<p>This research conducts a thermal analysis of the mixed convective flow of a hybrid nanoliquid within the square cavity. The base fluid is comprised of a binary mixture of water and propylene glycol. The SWCNTs and MWCNTs nanoparticles are dispersed into the binary mixture to formulate a hybrid nanoliquid. The Yamada–Ota model is adopted to evaluate the thermal conductance of the nanoliquid. A heat sink made of a square-shaped copper block is considered in this study. Within the cavity, the left wall is taken as a cold wall, nonetheless, the right wall is heated considering the top and the bottom walls to be adiabatic. The analysis explores different aspect ratios between the block-shaped heat sink and the surrounding square cavity. This exploration advances the development and design of advanced thermal management systems considering the collective effects of hybrid nanofluids, optimized heat sink geometry, and integrating a precise thermal conductivity model. COMSOL Multiphysics software is employed to perform CFD simulations for the described physical scenario, analyzing the role of various parameters on velocity, pressure, and temperature distributions, along with corresponding streamlines and isotherms. The results reveal that both velocity and temperature fields are most prominent when the aspect ratio is 0.5. Interestingly, velocity and temperature exhibit opposite behaviors as the Rayleigh number upsurges (Ra = 10², 10³, 10⁴). Additionally, across all temperature profiles, the warmer fluid rises due to its lower density, accumulating near the upper wall. The highest pressure is observed near the lower wall at an aspect ratio of 0.5 when the Rayleigh number reaches 10⁴. This indicates that an aspect ratio of 0.5, along with higher Rayleigh numbers, enhances thermal transport and optimizes pressure dynamics within the cavity.</p>