Hybrid Nanofluids Mixed Convection inside a Partially Heated Square Enclosure with Driven Sidewalls

This study investigates laminar convection in three regimes (forced convection, mixed convection, and natural convection) of a bi-nanofluid (Cu-Al2O3-water)/mono-nanofluid (Al2O3-water) inside a square enclosure of sliding vertical walls which are kept at cold temperature and moving up, down, or in opposite directions. The enclosure bottom is heated partially by a central heat source of various sizes while the horizontal walls are considered adiabatic. The thermal conductivity and dynamic viscosity are dependent on temperature and nanoparticle size. The conservation equations are implemented in the solver ANSYS R2 (2020). The numerical predictions are successfully validated by comparison with data from the literature. Numerical simulations are carried out for various volume fractions of solid mono/hybrid-nanoparticles (), Richardson numbers (0.001 ≤ Ri ≤ 10), and hot source lengths (). Isothermal lines, streamlines, and average Nusselt numbers are analyzed. The thermal performance of nanofluids is compared to that of the base heat transfer fluid (water). Outcomes illustrate the flow characteristics significantly affected by the convection regime, hot source size, sidewall motion, and concentration of solid nanoparticles. In the case of sidewalls moving downward, using hybrid nanofluid (Cu-Al2O3-water) shows the highest heat transfer rate in the enclosure at Ri = 1, and volume fraction of φ = 5% where a significant increment (25.14%) of Nusselt number is obtained.