A mathematical study was conducted for the mixed convection inside a cavity for three aspect ratios filled with hybrid nanofluids by moving the vertical walls down, where the upper wall was thermally isolated, and the two vertical walls with a temperature that is less than the lowest wall’s, which was at a sinusoidal temperature. The investigation and discussion focused on the Richardson numbers (0.1–100), hybrid nanoparticle sizes (0.0–0.08), and the impact of size on the thermal and hydrodynamic properties of hybrid nanoparticles. At lower Richardson numbers, hybrid nanoparticle volume fraction impacts the thermal behaviour model. Besides, it was observed that decreasing the effect of average Nusselt number and nanoparticle size was due to the increase in Richardson numbers.The present results also showed the vital role that sinusoidal temperature has on heat transfer.

The current study focuses on the effect of obstacles and their positioning within the square cavity (L = H) on heat exchange. This work considers heating the cavity's bottom wall to a steady, high temperature. The top wall of the cavity is adiabatic, while the two vertical side walls are cooled. Four cases are explored under these conditions: the first case is a square‐shaped cavity holding a square‐shaped obstacle h = l = 0,15 L, while the other three cases, respectively, each include two, three, and four square obstacles. The cavity was filled with Cu–Al2O3/H2O hybrid nanofluid with a volume fraction φ = 0.03. Numerical results for laminar and stationary flow regimes with Rayleigh numbers 104 ≤ Ra ≤ 106. The finite volume approach solves the governing equations numerically. The findings show that the number of square obstacles within the square‐shaped cavity significantly impacts heat exchange and hybrid nanofluid flow. The second example, with two square obstacles, improves heat exchange more than other cases with one to four barriers. In the second example, the obstacle location at the plane Y = 0.25H is suitable and helps boost heat transmission of the hybrid nanofluid. The ideal obstacle position in the fourth scenario, which has four square barriers, is at the plane Y = 0.75H.

The aim of this study is to investigate numerically the effect of sinusoidal temperature on mixed convection flow in a cavity filled with nanofluid and moving vertical walls by using a new temperature function, where thermal heating takes the form of the sinusoidal temperature; and could be found in various natural processes and industries such as solar energy, and cooling of electronic components. The heating is concentrated in the center and then distributed to both ends at different values of Rayleigh numbers, Reynolds numbers, and volumetric fractions of nanoparticles ranging from 1.47 × 103 to 1.47 × 106, 1 to 100, and 0 to 0.1, respectively. The impact of nanoparticle size on thermal characteristics and hydrodynamics was considered and evaluated. From the results, the volume fraction concentration of nanoparticles affects the flow shape and thermal performance in the case of a constant Reynolds number. Moreover, the effect of nanoparticles decreases with the increase of the Reynolds number. Besides this, with increasing the volume percentage of nanoparticles, the rate of heat transmission increases. It is worth noting that the presence of nanoparticles results in height convective heat transfer coefficient. On the other hand, the thickness of thermal boundary layers decreases with increasing Rayleigh number. The current investigation found that the (sinusoidal) temperature change significantly affects heat transfer.

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The aim of this work is to examine numerically the effect of using a rotating cylinder and porous layers on the forced convection in a bifurcating grooved channel (BGC) filled with two types of nanofluids (MgO-water, SiO2-water). The semi-implicit finite volumes method was used to solve the governing equations. The effects of Reynolds number, nanoparticles volume fraction, and cylinder rotation speed on hydro-thermal performances have been investigated. According to the obtained results, the rotation direction plays a significant role in the formation of vortices at the branching channel, such that when the cylinder rotates clockwise, the vortex occurs in the vertical channel, and it decreases with increasing Reynolds number. Besides, using BGC with a porous medium enhances the heat transfer rate by 52% and 49% at the vertical and horizontal walls of the porous layer, respectively. On the other hand, the heat transfer rate is improved by 2.6% when using MgO nanoparticles compared to SiO2. Therefore, the use of bifurcating grooved channels can improve the thermal performance of various applications in thermal engineering, from fuel cells to electronic cooling.