One of the commercially most successful applications of ferrofluids in consumer
products is in loudspeakers, where the ferrofluid plays three important roles: (i) it
centers the voice coil within the magnet; (ii) it acts as a coolant for the voice coil, by
removing the heat caused by Ohmic losses; and (iii) it acts as damping medium. The
design of a loudspeaker using a ferrofluid is shown schematically in Figure 6.9.
One other possible future application of nanofluids has been reported by Krauß et al.
[7], who demonstrated the pumping of ferrofluids in a channel by an alternating
current (AC) magnetic field. The magnetic particles in the fluid were cobalt-based. The
set-up, which consists of a circular channel and two coils, is shown in Figure 6.10.
Here, coil 1 produces a vertical magnetic field, while coil 2 is wrapped around the
channel and produces a magnetic field in the direction. Both coils are driven with an
alternating current from the same source, although with a phase difference of 90
. The
two coils together generate a rotating magnetic field, and changing the phase
difference from þ90
to À90
reverses the flow direction in the channel. The
nanofluids used by the authors had a viscosity of 5.5 Â 10
À3 PaÁs.
Figure 6.10 Magnetic pumping system for
ferrofluids (according to Krauss et al. [7]). Coils
1 and 2 are connected to the same AC source.
The electric currents show a phase difference of
90
, which leads to a rotating magnetic field at
the location of the circular channel (Reproduced
with permission by The American Institute of
Physics.)
Figure 6.9 Design of a high-performance loudspeaker using a ferrofluid.
130j 6 Nanofluids
products is in loudspeakers, where the ferrofluid plays three important roles: (i) it
centers the voice coil within the magnet; (ii) it acts as a coolant for the voice coil, by
removing the heat caused by Ohmic losses; and (iii) it acts as damping medium. The
design of a loudspeaker using a ferrofluid is shown schematically in Figure 6.9.
One other possible future application of nanofluids has been reported by Krauß et al.
[7], who demonstrated the pumping of ferrofluids in a channel by an alternating
current (AC) magnetic field. The magnetic particles in the fluid were cobalt-based. The
set-up, which consists of a circular channel and two coils, is shown in Figure 6.10.
Here, coil 1 produces a vertical magnetic field, while coil 2 is wrapped around the
channel and produces a magnetic field in the direction. Both coils are driven with an
alternating current from the same source, although with a phase difference of 90
. The
two coils together generate a rotating magnetic field, and changing the phase
difference from þ90
to À90
reverses the flow direction in the channel. The
nanofluids used by the authors had a viscosity of 5.5 Â 10
À3 PaÁs.
Figure 6.10 Magnetic pumping system for
ferrofluids (according to Krauss et al. [7]). Coils
1 and 2 are connected to the same AC source.
The electric currents show a phase difference of
90
, which leads to a rotating magnetic field at
the location of the circular channel (Reproduced
with permission by The American Institute of
Physics.)
Figure 6.9 Design of a high-performance loudspeaker using a ferrofluid.
130j 6 Nanofluids