Abstract
In this study, a new cavity shape was filled with an extension multi-walled carbon nanotubes-Fe2O3/H2O nanofluid under a constant magnetic field. The Darcy–Forchheimer model is used to account for the inertial impact of advection in the porous layer while maintaining the laminar and incompressible nature of the nanofluid flow. The dimensionless version of the governing equations is used to describe the issue and the finite element approach is used to resolve it. Through this complex geometry, various thermophysical factors such as Rayleigh number
Introduction
In recent years, many academics have worked on improving heat transmission by altering the thermo-physical parameters of the working fluid. Because of its superior thermal conductance and convection heat transference coefficient compared to the conventional liquid, nanofluid, an engineered dispersion suspension of nanoparticles in a conventional liquid, has proven its remarkable potential applicability in many industrial implementations. Energy management is one of the most important issues in our society. It is, therefore, necessary to improve our energy consumption to protect our natural resources. Convective evaporation is involved in energy storage, generation, and cooling. This motion causes a mixture of fluid particles. The process of heat transfer is called natural convection. In their investigation of the convection of aluminum and water hybrid nanofluid (HNF) in a cavity, Bordaniani et al. 1 observed the impact of magnetic fluidity on the effectiveness of heat transfer. A water nanofluid Al2O3 was explored by Pure et al. 2 in an inclined square cavity. Using a revolving cylinder, Mebarek-Oudina et al. 3 examined the behavior of convective heat in a hollow filled with pores. They considered the magnetic field of aqueous Al2O3 HNFs in a motivated square cavity.
Carbon nanotubes (CNTs) were discovered and have since developed into one of the most intensely investigated nanostructures, perhaps contributing to the nanotechnology revolution due to their superior thermal, physical, optical, and electrical capabilities. A Japanese scientist discovered CNTs. Because of CNTs’ extraordinarily high thermal conductivity, many scientists have changed their emphasis to better comprehend the basic properties of CNTs and their applicability in heat transference systems. Furthermore, Selimefendigil and Chamkha 4 studied the properties of convection and entropy generation in a magnetic field container. A vertical beam was used to divide the room into two parts. The higher and lower lips were fixed, whereas the left and right lips were warm and icy, respectively. On the other hand, Selimefendigil and Öztop 5 and Hamzah et al. 6 used the finite element method to study the convection properties and entropy generation in a split cavity filled with CNTs/aqueous HNFs under magnetic flux. A Boltzmann grid technique was used to investigate the impact of cooling fan size on MHD natural convection in a partly differentiated box in a work by Gangawan and Bharti. 7 Furthermore, results of thermophysical characteristics on spontaneous laminar convection in containers where HNF experiments are monitored using the nuance approach are now accessible, according to research by Ismail. 8
Numerous scholars have examined and reviewed the usage of mono nanofluids in heat transfer applications. The reports regarding the nanofluid have been published, subjected to the Cattaneo–Christov magnetized nanofluid model, 9 the radiating nanofluid with a magnetic dipole, 10 and convective heat and mass transfer in a nanofluid flow with the activation energy. 11 The use of HNF is a relatively new notion that has lately attracted greater study interest. The use of HNFs in heat transference implementations such as plate heat exchangers, passive heatsinks, heat pumps, photo-voltaic modules, free convection housings, cooling and air-conditioning systems, vaporization implementations, impeller coolers, and thermal energy storage systems is thoroughly discussed. Abstract analysis of a porous crack occupied by a copper/water HNF with LBM was performed by Hoseinpour et al. 12 The HNF containing Ti6Al4 V and AA7075 nanoparticles with a base fluid sodium alginate over a stretching sheet in a porous media with magnetic effect is studied by Alsulami et al. 13 Heat transfer analysis in the three-dimensional unsteady magnetic fluid flow of water-based ternary HNF is reported by Sarada et al. 14 Subsequently, Sarada et al. 15 reported the convective boundary layer flow of ternary HNF (water-based graphene-CNT-Silver) with activation energy. Recently, Varun Kumar et al. 16 analyzed the Arrhenius activation energy on kerosine oil HNF with manganese zinc ferrite and nickel zinc ferrite as nanoparticles over a curved stretchable surface.
The higher the porosity, the better the overall entropy generation. Abu Abdulsahib et al. 17 considered the effect of different thermophysical factors on hydrothermal generation and entropy within a new porous cavity. Kasaypur et al. 18 performed an analysis of heat transfer by convection and entropy generation in a container with multi-walled carbon nanotubes (MWCNT)–MgO/water HNF-charged solid-cooling element. More Rahimi et al. 19 completed a mathematical analysis of natural convection and entropy generation in a container, which is to be shipped with double dividers of CNTs and liquid nanotubes equipped with cold and hot baffles, while the scheme has succumbed to LBM. Ikram et al. 20 deliberated the optimization of entropy generation contained by a square crack overloaded with an Ag/water HNF. A square cavity filled with HNF that contains multiple configurations of a solid corrugated conductor. Brahimi and co-workers 21 studied the thermal behavior of a porous container filled with a water-based Ag–MgO HNF in the attendance of a fixed magnetic field. A parametric study by Hua et al. 22 was carried out on a triangular cavity of a porous nature with an undulating inclined side. The parametric influence can be classified into two categories for this work. One on the structural aspects such as shape and size and the other hand the parameters influencing the physical nature.
CNTs and magnetic nanocomposites (Fe3O4) have attracted great interest in recent years due to their interesting properties, especially at the nanoscale.23,24 Sajadi et al. 25 used MWCNT–Fe3O4/water hybrid nanotube Hydrothermal assay for MHD natural convection in a porous environment using Boltzmann's double-clamp MRT technique inside a square bore. The working fluid composed of MWCNT, Fe3O4 nano-solids, and water is considered Newtonian and incompressible. Small et al. 26 conducted an experimental study to compare the heat-enhancing properties of different types of HNFs. And MWCNT-Fe3O4 HNF. Shen et al. 27 studied the magnetic effect on improving the photothermal energy conversion performance of the MWCNT/Fe3O4 HNF. Their study aims to experimentally determine the effect of external magnetic forces on the photothermal energy conversion efficiency of the MWCNT/Fe3O4 HNF with variable magnetic forces. Zafar et al. 28 studied the thermophysical properties and stability of water-based magnetite (Fe3O4) HNFs coated with MWCNT using a multi-level sensor coupled with an artificial neural network. Al-Kulaibi and co-workers 29 conducted an experimental investigation to evaluate the efficacy of water-based MWCNT/Fe3O4 HNFs for cooling plate heat exchangers.
Several parameters showed that MWCNT + Fe3O4/water nanofluids improved plate heat exchanger performance. Increases in coolant flow velocity and nanoparticle concentration both contribute to amplification. The main objective of our research is to examine rectangular cavities. In addition, this effort aims to discuss the natural convective heat transfer of nanofluids (MWCNT-Fe3O4/H2O). The effect of different control variables such as
Problem explanation
Figure 1 displays the analyzed geometry. It displays a 2D rectangle. The walls that are entirely insulated are shaded. Additionally, while maintaining temperatures at Th and Tc, respectively, the sides are provided with hot and cold sections, and the other components are similarly segregated. B applies a constant magnetic field in the x direction. HNF (MWCNT-Fe3O4/H2O), a Newtonian, incompressible substance with laminar flow and no viscous dissipation, fills the hollow. Table 1 is a list of the thermophysical characteristics of HNF.

(a) The somatic design and (b) the network problem.
The main thermo physics of the improper liquid (water) and the auxiliary nanoparticles are in Table 1.
Mathematical model
For numerical modeling of porous media, the Darcy–Brinkman–Forchheimer model is used. For predicting high-velocity flow in porous media, especially in the vicinity of gas wells, 41 the governing equations given in Cartesian coordinates can be written in the dimension model.42,43
In the HNF:
The non-dimensional equations are as given in the following structures:
Boundary conditions for cavity walls are explained as follows:
hot wall: cold wall: insulated walls:
The multidimensional local entropy given by Woods
46
through the process of convection and the magnetic field is given as:
Authentication and grid independence analysis
The effect of the network on the numerical solution was examined before moving on to the calculations in our study. For this, we have studied the state of flow in mixed convection and the Prandtl number equal to 6.2. The current problem is solved using the GFEM, and the GFEM described by Redouane et al.
35
has become our main reference in this model. GFEM transforms the nonlinear differential equations (15)-(25) into a system of integral equations. In addition, the non-uniform triangular grids are utilized to decertify the field solution. Furthermore, the mesh assessment process is accomplished to ensure that the current technique is independently grid. Eight alternative networks were tabulated in Table 2. This table gives results of average Nusselt number

Comparison of streamlines (left) and isotherms (right) (a) current work and (b) Corcione et al.
47
for
Contrast
Results and discussion
Five parameters related to simplification, isotherm, and general entropy are presented, these parameters refer to Rayleigh amount (
Effect of Rayleigh’s number
Figure 3 shows the smooth and isometric lines in the considered cavity filled with a Fe3O4–MWCNT HNF of different Rayleigh records. It is clearly observed that rationalizes designed two circumferences near the heated vertical wall and one circumference next to the cooled vertical wall of the cavity. For lower Rayleigh number values, the heated aerodynamic contours dominate over the cooled particular contour. Growing the Rayleigh amount (

Streamlines and isothermal for different Rayleigh numbers (
From both ends of the thermal points, isotherms with a reduced Rayleigh number (
Figure 4 illustrates the example of the mean Nusselt number across the cavity for various physical parameters. After 102, all the physical factors involved in the problem, the Rayleigh number (

Average Nusselt presentation with different Rayleigh numbers
Hartmann number effect
The confrontation of the forces caused by electromagnetism with viscous changes to changes in temperature can be designed via the Hartmann number (
Figure 5 shows the streamlines in which the transverse magnetic field B was applied to isotherms inside the investigated cavity that had temperature variations on each side. When the magnetic field was absent (

Differences in simplifications and equivalencies as a function of Hartmann number
Influence of Darcy's number
Around the cavity's porous structure, the result of Darcy's number becomes important. The porousness of the medium rises with Darcy's number, enabling flow across it. Higher values of Darcy's number can be obtained by dregs building up on each side of a porous medium and flowing toward it (
Figure 6 shows the flow line variation of the flow lines (top) by the variation of the Darcy number, and the obtained results show that the distribution of the flow lines decreases in the porous medium and increases in the non-porous medium by an amount. Thus, the increase in the number of Darcy varies relatively someone opined that the opposition to isotherms such as the increase in temperature increases with the increase in the number of Darcy.

Simplifying differences and equals by the difference of Darcy number
Influence of porosity
In nanofluid flows including a porous media, porosity becomes a crucial characteristic in contrast to issues with regular fluid flow. The nature of the dispersed nanoparticles may be the cause of this. Porosity (
Regarding Figure 7, the isotherms of the porosity effect appear to be negligible. It is clearly noted from the graphs that no such significant changes have occurred.

Rheological and isometric differences as a function of porosity
Entropy
Figure 8 displays entropy changes as a function of Rayleigh; we note that the heat transfer rate increases in the non-porous medium and decreases in the porous medium in addition to increasing the Rayleigh number values.

Entropy variations with Rayleigh number (
Conclusion
Based on the finite element method, the parametric organization was studied on the MWCNT–Fe3O4 hybrid Nano-fluid/water packed in the middle of the porous cavity in layers and under the influence of a magnetic field. We extracted the following.
Activation of the dual streamlines for the hot side and individual cooling for the lower values of Darcy's number, Rayleigh's number, and higher Hartmann values. At the top of the cavity, a cryogenic temperature is required below at the changing values of physical parameters. Low Darcy and Hartmann index, Rayleigh index, high porosity, and low Fracture Volume controlled by high The higher rate of heat transfer within the cavity is due to an increase in the Darcy number with The components of entropy are determined by the production of entropy.
Footnotes
Acknowledgments
This work is funded by the Deputyship of Research & Innovation, Ministry of Education in Saudi Arabia, through project number 804 (Group Research Program 1). In addition, the authors would like to express their appreciation for the support provided by the Islamic University of Madinah.
Data availability
All data generated or analyzed during this study are included in this published article.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Length of porous aria ( Coordinates ( Hartmann number Permeability ( Nusselt number Prandtl number Darcy number Dimensional velocity components The intensity of the magnetic field Forchheimer coefficient Thermal conductivity ( Height of cavity ( Pressure ( Rayleigh number Velocity components ( Temperature ( Entropy Thermal diffusivity ( Porosity Dynamic viscosity ( Adimentional temperature Electrical conductivity ( Thermal expansion coefficient ( The length of the Baffle ( Kinematic diffusivity ( Density ( Solid volume fraction Average Fluid Local Total Cold Hot Hybrid nanofluid Base fluid
