Magnetocaloric Fluids - Magnetocaloric Energy Conversion: From Theory to Applications - page 182

(continued)
Title Average particle magnetization as an experimental scaling parameter

for the yield stress of dilute magnetorheological fl uids (Vereda et al.

[ 84 ])
The dynamic yield stress was estimated by extrapolating the tting of
a Bingham equation (Eq. 5.14) to zero shear rate (determined by a t
to data points of non-negligible shear rate). By this the static yield
stress depends only on the interparticle magnetic interactions (with
the exception of the rod-based MR fluids), whereas the dynamic
yield stress depends on hydrodynamic interactions between particles
or aggregates. The dynamic yield stress was dened by the following
relation:
s 0 dynamic ¼ / V M p 2 : 1 0 : 001824 (5.32)

Title Improved thermooxidation and sedimentation stability of covalently-

coated carbonyl iron particles with cholesteryl groups and their
in fl uence on magnetorheology (Mrlik et al. [ 89 ])

Materials used for
investigation

Bare carbonyl iron (CI) microparticles and carbonyl iron (CI)
microparticles coated with a low density substance, cholesteryl
chloroformate (CI-chol) were suspended in silicone oil with 40, 60
and 80 % of mass particle concentrations. The size of most of the
bare CI particles was in the range of 0.5 - 2 μ m, and the surfaces of
these particles were roughened with small pieces of milled iron

Constitutive model Both suspensions exhibited pseudoplastic behaviour with a certain

level of yield stress. The increase of the magnetic eld resulted in
stiffer internal chain-like structures and consequently increased shear
stress. Authors have applied Herschel - Bulkley model (Eq. 5.17).
Yield stress was de ned by the Ginder ' s equation (see
Eqs. 5.26 - 5.28 ). There, the exponent of the magnetic eld intensity
was de ned to be 1.60, 1.67 and 1.75 for suspensions consisting of
mass concentration of 40, 60 and 80 % of modi ed CI particles (CI-
chol), respectively

Title A low sedimentation magnetorheological uid based on platelike

iron particles, and veri cation using a damper test (Shah et al. [ 90 ])

fl

Materials used for
investigation

Iron micro-sized particles of different sizes having a plate-like
structure. The average particles size was about 2 μ m (small size) and

19 m (large size). Both the particles and heavy paraf n oil were

mixed using a mechanical stirrer. Less than 4 % of commercial
grease was used to prevent sedimentation. The total particle volume
fraction of the bidisperse magnetorheological

μ

fl uid was 16 %

The applied magnetic eld strength varied from 0 to 228 kAm − 1 . The
yield stress was obtained using the Bingham model (Eq. 5.14) by
linear extrapolation of the

Constitutive model

ow curve to zero shear. Shear stress
increased faster at a low shear rate and then changed very slowly at
high shear rate, where the viscosity became eld independent

fl

Viscosity The viscosity versus shear rate was measured for the magnetorhe-

ological uid in the zero eld at various magnetic eld strengths in

the range of shear rate of 0.01

fl

800 s − 1 . A strong shear thinning effect
was observed as viscosity decreased with increased shear rate

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