The impact of the forced convection flow of the nanofluids on the thermal performance of the different ribbed/smooth rotating U-type cooling channels is investigated in this work. The U-type channel rotates about the axis perpendicular to the main flow direction. The 45° angled ribs are attached to the leading and trailing walls in parallel for ribbed channels. The nanofluids are provided by the inclusion of the nanoparticles of TiO 2 and Al 2 O 3 in water as the base fluid, namely water/Al 2 O 3 and water/TiO 2 nanofluids mixtures. The numerical simulations are performed for three different geometries including macro, micro and minichannels. In order to understand the effects of the ribs on the fluid flow and heat transfer in the channel, the flow of nanofluids in the same channel with no ribs (smooth channel) is also simulated. To improve the heat transfer enhancement of the employed macrochannel, parallel arrangements of the micro/mini channels are also evaluated. Also the convergent-divergent U-type minichannel is investigated. Three dimensional laminar and turbulent simulations are carried out based on the employed geometries. For the cases with turbulent flow and heat transfer (Re=5000-20000), numerical simulations are performed by using Reynolds-Averaged Navier-Stokes equations (RANS). In order to calculate turbulent viscosity, different one and two-equation turbulence models are tested and finally a RNG K-? turbulence model is employed. To show the effectiveness of the rib and nanofluids, the thermal performance factor is used to evaluate the amount of heat transfer enhancement relative to power consumed. The combinatorial effects of the ribs and nanofluids on the results and also the contribution of each one in the heat transfer enhancement for the different geometries are determined. It is found that the inclusion of the nanoparticles into the base fluid is provided a considerable augmentation on the heat transfer that clearly increases with an increase of the particle concentration and Reynolds numbers. The results also show using ribs on the walls of the macrochannel improve heat transfer enhancement. A comparison between the results of different type of channels employed show that the fluid flow through the minichannels provides the best performance on heat transfer augmentation. Keywords Nanofluids; U-shaped channels; smooth and ribbed; micro/minichannels heat sink; heat transfer enhancement; thermal performance; numerical simulation; convergent-divergent; turbulent flow
