Mixed convection heat transfer in a two-dimensional trapezoidal lid-driven enclosure filled with nanofluids
heated from below is numerically studied. The governing equations for both fluid flow and heat transfer are
solved by using the finite volume method (FVM). The bottom wall of the enclosure is heated while the upper
wall is cooled at lower temperature and the other two sidewalls are adiabatic. Four types of nanofluids (Al2O3,
CuO, SiO2, and TiO2 with purewater)with nanoparticle volumefraction (?) inthe rangeof 1–4% and nanoparticle
diameter in the range of 25–70 nm were used. This investigation covers Richardson number and Reynolds number
in the ranges of 0.1–10 and 100–1200, respectively. The trapezoidal lid-driven enclosurewas studied for different
rotational angles (?) in the range of 30°–60°, different inclination sidewalls angles (?) in the range of 30°–
60° and various aspect ratios (A) ranged from 0.5 to 2. This investigation is also examined the opposing and
aiding flow conditions. The results show that all types of nanofluids have higher Nusselt number compared
with pure water. It is found that SiO2–water has the highest Nusselt number followed by Al2O3–water, TiO2–
water, and CuO–water. The Nusselt number increases as the volume fraction increases but it decreases as the diameter
of the nanoparticles of nanofluids increases. The Nusselt number increaseswith the decrease of rotational
angle and inclination angle from 30° to 60° and with the increase of aspect ratio. The results of flow direction
show that the aiding flow gives higher Nusselt number than the opposing flow.