Mixed convection heat transfer in a cubical cavity with an isothermally heated blockage inside filled with a hybrid nanofluid (HBNF) is numerically studied. The natural convection is created by the temperature difference between the hot block and the cold lateral walls, while the forced convection is generated by moving the upper wall. The influence of some variables, like the aspect ratio (0.1 ≤ r ≤ 0.5), Richardson number (0 ≤ Ri≤ 20), Reynolds number (50 ≤ Re ≤ 200), volume concentration of nanoparticles (0 ≤ ϕ ≤ 0.06), and the concentration ratio (2:8, 5:5, and 8:2) on the flow field and heat transfer is analyzed. A comparison between hybrid and mono nanofluids (NFs) is realized to investigate the energy transport enhancement. Results show that the increase of each parameter causes an increase of average Nusselt number Nuavg and improves the heat transfer; besides the use of HBNF gives better Nuavg values. Three correlations of the effect of r, ϕ, Ri, and Re on Nuavg are determined for both hybrid and mono NFs.

A three‐dimensional numerical laminar mixed convection analysis has been examined to investigate thermal transfer, fluid flow, and second law behaviors in an inclined channel with four heated blocks within, submitted under a constant heat flux using Al2O3–Cu water‐based hybrid nanofluid as a circulating fluid. Our main purpose is to perform a close‐to‐reality approach, which leads to results that can be applied in many experimental and industrial fields. This study focuses on the analysis of the effect of Reynolds number (100 ≤ Re ≤ 500), Richardson number (0.1 ≤ Ri​​​​​​​ ≤ 2), nanoparticles concentration (0 ≤  ϕ $\phi $ ≤ 0.05), blocks positions, and inclination of the channel (0° ≤ θ ≤ 90°) to examine the variation of Nusselt number Nu, temperature gradient entropy Sh, fluid friction entropy Sf, and the number of Bejan Be. Results show that the enhancements provided to the Nu number by elevating previous parameters reached a percentage rate of 3.2% when increasing ϕ $\phi $, 12.9% with Ri, and 8.58% with Re; however, the aligned position reveals higher values. There is also an increment in Be number when Ri and Re increase, but in this case, the not‐aligned position reveals the highest values. To predict Nu number values, correlations were developed to examine the effects of ϕ $\phi $, Ri, and Re on Nu, for both aligned and not‐aligned positions.