Mixed convection of nanofluids in a three dimensional cavity with two adiabatic inner rotating cylinders

In this study, mixed convection of nanofluids in a three dimensional cavity with two inner adiabatic rotating circular cylinders were analyzed by using finite element method. Vertical surfaces are kept at constant temperature while other walls and rotating cylinder surfaces were taken as adiabatic. The three dimensional cavity was filled with water and various types of nanoparticles (Cu, Al2O3 and TiO2). The water-Cu nanofluid provided the highest heat transfer rate and at the highest value of Rayleigh number, 4% higher average heat transfer rate is obtained when compared to other particles. When cylinders rotate, depending on the rotational direction either enhancement or deterioration of average Nusselt number is observed. For the highest value of rotational speed of the cylinders, 8.5% discrepancy between the average Nusselt number is observed for the nanofluid with Cu and Al2O3 nanoparticles. For Cu-water nanofluid at the highest volume fraction as compared to base fluid, 38.10% of enhancement in the average heat transfer is obtained. A correlation for the average Nusselt number in polynomial form was developed which is a function of Rayleigh number and angular rotational speed of the cylinders. (C) 2017 Elsevier Ltd. All rights reserved.