In this paper, natural convective heat transfer in a rectangular cavity filled with (50% CuO-50% Al2O3)/water hybrid nanofluids connected to a wall containing a phase change material (PCM) has been experimentally investigated. The vertical walls were heated at varying temperatures while the horizontal walls were kept adiabatic. The considered parameters were the concentration of hybrid nanomaterial (Φ = 0.03, 0.05), the cavity inclination angle (θ = 0°, 30°, 45°), and the temperature difference between the hot and cold sides (∆T = 10, 15, 20 °C). The results have been validated and agree well with previously published papers. Furthermore, the main results stated that when the nanomaterial concentration increased, the heat transfer rate by free convection also increased. By increasing the natural convection flows via high temperature, symmetrical vortexes may appear near the heated wall. It also found that the PCM can potentially reduce the temperature of the hot side by up to 22% due to its high absorbability and heat storage. Furthermore, the inclusion of hybrid nanofluids in addition to the PCM enhanced its efficiency in heat storage and, therefore, its capacity to cool the hot side. Moreover, the influence of the inclination cavity enhanced the heat transfer, where θ = 30° was the optimal angle in terms of thermal conductivity.

An empirical evaluation of free convective heat transmission was conducted in a rectangular enclosure containing a hybrid nanofluid of (50% CuO-50% Al2O3)/water linked to a PCM-containing wall. The enclosure's left and right surfaces were kept at constant warm and cold temperatures, whereas the remaining surfaces were assumed to be isolated. The left side was filled partially with PCM. Several variables were examined, such as the hot-side temperature differential (∆T =10, 15,20 ◦C) and the hybrid nanofluid concentration (Φ=0.03,0.05,0.07)%. The findings show that the rate of heat transmission through natural convection rises as the concentration of nanomaterials rises. Due to its great absorbability and heat storage capacity, PCM was also shown to have the potential to lower the hot side temperature by up to 15.5%. The Nusselt number rises over time as the left cavity is filled partially with PCM. When added hybrid nanofluid is, PCM’s heat-storage efficiency and, by extension, its ability to cool the hot side is greatly improved.