Modeling of a room temperature magnetic refrigerator based on nanofluid

ICNMRE, Safi Morocco 1

MODELING OF A ROOM TEMPERATURE MAGNETIC REFRIGERATOR BASED ON

NANOFLUIDMoulay Youssef El Hafidi and Mohamed El Hafidi

Laboratoire “Modélisation et Instrumentation”Faculté des sciences Ben M’sik - Département de Physique

Université Hassan II Mohammedia-Casablanca

08/07/2010


Outline of this talk Introduction Model specifications Model design Magnetic cooling Nanofluids Conclusion & perspective

08/07/2010


Introduction Conventional techniques of coolingGas compression and expansion:

Chlorofluorocarbon (CFC) Hydrofluorocarbon (HFC) Hydrochlorofluorocarbon (HCFC)

These greenhouse gases contribute to global warming.

vs Magnetic cooling

Ecology (Absence of greenhouse gas emissions) Energy efficiency (up to 60%)

08/07/2010


I- Model specifications Magnetism source:

NdFeB permanent magnets Magnetic field:

1.3 Tesla Magnetocaloric material:

Porous Gadolinium Base liquid:

Water Nanoparticles:

Carbon nanotubes (CNT) Temperature:

20°C

08/07/2010


I- Model specifications Fluid flow rate:

1L/min = 60g/s Cycle time:

2 seconds Porous Gd caracteristics:

200g flat disc, 400µm diameter Generated refrigeration power:

50-60W COP:

about 26 ΔT:

6 K

08/07/2010


II.Model design

08/07/2010


III.Magnetic cooling Magnetocaloric Effect (MCE)It is an intrinsic property of certain materials resulting in

a change in temperature (hot / cold) during the change of magnetic state (magnetized / demagnetized) induced by an external magnetic field.

Material magnetic moments are oriented in the direction of magnetic field.

08/07/2010


MCE and thermodynamicsEntropy is a state function that measures the degree of system disorder at

microscopic level.Total entropy:

Magnetic entropyStructure entropyElectrons entropy (negligible)

Under the action of a magnetic field, the magnetic moments are aligned and lead to the reduction of the magnetic entropy. If this process is adiabatic and reversible, this increases the temperature of the material [Tura 2002].

This effect is maximum around the phase transition temperature of magnetic material (Curie temperature).

rmerm sssssBTS ,

msrses

08/07/2010

III.Magnetic cooling


MCE calculationTotal entropy is given by:

Adiabatic process:

Isothermal process:

dBTM

CTT

B

B

B pab

f

i

dBTMS

B

B

Bis

f

i

dBBSdT

TSBTdS

TB

),(

08/07/2010



)(

21sinh

212sinh

ln)( xxBx

J

xJJ

Rxs Jm

Molecular field theory (Weiss model)The applied magnetic field is increased by an additional

magnetic field proportional to the induced magnetization.

with:R: universal gas constantJ: total angular momentum : Brillouin function

08/07/2010



MCE experimental results for Gd

08/07/2010



Magnetic cooling cycles

08/07/2010



Coefficient of performance (COP)It is the ratio of cold energy to the supplied

workwqCOP c

3

2

4

1

4

1

TdSTdS

TdSCOPBrayton

231410

410

SSTSSTSSTCOPEricsson

08/07/2010



III.Magnetic coolingA powerful magnetic refrigerator has the following

characteristics:A giant magnetocaloric effect(MCE).A Curie temperature near the cold source.A high heat capacity of fluidA high thermal conductivity in the direction of the

exchanges with the fluid and low in other directions to reduce losses by diffusion.

A low viscosity fluid to reduce losses of the flow. A high coefficient of heat exchange to have the

maximum possible exchange between the magnetic material and the fluid.

08/07/2010


What is a nanofluid?A fluid in which nanometer-sized particles

(with typical length scales of 1 to 100nm) are suspended.

08/07/2010

IV. Nanofluids


Why nanofluids? Nanofluids have the potential to reduce thermal resistances They have been shown to enhance the thermal conductivity and

convective heat transfer performance of the base liquids. Significant increase of thermal performance. For example, the addition of a small amount (less than 1 percent

by volume) of nanoparticles to conventional heat transfer liquids increased the thermal conductivity of the fluids up to approximately two times (Choi, et al. 2001).

Why carbon nanotubes?

The conductivity ratio goes up to 1,7 for volume concentration of 2% only.

f

nf

kk

08/07/2010

IV. Nanofluids


Base LiquidsWaterEthylene glycolLight oils

Nanoparticle materialsOxide ceramics (AlO3, CuO)Nitride ceramics (AlN, SiN)Carbide ceramics (SiC, TiC)Metals (Ag, Au, Cu, Fe)Semiconductors (TiO2)Single-, double- or multi-walled carbon nanotubes

(SWCNT, DWCNT, MWCNT)

08/07/2010

IV. Nanofluids


Nanoparticles production methodsPhysical methods

○ Mechanical grinding○ Inert-gas-condensation

Chemical methods○ Chemical precipitation○ Chemical vapor deposition○ Micro-emulsions○ Spray pyrolysis○ Thermal spraying

08/07/2010

IV. Nanofluids


Nanofluids production techniquesTwo-step technique

It starts with nanoparticles produced by one of the physical or chemical methods and proceeds to disperse them into a base fluid.Single-step technique

It makes and disperses simultaneously the nanoparticles into a base fluid.

Most of nanofluids containing carbon nanotubes are produced by the two-step technique.

08/07/2010

IV. Nanofluids


Nanofluid thermal conductivity enhancement parameters:Particle volume concentrationParticle materialParticle sizeParticle shapeBase fluid materialTemperatureAdditiveAcidity (pH)

08/07/2010

IV. Nanofluids

ICNMRE, Safi Morocco 2108/07/2010


Nanofluid Thermal conductivityHamilton-Crosser formula:

Nanofluid viscosityBrinkman formula:

Nanofluid density

Nanofluid specific heat

sffs

sffs

f

nf

kkknkkknknk

kk

1

11

08/07/2010

5.21

fnf

fsnf 1

fpspnfp ccc 1


Conclusion & perspective We proposed in this study a self magnetic

refrigerator design. The originality of this work relates to the

connection between magnetic cooling technology and Nanofluid technology.

The design is mainly dedicated to air conditionning.

We still need to perform experimental test to validate theory

As perspective, we will try to replace porous Gd by Nanoporous Gd.

08/07/2010


Thank you for your attention

08/07/2010

Documents

Modeling of a room temperature magnetic refrigerator based on nanofluid