Comprehensive simulation of nanofluid flow and heat transfer in straight ribbed microtube using single-phase and two-phase models for choosing the best conditions

In this paper, the hydrodynamics and heat transfer parameters of nanofluids are investigated using CFD analysis. Laminar convective heat transfer of alumina-water nanofluids with 0, 1%, and 2% volume fraction in a straight microtube heat sink under constant wall heat flux condition is studied. This work is performed in two parts. In the first part, the single-phase and two-phase approaches have been used for modeling heat transfer of pure water and alumina-water nanofluids in a straight microtube. The results of simulation are compared with the experimental data. The results showed that CFD predictions via a two-phase model show better agreement with the experimental measurements. For nanofluid with 1% concentration, the average relative error between the experimental data and CFD result based on a two-phase model is 5.85%, while for nanofluid with 2% concentration that is 2.54%. In the second part of this work, the effects of ribs through the microtube are investigated. The effect of the geometry on the Nusselt number and friction factor in the microtube is studied. We found that spiral pitch increment increases the thermal performance by an average of 19.8%. Finally, the best performance is obtained for the ribs height 1 mm and the pitch 1.5 mm.