Heat transfer augmentation and entropy generation minimization by employing synergistic aspects of hybrid (Fe3O4 + MWNTs) nanoliquid in star shaped enclosure with thermally conductive cylinder and inclined magnetic field aspects.

• It is found that average Nusselt number elevates against escalation in the magnitude of Rayleigh number (Ra) and hybrid nanoparticles volume fraction (ϕ) whereas, opposite trend is depicted against Hartmann number (Ha). • Heat transfer coefficient is found to be more in the situation when star shaped cylinder is installed in comparison to circular and square cylinders. • Positive trend in total entropy is depicted against elevation in Rayleigh number (Ra) and volume fraction of hybrid nanoparticles (ϕ) whereas, decrement is demonstrated against Hartmann number (Ha). • Average Bejan number increases up to 8% against upsurge in the magnitude of hybrid nanoparticles volume fraction (ϕ) and experiences 50% decrement against Rayleigh number (Ra). • Lowest value of ECOP is attained in the absence of hybrid nanoparticles (ϕ = 0) whereas, contrasting aptitude is observed in the situation when magnetic force is absence (Ha = 0). • Maximum magnitude of velocity is attained at wave number (N = 4) whereas, maximum heat is transferred at wave number (N = 5). This article aims to simulate optimum thermal convection and minimization in entropy generation in viscous hybrid nanofluid (Fe 3 O 4 -MWNTs/H 2 O) flow in thermally cold star shaped enclosure and containing heated cylinder. Shape effect of cylinder in managing associated hydrothermal attributes is also interrogated. Physical aspect of magnetic field making angle of inclination with domain is accounted. Formulation of transport equations is expressed in the form of dimensionless partial differential setup containing the thermophysical relations of induced hybrid nanoparticles. The constructed flow issue has been simulated by using Galerkin finite element method (G-FEM) with appliance of COMSOL Multiphysics® software computer package. Results and grid convergence assessment tests are also executed in the study. Significant impact of flow controlling parameters on velocity, temperature and entropy generation profiles has been presented in graphical and tabular manner. Variation is three different types of entropies namely, viscous, thermal and magnetic are estimated. Quantities of interest like, total entropy, average Nusselt and Bejan numbers are also calculated against the sundry parameters. Ecological coefficient of performance which measures the efficiency of physical systems is interrogated which is important physical quantity in practical problems. It is inferred from the outcomes that induction of hybrid nanoparticles (Fe 3 O 4 − MWCNT) produces considerable augmentation of thermal attributes of base fluid. Moreover, it is depicted that average Nusselt number exceeds up to 26.5 % for star shaped inner cylinder in comparison to the square cylinder. Increment up to 6 % in average Nusselt number and 2.19 % decrease in entropy is depicted when hybrid nanoparticles are added in the base fluid (ϕ ≠ 0) in comparison to the situation when nanoparticles are not induced (ϕ = 0). [ABSTRACT FROM AUTHOR]