Water/silica nanofluid. Due to the lack of reliable models,
especially for suspensions with non-spherical nanoparticles,
thermal conductivity and dynamic viscosity have been measured.
Thermal conductivities have been measured using a thermal
property analyzer (model Lambda system 1, F5 Technology GmbH)
based on the transient hot wire method. The accuracy was carefully
checked with pure water. The relative error of the thermal
conductivity given by the manufacturer is 0.5%. However ,we have
compared experimental values obtained with purewater and those
given by usual recommended values [10] between 20 and 80 C.We
have found a relative difference of 1% below 70 C and up to 2%
above. Error bars of 2% are smaller than point sizes in Fig. 3.
Results are presented in Fig. 3(a) as a function of temperature.
Two points can be underlined: (i) thermal conductivity of nanofluids
with spherical nanoparticles is less than that of water. This can be
explained by considering that the SiO2 nanoparticles are made of
a porousmaterial andthat thenanoparticle conductivity isnot that of
pure silica. (ii) It is observed that thermal conductivity of nanofluid
with non-spherical nanoparticles appears to be slightly higher than
that of spherical particles. However, the increase is not as high as the
onecalculated fromtheHamiltoneCrosser relationship.The bananashaped
nanoparticles have a surface area in contact with stabilizing
chemicals greater than the spherical ones leading to largeramount of
these chemicals inside the porous core. On the other hand, the
interfacial resistance is greater for banana-like nanoparticles than for
the spherical onesand thendiminishes the effect related to the shape
factor. The effect of interaction of nanoparticles with base fluids has
also been reported by Timofeeva et al. [3].