, a practical model for predicting the performance and efficiency of an AMRR cycle has been developed. The model simulates both the ferromagnetic material and the entire cycle of an AMRR operating in conformity with a Brayton regenerative cycle. The model simulates different kinds of layered regenerators operating at their optimal operation point. The program study the Gd Àx Tb 1Àx alloys as constituent materials for the regenerator over the temperature range 275-295 K, and Gd x Dy 1Àx alloys in the temperature range 260-280 K. With this model, the refrigeration capacity, the power consumption and consequently the coefficient of performance can be predicted. The results show a greater COP for the refrigerator based on the magnetocaloric technology compared with the COP of a classical vapour compression plant working between the same thermal levels.
Analysis of room temperature magnetic regenerative refrigeration
International Journal of Refrigeration, 2005
Results of a room temperature magnetic refrigeration test bed and an analysis using a computational model are presented. A detailed demonstration of the four sequential processes in the transient magnetocaloric regeneration process of a magnetic material is presented. The temperature profile during the transient approach to steady state operation was measured in detail. A 5 8C evolution of the difference of temperature between the hot end and the cold end of the magnetocaloric bed due to regeneration is reported. A model is developed for the heat transfer and fluid mechanics of the four sequential processes in each cycle of thermal wave propagation in the regenerative bed combined with the magnetocaloric effect. The basic equations that can be used in simulation of magnetic refrigeration systems are derived and the design parameters are discussed. q
Review of Multi-Physics Modeling on the Active Magnetic Regenerative Refrigeration
Mathematical and Computational Applications, 2021
Compared to conventional vapor-compression refrigeration systems, magnetic refrigeration is a promising and potential alternative technology. The magnetocaloric effect (MCE) is used to produce heat and cold sources through a magnetocaloric material (MCM). The material is submitted to a magnetic field with active magnetic regenerative refrigeration (AMRR) cycles. Initially, this effect was widely used for cryogenic applications to achieve very low temperatures. However, this technology must be improved to replace vapor-compression devices operating around room temperature. Therefore, over the last 30 years, a lot of studies have been done to obtain more efficient devices. Thus, the modeling is a crucial step to perform a preliminary study and optimization. In this paper, after a large introduction on MCE research, a state-of-the-art of multi-physics modeling on the AMRR cycle modeling is made. To end this paper, a suggestion of innovative and advanced modeling solutions to study magn...
Applied Thermal Engineering, 2015
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Review on numerical modeling of active magnetic regenerators for room temperature applications
International Journal of Refrigeration, 2011
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 fields, 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.
International Journal of Air-Conditioning and Refrigeration, 2013
In the present study, a thermodynamic model is proposed to analyze and assess the performance, through energy and exergy, of a cascade active magnetic regenerative (AMR) refrigerator operation a regenerative Brayton cycle. This cascade refrigeration system works with Gd x Tb 1–x alloys as magnetic materials where the composition of the alloy varies for different stages. In this model, the heat transfer fluid considered is a water– glycol mixture (50% by weight). The refrigeration capacity, total power consumption, coefficients of performance (COP), exergy efficiency and exergy destruction rate of a cascade AMR refrigeration (AMRR) system are determined. To understand the system performance more comprehensively, a parametric study is performed to investigate the effects of several important design parameters on COP and exergy efficiency of the system.
Thermodynamics of magnetic refrigeration
International Journal of Refrigeration, 2006
A comprehensive treatment of the thermodynamics of cyclic magnetic refrigeration processes is presented. It starts with a review of the work, heat and internal energy of a magnetized specimen in a magnetic field, and a list of the thermodynamic potentials is given. These are based on the very recent discovery of an alternative Kelvin force. It is shown that this force is compatible with the internal energy proposed by Landau and Lifshitz. New formulas for the specific enthalpies are presented. Cyclic processes are discussed in detail, e.g. the Brayton, Ericsson and Carnot cycles. Magnetic refrigeration and magnetic heat pump cycles are preferably designed by applying the cascade or/and regeneration principle. Cascade systems allow wider temperature ranges to be obtained. The main objective of this article is to yield a theoretical basis for an optimal design of new magnetic refrigeration and heat pump devices. q