Biomedical Engineering Reference
In-Depth Information
in thermal resistance of the heat pipe with the nanofluid as compared with de-
ionized water (Tsai et al., 2004). Nanometer sized particles suspended in
nanofluids can easily flow in the microchannels without clogging, thus
enhancing the cooling of micro-electro-mechanical systems (MEMS) under
high heat flux conditions. This has been numerically tested by Chein and
Huang (2005) using copper dispersed water nanofluids in silicon micro-
channels. The performance of the microchannels was found to improve due
to increased thermal conductivity and thermal dispersion effects.
Nguyen et al. (2007a) investigated the heat transfer enhancement and
behavior of Al
2
O
3
-water nanofluid with the intention of using it in a closed
cooling system designed for microprocessors or other electronic devices. The
experimental results indicate that the inclusion of nanoparticles into distilled
water produces a significant increase in convective heat transfer coefficient.
Further research on the use of nanofluids in electronic cooling
applications will lead to the development of the next generation of cooling
devices that will eventually incorporate nanofluids for ultrahigh heatflux
electronic systems.
10.4.4 Coolants in transportation
The transportation industry has strong demands to improve the perfor-
mance of vehicle heat transfer fluids and related cooling technologies.
Ethylene glycol (EG) and water mixed in a ratio of 50:50 is almost
universally used as an automotive coolant. However, the heat transfer
properties of this anti-freeze coolant are quite poor, and could be improved
by the addition of nanoparticles in suspension. To observe the heat transfer
properties of nanofluids as automotive coolants, numerical simulations have
been carried out on nanofluids containing CuO dispersed nanoparticles in a
mixture of EG and water. By using the same engine and cooling parameters
as used for standard coolant, nanofluids have been observed to exhibit a
higher heat transfer coefficient, resulting in lower engine and coolant
temperatures (Yu et al., 2007b).
Nanofluids have also been studied for the automatic transmission of four-
wheel drive vehicles. Tzeng et al. (2005) used CuO and Al
2
O
3
dispersed
engine oil based nanofluids to study the temperature distribution on the
exterior of a rotary-blade-coupling transmission at four engine operating
speeds (400, 800, 1200, and 1600 rpm). It was observed that CuO nanofluids
produced the lowest transmission temperatures both at high and low
rotating speeds.
The drive to employ nanofluids as automotive fluids carries on with
several projects exploring various aspects of design, synthesis, and proper-
ties of nanofluids. Timofeeva et al. (2009) attempted to utilize boehmite
alumina dispersed EG/water based nanofluids in actual truck cooling
