Chilling out with magnetic attraction

Chilling out with magnetic attraction The domestic refrigerator and magnets have had an intimate relationship for decades, least on the surface. But research in the US is pointing the way to a closer, if chillier, involvement...

T

HE idea of a domestic without seem

refrigerator

using ozone-depleting

to be pie-in-the-sky.

fridge that that is driven by magnets it to be straight

from science

that

cools

refrigerants

may

And

the

idea of a

looks on the face of

Gschneidner, “There

may be so, but fiction

from being pie-in-the-sky, a magnet-driven temperature domestic

can become

fact. And far

“Magnetic

carbon

(HCFC)

compression-expansion

that works at room

instead

refrigerators

of having

and hydrochlorofluoro-

used in the conventional

cycle costly

of current

recovery

models.

systems

So

to remove

from worn out units, all that needs to be dis-

posed of is water.”

and air conditioners

than conventional

(CFC)

refrigerants

in the US say that

refrigerants

too,” he says,

water or relatively

fluids, rather than the ozone-depleting

researchers

could be in use in around five years, with

of

of Iowa.

advantages

would circulate

fluorocarbon

industrial refrigerator

versions to follow.

be more efficient

appliances

benign antifreeze

fiction.

at the University

are environmental

chlorinated That

leader of a team at the US Department

Energy’s Ames Laboratory “Magnetic

at

promise to

models,” says Karl A

Magnetic

cooling

is by no means a new technology.

has been used for more than 50 years by cryogenics cialists

to chill

substances

It spe-

already

cold

to even lower tem-

peratures. A few years ago, a team lead by Karl Gschneidner

and Carl

B Zimm of the Astronautics Corporation

of

Technology Madison,

America’s

Center Wisconsin,

in demon-

strated a magnetically refrigeration

driven

unit that operat-

ed at room temperature. there

was

one

snag

device required genically

a large, cryo-

cooled,

powered

But _ the

electrically

superconducting

magnet, making it impractical

Demagnetized

for domestic But

use.

now

replaced

the

team

has

the superconducting

magnet

with

a

custom-

designed

permanent

magnet

that works at room temperature, the

dramatically unit’s

where

it

could

accommodated cooling As gadolinium enters a magnetic field and becomes magnetised, its atoms align, causing it to get hot. A fluid (red) carries that heat away. As hte gadolinium exits the field, the atoms absorb heat from the recirculated fluid (blue) that chills a space. The ring round which the packets of gadolinium move is about the size of a compact disc. Courtesy Vitalij Pecharsky/Ames Lab

44

MPR June 2002

ooz6-0657/02/$

- see front matter 0

2002

green

shrinking

size to the

point

easily

be

in a domestic

unit. Besides being a technology

that

water as its heat-transfer

uses fluid,

the unit runs virtually silently and vibration-free.

Elsevier Science Ltd. All rights reserved.

The team had to overcome

some chewy technical

lenges on the way, such as synchronising heat-conducting

of

fluids through portions of a rotating ring

the diameter of a compact Like

chal-

movements

disc.

its superconducting

takes

advantage

of

effect.

Conventional

predecessor,

the

so-called

refrigerators

the new unit

magnetocalorific compress

a volatile

gas and then allow it to expand rapidly, drawing in heat from

the surroundings

to provide

the

energy

for the

expansion. By contrast, cally

the magnetic

induced

heating

of the element netic The

gadolinium

member powder

carries

of

the the

exploits

cooling

of

permanent

ferromag-

series

in pockets

magnetia powder

- a silvery-white

lanthanide

is contained

it through

device

and

of

metals.

in the ring that

magnet’s

magnetic

field. The magnet is made up of an array of neodymium-ironboron

(Ne2Fe14B)

sections

(FeVCo)

near the centre

magnetic

shell.

Astronautics

with

soft

and surrounded

Corporation

ferromagnets by a soft ferro-

is now thoroughly

magnet refrigerator with a view to optimising larger temperature for specific

testing the it to achieve

swings. The aim is to tailor the system

marketplaces

such as domestic

refrigeration,

looking forward. Magnets are set to be more than mere door decoration or message holders.

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June 2002

45

efficiency ly

will lower costs significant-

compared

methods

with

the

traditional

in use today.”

Astronautics magnetic

has been involved

refrigeration

development

research

in and

for more than 15 years,

based on work carried out at the Los Alamos

National

Laboratory

(LANL).

Collaboration

has contin,

ued with LANL Laboratory. have

and with the Ames

Researchers

been

at

Ames

instrumental

development

of

in

the

magnetocalorific

materials. Work being The Ames team.

From left: Vitalij

Pecharsky,

on

magnetocalorifics

carried

other

locations

The

Cryogenics

David Jiles and Karl Gschneidner

University

strong

electronics

early candidate

technology

is the

clean-burning

around the

for industrial

liquefaction

looking

Refrigeration,

for use as

the National Maryland

Vitalij

process

would

15 separate

cooling

temperature

gramme

of the

application

of hydrogen

A

fuel.

Ames Laboratory’s uefaction

cooling and fluid chilling.

K Pecharsky require

says: “The liq-

refrigerators

stages, combining

to 20 Kelvins.

This

with

to reduce

methods

greater

into

in

at

at

Victoria

it calls

while the Magnetic

in

of Standards

has carried

out extensive

the

British

has

Active

a

pro-

Magnetic

Materials

Institute

two

America.

Group

Canada,

what

is

least

in North

of

Columbia, air-conditioning,

out

Group

at

and Technology

in

work on magnetic

nanocomposites. Group

leader

several

years

Bob

ago

Shull

that

says:

large

magnetocalorific

effect

looking

nanocomposites

at magnetic

magnetic

clusters

non-magnetic the

material

could

were

or

be

recognised of

the

obtained

by

where small ferro-

embedded

weakly

possessed

“We

enhancements

in

magnetic

either

matrix,

a magnetic

state

a

so that known

as

superparamagnetism. “One way we found to make such a material add an atom possessing a magnetic (Fe), to a paramagnetic garnet

material

so as to promote

interaction moment

between

moment,

like gadolinium

a magnetic

gadolinium

has

the

deep red stones

same

gallium

‘superexchange’

atoms via the magnetic

of the newly introduced

component

was to

such as iron

Fe atoms. The garnet

crystal

used in jewellery,

structure

as the

but is of a different

composition. “The

resulting

the

expected

The

addition

response tures

and

magnetic

a

magnetic

tripled

field.

the enhancements lower

material

showed

magnetocalorific

of iron effectively

to

of material

superparamagnetic ‘enhanced’

effect.

the materials

For

this

are at higher fields

than

type

tempera-

conventional

materials. “Since then, we have looked at other similar materials, such as neodymium-iron-aluminium-boron recently

we have

holmium-based netocalorific collaboration

examined

materials,

several

again finding

alloys. Most dysprosium enhanced

and mag-

effects. Much of this work is carried out in with scientists

from the Ames

Laboratory

and NASA-Goddard. “Our focus is to increase which

magnetic

magnetic

46

MPR

June

2002

cooling

the temperature

is feasible,

range over

while reducing

fields required to carry it out.”

www.metal-powder.net

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