Enhanced Heat Transfer in Methanol-Based Magnetic Hybrid Nanofluids: Influence of Thermal Radiation, Viscous Heating, and Velocity Slip on Stretchable Cylindrical Surfaces

Hybrid nanofluids have become important for improving heat transfer in various engineering fields, especially in rotating cylinders, energy conversion systems, and efficient heat exchangers. Motivated by the need to elevate heat transfer efficacy, the present research explores the thermal transportation behaviour of a hydromagnetic hybrid nanofluid composed of methanol enriched with nanoparticles coursing over a stretchable cylindrical surface. The flow regime is defined by the inclusion of viscous and Joule heating, linear thermal radiation, and slip-flow phenomena, governed by velocity slip and temperature jump conditions (Smoluchowski) at the boundary. The model also integrates the role of variable electrical conductivity, dynamic viscosity, and thermal conductivity, critical factors inspired by their real-world relevance in temperature-sensitive microfluidic systems, energy-efficient thermal insulation, and smart fluidic cooling technologies. The nonlinear partial differential equations were converted into ordinary differential equations through similarity transformations, then solved with the reliable fourth-order Runge-Kutta method and a shooting technique. Graphical insights elucidate how key parameters such as thermal radiation intensity, viscous heating, and boundary slip phenomena intricately influence velocity and temperature fields. Notably, enhanced fluid momentum is associated with higher Maxwell slip and Reynolds numbers, while elevated Eckert and radiation parameters amplify thermal diffusion. Quantitatively, the wall shear stress exhibits a 23.6% reduction with increasing magnetic parameter (M) and a 17.8% decrease under suction enhancement (S), while hybrid nanofluids outperform conventional nanofluids in drag reduction. The Hybrid Nanofluid (HNF) achieves a Nusselt number (Nu) that is up to 8.71% higher than the conventional Nanofluid (NF) at Pr = 8.0, confirming its superior heat transfer capability. Validation against established benchmark scenarios confirms the robustness and accuracy of the numerical formulation. This study is vital for advancing magnetic-assisted thermal regulation and thermal energy storage solutions in high-performance engineering systems where precise thermal control is critical for operational efficiency.