## 1 Introduction
The influence of the variation in different parameters, such as the geometric shape, the intensity of the magnetic field's non-dimensional number, and the Reynolds number on heat transfer was also investigated. The obtained results showed the sinusoidal formation of the internal tube significantly increased the Nusselt number inside a two-tube heat exchanger. In addition, the magnetic field enhanced the diffusion of the cold boundary layer to the central parts of the inner tube for various geometric shape coefficients. Their findings showed that the diffusion was also elevated as the intensity of the magnetic field was increased. Thus, the Nusselt number and heat transfer increased, and this augmentation intensified with a high Reynolds number\". \"The study of [PERSON] et al. [14] presented a critical review of nanofluids that are considered to be next-generation heat transfer media due to their excellent thermal performance. The study investigated the effect of electric and magnetic fields on the heat transfer of nanofluids. Based on a literature review, the authors analyzed the mechanism of thermal conductivity enhancement of nanofluids, the chaotic convection, and the heat transfer enhancement of nanofluids in the presence of an applied electric field or a magnetic field\". Reference [14] also presented research that showed that applied electric and magnetic fields can significantly affect the heat transfer performance of nanofluids, although numerous different opinions exist about the effect and mechanism of heat transfer\". Their work was intended to present the current state of research into the heat transfer of nanofluids under the influence of a magnetic field\". \"[PERSON] et al. [15] conducted a numerical investigation of the magnetohydrodynamic forced convection effects of Al\({}_{2}\)O\({}_{3}\)-CuO-water nanofluid inside a partitioned cylinder within a porous medium. They indicated that their calculations were carried out for a broad range of governing parameters. They also stated that \"the nanofluid flow was modeled as a two-phase flow using a two-phase mixture model, and the Darcy-Brinkman-Forchheimer equation was employed to model the fluid flow in porous media. The simulation in this study was also conducted under a laminar flow regime using the finite volume method. Furthermore, it was reported that \"the thermal boundary condition of constant uniform heat flux was imposed on the cylinder walls. The average Nusselt number, in addition to the performance evaluation criteria (PEC), was examined for diverse Darcy numbers (0.0001 \(<\) Da \(<\) 0.1) and Hartmann numbers (0 \(<\) Ha \(<\) 40). The results of their research indicated that increasing the Hartmann and Darcy numbers significantly elevated the heat transfer coefficient. Additionally, the incorporation of nanoparticles into the base fluid increased the PEC in all cases. Moreover, the PEC reached its maximum value in configurations involving permeable porous media (i.e., a medium with Da = 0.1 and Ha = 40)\". \"The review paper by [PERSON] et al. [16] paid great attention to the benefits of controlling the natural convection heat transfer and flow performance of nanofluids in square cavities using magnetic field sources. In addition, they reported that the aspect ratio, porous media, cavity, and magnetic field inclination on nanofluids in hybrid systems. The influence of several variables has been also reviewed and reported on heat distribution methods, thermal and concentration boundary conditions, governing parameters, magnetic field types, numerical schemes, thermophysical correlation types, nanofluid types, slip conditions, Brownian motion, and thermophoresis regarding the magnetohydrodynamic (MHD) natural convection behaviors of nanofluids in square cavities\". \"The paper by [PERSON] et al. [16] also focused on the application of numerical and experimental methods to hydromagnetic behaviors of nanofluids in square-shaped enclosures.