Stirling-cycle rotating magnetic refrigerators and heat engines for use near room temperature

Steyert, W.A.

doi:10.1063/1.325009

Cited by 115 publications

(34 citation statements)

References 5 publications

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“…Left: The negative of the isothermal entropy change in a MnFeP 1 − x As x sample with a transition temperature of 298 K and an applied fi eld ranging from 0.1 to 1.5 T. The curves were derived from isothermal magnetization measurements. Right: Entropy curves rescaled using Equation 33 . Although the material is fi rst order, a collapse to a single curve is seen.…”

Section: S(t H) = S Mag (T H) + S Lat (T ) + S El (T )mentioning

confidence: 99%

Materials Challenges for High Performance Magnetocaloric Refrigeration Devices

Smith

Bahl

Bjørk

et al. 2012

Advanced Energy Materials

497

262

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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.

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Section: S(t H) = S Mag (T H) + S Lat (T ) + S El (T )mentioning

confidence: 99%

Materials Challenges for High Performance Magnetocaloric Refrigeration Devices

Smith

Bahl

Bjørk

et al. 2012

Advanced Energy Materials

497

262

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“…The anomalous behavior of the magnetocaloric effect is closely related to the anomalous changes in the magnetic structure of solids that cause an unusual behavior of ∂M/∂T and C(T, H ), which carries over to both S M (T ) H and T ad (T ) H (see Equations 4,5,8,and 9). One of the most commonly observed MCE anomalies occurs when a material undergoes two or more successive magnetic orderings in close proximity to one another.…”

Section: Anomalous Magnetocaloric Effectmentioning

confidence: 99%

“…The adiabatic temperature change indirectly characterizes both the cooling capacity and the temperature difference between the cold and the hot ends of the refrigerator (generally a larger T ad corresponds to a larger cooling capacity of the material and to a larger temperature span of the refrigerator). It should be noted that the difference between the hot end and the cold end temperatures of a magnetic refrigerator greatly exceeds that of the maximum magnetocaloric effect in a properly designed active magnetic regenerator cycle (8)(9)(10)21). If both the magnetization and entropy are continuous functions of the temperature and magnetic field, then the infinitesimal isobaric-isothermal magnetic entropy change can be related to the magnetization (M ), the magnetic field strength (H ), and the absolute temperature (T ) using one of the Maxwell relations (23) …”

Section: S M (T ) H = S(t ) H F − S(t ) H I Tmentioning

confidence: 99%

“…The most interesting example is found in the Gd 5 (Si x Ge 1−x ) 4 alloys where 0 ≤ x ≤ 0.5 (39-42). Here, since the phase transition is of the first order, the |∂M/∂T| is larger than usual (but not infinite and undefined as could happen if the transition occurs infinitely fast at constant temperature, pressure and magnetic field) and, therefore, the magnetocaloric effect is also large (see Equations 4,5,8,and 9). In Figure 7 it is easy to see that increasing the magnetic field beyond 3 T hardly increases the maximum magnetocaloric effect, but continues to increase considerably the δT FWHM , which shifts the upper temperature limit of the MCE toward higher temperatures and, therefore, continues to increase the cooling capacity of the material.…”

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confidence: 99%

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Magnetocaloric Materials

Gschneidner

Pecharsky

2000

Annu. Rev. Mater. Sci.

1,238

568

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Key Words magnetocaloric effect, mixed lanthanide materials, 3d-materials amorphous alloys, manganites s Abstract In the last decade of the twentieth century there has been a significant increase in research on a more than 100-year old phenomenon-the magnetocaloric effect (MCE). As a result, many new materials with large MCEs (and many with lesser values) have been discovered, and a much better understanding of this magneto-thermal property has resulted. In this review we briefly discuss the principles of magnetic cooling (and heating); the measurement of the magnetocaloric properties by direct and indirect techniques; the special problems that can arise; and the MCE properties of the 4f lanthanide metals, their intra-lanthanide alloys and their compounds [including the giant MCE Gd 5 (Si x Ge 1−x ) 4 phases]; the 3d transition metals, their alloys and compounds; and mixed lanthanide-3d transition metal materials (including the La manganites). INTRODUCTIONCommercial and residential refrigeration is a mature, relatively low capital cost but a high-energy demand industry. Even the newest most efficient units operate well below the maximum theoretical (Carnot) efficiency, and few, if any, further improvements may be possible with the existing vapor-cycle technology. Magnetic refrigeration (MR), however, is rapidly becoming competitive with conventional gas compression technology because it offers considerable operating cost savings by eliminating the most inefficient part of the refrigerator-the compressor. In addition to its energy savings potential, MR is an environmentally sound alternative to vapor-cycle refrigerators and air conditioners. Most modern refrigeration systems and air conditioners still use ozone-depleting or global-warming volatile liquid refrigerants. Magnetic refrigerators use a solid refrigerant(s) and common heat transfer fluids (e.g. water, water-alcohol solution, air, or helium gas) with no ozone-depleting and/or global-warming effects.Magnetic refrigeration is based on the magnetocaloric effect (MCE). The MCE, or adiabatic temperature change ( T ad ), which is detected as the heating or the cooling of magnetic materials due to a varying magnetic field, was originally discovered in iron by Warburg (1). The thermodynamics of the MCE was understood 0084-6600/00/0801-0387$14.00 387 Annu. Rev. Mater. Sci. 2000.30:387-429. Downloaded from www.annualreviews.org by Fordham University on 11/22/12. For personal use only. 388GSCHNEIDNER PECHARSKY by Debye (2) and by Giauque (3), both of whom independently suggested that it could be used to reach low temperatures in a process known as adiabatic demagnetization. Soon after this discovery, an operating adiabatic demagnetization refrigerator was constructed and utilized by Giauque & McDougal (4) to reach 0.53, 0.34, and 0.25 K starting at 3.4, 2.0, and 1.5 K, respectively, using a magnetic field of 0.8 T and 61 g of Gd 2 (SO 4 ) 3 ·8H 2 O as the magnetic refrigerant. The MCE is intrinsic to any magnetic material. In the case of a ferromagnet near its mag...

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“…He applied a regenerative Stirling-like thermodynamic cycle (very similar to AMR), which significantly increased the temperature span of the device [4,5]. A few years later Steyert [6] and Barclay and Steyert [7] presented and explained the active magnetic regenerator, which remains the most applied method for the exploitation of the magnetocaloric effect at room temperature. Furthermore, all prototypes of magnetic refrigerators built since then have been based on the AMR process [5].…”

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confidence: 99%

Active Magnetic Regeneration

Kitanovski

Tušek

Tomc

et al. 2014

Green Energy and Technology

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It is well known that the magnetocaloric effect of most magnetocaloric materials at moderate magnetic fields (up to 1.5 T) is limited to a maximum adiabatic temperature change of 5 K [1,2]. This value is not sufficient for such materials to be directly implemented into a practical cooling or heating device where temperature span over 30 K is required. Therefore, in order to increase the temperature span, one and so far the best option is for a heat regenerator to be included in the magnetic thermodynamic cycle.A heat regenerator is a type of indirect heat exchanger where the heat is periodically stored and transferred from/to a thermal storage medium (regenerative material) by a working (heat-transfer) fluid. The regenerative material usually has a porous structure, through which a working fluid is pumped in an oscillatory, counter-flow manner (which is more efficient than a parallel flow system). During the 'hot period', a warmer fluid flows through the regenerative material, which cools down, while the material heats up. As a result, heat is stored in the material. During the 'cold period', a cooler fluid flows through previously heated regenerative material, so the fluid heats up, while the material cools down. The heat is therefore transferred back to the fluid (the same fluid or a different one) at a different phase of the thermodynamic cycle. After a certain number of such steps, a periodic steady state is reached and, as a result, a temperature profile can be established along the length of the regenerator [3].The need to apply heat regenerators in a magnetic refrigerator was already realized by Brown [4] in the first prototype of a magnetic refrigerator, built in 1976. He applied a regenerative Stirling-like thermodynamic cycle (very similar to AMR), which significantly increased the temperature span of the device [4,5]. A few years later Steyert [6] and Barclay and Steyert [7] presented and explained the active magnetic regenerator, which remains the most applied method for the exploitation of the magnetocaloric effect at room temperature. Furthermore, all prototypes of magnetic refrigerators built since then have been based on the AMR process [5]. An AMR, unlike a passive (regular) heat regenerator, contains a magnetocaloric material as the regenerative material. It has a double function in a magnetic regenerator, i.e. it works as a regenerator and enables an increase in the temperature span as well as working as a coolant and generating/absorbing heat between the particular phases of the

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Stirling-cycle rotating magnetic refrigerators and heat engines for use near room temperature

Cited by 115 publications

References 5 publications

Materials Challenges for High Performance Magnetocaloric Refrigeration Devices

Materials Challenges for High Performance Magnetocaloric Refrigeration Devices

Magnetocaloric Materials

Active Magnetic Regeneration

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