Investigation of nanofluids mixed convection in an enclosure with cylindrical obstacles and movable top surface

The lid-driven cavity with flow is widely used in mixing, coating, and drying applications and constitutes a significant factor in the study of heat transfer rates and fluid fields. This study uses a numerical approach to analyze the temperature and velocity distribution in a square enclosure driven by a lid. The enclosure has a length of 30 cm and a width of 25 cm and contains five interior adiabatic different shapes obstacles with a radius of 1 cm. The top wall of the enclosure is cooled isothermally at temperature Tc and moves at a speed of U, The bottom wall is maintained at constant heat flux of (q´=400 and 900 W/m^2), and the left and right walls are perfectly insulated. Three different working fluids were employed: water, Al_2 O_3, and CuO-water nanofluid, with varying volume fractions of 0.01%, 0.02%, 0.04%, and 0.06%. The outcomes displayed that for the five circular obstacles with r=0.5 cm, the Nusselt number is improved by 23 %, and augmented by 8 % for r=0.5 cm. Finally, the average Nusselt number increased by 15% for TiO2-water, by 17% for CuO-water, and by 24% for Al_2 O_3-water nanofluids at φ=0.1% vol., with a top wall velocity V=0.2 m/sec, and a heat flux q´=900 W/m2.