Effect of Internal Heat Generation on Heat Transfer of Trihybrid Nanofluid in an Open Enclosure with a Hot Baffle

• The Thermocapillary forces cooperate with buoyancy forces to enhance heat transfer at negative Ma values. • The increase of the external Rayleigh number by up to 50,000 improves the heat transfer by 58%. • Internal heat generation intensifies convection, with RaI values increasing heat transfer by up to 500%. • Hybrid nanofluids enhance heat transfer, with a 6% nanoparticle concentration increasing Nuav by 23.3%. • A V-shaped trend in Nuav as a function of Ma reveals the complex interplay between thermocapillary and buoyancy forces. This study investigates natural convection (NC) heat transfer (HT) in a two-dimensional square cavity filled with a triphasic hybrid nanofluid (HNF) mixture (Al₂O₃, Cu, and MWCNT dispersed in thermal oil). The analysis examines the combined effects of thermocapillary forces (Marangoni number, Ma), buoyancy forces (internal and external Rayleigh numbers, Ra I and Ra E ), and internal heat generation. Numerical simulations are conducted to explore how these parameters influence fluid flow and thermal behaviour. The results indicate that negative Ma values enhance the HT due to the cooperative effect of thermocapillary and buoyancy forces, while positive Ma values tend to hinder convective motion, leading to either reduced or stabilized heat transfer. Increasing Ra E from 5,000 to 50,000 improves heat transfer by up to 58%, whereas varying Ma from -10,000 to 10,000 results in a more moderate 20% enhancement. Additionally, at high Ra I values, thermal forces dominate over viscous and thermocapillary effects, further intensifying convection. The presence of hybrid nanoparticles significantly improves heat transfer efficiency, with a 6% volumetric concentration increasing the average Nusselt number by 23.3%. A V-shaped trend in Nu as a function of Ma is observed, highlighting the complex interplay between thermocapillary and buoyancy forces.