recent developments in room temperature active magnetic regenerative refrigeration.
Accept active magnetic regeneration refrigeration in February 23, 2007 (AMRR)
The system represents an alternative that is attractive to the environment, rather than a steam compression system that does not work fluid using carbon fluoride.
The concept of AMRR has previously been shown to be used for small-
Expand business applications.
However, the recent AMRR prototype using a more practical permanent has demonstrated that the AMRR system can generate cooling within a useful temperature range with relatively low magnetic fields.
In addition, a family of materials with large magnetic thermal effects and adjustable temperature has been developed;
These materials can be used to build a layered regeneration bed that may be lower cost and more performance than existing materials.
This paper reviews the latest developments in the field of room temperature magnetic refrigeration and discusses some design issues that may affect the actual system.
Active magnetic regeneration refrigeration (AMRR)
The system represents an attractive alternative to steam compression refrigeration and air
Air conditioning system.
The AMRR system does not use the working solution of carbon fluorine compounds;
Solid refrigerant is used instead.
Solid refrigerant, a magnetic heat material that communicates with the environment through a heat transfer fluid.
Since the evaporation pressure of Solid refrigerant is basically zero, there is no ozone consumption potential in the AMRR system (ODP)
No direct potential for global warming (GWP).
The heat transfer fluid is likely to be water and therefore has little impact on the environment.
In theory, a well
The designed AMRR system can compete with the steam compression system and is even more efficient than the steam compression system, provided that the volume of the active magnetic recycler is large enough.
The temperature and magnetic field of the thermodynamic magnetic thermal material of the AMRR cycle are highly coupled in some usually limited operating ranges;
This feature allows them to be used in energy conversion systems.
A thermodynamic substance can change its internal energy (U)
The result of work or heat, resulting in poor energy balance: dU = TdS dW (1)
The first item in equation 1 corresponds to the inflow of heat (TdS)
The second is the inflow of work (dW).
Generally speaking, work can flow in many forms (e. g.
Mechanical, Electrical, etc. ).
When only volumetric compression work is performed, a familiar basic property relationship describing the results of most fluids (P-V)is considered;
However, in magnetic thermal materials,[mu]. sup. 0]H)
Magnetic moment (M)
Ignore the work item lag effect in equation 1 (Guggenheim 1967). dU = TdS + [[mu]. sup. 0]HdM. (2)
Increasing the applied magnetic field of the magnetic material will align the magnetic poles, which requires work and reduce entropy.
Using this relationship between entropy, internal energy, and magnetic fields, it is possible to apply all the typical thermodynamic results and identities commonly used in a pure compressed material environment to magnetic heat materials.
For example, the relationship between Maxwell (Guggenheim 1967)
It can be used to describe the interaction between partial derivatives of properties, and magnetic heat materials will be characterized by a state equation that describes the magnetism as a function of temperature and an additional field. A temperature-
The entropy diagram of the magnetic material will include the line of the constant applied magnetic field, not the Isopress line;
However, the diagram is similar in other respects to a more familiar diagram describing the working fluid that can be compressed.
For example, Figure 1 shows the temperature-
Entropy diagram of 94% gd and 6% er, G [Alloy]d. sup. [0. 94]]E[r. sup. [0. 06]](Zimm et al. 2003).
A careful study of Figure 1 shows that by changing the applied magnetic field, the temperature of the magnetic material can be changed during the thermal insulation process.
Fig. 2 Change of thermal insulation temperature of G [d. sup. 0. 94]E[r. sup. [0. 06]]
When the magnetic field increases from 0 Tesla to 2 Tesla and from 0 Tesla to 5 Tesla.
Figure 2 shows the change of thermal insulation temperature (
This is a direct indicator of the magnetic thermal effect)
Depending on the initial temperature of the material, and only in a relatively limited temperature range can a large magnetic thermal effect be shown.
In a material like [d. sup. [0. 94]]E[r. sup. [0. 06]]
Showing the second one.
In the order phase transition above the magnetic order temperature, there is no magnetic stereo.
Generally speaking, when approaching the magnetic order temperature, the magnetic asymmetry will be zero.
In this case, it is an equal entropy process to be magnetized and demagnetized;
Therefore, when the material is subsequently demagnetized, its temperature will return to the original zerofield value. [
Figure 1 slightly]
Figure 2 reveals several details related to the practicalAMRR system.
First, the thermal insulation temperature changes are relatively small compared to the temperature span required for most actual cooling systems.
This feature requires the use of a production cycle in order to provide a cold load within a useful temperature range.
Second, the magnetic thermal effect is the largest in a relatively narrow temperature range.
In order to maximize the magnetic thermal effect and thus improve the performance of the AMRR system, it is better to build a regeneration bed from several materials with a Curie point temperature customized according to the local regeneration temperature. [
The magnetic cooling system is configured with an early magnetic cooler for extreme low temperatures and uses a heat-insulated demagnetic refrigeration (ADR)cycle.
Giauque and McDougall (1933)
The use of an ADR system to reach temperatures below 1k breaks the temperature barrier caused by previously compressed fluid properties.
The adr system used by them and other researchers consists of a solid magnetic hot alloy, which is magnetized using a constant temperature, places the material in contact with the heat reservoir, and then conducts thermal insulation and demagnetism.
All the materials in ADRcycle go through the same thermodynamic cycle, so the temperature increase is limited to the change of the thermal insulation magnetized temperature shown by the material.
ADR cycles also require complex thermal switches with limited capacity.
For these reasons, ADR cycles are not a practical alternative for commercial equipment close to room temperature.
Technical barriers related to ADR cycles have been overcome by the use of a recycler in active magnetic regeneration refrigeration (AMRR)cycle. Brown (1976)
The regenerative magnetic refrigerator was first constructed and showed that none can be provided using the regenerative magnetic refrigerator
The load temperature span is much larger than the thermal insulation temperature change of the magnetic heat material used to construct the heat-returning body. Greenet al (1986)
The first successful AMRR was built to achieve a temperature span of 40 k.
In the AMRR system, exposure to time-
Magnetic field and time of change-
Change flow of heat transfer fluid.
Each part of the bed experiences a unique cooling cycle and interacts with adjacent materials through a heat transfer fluid.
The final result of these cascade refrigeration cycles is the temperature increase, which is much larger than the temperature increase that the ADR cycle can achieve.
The AMRR cycle consists of four processes.
A conceptual diagram of the processes that constitute the operation of rotating AMRR, as described by Zimm et al. (2006)
, As shown in figure 3.
The area generator consisting of six beds is discussed here;
Figure 3 highlights one of the six beds and is considered in the following discussion.
By rotating the bed into a permanent magnetic field, the bed is magnetized, Figure 3a.
The magnetic thermal effect causes the material in the bed to rise in temperature when magnetized.
When the bed is in a magnetic field, it experiences a series of heat transfer fluids from the cold end to the hot end;
This flow causes heat suppression in the heat exchanger (Figure 3b)
Because the temperature of the fluid leaving the hot end is hotter than the ambient temperature.
When the bed rotates from a permanent , the bed is demagnetized (Figure 3c)
Causing the temperature of the bed to drop.
Then, when the recycler leaves the magnetic field, it experiences the flow of heat transfer fluid from the hot end to the cold end (Figure 3d)
, This causes the cold and heat exchanger to accept the cold load because the fluid temperature leaving the bed is less than the cold load temperature. [
Figure 3 slightly]
The development of magnetic thermal materials the properties of magnetic thermal materials used in the anAMRR system are mainly responsible for the system performance that can be achieved.
Review of recently developed Room materials
Brueck gives the temperature refrigeration (2005).
Recently, researchers have developed several promising materials with large magnetic thermal effects and adjustable dwell point temperatures that may be suitable for room temperature
Temperature Application (
Gschneidner and others. 2005).
Magnetic thermal materials usually have nonlinear properties that are highly temperature dependent;
Therefore, it is not simple to evaluate the relative properties of one material with another.
A rigorous comparison of the material would require that these properties be combined with a detailed model of the AMRR system, even so, the results will also depend on the geometry of the recycler, the operating temperature, the fluid properties of the heat transfer and several other system or operating parameters.
Although there is no simple set of properties that define the performance of the magnetic thermal material used in the AMRR, the two parameters that provide the most meaningful basis for comparison are varying with the temperature of the magnetized ([T. sub. ad])
The change of specific entropy with the magnetic intensity ([DELTA][s. sub. M]).
Many magnetic thermal materials exhibit magnetic lag, in which the properties of the materials depend on the history of the magnetic field.
The lag will reduce the performance of the AMRR system, and the lag should also be considered when selecting magnetic thermal materials.
The thermal conductivity of the magnetic thermal material also has an important impact on the performance of the amrrdevice, although not very intuitive.
Materials with a large thermal conductivity may result in regional generators plagued by large axial conduction, which may be the main loss mechanism for AMRRs.
However, by placing a low conductivity gasket in the generator, it is possible to reduce the coaxial conduction loss.
In contrast, in each cycle, materials with low conductivity do not fully interact with the heat transfer fluid;
The diffusion conduction wave that transmits energy between the substance and the fluid travels too slowly, so that the substance at the center of the solid matrix (e. g.
, In the center of a spherical particle)
No heat is involved in the AMRR cycle.
Renewable energy characterized by high mobilityto-
The solid heat transfer coefficient or high working frequency is particularly vulnerable to losses related to the temperature gradient inside the solid material (
Engel Brecht, etc. 2006a).
Therefore, materials with very high or very low thermal conductivity may not be suitable for some amrrapplication;
The threshold conductivity is strongly dependent on the specific geometry of the recycler being considered.
The Curie point refers to the temperature at which the material changes from ferromagnetism to normal magnetic state;
This temperature is important because the material exhibits the largest magnetic thermal effect near the Curie temperature.
There may be two types of magnetic phase changes in the inner point, first of all-
Orderly magnetic transition (FOMT)and second-
Orderly magnetic transition (SOMT).
For some materials, the moment of the material is aligned during the transition from the iron to the parameter network.
There is no discontinuous jump in the magnetism, and there is no potential heat in the transition related to the transition.
FOMT materials undergo both ordered and transition-related latent heat of the magnetic poles.
Some FOMT materials have undergone changes in crystals
Lattice related to the phase transition of the Curie point.
According to Gschneidner and others. (2005)
, The temperature change of some materials when they are magnetized is almost instantaneous (
In the order of nanoseconds).
However, for FOMT materials where the structure changes, during the crystal structure changes, the atoms are replaced, so when some FOMT materials are magnetized, the time required to achieve the temperature change may be several orders of magnitude larger than the time.
Scale related to SOMT materials.
This period of time is between the application or removal of the magnetic field and the relevant thermal response of the FOMT material, which may reduce the cycle performance by 30%--
50% when FOMT material is used in the AMRR working at a frequency of 1 to 10Hz.
However, according to Russekand Zimm (2006)
, FOMT materials with large magnetic thermal effect using cheaper raw materials may be more eco-friendly
It is more effective than SOMT materials such as Gd.
Figure 2 shows that the magnetic material only exhibits a large magnetic thermal effect in a narrow temperature range close to the temperature of the Curie point ([T. sub. Curie])
Therefore, the AMR consisting of a single magnetic material can maintain its potential high performance only in a small temperature range.
In order to maximize the magnetic thermal effect in a large temperature range, a regeneration bed consisting of several materials can be constructed with engineering spatial changes in its temperature, selected to match the local average generator temperature.
A recycler constructed of several magnetic thermal materials is called a layered recycler, and the amrr system utilizing a layered recycler has the potential to achieve higher system performance than a single recycler
Material AMRR system.
Therefore, researchers are working to develop a family of material compounds that have similar properties but whose curve temperatures can be changed by changing the material composition.
For example, the Curie temperature of Gd, Gd, and Dy alloys can be adjusted by changing the fraction of each element (
Gschneidner and others. 2005).
Gschneidner et al conducted a comprehensive review of the scanning of magnetic thermal materials. (2005).
This paper will discuss some of the most promising material families proposed by Gschneidner et al in the paper.
And recently developed materials not included in the review.
According to Allab and others. (2006)
The upper limit of the magnetic field strength that can be achieved by using a permanent is about 2 Tesla;
Therefore, the performance of magnetic materials is compared using magnetic field changes from 0 to 2 Tesla.
Table 1 lists a summary of the magnetic properties of selected materials.
Note that in Table 1, the lag is defined as the observed temperature change with the increase of the magnetic field, compared to the value increased with the decrease of the magnetic field.
Gd and its alloy Gd is a SOMT material with a Curie temperature of about 293 K.
It is the only pure substance with a dwell point near room temperature, showing significant magnetic thermal effects over a large temperature range. Dan\'kov et al. (1998)
The magnetic thermal properties of Gd were studied and the largest [DELTA][T. sub. ad]
About 5 years old.
8k when the direct measurement from 0 to 2 Tesla is magnetized using [DELTA][T. sub. ad].
The magnetic hyperstatic magnetism caused by gd is very low, dan \'kov and others.
It is reported that there is no detectable lag in a single gd crystal.
The thermal conductivity of Gd near room temperature is about 10 W/m. K (Fujieda et al. 2004).
Since gd has a larger magnetic thermal effect and a lower lag, it has been used in many prototype room temperature AMRR systems (Yu et al. 2003).
At room temperature, gd will offset in the presence of water, which may affect long periods of time
Long term performance and durability of the AMRR system.
However, Zhang et al. (2005)
It is found that adding sodium hydroxide to the water can eliminate this corrosion problem.
The actual AMRR system using gd may require some type of inhibitor to be added to the heat transfer fluid.
Gd can be with tb (Tb)(
Gschneidner andPecharsky 2000), dysprosium (Dy)(Dai et al. 2000), or erbium (Er)(Nikitin et al. 1985)
To reduce the temperature of the Curie point. Canepa etal. (2002)
Can be added to Gd to form [Gd. sub. 7][Pd. sub. 3]
, Has a higher dwell point than pure Gd.
All of these Gd alloys have a magnetic thermal properties similar to Gd, and these Gd alloy families can be used to build alayered recycler beds. G[d. sub. 5]S[i. sub. 4-x]G[e. sub. x]
Alloys composed of gd, silicon and ge exhibit a magnetic thermal effect significantly greater than gd and have phase change temperatures close to room temperature (
Pecharsky and Gschneidner 1997).
The Dwell temperature of the material can be adjusted by changing the ratio of silicon, and compounds with a wide dwell temperature can be synthesized (
Pecharsky and Gschneidner 1997 B).
Unlike gd, mostG [d. sub. 5]S[i. sub. 4-x][Ge. sub. x]
The compound is a FOMT material, and the entropy change is greater than gd-butis with the change of the magnetic intensity, occurring in a narrower temperature range.
TheFOMT involves changes in crystal symmetry, magnetic hysteresis greater than gd, and the value of forG [is reported to be 2 k]d. sub. 5]S[i. sub. 2]G[e. sub. 2](
Pecharsky and Gschneidner 1997 B).
Thermal conductivity of G [d. sub. 5]S[i. sub. 2]G[e. sub. 2]
Determined by the experiment to be about 5-7 W/m.
Near room temperature (Fujieda et al. 2004).
The lag phenomenon can be greatly reduced by the alloy with other elements, but the material then becomes a SOMT (
Pecharsky and Gschneidner 1997 c; Shull et al. 2006).
Pecharsky and others. (2003)
Found by using high
Purity start-up assembly and heat treatment different from Pecharsky and Gschneidner used in previous work (1997a)
, The change of entropy with the magnetic strength and the change of the thermal insulation temperature [d. sub. 5]S[i. sub. 2]G[e. sub. 2]
Both can increase by more than 50%.
Change of entropy ,[DELTA][s. sub. M]
This best preparation material is about-27 J/kg.
Change in K and thermal insulation temperature ,[DELTA][T. sub. [ad]]
When the material is magnetized from 0 Tesla to 2 Tesla, it is about 7 k.
The change of the thermal insulation temperature was determined from the thermal capacity and the magnetic strength measurement, rather than the direct measurement. G[d. sub. 5](S[i. sub. [1-x]]G[e. sub. x])
4 high potential for materials-
Performance AMRR refrigerant because they have a relatively high change in magnetic entropy and a larger change in thermal insulation temperature.
These family of materials with similar magnetic properties can be made with a large span of curve temperatures. LaF[e. sub. [13-x]]S[i. sub. x]H[. sub. y]
The alloy of La, iron, silicon and hydrogen has experienced
Orderly magnetic phase transition and show greater but sharper than gd (i. e.
, It happens in a narrower temperature range)
As discussed by Fujita and others. (2002).
The properties of the material can be adjusted by replacing silicon with iron (
Gschneidner and others. 2005)
Or by addinghydrogen (Fujita et al. 2003).
It is reported that the Curie temperature of this material family ranges from 195 K to 336 K depending on the composition.
However, the lag changes a lot depending on the composition of the material.
The thermal conductivity of these materials is about 10 W/m.
K near room temperature (Fujieda et al. 2004).
Lais is one of the most common rare earth elements at a much lower cost than Gd, which makes these materials more economically promising than Gd.
The performance of this material series can be enhanced by replacing la with other elements.
By replacing ce (Ce)
For la, Fujita, etc. (2004)
It can change entropy with the increase of magnetism-30 J/kg.
K is a compound of 10% ceriumsubstitution. Fujieda et al. (2006)
Modern Hair (Pr)
For la, when magnetized from 0 to 5 Tesla compared to similar materials without la replacement, entropy change and temperature change increased by more than 30%.
No data were found for 2 Tesla magnetic field changes;
However, materials that replace la with ase may have similar advantages compared to 2 Tesla\'s unreplaced materials.
Replacing la with ase does not affect the lag phenomenon. MnA[s. sub. 1-x][Sb. sub. x]
Recently developed Mn [As. sub. [1-x]][Sb. sub. x]
Compounds are materials that may be suitable for magnetic refrigeration systems.
The Curie temperature of MnAs is about 318 K, which varies with the entropy of the magnetic strength ,[DELTA][s. sub. M]
[Dan, K]DELTA][T. sub. [ad]]
, About 5k when Tesla is magnetized from 0 to 2 (
Wada and Tanabe 2001.
The thermal insulation temperature is indirectly measured by thermal capacity measurement.
MnAs has a relatively large 5k lag and a low thermal conductivity of about 2 W/m.
K near room temperature (Fujieda et al. 2004).
The Dwell temperature of this alloy can be adjusted between 230 K and 318 K by replacing antimony (Sb)forarsenic (As).
When Sb scores (x)
Greater than or equal to 0.
05, when the magnetic thermal effect remains roughly the same, the thermal lag becomes quite small (Wada et al. 2005).
Materials containing Sb and [DELTA][T. sub. [ad]]
When magnetized from 0 to 1, it is determined to be 3 k.
Use 45 Tesla, which directly measures the change in thermal insulation temperature.
These materials are attractive as magnetic refrigerants, because they have a large entropy change with the change of the magnetic strength, the dwell point temperature can be adjusted within a large temperature range, and
However, for this class of materials, the change in thermal insulation temperature is relatively low, and the thermal conductivity is significantly lower than that of gd and other magnetic thermal materials already discussed;
These features may reduce performance under some AMRR operating conditions.
The properties of MnFeP materials such As these can be achieved by adding elements As, Mn, Ge, cobalt (Co)Chromium (Cr)(Teguset al. 2004).
Temperature of the inner point]Mn. sub. 1. 1][Fe. sub. 0. 9][P. sub. 1-x][Ge. sub. x]
Adjustable between250 K and 380 K change times, suitable GEGe)
In the pound (Dagula et al. 2005). Yan et al. (2006)
The performance of this alloy is strongly dependent on the material processing technology used, the report said.
The temperature of the melt
It is found that the spinning-stick alloy is 18 K higher than the annealing bulk alloy with the same composition. The melt-
The rotating material also exhibits a higher entropy change with the magnetized strength and low lag.
This family of materials is usually FOMT;
However, of course, this structure is currently only feasible at very low temperatures, or at this temperature, a super capacitor can be used to effectively deal with the large amount of costs required to generate useful magnetic fields
Practical systems for residential and other small homes-
Scale applications may use permanent magnets to generate a magnetic field, because the power required for the low-temperature equipment needed to maintain the superconductive temperature of the solenoid may greatly exceed the small-to medium-
Scale AMRR equipment (Zimm et al. 2006).
However, for large
The scale system, which increases performance, is possible with magnets that can offset the required power to keep the magnets at low temperatures.
A system using a permanent can change the applied magnetic field by physically moving the magnetic recycler relative to the magnetic field, whether it is moving linearly in a reciprocating device or rotating in a rotating device (e. g. ,Figure 3);
As shown in figure 4, a schematic diagram of the reciprocating AMRR system.
Several AMRR prototypes have been built recently and their measurement performance has been announced.
Some of these prototypes have implemented a layered regeneration bed to try to improve performance, and many new systems are using a more practical permanent option instead of a super solenoid to generate a magnetic field. Yu et al. (2003)
Provide a summary of the prototype system and its related performance covering the period up to 2003;
Only the most important systems discussed in this paper are cited here.
The latest results of the new prototype system and the new system configuration are summarized in Table 2 and discussed below.
The inspection of Table 2 shows that the performance of the AMRR system is highly dependent on the test used to manufacture the recycler and the operating conditions of the material.
In each case, the maximum cooling power ([Q. sub. C])
This can happen through a system that spans the thetemature ([DELTA]T)
Close to zero, the maximum temperature span will appear when no refrigeration load is generated.
Therefore, when evaluating and comparing the performance of the prototype AMRR system described in table 2 and discussed in this section, it is important to pay close attention to the operating conditions of the system.
Victoria University prototype Victoria University AMRR consists of two regeneration beds that move linearly through a magnetic field generated by a stationary Super solenoid (Rowe et al. 2004);
Figure 4 shows the chemistry of the system.
The maximum magnetic field generated by the is 2 Tesla.
The heat storage body is constructed from \"folds\" of 1 to 3 magnetic heat materials. Eachpuck is 2.
The diameter is 5 cm, 2.
5 cm long, can be made with different materials of different geometric shapes.
The heat transfer fluid at 10 bar is controlled by the displacement device.
The cooling load is controlled by two 25w fin-like heaters installed between two recyclers beds.
The device can operate from 0. 2 to 1 Hz;
The maximum frequency is bound by the inertia force. [
Figure 4 omits the prototype to be tested in a series of operating frequency ranges with several layered recyclers beds.
The performance of the layered bed is directly compared with that of the single bed
Material bed frequency.
The performance of the layered bed is directly compared with that of the single bed
First run the system with 2 Gd puc and then run the system with a gdp and [Gd. sub. 0. 74][Tb. sub. 0. 26]puck.
Layered bed for production
The load temperature span is about 19 k.
The material bed produces a span of about 15. 5 K (Rowe et al. 2004).
Using a single \"puck\" of Gd, the prototype is 288--302 K. Rowe and Tura (2006)
Built three \"puc\" beds composed of Gd and [Gd. sub. 0. 74][Tb. sub. 0. 26], and [Gd. sub. 0. 85][Er. sub. 0. 15]
In order to reduce the temperature
Working frequency is 1Hz, ano-
The load temperature span of 51k is reached, indicating that the layered bed frame AMRR system operates at a much greater temperature than can be achieved using a single bed frame
Chubu Electrical and Toshiba equipment Chubu Electric/Toshiba AMRR has two regeneration beds that move linearly in the presence of a 4 tesla magnetic field generated by a super solenoid.
The diameter of each recycler is 6.
Length of 2 cm and 8 cm, consisting of a sphere filled with Gd.
Heat transfer fluid is a mixture of water and ethanol.
Fluid flow is controlled by two valves and one variablespeed pump. Hirano et al. (2002)
The reported cooling power of COP 5 is 100 W.
When the system is running between 302 K and 276 K.
The reported COP, however, is somewhat misleading as it does not include the power required for any motor or pump to be inefficient or to cool the super solenoid.
When the maximum magnetic field is reduced to 2 Tesla, the cooling power between 298 and 274 K drops to about 40 W, indicating that the magnetic field strength will significantly affect the AMRRperformance.
Aerospace reciprocating and rotary transformation prototyperoom-
The temperature AMRR prototype is a simulation device with a 5 Tesla magnetic field, which is generated by a superconductive solenoid.
Make two generators with packaged 0 gdsphere. 15-0. 30 mm diameter.
The total volume of recycled materials is about 600 [cm. sup. 3].
The maximum cooling power of the unit is 600 W, which is obtained with the temperature of Spain close to 0, and the cooling power of 100 W is obtained with the temperature span of 38 K (Zimm et al. 1998).
Although the original equipment produced a relatively large cooling power in a large temperature range, the equipment itself is quite large and uses a superconductive , so as a commercial productZimm et al. 2006).
Recently, the space company has created a more compact and practical rotating device. 5 Tesla [Nd. sub. 2][Fe. sub. 14]
The heat reservoir is divided into six separate bed layers that rotate through a permanent magnetic field, as shown in figure 3.
Heat transfer fluid is water-based, using variables to control fluid flow rate
High speed pump and two rotary valves.
The piping setting of the system makes the pump run continuously, and during operation, the flow through the external pipe and heat exchanger is one-way, while the flow through each separate bed is reversed.
The rotation configuration allows the device to operate at frequencies up to 4 Hz (240 RPM)
, Which is higher than any return on construction so far. Zimm et al. (2006)
The performance of the layered bed of Gdand [Gd. sub. 0. 94][Er. sub. 0. 06]and a single-
The material bed of lafesh material using a rotating device.
They found that when the temperature span was large, the layered bed was able to produce a greater cold load than a similar bed made of gd.
The rotating device reaches the maximum
The load temperature span of the layered bed and no-is about 25k
Load temperature span of single-is less than 19kmaterial Gdbed.
The cooling power of the layered bed in the 14k span is 80% higher (27 W)
15w cold load than ingle-generated
However, for a single-
When the temperature span is close to zero, the material Gd bed;
The layered bed is able to produce a cooling of 41 W at zero temperature, while the Gd bed produces a cooling of 44 W under the same conditions.
This behavior is expected because the magnetic thermal effect of Gd is greater than that [Gd. sub. 0. 94][Er. sub. 0. 06]
At room temperature
An area generator consisting of irregular particles ([Fe. sub. 11. 44][Si. sub. 1. 56c)[H. sub. 1. 0]
Size in the range of 025-0.
Also studied 5mm using a rotating device.
LaFeSiHmaterial produces a higher cold load than the Gd or Gd andGdEr recycler bed at a zero temperature span.
However, when the temperature span increases, the cooling power of the Lafite material is reduced.
Based on this result, Zimm et al.
It is concluded that LaFeSiHmaterials are promising materials for the AMRR system, but if these alloys are to achieve high performance in a useful temperature range, the layered bed is necessary.
Nanjing University has built a reciprocating device consisting of a generator bed that linearly enters and exits the magnetic field generated by a stationary 1.
Tesla permanent .
The generator is installed in the hole with a diameter of 3 cm. Lu et al. (2005)
The system was operated using Gd generators and recently developed more advanced magnetic thermal materials.
The maximum reported cooling power of the system is 40w and the temperature span is 5k when using [Gd. sub. 5][Si. sub. 1. 895][Ge. sub. 1. 89][Ga. sub. 0. 03]regenerator. The no-
For a single device, the load temperature span of the device is 23 K
Material Gd recycler, a [25 k]Gd. sub. 5][Si. sub. 1. 895]
A [Regenerator and 10 k]Gd. sub. 5][Si. sub. 2][Ge. sub. 2]regenerator.
I don\'t know why [Gd. sub. 5][Si. sub. 2][Ge. sub. 2]
Compared with pure Gd recyclers, the temperature span of the recyclers is lower.
However, Shull and others. (2006)
It is found that a small amount of substances such as gallium (Ga)to [Gd. sub. 5][Si. sub. 4-x][Ge. sub. x]
The material changes the magnetic properties from FOMT to SOMT, increasing the bending temperature of the material and greatly reducing the lag.
The reduction lag of [and the increase of the temperature of the Curie point]Gd. sub. 5][Si. sub. 1. 895][Ge. sub. 1. 89][Ga. sub. 0. 03]
Material may explain no-
The load temperature span is more than double the compound without Ga.
The Tokyo Institute of Technology and the central rotary unit central system is a rotating device that resembles a space device in addition to the rotation and the generator is still.
The regeneration device is composed of four 0.
2mm ball generator beds;
Each bed consists of four different layers of material.
From the cold end to the hot end, the layer is [Gd. sub. 0. 91][Y. sub. 0. 09], [Gd. sub. 0. 84][Dy. sub. 0. 16],[Gd. sub. 0. 87][Dy. sub. 0. 13], and [Gd. sub. 0. 89][Dy. sub. 0. 11].
0 when operating.
77 Tesla nd permanent rotates on the generator bed and then stops when the fluid flows through the bed.
Then Themagnet rotates 90 [degrees]
To the next regeneration bed, this process continues in this way.
The heat transfer fluid is water and its flow is controlled by rotary valves and variables-speed pump.
The system generates a maximum cooling power of 60w at a frequency of 0.
42Hz, the fluid flow rate is 4 L/min when the temperature show is close to 0k (Okamura et al. 2006).
In the temperature range of 4 k, when the frequency is 0, the maximum cooling power of 14w is reached.
The fluid flow rate is 3 liters/min at 55Hz.
Other system blocks, etc. (2003)
A reciprocating AMRR is established using 1mm parallel plates of Gd separated by 0.
15mm clearance allowing fluid flow.
The magnetic field is provided by one 0.
8 Tesla permanent , the system runs at 0. 42 Hz.
Cold load of 8.
8w is obtained when the temperature span is from 298. 5 to 302.
5 K, COP 2. 2;
COPincludes includes all power inputs for the system.
Xi\'an Jiaotong University built a reciprocating AMRR with a 2 regeneration bed.
18 tesla (Yu et al. 2006).
The size of the bed is not reported, but the bed layer holds 930g of Gd particles.
Assuming the hole rate is 0.
4. The volume of the generator is about 200 [cm. sup. 3].
The device uses Gd balls as a heating agent and can produce up to 18.
Cool 7w between 294. 5and 291.
4 K, fluid flow rate 3. 5 L/min.
Operate the same device using a recycler consisting of irregular particlesGd. sub. 5][Si. sub. 2][Ge. sub. 2]
The cooling power is reduced to a maximum of 10.
The temperature between 3w is 300. 1 and 297.
1 k, fluid flow rate 3. 6 L/min.
Reasons for the low cooling power measured [Gd. sub. 5][Si. sub. 2][Ge. sub. 2]
Do not know the material;
However, this may be due to the fact that the system is not operating near the inner point of the material.
Vasily and Mueller (2006)
A prototype is described using a rotating permanent and a static check-back heater.
The heat storage body consists of a series of parallel plate heat storage bodies \"inserts\" which are insulated from each other and can be made of different magnetic thermal materials to construct a layered heat storage body
However, there is very little publicly available performance data for this prototype.
The actual AMRR problem magnetic refrigeration is not a mature field and there will be some problems that must be overcome before the AMRR equipment is used for commercial applications.
The recent prototype has solved some practical problems related to previous experiments.
For example, some recent systems show relatively high cooling power using permanent magnets;
This no longer requires a low temperature cooler and a low temperature solenoid.
By using a rotation instead of a reciprocating configuration, the maximum operating frequency of AMRRsystems is improved;
The increase in operating frequency allows the use of smaller beds and magnets, so it is more economical and feasible.
Despite these progress, there are several practical issues that need to be considered.
The system size prototype AMRR system is currently much larger than the equivalent steam compression system they will replace.
Lu and others, for example. (2005)
Reporting the use of permanent magnets with an external diameter of 14 cm and a length of 20 cm for systems that provide a maximum cooling power of 40w
In a steam compression system, systems including magnets, regenerators, pumps, pipes and motors are significantly larger than compressors and motors;
Note that the AMRR system needs a heat exchanger of approximately the same size as the evaporator and condenser in the evaporation compression system.
As the AMRR system becomes more efficient through material selection and the design of the recycler, its size will be reduced;
However, even awell-
The use of SOMT material design and advanced AMRR systems may be larger than the equivalent steam compression system.
In order to produce 8 AMRR with Gd filled spherical recycler.
Kwbrecht et al. Believe that kWcooling is carried out in order to compete with the efficiency of steam compression. (2006b)
It has been shown that the total regeneration volume of about 4l is required.
This regenerator volume does not include the volume associated with the , pump, valve or the housing of the regenerator.
Therefore, the total volume of the AMRR system may be significantly higher than that of the steam compression system that meets the same load.
However, Engel Brecht (2005)
It is also shown that the volume of heat storage can greatly reduce the performance of withoutsacrificing such as layered bed by low
The lagging material compound is used in conjunction with the geometry of the more complex recycler.
If the material works in the itsFOMT area, the high latent heat of the material provides an important advantage.
First of all, potential heat will minimize the reduction of effective [DELTA][T. sub. ad]
Through the pore liquid product, more porous beds with lower pressure drop and lower longitudinal conduction are allowed to be used to reduce losses.
Second, for a given AMRR frequency, a large potential heat will allow a higher flow rate of specific fluid, thus allowing the use of a smaller generator bed and a corresponding smaller .
Unlike the steam compression system, there is no phase change in the fluid in the AMRR cycle.
As shown in Table 1, under a reasonable magnetic field swing, the temperature rise of the current magnetic heat material is less than 8 Kfor, due to heat transfer loss and the specific heat of the fluid, the temperature change of the heat transfer fluid will be lower than this value.
Heat transfer from fluid to load is a product of mass flow rate, fluid temperature change, and fluid specific heat.
Therefore, under a given cooling capacity, the flow rate of fluid mass in the AMRR system must be significantly greater than the flow rate of refrigerant in the avapor compression cycle. Zimm et al. (2006)
The AMRR cooling power of 30 W in the 8k temperature range is reported, which requires a fluid flow rate of about 0. 7 kg/min;
This is equivalent to the cooling power of the fluid mass flow ratio of about 43 W. min/kg.
Engel Brecht, etc. (2006b)
Predict the water flow rate in the filled sphere AMRR that produces 8.
8 kWof cooling is about 84 g/min, resulting in a ratio of cooling power to fluid flow of about 105 W. min/kg.
These two data points show that the ratio of cooling power to mass flow rate of the AMRR system will be 25--150 W.
According to the magnetic heat material designed and used by the cycle, the minimum/kg.
For steam compression systems, the ratio of cooling power to fluid mass flow rate will be much higher due to the steam heat of the refrigerant.
For example, the DOE/ORNL heat pump model (Rice 2006)
Predict the steam compression system that produces 8.
The refrigerant flow rate required for the cooling of 8 KW is 3. 3kg/min;
This is equivalent to the cooling power of the fluid mass flow ratio of about 2700 W. min/kg.
For equal fluid flow rates, the predicted cooling power of the steam compression system is approximately 25 times that of the well forecast
The AMRR system was designed, about 60 times the experimental value reported by Zimm etal. (2006).
In the design of the AMRR system, this high fluid mass flow rate must be carefully considered to prevent excessive pumping losses in the heat exchanger and connecting pipes.
Care must be taken in the design of the heat exchanger circuit and the connecting pipe and valve associated with the AMRR system to limit the loss of parasitic pumping. The single-
The phase fluid of the AMRR can allow the use of an improved heat exchanger design, which may compensate for higher fluid flow rates in some applications. In air-
In the application of air conditioning, air conditioning dominates.
Therefore, the increased fluid flow rate may not have much impact on the size or cost of the heat exchanger.
In addition, since the pressure in the AMRR system is much lower than the steam cycle system, plastic pipes can be used, which may reduce the cost of connecting pipes and installation.
Material Processing of magnetic thermal materials may be a problem for commercial AMRR equipment.
Most of the materials recently developed are produced only on a laboratory scale, many of which require long-term heat treatment or high
Purity start-up material for optimum magnetic thermal properties.
For example, arc-
Melting samples of LaF [e. sub. x]S[i. sub. 1-x][H. sub. y]
Annealing for ten days at 1323 K (Fujita et al. 2003)andMnA[s. sub. 1-x][Sb. sub. x]
The compound is hot.
Seven days of treatment (Wada et al. 2005)
To achieve the desired results.
Many magnetic heat materials are sensitive to the purity of the starting elements used in synthetic materials (Tishin 2005)
This may make the cost of raw materials very high.
Pecharsky and others. (2003)
It is reported that when 99 is used, the entropy change and temperature increase significantly with the magnetic intensity.
9% purity for pure insteadof Gd is 95%-98%.
Requirements for materials with high purity, long heat treatment time, and expensive raw materials may make the commercial production of some types of magnetic thermal materials simple.
Conclusion The recent prototype AMRR system has demonstrated that a layered regenerative bed can produce greater cooling capacity than a single-layer regenerative bed
When the recycler material is correctly selected in order to match the operating temperature range, the material recycler.
Other prototypes have shown that the amrr system can provide a cooling load using a practical permanent instead of an ultra-magnetic solenoid over a relatively large temperature range.
Continue to develop new materials with high magnetic effect;
In practice, however, Gd and itsalloys continue to produce maximum cooling power and maximum no-
Load temperature span.
FOMT materials usually show higher change of magnetic entropy and thermal insulation temperature than SOMT materials;
However, to date, the only FOMT material proved to be superior to Gd and its alloys by experiments is [LaFe. sub. x]S[i. sub. 1-x][H. sub. y]compound (Zimm et al. 2006).
Compared with SOMT materials, the low experimental performance of some FOMT materials may be related to the high lag and longer time required for the magnetic phase transition associated with FOMT materials.
Although some promising progress has been made in the field of magnetic refrigeration, there are still many practical issues that must be addressed before the AMRR system competes with the steam compression system for residential applications.
Thanks to Andrew Luo of Victoria University for his technical assistance.
This work is funded by ASHRAE Grant-In-
University of Wisconsin and Wisconsin-
Graduate School of Madison
Pressure, Pa [Q. sub. C]
= Cooling power at cold end, w s = entropy, J/K [DELTA][s. sub. M]
= The specific entropy varies with the magnetic intensity, J/kg.
K t = temperature, K [DELTA][T. sub. ad]
= Change of thermal insulation temperature under magnetized, K [T. sub. Curie]
= Curie point temperature, k u = internal energy, j v = volume ,[m. sup. 3][[mu]. sub. 0]
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