Heat transfer and flow field of water-Al2O3 nanofluid were simulated three-dimensionally in the shell-side of shell-and-tube heat exchanger with helical baffles. The effects of Reynolds number and volume fraction on heat transfer and pressure drop were evaluated. Increasing the volume fraction and Reynolds number intensified both heat transfer and pressure drop. Reduction of the Reynolds number increased the friction factor, but no considerable change was observed in the friction factor by increasing the volume fraction at constant Reynolds number. Heat transfer of the nanofluid revealed greater dependency on the volume fraction of particles at This study aims to evaluate the energy efficiency of nanofluid as a heat transfer fluid in a chaotic channel. To this end, hydrothermal characteristics of the water–Al2O3 nanofluid are numerically investigated in C-shaped and straight channels using single- and two-phase methods and then, the results are compared with each other. In the C-shaped channel, heat transfer and pressure drop show higher values in comparison with the straight channel, which is due to intense mixing in the chaotic geometry, such that the velocity and temperature contours in the C-shaped channel are more uniform than those in the straight one. Using the two-phase method, the concentration distribution is obtained non-uniform at the cross section of the straight channel, while intense mixing in the C-shaped channel makes distribution of the nanoparticles uniform. In comparison with water, using the nanofluid through both channels presents higher heat transfer and pressure drop. However, merit of using the nanofluid in the C-shaped channel is greater than that in the straight one. In this regard, simultaneous application of nanofluids, as heat transfer fluids, and chaotic channel, as a modified geometry, can result in not only higher energy efficiency, but also preventing nanoparticles agglomeration due to the intense mixing.
