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A numerical study is carried out to investigate the effects of different geometrical parameters and various nanofluids on the thermal performance of rib–grooved channels under uniform heat flux. The continuity, momentum and energy equations are solved by using the finite volume method (FVM). Three different rib–groove shapes are studied (rectangular, semi-circular and trapezoidal). Four different types of nanoparticles, Al 2 O 3 , CuO, SiO 2 and ZnO with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 20 nm to 60 nm, are dispersed in the base fluids such as water, glycerin and ethylene glycol. The Reynolds number varies from 5000 to 25,000. To optimize the shape of rib–groove channels different rib–groove heights from 0.1 D h (4 mm) to 0.2 D h (8 mm) and rib–groove pitch from 5 e (20 mm) to 7 e (56 mm) are examined. Simulation results reveal that the semi-circular rib–groove with height of 0.2 D h (8 mm) and pitch equals to 6 e (48 mm) has the highest Nusselt number. The nanofluid containing SiO 2 has the highest Nusselt number compared with other types. The Nusselt number rises as volume fraction increases, and it declines as the nanoparticle diameter increases. The glycerin–SiO 2 nanofluid has the best heat transfer compared to other base fluids. It is also observed that in the case of using nanofluid by changing parameters such as nanoparticle diameter, volume fraction and base fluids the skin friction factor has no significant changes. [ABSTRACT FROM AUTHOR]

In this article, laminar mixed convective heat transfer at different nanofluids flow in an elliptic annulus with constant heat flux boundary condition has been numerically investigated. The three dimensional governing equations (continuity, momentum and energy) are solved using the finite volume method (FVM). The investigation covers Reynolds number and nanoparticle volume fraction in the ranges of 200–1000 and 0–4% respectively. In the present work, four different types of nanofluids are examined in which Al 2 O 3 , CuO, SiO 2 and ZnO are suspended in the base fluid of ethylene glycol (EG) with different nanoparticle sizes 20, 40, 60 and 80 nm. The results show that SiO 2 -EG nanofluid has the highest Nusselt number, followed by Al 2 O 3 -EG, ZnO-EG, CuO-EG, and lastly pure ethylene glycol. The Nusselt number increased as the nanoparticle volume fraction and Reynolds number increased; however, it decreased as the nanoparticle diameter increased. It is found that the glycerine-SiO 2 shows the best heat transfer enhancement compared with other tested base fluids. Comparisons of the present results with those available in the literature are presented and discussed. [ABSTRACT FROM AUTHOR]