Abstract:
Nanofluids, which are suspensions of nanoparticles in conventional heat transfer fluids,
attracted research studies on different heat transfer applications, while they enhance
thermal transport properties in comparison with conventional base fluids.
Recently, the use of these new fluids has been growing increasingly. However, the
ambiguities of their thermo-physical properties cause them to function inefficiently in
industrial design. The recognised important parameters that affect the properties of
nanofluids include the volume fraction of the nanoparticles, temperature, nanoparticle
size, nanolayer, thermal conductivity of the base fluid, pH of the nanofluid and the
thermal conductivity of the nanoparticles. However, there is a distinct lack of
investigation and reported research on the nanolayer and its properties.
In this study, the effect of uncertainty of the nanolayer properties on the effective thermal
conductivity and viscosity of nanofluids, and heat transfer are discussed in detail. The
results show that the uncertainties can cause 20% error in the calculation of the Nusselt
number and 24% for the Reynolds number. Therefore, more research needs to be
conducted on nanolayer properties in order to identify them accurately.
The density of some nanofluids, such as SiO2-water, SiOx-EG-water, CuO-glycerol and
MgO-glycerol, has also been investigated experimentally. Therefore, the effects of
nanolayer thickness and density on nanofluid properties are discussed in detail. The
results show that nanolayer density and thickness have a significant effect on nanofluid density, and nanolayer density is found to be between void and base fluid density.
Consequently, by analysing experimental results and performing a theoretical analysis,
a model has been derived to calculate the density of nanofluids.
Specific heat capacity is the other nanofluid property that is discussed in this study.
Experimental data from literature, available formulae and the presented model for
nanofluid density have been used to identify nanofluid-specific heat capacity, while
nanofluid density is one of the parameters in calculating specific heat capacity. This
investigation was performed using a model ? used by different authors ? that also
considers the nanolayer. The specific heat capacity of nanofluids that resulted from two
methods of calculation has been compared with available experimental data. This
investigation shows that the proposed model for the density of nanofluids provides better
agreement for specific heat capacity in comparison to experimental data.
