Magnetohydrodynamic nanofluid flow in a U-shaped enclosure under radiative heat flux and exothermic chemical reactions

Nanofluids exhibit enhanced thermophysical properties , making them highly effective in improving heat transfer, energy storage, and cooling systems . The limited understanding of nanofluid behavior and performance hinders their widespread use. The exothermic chemical reactions and fundamental attributes of nanofluids have complex mechanisms to advance flow and heat transfer. To understand the mechanisms and challenges associated with chemical reactions in nanofluids, this study investigates the flow dynamics and heat transfer of nanofluid in a U-shaped enclosure with a colder rib, considering the effects of radiative heat flux, magnetohydrodynamics (MHD), and exothermic chemical reactions. The finite element method is used to solve the fundamental equations of nanofluids. The accuracy of the numerical scheme is confirmed against published works. The distribution of velocity magnitude, isotherms, vorticity function, and Nusselt number are examined across a wide range of critical parameters of the problem for the copper oxide-water nanofluid. The results show that higher Rayleigh numbers ( R a ) enhance convection, increasing fluid velocity, vorticity, and heat transfer efficiency, while lower R a values result in conduction-dominated heat transfer. The Frank-Kamenetskii number ( F k ) significantly impacts thermal and flow behavior. Notably, the average Nusselt number decreases by 62.86 % as F k increases from 0 to 6, followed by a significant increase of 209.38 % as F k rises from 6 to 12. The radiation parameter ( R d ) reduces the velocity magnitude and Nusselt number while increasing pressure, reducing the heat transfer efficiency. The Hartmann number ( H a ) suppresses the velocity magnitude and vorticity, causing a decrease in the Nusselt number, while specific magnetic field inclination angles, such as 30 ∘ , optimize the velocity and heat transfer. However, the horizontal and vertical aspect ratios ( A R w and A R h ) play a critical role in shaping thermal and flow performance, with optimal configurations improving the Nusselt number distribution and overall efficiency. These findings provide a strong foundation for optimizing enclosure designs to maximize thermal performance.