Biomedical Engineering Reference
In-Depth Information
mobility of the particles, attributable to their tiny size, which may bring
about micro-convection in the fluid and hence increased heat transfer. It
has already been found that the thermal conductivity of nanofluids
increases significantly with a rise in temperature (Das et al., 2003a),
which may be attributed to heat conduction due to micro-convection
and particle morphology.
.
Suspension of particles of nanometer size reduces the probability of
particle clogging as compared to conventional slurries, thus enabling
system miniaturization.
.
Nanoparticles used as dispersoids in nanofluids are very small and do
not carry as much momentum as their milli- or micro-counterparts;
thus, the kinetic energy and momentum they impart to solid surfaces is
small. Consequently, erosion of components such as pipelines, pumps,
and heat exchangers will be greatly reduced.
.
Enhanced thermo-physical properties (including thermal conductivity)
by varying the particle concentration make nanofluids suitable for
various applications. The increased thermal conductivity of the fluids
also ensures an increment in heat transfer rate and is expected to save
much pumping power.
10.4 Applications of nanofluids
The improved thermo-physical properties and the above stated benefits of
nanofluids make them a promising candidate for a wide range of industrial
and medical applications (Yu et al., 2007a). Some of the fields of
application, including transportation, microelectronic cooling, manufactur-
ing, biomedicine, and defense, are now briefly discussed.
10.4.1 Heat transfer devices
Heat rejection requirements are continually increasing due to trends towards
faster speeds (in the multi-GHz range) and smaller features (towards
<
100 nm) for microelectronic devices, more power output for engines, and
brighter beams for optical devices. Nanofluids, due to their projected
enhanced heat transfer capability, can be used to combat such ever
increasing heat rejection requirements. Since nanofluids utilize particles in
suspension that are in the nanometer range, problems due to sedimentation
and clogging should not pose a major problem. Hence they can be used as
cooling agents even in microchannel heat transfer devices. Nanofluids can
also be used as a coolant in heat exchangers, including car radiators, to
efficiently extract heat at a much faster rate. In addition, experiments have
shown that the critical heat flux is improved by using nanofluids compared
