Magnetocaloric Fluids - Magnetocaloric Energy Conversion: From Theory to Applications - page 175

(continued)
Title In uence of large size magnetic particles on the magneto-viscous

properties of a ferro

fl

fl uid (Shah et al. [ 32 ])

Constitutive model The authors applied the Bingham model (Eq. 5.14). The rheological

properties of the rst two suspensions were measured for varying
shear and eld values. The yield stress varied from 2.2 to 5.5 Pa for a
magnetic eld from 0 to 1 T. The second fluid with 30-nm particles
exhibited magneto-viscous behaviour with an increased magnetic
eld. The yield stress obtained was almost 15 times higher than that
of the rst fluid

Viscosity For the ferrofluid: the magneto-viscous effect was measured for a

xed shear rate of 10 s − 1 and a varying magnetic eld. A clear
dependence of the magneto-viscosity on the eld is observed. The
increase in the MVE with magnetic eld in the small range of shear
rate was calculated with the help of relations given by Martsenyuk
et al. [ 37 ] and Shliomis [ 19 ]
For MRF: the authors expected strong dipolar interactions between
the particles. The suspension showed a magneto-viscous effect, an
increase in the viscosity and the occurrence of yield stress

Title Rheological properties of water-based Fe 3 O 4 ferrofluids (Hong et al.

[ 29 ])

Materials used for
investigation

Water-based ferrofluids were prepared from Fe 3 O 4 ferromagnetic
nanoparticles, and oleate sodium and Polyethylene Glycol (PEG)
surfactants. For bilayer-stabilized ferro uids, oleate sodium was used

to modify the surface of a ferromagnetic nanoparticle as the rst
layer. Then PEG was utilized to cover the second layer. The average
size of 98 % of nanoparticles was about 23 nm. The viscosity and
yield stress were analysed for the ferro

fl

fl uid with a high solid mass

fraction (>25 %)

Constitutive model Bingham (Eq. 5.14), Casson (Eq. 5.16) and Herschel - Bulkley model

(Eq. 5.17) were applied to describe the rheological properties of
high-concentration ferro fl uids without the application of a magnetic

eld. Einstein s equation (Eq. 5.2 ), the best tting with the

experimental results was obtained with the Herschel

'

Bulkley model
The authors investigated the magnetic eld with intensities of 22, 49
and 73 mT. It was found that the Herschel-Bulkley (Eq. 5.17) model
gives the best tting results with respect to the experiments. In this
model the authors separated the yield stress caused in the absence of
a magnetic eld and the yield stress associated with the magnetic
eld. They also proposed a correlation for the prediction of the
magnetic-eld-dependent yield stress

-

Viscosity The authors applied Einstein ' s equation (Eq. 5.2 )

Title Rheological properties of a ʳ -Fe 2 O 3 parafn-based ferrofluid

(Hosseini et al. [ 30 ])

Materials used for
investigation

ʳ -Fe 2 O 3 magnetic nanoparticle powder, (mean particle size of

<50 nm), coated with oleic acid (OA) and dispersed in a suitable
amount of parafn. The concentration was adjusted to a 30 % mass
fraction of particles. The average particle size of the aggregates was
398 nm, which varied in the range 210 686 nm. Referring to this, it

(continued)

-