A numerical investegation of two-dimensional, laminar, steady and mixed convection of heat transfer in a lid-driven cavity filled with Al₂O₃-water nanofluid for various aspect ratios has been conducted. The left wall of the cavity is maintained at a higher temperature with respect to the right wall. The top wall of the cavity is sliding toward the right with a constant velocity whereas the remaining walls are stationary. The combined effects of buoyancy produced due to temperature difference between the sidewalls and the shear action on account of the top moving wall in +x direction causes mixed convection transport of heat across the domain. A two-phase mixture model is used in this study. The Grashof number fixed at 10⁴ and the effects of Richardson number (0.1,1,10), aspect ratio (0.5≤AR≤2), and solid volume fraction (0≤ø≤8%) on the rate of heat transfer is numerically investigated. The results showed that the Nusselt number increases with volume fraction, Nusselt number distribution along the heated wall in the low aspect ratio cavity has depicted comparatively greater values than the high aspect ratio cavity. The results also show a satisfactory prediction of averaged nusselt number in a two-phase approach compared to a single phase analysis.