Magnetocaloric Fluids - Magnetocaloric Energy Conversion: From Theory to Applications - page 181

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Title Synthesis and magnetorheology of suspensions of submicron-sized

cobalt particles with tunable particle size (Lopez et al. [ 83 ])
appropriate amounts of cobalt powders in silicone oil. Aluminium
stearate was used as dispersant

Constitutive model Authors applied the Bingham model (Eq. 5.14)

Title Average particle magnetization as an experimental scaling parameter

for the yield stress of dilute magnetorheological fluids (Vereda et al.
[ 84 ])

Materials used for
investigation

Authors have applied a large number of different particles suspended
in the carrier fluid. The properties of the different types of particles
used for the preparation of MR fluids are shown below
Solid iron particles; spherical; size ( μ m) 0.76 ± 0.40; M S
(kAm − 1 ) = 1,600
Porous iron spheres; spherical; size (

μ m) 0.7 ± 0.2; M S

(kAm − 1 ) = 766 (de Vicente et al. [ 85 ])
Porous iron plates; plate-like; diameter ( μ m) 2.1 ± 0.5; thickness

0.05; M S (kAm − 1 ) = 766 (de Vicente et al. [ 85 ])
Porous iron rods; rod-like; diameter ( μ m): 0.45 ± 0.08; length ( μ m):
4.7 ± 2.2; M S (kAm − 1 ) = 707 (de Vicente et al. [ 85 ])
Solid magnetite spheres; spherical; size (

( μ m): 0.25 ±

0.15; M S
(kAm − 1 ) = 475 (de Vicente et al. [ 86 ], Vereda et al. [ 87 ])
Solidmagnetite rods; rod-like; diameter (

μ m) 0.68 ±

μ m) 0.56 ± 0.12; length ( μ m):

0.4; M S (kAm − 1 ) = 475 (de Vicente et al. [ 86 ], Vereda et al. [ 87 ])
The MR

0.7 ±

uids were prepared by dispersing particles silicone oil with
viscosity of in 20 m Pa s. Particle volume fraction was in all cases
low, ranging from 0.5 to 2.1 %, mainly because the authors wanted
to work with dilute dispersions for which the yield stress is expected
to depend linearly on the volume fraction of particles

fl

Constitutive model The experimental parameter that was chosen for the denition of the

yield stress was an average volumetric particle magnetization as the
function of magnetic eld, which was calculated from magnetization
curves taken either from powder samples or from the suspensions. In
the case of suspensions the following equation was applied for the
average particle magnetization
M p ð H Þ ¼

M suspension ðÞ
/ V

(5.30)
The static yield stress of a dilute suspensions was dened by the
following relation
s 0 static ¼ / V 0 : 00219 M p 2

(5.31)
The static yield stress is dened as the minimum stress required to
start the ow. Authors have also dened the dynamic yield stress,

which is the stress needed to continuously break the aggregates that
reform by the in

fl

fl uence of the eld once the fl ow has started (de

Vicente et al. [ 88 ])

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