Magnetic heating and refrigeration: A new technology of

Magnetic heating and refrigeration:A new technology of heat and cold production

University of Applied Sciences of Western SwitzerlandYverdon-les-Bains, Switzerland

Peter W. Egolf

Journée du CUEPE 2006Geneva, 6th of April 2006

Thermique Industriel et Systèmes:O. Sari, N. Erbeau, J. Brulhart,M. Zaghoudi, G. Wyss, G. Chollet,K. Martin-Drezet

Simulation des Systèmes Thermique: P.W. Egolf, F. Gendre, A. Kitanovski, D. Ata-Caesar, H. Bajpai, K. Winkelmann

The Divisons TIS and SIT

ExperimentsTheory

Collaboration and Help

• Prof. Dr. O. Sari• F. Gendre• N. Erbeau• N. Alber• F. Brun• J. Hu

University of Ljubljana

Prof. Dr. Alojz PoredosDr. Andrej KitanovskiDr. Alen Sarlah

New name:

Table of contents

• Brief history of magnetocaloric materials and systems• The magnetocaloric effect• Magnetic heating and refrigeration at room temperature• Existing prototypes• Magnetic forces and thermodynamic potentials• Possible systems• Porous rotary magnetic refrigerators• Thermodynamic cycles, cascades, regeneration• Numerical method and simulations• Alternative machines• Magnetic heat pumps for Switzerland?• International activities• Conclusions and outlook

„Giant“ magnetocaloric effect

New materials ... may bring practical magnetocaloric cooling a step closer. A large magnetic entropy change has been found to occur in MnFeP0.45 As0.55 at room temperature, making it an attractive candidate for commercial applications in magneticrefrigeration.

Nature Highlights10 th of January 2002


In an article published in the journal Nature last month, scientistsat the University of Amsterdam reported that they had created an iron-based compound that also exhibits a large warming effect in a magnetic field. Iron and other ingredients in the compound areconsiderable less expensive than gadolinium.

The New York Times9 th of February 2002


• 1881 : Warburg discovers the magnetocaloric effect in iron

• 1926 : Debye proposes the first practical application at low tempera-tures. The process is named adiabatic magnetization/demagnetization

• 1927 : Giauque proposes the same process independently of Debye

• Since 1930 : Application of magnetic cooling becomes standard in low temperature physics (T<<1 K)

• At present : Discovery of magnetocaloric materials with Currie tem-peratures TC around room temperature

• Development of new magnetic cooling systems operating at roomtemperature: Promising new technology !

Brief history of magnetocaloricmaterials and systems

The magnetocaloric effect

For the entropy of rare earth alloys (no electron phonon interactions)a superposition of the partial entropies is possible (Tishin, 2003):

The entropy of the electronic (e) and the lattice (l) subsystemsshow no dependence on the magnetic field! Then:

Some basic thermodynamic relations and definitions:

),()()(),( THSTSTSTHS mle ++=

dTTHTsdHTHH

sdTTdTdsdTTdT

dsTHdsH

m

T

mle ),(),()()(),( ⎟⎠⎞

⎜⎝⎛∂∂

+⎟⎠⎞

⎜⎝⎛∂∂

++=

χχ

δ⎟⎠⎞⎜

⎝⎛∂= T

qcTdsq=δ ( )χχ

δTsTc ∂=


Combining these equations:

With the Mayxwell relation (e.g. Kitanovski & Egolf, Int. J. Refr. 29, 3-21, 2006:

because:( ) ( )HT T

MHs

∂−=∂δμδ

0TT

mHs

Hs

⎟⎟⎠

⎞⎜⎜⎝

⎛∂

=⎟⎠⎞

⎜⎝⎛∂

δδ

dHTHHsdTT

THcdTTTcdTT

TcTHdsT

m

H

mle ),(),()()(),( ⎟⎠⎞

⎜⎝⎛∂∂

+++=


and:

mleH cccc ++=

In an adiabatic magnetization or demagnetization process:

0=ds

Therefore, it follows that:

( ) ( )HHH

HTM

cTdT

TMdTT

c∂=⇒=∂− δμδμ 0

0 0

Moving magnetocaloric material into (out of) a magnetic fieldincreases (decreases) the magnetisation and the temperature.

dH

The magnetocaloric effect occurs at a phase transition betweendifferent magnetic states.

The temperature of phase change is the Curie temperature.


Data from:

Pecharsky VK, GschneidnerKA Jr. Tunable magnetic regenerator alloys with a giant magnetocaloric effect for magnetic refrigeration from ~ 20 to ~ 290 K. Applied Physics Letters 1997; 70 (24): 3299-3301.

Still limited temperaturedifferences!


Tegus, PhD thesis

Van der Waals-ZeemannInstitute

University of Amsterdam

2003

Magnetic heating and refrigerationat room temperature

0

50

100

150

200

250

260 280 300 320 340

T (K)

q (J

/kg)

Gd

Gd5Ge2Si2

MnAs1-xSbx

x=0

x=0.05

x=0.1

x=0.5

x=0.55

x=0.65

x=0.9

x=1

x=1.1

MnFeP1-xAsx

Mn2-xFexP0.5As0.5

Mn1.1Fe0.9P0.47As0.53

Field change: 0 - 2 TTc-12<T<Tc+12

200

300

400

500

600

700

260 280 300 320 340

T (K)

q (J

/kg)

Gd5Ge2Si2

Gd

x=0.1

x=0.05

x=0

MnAs1-xSbx

MnFeP1-xAsx

x=0.65x=0.55

x=0.5

Gd5(Si1.985Ge1.985Ga0.03)

Field change: 0 - 5 TTc-25<T<Tc+25

Heating and refrigeration „capacities“:

Zimm et al., 2001Tegus et al., 2002


Magnetocaloric materials should (partly by Yu et al., 2003):

• Modest Debye temperature (a high temperature makes the fraction of latticeentropy small correspondingly at a high temperature)

• High temperature difference at phase transition• Large width of transition• No magnetic hysteresis (irreversibility of cycle)• Small specific heat and large thermal conductivity to guarantee fast heat exchange• Large electric resistance to avoid the eddy current loss• Fine molding and processing must be possible• No poison substances (arsenic, etc.) for direct contact applications


Hallbach Magnet > 4 Tesla

Development of magnets

High flux line density



Four stage process each:

A) Magnetic heat pump:1) Increase of magnetic flux density2) Rejection of heat for heating purpose

at high temperature level3) Decrease of magnetic flux density4) Injection of heat at low level to the

heat pump

B) Conventional heat pump:1) Compression (Increase of pressure)2) Rejection of heat for heating purpose

at high temperature level3) Expansion (decrease of pressure)4) Injection of heat at low level to the

heat pump

Advantages:• Green technology (no use of conventional refrigerants)

• Noise-less technology (no compressor)

• Very high thermodynamic efficiency (20-30% higher than in conven-tional cycles due to the reversibility of the magnetocaloric effect)

• Lower energy consumption

• Simple construction

• Low maintenance costs

• Low pressures (operation at atmospheric pressure, advantage e.g. for air-conditioning applications and refrigeration systems in automobiles)


• Strong magnetic fields with not completely known influences on living creatures

• Protections to avoid disturbances of electronic components

• The field strengths of permanent magnets are still limited, superconducting magnets are too expensive

• The temperature differences are still not so high

• In moving material applications the precision of the machinemust be high (small gap between magnet and magnetocaloricmaterial)

Disadvantages:


Existing prototypes

A development in Japan

Chubu – Toshiba (2000)

This machine consists of a cascade with three pistons of differentmagnetocaloric materials. A low magnetic field of B=0.7 T is in-duced by permanent magnets.

Existing prototypes

AMES Laboratory - 1997

The kernel are two pistons of packed beds of gadolinium spheres. A superconducting magnet with a high magnetic field is applied.

Development in the USA

Existing prototypes

AMES Laboratory - 2001

Rotary magnetic refrigerator with permanent magnets(with complicated fluid switches)

Development in the USA

Existing prototypes

University of Victoria

Developments in the USA

dVHMF iiK ∇∫=Γ

0μr

dVBMF iiV ∇∫=Γ

0μr

dVMHF iiV ∇∫=Γ

00μr

extensive vector analyticaltreatment

Kelvin (K):

Liu & Odenbach (V):

FVgrad H

N

S

Kitanovski & Egolf, 2005 (in print)

A. Lange, Kelvin force in a layer of magnetic fluid.J. Magn. Mat. 2001; 241: 327-329:

Magnetic forces and thermodynamic potentials

Dilute limite only (ferrofluids)!

N

S

What is the difference?We still may have the external work:

But now additionally a flux of magnetisationoccurs. Its infinitesimal change is:

Then the technical work is:

In turbo machinery this work is also namedshaft work

dMHdw ext00

)(1 μ−=

( )MHddw abs00

)(1 μ−=

( ) 00)(

1)(

1)(

1 MdHdwdwdw extabstech μ=−−=


pdvdw ext −=)(1 dMHdw ext

00)(

1 μ−=

Quantity Gas thermodynamics

Magneto-thermodynamics

Driving “force”(stress parameter)

Pressure p Field H0

Order parameter(reaction of system)

Specific volume v Magnetization M(orientation of spins)

External work(closed system)

(related to force of Liu)

Technical work(open system)

(related to Kelvin force)

vdpdw tech =)(1 00

)(1 MdHdw tech μ=

H0p

v M


p, V

dW1

S

Fluid

p.

N

S

dW1

H0

H0

M, H

Magneto-caloric

material

.

.

Possible Systems

p(1), v(1) p(2), v(2)

W1abs

W1tech

Fluid

p H0

H(1), M(1)H(2), M(2)

W1tech

W1abs

Magnetocaloricmaterial

Possible systems:Open systems

1) Static system with two storage blocks and valves2) Linear movement3) Rotational movement

Solution A: Rotary wheel, magnet fixed, axial current.

Solution B:Wheel fixed, rotating magnet, axial current.

Solution C:Rotary wheel, fixed magnet, radial current.

Solution D:Fixed wheel, rotary magnet, radial current.

Possible systems

Porous rotary magnetic refrigerator

A. Kitanovski, P. W. Egolf,O. Sari, 2003.Procédé et dispositif pourgenerer en continue du froidet de la chaleur par effetmagnetique.

PCT BR – 10’463 - IN

Four functions arerealized in a verysimple manner!

Porous rotary magnetic refrigerator

[ ][ ] [ ])3()4()1()2(

)4()1(

hhhh

hhCOPBrayton

−+−

−=

A. Kitanovski, P.W. EgolfInternational Journal of RefrigerationThermodynamics of Magnetic Refrigeration (in print):

Internal energy:

Legendre Transformation:

„Coefficient of performance“:

MdHdsTdurr

001 μ−=

MHuhrr

0011 μ+=Work

Fast process(adiabatic)

0001 ),( MdHdsTHsdh μ+=

Heating energy

Thermodynamic cycles, cascades, regeneration

To improve the available temperaturedifferences cascade systems..


...or regeneration systems are required!


Numerical method and simulations

z

qq

rzvt

n

i

n

ii

zi

∂+∂+⎟⎠⎞

⎜⎝⎛

∂Λ∂+∂

Λ∂+∂Λ∂

∑∑== 11

)()(

1χχ

φφωρφ

&&

πφπφφ 2,),(,),( )()()( ≤<Δ+== hothotinRRhot

inFF TTLTTLT

πφφφ ≤<Δ+== 0,)0,(,)0,( )()()( coldcoldinRRcold

inFF TTTTT

LzzTzT RR ≤≤= 0),,0(),2( π

Energy conservation:

( ) 0=−+∂∂

RFF

pF TTLzTcv

ξαρ

( ) 0=−+∂∂

FRR

HR TTTc δαψφωρ

Mapping of a cylinder to a square:

(Periodicity condition)

Thermal inertia and conductivities negligible!


20

25

30

35

40

0 30 60 90 120 150 180

Azimuth pos ition (de gre e s )

Tco

olin

g flu

id (°

C)

00.250.50.751

Downstream position

(x/L)

20

25

30

35

40

0 30 60 90 120 150 180


Tw

arm

whe

el (°C

)

00.250.50.751

Downstream position

(x/L)

10

15

20

25

30

180 210 240 270 300 330 360


Tch

illed

flui

d (°C

)

00.250.50.751

Downstream position

(x/L)

10

15

20

25

30

180 210 240 270 300 330 360


Tco

ld w

heel (

°C)

00.250.50.751

Downstream position

(x/L)

Temperature distributions in a steady state condition: L=0.2 m, D=0.198 m., vcold=vwarm=6 m/s, ω=0.6 s-1,=704 W, mwheel=8.09 kg, ΔB= 5 Tesla. Material: Gd5(Si1.985Ge1.985Ga0.03) Q&

Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Q&Withoutoptimi-sation:

COP=5.8

Azimutal position (°) Azimutal position (°)

Azimutal position (°) Azimutal position (°)

Newest work:Analytical optimization

( ) )()(

)(

1

)(

)(,

1

)(

)(

,1121 )(

coldR

hotR

hotR

CarnotCarnothotR

hotinF

hotF

hotR

TTTCOPCOP

TT

eCOPhot

F

−=⎟

⎟⎠

⎞⎜⎜⎝

⎛−−=

≤≤

−

4342144 344 21

χ

χχ

More simple (also analytical) models:

1,

,1

<<==

==

vLf

Svc

hSt

SStL

cfh

rHR

R

r

R

HRR

ρ

δψρδψχ

vchSt

NTUStcv

h

pFFF

FpFF

F

ρ

ξρ

ξχ

=

=== ,


Verticalslabs arevery bad!

Ferromagnetic kernel


Alternative machines

Second generationof a rotative proto-type with regeneration.

Alternative machines

A system withradial flow isbeing built andwill be presen-ted at the Hann-over industrialexhibition 2006.

Heat pumps for new buildings with floor heatingFluids: Brine/water (brine: 25 % ethylen-glycol)Temperature primary side: 0 °C (e.g. water of a river)Temperature secondary side: 35 °CPower: 8 kW

Renovation building with radiator heatingFluids: Air/waterTemperature primary side : -7 °CTemperature secondary side : 50 °CPower: 15 kW.

Magnetic heat pumps for Switzerland?

Conventional heat pump application Analogous design of a magnetic heat pump

Simple magnetic heat pump system with only two pumps. A requirement is identicalfluids in the two circuits, e.g. water/glycol.

Magnetic heat pumps for Switzerland:New building with floor heating

The system shows an air/waterheat exchanger, a pump in thesmall heating cicuit and two airventilators.

Schematic drawing of a complete heating system with a magnetic heat pump. By the heat recovery system therequired temperature difference becomes smaller and a magnetic heat pump appplication becomes realistic.

Magnetic heat pumps for Switzerland:Renovation building with radiator heating

New IIR Working Party on Magnetic Refrigeration

See on the web:www.iifiir.iifiir.org

First Int. Conf. on MagneticRefrigeration at Room Temperature

27-30. September 2005in Montreux Switzerland

140 participants

Interested:Coca Cola, Néstle,Daewoo, Danfoss, Peugeot, Citroen, Axima, Arcelik,…

Next conference:Protorosz, Slovenia11-13 April 2007

Swiss Technology Award 2006First prize

Conclusions and Outlook

• Magnetic refrigerators at room temperature have been designed(and several patents for different systems submitted)

• The basic theory has been established, but will be further prepared

• First numerical simulations results have been made available

• Experimental validation is planned to be performed

• Optimisation calculations are very important to reach high COP values and are still missing

• More powerful systems as cascades and systems with regene-ration must be designed, their behaviour measured and modeled.

Thank you for your attention!

Magnetic coolingat room temperature:

A future major evolution in refrigeration?

Documents

Magnetic heating and refrigeration: A new technology of