Optimization of heat transfer in Al2O3-TiO2/water hybrid nanofluids: A semi-analytical approach

This paper explores the Al${}_2$O${}_3$-TiO${}_2$/water hybrid nanofluid flow and heat transfer within a convergent/ divergent channel along with irreversibility analysis. The assumptions taken are the heat source/sink, radiation, viscous dissipation, velocity, and thermal slip effects. The nanoparticle shapes and nanoparticle mixture ratios are also taken into account. Similarity transformations are used to convert the governing partial differential equations into ordinary differential equations, which are solved using the Adomian decomposition technique. As velocity slip increased, velocity profiles increased, while temperature and entropy generation profiles decreased in both the convergent and divergent channels. Temperature and entropy generation increased with thermal slip. Cylindrical and brick-shaped nanoparticles yielded higher heat transfer and entropy generation than spherical shapes. The Al${}_2$O${}_3$(10%)-TiO${}_2$(90%)/H${}_2$O mixture provided superior heat transfer compared to other ratios. Additional analysis using multiple linear regression highlights the influence of various parameters on heat transfer rates and skin friction. In divergent channels, Reynolds number and velocity slip positively affected skin friction, while in convergent channels, Reynolds number had a negative impact and velocity slip had a positive effect. The Eckert number, thermal slip, and heat source parameters positively influenced, whereas the velocity slip parameter negatively influenced, the Nusselt number in both channels. Specifically, the heat transfer rates for a 5% nanoparticle suspension in water improve by 3.61%, 32.23%, and 109.67% in the divergent channel and 3.57%, 30.45%, and 104.60% in the convergent channel for spherical, brick, and cylindrical-shaped nanoparticles, respectively.