Nanoscale solid particles suspended in a base liquid are a new class of nano-engineered colloidal suspension, defined with a coined name of nanofluids (NFs). The effect of dispersing nanoparticles (NPs) on the hydraulic and thermal (hydrothermal) performance of the conventional coolants is a matter of importance in many applications. This work experimentally and numerically presents the effect of different parameters, including the concentration and size of the NPs, on two primary parameters, namely heat transfer coefficient and friction factor in a microtube. The numerical modeling of colloidal suspensions was conducted based on single-phase as well as Eulerian-Mixture two-phase approaches and showed a good agreement with experimental results. The numerical results displayed that the suspended NPs remarkably increased the convective heat transfer coefficient as well as friction factor by as much as 42% and 22% (in NP concentration range of 1%–9%, and NP size range of 13–130 nm and Reynolds number of 400) respectively. Besides, two new correlations were developed based on the results obtained from experimentally validated models to predict the hydrothermal response of NFs in the laminar regime. Moreover, correlations were successfully created to predict the Nusselt number and friction factor of nanofluids, with ±8% and ±5% agreement between numerical data and predictions, respectively.

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