<p>This review evaluates the effects of natural convection in square cavities using both mono-and hybrid Nano-fluids, focusing on the thermal management limitations of conventional fluids. The review highlights that there is a need for improved thermal solutions in engineering since regular fluids fail under low Rayleigh number conditions. Particularly, it shows that nano-fluids can increase significantly the rate of heat transfer with the Nusselt (Nu) number increasing as high as 60% compared to pure fluids, depending on nano-particle concentration, particle size, and material properties. For instance, the introduction of 4% Al₂O₃ nano-particles into a water-based solution can increase the average Nusselt number from 7.5 to around 12.0 under corresponding conditions of heating. Moreover, hybrid nano-fluids possess excellent opportunities as efficient heat transfer promoters with over 30% improvement in efficiency rates. This kind of assessment indicates the revolutionary impact of nano-fluids on thermal applications, but more work is needed to explore their behavior when considering various ranges of temperatures and flow rates in order to develop trustworthy predictive models.</p>