Hydrodynamic Behavior of Nanofluids in Microchannel Heat Sinks: A CDF Approach

Abstract

The introduction of nanofluids into thermal systems is often hindered by the lack of knowledge on the hydrodynamic penalties of nanofluids, specifically the contribution of the increased friction factor and the related pumping power needs; although results already appeared on the modification of the pressure drop, a notable gap still exists in separating the intrinsic effect of the presence of nanoparticle material from the prevailing effect of the flow regime, leading to conflicting conclusions about the effects of the material specificities. This study was designed so that the effect of nanoparticle type on the friction factor could be definitively quantified by controlling the confounding variable of Reynolds number (Re). An analysis of covariance (ANCOVA) was used with Re as a covariate to analyze the experimental data on friction obtained from three water-based nanofluids (Al2O3, SiO2 and TiO2 at a 0.1% volume concentration) at laminar flow (Re range: 500-2000) in a circular tube test section. The overall model was highly significant (F(3, 71) = 12450, p < 0.001) and an almost perfect variance (R2=0.998). Crucially, after controlling for Re, the major effects of nanoparticle type were shown to be statistically non-significant (F(2, 71) = 1.97, p = 0.146). This proves that the observed differences in pressure drop are only due to nanofluid - induced variations of the effective viscosity and density that modify the operating Re, and not to an intrinsic property of the nanoparticle material itself. This finding offers critical clarity to system designers in that predictive hydrodynamic performance does not depend on material-specific friction correlations but rather on  accurate thermophysical property data, thereby reducing the engineering analysis complication for nanofluid-based systems.