Biomedical Engineering Reference
In-Depth Information
ratio was modified as:
Z
Z
0
¼
1
þ
10
f
½
10
:
7
Masoumi et al. (2009), considering the effect of Brownian motion of the
nanoparticles, showed a negligible contribution of Reynolds number for
10 nm Al
2
O
3
particles dispersed in water and assumed no interparticle
interaction to predict the effective viscosity of nanofluids as:
r
p
V
B
d
2
Z
Z
0
¼
p
72C
dZ
f
1
þ
½
10
:
8
where
is the distance between nanoparticles, V
B
is the Brownian velocity,
d
p
is the particle diameter, and c is the correction factor. Experimental
results from Namburu et al. (2007b), Chen et al. (2007a), and Nguyen et al.
(2007b) have been compared using this model and the data quite accurately
fit the values predicted by the model, suggesting that Brownian motion has a
major contribution in the phenomenal increase in viscosity of nanofluids.
δ
10.7 Summary and future trends
Since the advent of nanofluids in the late 1990s, extensive investigations
have attempted to characterize the different properties of nanofluids. This
chapter has provided an insight into the study of the synthesis and thermo-
physical properties of nanofluids, including a discussion of the potential
fields for application of nanofluids. Although an amount of experimental
research has been carried out by several research groups across the globe,
there is a severe void regarding explanation of the experimental results. As
surveyed from the literature, the viscosity of nanofluids has been observed to
increase in comparison to the base fluid, sometimes the increase being many-
fold; theories that can explain such level of enhancement still remain elusive.
Several mechanisms have been proposed to explain the anomalous
enhancement in viscosity of nanofluids, but one integrated theory has still
not been predicted that can singlehandedly explain the enhancement in
viscosity irrespective of the nature and type of nanofluid. Further detailed
research in theoretical explanation of the experimental results observed in
nanofluids is thus a major area for future focus.
