Magnetic field promoted irreversible process of water based nanocomposites with heat and mass transfer flow

Analytical analysis of two-dimensional, magnetohydrodynamic, heat and mass transfer flow of hybrid nanofluid incorporating Hall and ion-slip effects and viscous dissipation in the presence of homogeneous-heterogeneous chemical reactions and entropy generation is performed. The governing equations are modified with the help of similarity variables. The reduced resulting nonlinear coupled ordinary differential equations are solved with the help of homotopy analysis method. The effects of all the physical parameters are demonstrated graphically through a detailed analysis. The main outcome of the study is the use of applied strong magnetic field which generates the cross flow of hybrid nanofluid along the z-axis. The numerical comparison to the existing published literature is also provided.


List of symbols
Homogeneous chemical reactions parameter k 2 Heterogeneous chemical reactions parameter e Electron n a Neutral particle density n e Electron number density Concentrations of chemical species B and C respectively s Solid nanoparticles f ′ (ζ) Dimensionless axial velocity g(ζ) Dimensionless transverse velocity B Magnetic induction B 0 Applied magnetic field strength C f x Local dimensionless skin friction coefficient in x-direction C g z Local dimensionless skin friction in z-direction coefficient Nu x Local Nusselt number Re x Local Reynolds number q w Local wall heat flux (J m −2 s −1 ) N G

Dimensionless entropy generation
Greek symbols ω e Electron frequency σ Electrical conductivity σ 1 Dimensionless timing parameter Stretching/Shrinking parameter ψ Physical stream function ( m 2 s −1 ) β T Thermal expansion coefficient ζ Similarity variable ϕ(ζ ) Concentration of homogeneous chemical reactions ϕ 1 (ζ ) Concentration of heterogeneous chemical reactions φ Total volume fraction of nanoparticles φ 1 Volume fraction of magnetite φ 2 Volume fraction of copper i , i = 1, 2, 3, 4, 5 Dimensionless hybrid nanofluid constants θ(ζ) Dimensionless temperature θ w Temperature difference parameter ν f Kinematic viscosity ( m 2 s −1 ) µ hnf Dynamic viscosity ( kg m −1 s −1 ) ρ hnf Density ( kg m −3 ) τ e Electron collision time τ w x Surface shear stress in x-direction ( kg m −1 s −2 ) τ w z Surface shear stress in z-direction ( kg m −1 s −2 ) γ Leading edge accretion/ablation parameter γ 1 Diffusion constant parameter due to nanoparticles concentration Magnetism has revolutionized a wide spectrum of technologies such as data storage and biomedical imaging and continues to bring forth new phenomena in emergent materials of reduced dimensionalities. In 2017, magnetic 2D materials emerged as ideal solid-state platforms where both crystalline structural order and long-range magnetic order coexist and couple in atomic-thin region, which makes the unprecedented experimental explorations of 2D magnetism routinely feasible in numerous laboratories worldwide. Furthermore, the seamless integration Scientific Reports | (2021) 11:1692 | https://doi.org/10.1038/s41598-020-80554-0 www.nature.com/scientificreports/ of 2D magnets with dissimilar electronic and photonic 2D materials, backed by the already mature techniques on high-quality van der Waals heterostructure constructions, opens up remarkable opportunities for a plethora of designer quantum heterostructures with previously inaccessible magnetoelectric and magneto-optical properties.
Scientists and engineers are devoted to research perspectives and reports on recent advances in material innovations on new 2D magnets, magneto-optical, magnetoelectric, and a variety of nanoscale characterizations of 2D magnetic systems, and theoretical prediction and understanding of novel 2D magnetic, spintronic, and magnonic properties, as well as exotic magnetism in relevant systems including twisted bilayer graphene, topological insulators, and Weyl semimetals. The addition of 2D magnets greatly expands the family of 2D materials, and the advanced spintronic devices they enable could reshape the landscape of nanoelectronics and nanospintronics in miniaturized form factors. Mahdy et al. 1 established a mathematical analysis for the magnetohydrodynamics, homogeneous-heterogeneous chemical reactions in flow resulted by an impulsively rotating sphere. Using finite difference technique in combination with quasi-linearization scheme for the solution, they proved that magnetic field reduces the velocity components due to resistive type Lorentz force. Basha et al. 2 applied the Runge-Kutta fourth order integration scheme with shooting technique to compute the solution for magnetohydrodynamic boundary layer flow of viscous incompressible fluid with leading edge accretion and ablation. Ilias et al. 3 studied theoretically the unsteady aligned magnetohydrodynamic boundary layer flow and heat transfer of magnetite and alumina nanoparticles through a vertical flate plate with leading edge accretion. Mabood and Khan 4 investigated the effects of magnetic field on Blasius and Sakiadis flow with leading edge accretion and ablation whose most relevant outcome is that for the magnetic field strength the thinner boundary layer is established in Blasius and Sakiadis flows.
For decades, the field of thermoelectricity has been dominated by inorganic materials. The demonstration of reasonably stable polymer-based materials with a figure of merit of 0.1 and above has triggered considerable interest in organic and hybrid thermoelectric materials during the last 10 years. Materials of current interest include both small-molecule and polymeric semiconductors, carbonaceous nanoparticles such as carbon nanotubes, graphene and graphene oxide, as well as composite materials of organic or inorganic nanoparticles embedded in a polymer matrix. However, these materials pose numerous fundamental challenges with regard to their thermoelectric properties in relation to processing and doping, molecular and solid-state structures as well as electronic properties. Key aspects of current interest for the community concern (1) the synthesis of tailormade materials, (2) doping mechanisms of both n-and p-type materials, (3) the interplay of the rich nano-and microstructure with charge and heat transport, as well as (4) the environmental and thermal stability of novel materials. New device architectures and device concepts such as flexible thermoelectric generators printed on plastic foils or integrated into textile substrates are now accessible thanks to the inherent mechanical robustness of polymers. This special topic issue will bring together the scientific sectors in the field and assess recent progress in organic and hybrid thermoelectrics. Tabasum et al. 5 offered a mathematical study of oblique transport of titanium water-based nano-polymer gels with mixed convection effects to simulate the real nano-polymer boundary interface dynamics, convective surface along with velocity slip. Sheikholeslami et al. 6 reported the aluminum oxide-water nanofluid free convection due to Lorentz forces through a porous cubic domain incorporating ellipse shaped obstacle by employing the Lattice Boltzmann method. Pourmehran et al. 7 used a semi exact method to compute the governing nonlinear coupled equations of nanofluid flow and heat transfer which shows that the least square method is suitable for computational work. Sheikholeslami et al. 8 examined numerically the hydrothermal analysis of nanofluid during solidification using time dependent mesh. Mehmood et al. 9 employed the scaling group of transformations to reduce the governing equations of crosswise stream of hydrogen-oxide through a porous media immersed with copper nanoparticles. AbdRabbuh et al. 10 experimentally investigated the performance of heat transfer, thermophysical properties and pressure drop of GNP-based water nanofluid in the different configurations of heat exchanger tubes. Pourmehran et al. 11 simulated the Patel model for the nanofluid flow and heat transfer between two contracting and rotating disks by investigating different types of nanoparticles. Samsudin et al. 12 elucidated the characteristics of cellulose nanoparticles extracted from microcrystalline cellulose by hydrolysis reaction using 1-butyl-3-methylimidazolium acetate as a catalyst and solvent at various temperatures. Abdelaziz 13 worked on the steady boundary layer magnetohydrodynamic slip flow past a stretching sheet in a water based nanofluid in the presence of Hall effect. Biglarian et al. 14 investigated numerically the problem of unsteady magnetohydrodynamic nanofluid flow and heat transfer between parallel plates using fourth-order Runge-Kutta method. Pourmehran et al. 15 worked on the Forchheimer-Brinkman-extended equation for the thermodynamics of a fin shaped microchannel heat sink cooled by different nanofluids. They used th KKL correlation for the calculation of effective thermal conductivity and viscosity and applied the central composite design to obtain the desirability of the optimum value of the nanofluid flow characteristics. Adesanya et al. 16 investigated the entropy generation in a gravity aided thin couple stress liquid film in an inclined heated substrate whose results show that slip and porosity parameters are turns out to be large at the free surface of the porous substrate. Seikh et al. 17 presented the effects of nanoparticles and uniform magnetic field on the slip blood flow conveyed through the hollow arterial tube as a third-grade fluid. Dutta et al. 18 considered the entropy generation in a human respiratory tract model with realistic length to diameter ratio at different branches for the body temperature 36 • C taken into account the ambient condition of air at 25 • C DBT and 50% RH. Other studies on nanofluids can be seen in the references [19][20][21][22][23][24][25] .
In recent years, hybrid nanocomposite materials have been considered as new generation of enhanced performance objects due to their unique characteristics emerging from the combination of hybrid materials. Hybrid nanofluids present the outstanding properties of rigidity, excellent thermal stability and improved mechanical strength. Akermi et al. 26 investigated the effects nanoparticle concentration on the efficiency of hybrid polymer thin layers for studying the morphology, the structure and the optical behavior of the different synthesized nanomaterials, FTIR transmission spectra, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometry. Waini et al. 27  www.nature.com/scientificreports/ copper and alumina in water based fluid. They used the BVP4c, available in Matlab software to notice that the bifurcation of the solutions occurs in the shrinking regions and between the two solutions, in which only one of them is stable. Sreedevi et al. 28 analyzed the unsteady, magnetohydrodynamic, heat and mass transfer hybrid nanofluid flow past a stretching surface with thermal radiation, chemical reaction, suction and slip effects. Waini et al. 29 reported the squeezed hybrid nanofluid flow past a permeable sensor surface for numerical solutions in which dual solutions exist for some values of the porosity parameter. They found that the thermal conductivity was greater for the hybrid nanofluid, compared to the regular nanofluid. Afridi et al. 30 carried out an analysis of the mono nanofluid and hybrid nanofluid with the entropy generation past a thin needle under the modified Maxwell Garnet and the Brinkman model using Runge-Kutta Fehlberg scheme. Hybrid nanofluids literature can also seen in the references [31][32][33] . Entropy generation is associated with the irreversible process of any thermodynamics system. Bhatti et al. 34 investigated the entropy generation past a moving surface with thermal radiation and chemical reaction using successive linearization method and chebyshev spectral collocation method for the reduced resulting non-linear coupled ordinary differential equations. Farooq et al. 35 presented the entropy analysis of three-dimensional bioconvection flow of nanofluid past a linearly moving plate in the presence of magnetic field and microorganisms by applying the BVP4c MATLAB algorithm. Mondal et al. 36 discussed the entropy generation and provided the dual solutions with the spectral quasiliearization method for the magnetohydrodynamic three-dimensional convective flow and heat transfer in a nanofluid. Afridi and Qasim 37 performed the theoretical analysis of entropy generation of three-dimensional boundary layer flow past a bidirectional exponentially stretching surface. Relevant studies about entropy generation can also be seen in the references [38][39][40] .
This research presents the modeling and computing dynamics of a wide range of applications, from heat transferring devices and chaotic behavior of power systems, to the design of a chemical reactions network aimed for synchronous the present system control whose solution is accomplished through HAM 41 .

Methods
An incompressible viscous fluid flow is investigated with free stream velocity U ∞ , homogeneous-heterogeneous chemical reactions and temperature T. In water base fluid, two types of nanoparticles namely Fe 3 O 4 (magnetite) and Cu (copper) are considered respectively. Magnetic field B = [0, B 0 , 0] is applied perpendicularly to the heat and mass transfer flow. Assuming that the strength of electric charge and magnetic field are maximum. The schematic diagram of the problem is shown in Fig. 1. The problem has the following governing equations for hybrid nanofluid as in 1- 4,13 (1) www.nature.com/scientificreports/ where u, v, w are the velocity components in x, y, z directions, m 1 = ω e τ e and m 2 = en e B 0 (1+n e /n a ) Fr are the Hall and ion-slip parameters in which e, ω e , τ e , n e , n a and Fr are the electron, electron frequency, electron collision time, electron number density, neutral particle density and friction coefficient between ions and neutral particles. β T is the coefficient of thermal expansion. B and C are chemical species having concentrations b and c respectively while D is diffusion of species. Also k c and k s manifest the rate constant. The subscript hnf denotes the hybrid nanofluid. µ hnf , ρ hnf , k hnf and (ρc P ) hnf are respectively the dynamic viscosity, density, thermal conductivity and heat capacity of hybrid nanofluid.
Boundary conditions are used as where u e is the external velocity and is the stretching/shrinking parameter. T w and T ∞ are the hybrid nanofluid temperature at surface and infinity respectively. The thermophysical properties of water, magnetite and copper nanoparticles are given in Table 1 while mathematical form to the thermophysical properties of nanofluid and hybrid nanofluid is given in Table 2. In Table 1, s 1 and s 2 are used respectively for the solid nanoparticles of Fe 3 O 4 (magnetite) and Cu (Copper). f is used for the base fluid. Introducing the similarity transformations for (f, g), ζ , θ , ϕ and ϕ 1 as the non-dimensional velocities, variable, temperature, homogeneous and heterogeneous chemical reactions respectively in the following form where ψ is the stream function. ν f is the kinematic viscosity. γ is the leading edge accretion or ablation parameter and ( ν f t cos γ + (ν f x/U ∞ ) sin γ ) must be greater than zero [2][3][4] .
The continuity Eq. (1) is identically satisfied through Eq. (9). The different values are used from Tables 1, 2 & Eq. (9) to get the following equations from Eqs. (2-8) on the case when D B = D C 1 ,  Table 2. Formulations of thermophysical properties of nanofluid and hybrid nanofluid 27,33 .
Thermal conductivity (k)  It is important to investigate the physical quantities like local skin friction coefficients (Cfx,Cgz ) and Nusselt number Nux having extensive applications in industries as where Note that τ w x , τ w z and q w are known as wall frictions and heat transfer on the surface respectively.
Application of Eqs. (17) in (16) with Eq. (9), provide where Re x = Ux ν hnf is the local Reynolds number with σ 1 = U ∞ t x is the non-dimensional timing parameter.

Entropy generation
The equation representing the entropy generation 34-40 is where R is the ideal gas constant while D is the diffusivity. In Eq. (19), the first and second terms are respectively entropy generation due to heat transfer and viscous dissipation. The third and fourth terms are the diffusivity effects due to nanoparticles. The characteristic entropy generation is The non-dimensional entropy generation rate N G (ζ ) is obtained with the help of Eq. (9) as k hnf is the diffusion constant parameter due to nanoparticles concentration.

Solution of the problem
Choosing the initial approximations and linear operators as where and E i (i = 1-9) are the arbitrary constants in general solution.

Zeroth order deformation problems.
where ℵ is the nonlinear operator and j is the embedding parameter in such a way that j ∈ [0, 1].
(63)  m 1 m 2 is strongly related to the magnetic Table 3. Comparison of f ′′ (0) values for accretion rate and the parameter γ.   Fig. 9. Through convection, the nanoparticles are excited, consequently, the flow is enhanced. It should be noted that for Gr = 0, the present system corresponds to the pure diffusive boundary layer which has a complete absence   www.nature.com/scientificreports/ of convection. Figure 10 demonstrates the role of leading edge accretion/ablation parameter γ . The flow of hybrid nanofluid (Cu-Fe 3 O 4 /water) is decreased. Different cases depend on the values of γ . The case, 0 < γ ≤ π 2 , corresponds to the leading edge accretion with the rate U ∞ cot γ . The case −π 4 ≤ γ < 0 , refers to backward boundary layer with trailing edge accretion. The case γ = 0 , is relevant to Rayleigh-Stokes problem and γ = π 2 , relates to the Blasius flat plate. Figure 11 depicts that velocity f ′ (ζ ) accelerates with stretching parameter . > 0 shows   www.nature.com/scientificreports/ the stretching phenomena, < 0 corresponds to shrinking case and = 0 is used for the static surface. Prandtl number Pr refers to the nanoparticles concentrations, therefore on increasing the Prandtl number, axial velocity f ′ (ζ ) is reduced as shown in Fig. 12. The reason is that due to the addition of nanoparticles, the thickness of the hybrid nanofluid and Brownian motion of nanoparticles are increased which resists the flow. Figure 13 is related to the Eckert number Ec and axial velocity f ′ (ζ ) . Velocity is easily enhanced on viscous dissipative effect.    1 & m 2 ). The reasons is that for the high values of ( m 1 & m 2 ), the effect of magnetic field is prominent. Therefore, the resistive effect of magnetic field is quite active. Figure 16 shows that the transverse velocity is decreased with the greater values of magnetic field parameter M. The magnetohydrodynamic   in Eq. (11) is responsible to reduce the transverse velocity g(ζ ) . The thermal buoyancy parameter namely Grashof number Gr is a convection parameter, so it increases the motion of nanoparticles through convection as shown in Fig. 17. Figure 18 reports that leading edge accretion/ablation   www.nature.com/scientificreports/ parameter γ reduces the transverse velocity g(ζ ) for γ = π 2 , π 3 , π 4 , π 5 (decreasing values of angle γ ). The stretching parameter in Fig. 19 shows that dimensionless transverse velocity g(ζ ) augments to be maximized. The effect is more pronounced and the boundary layer thickness is expanded. Figures 20 and 21 show that heat transfer is decreased for the various increasing values of ( m 1 & m 2 ). The thermal boundary layer thickness is reduced. Considering Fig. 22, it has been shown that temperature distribution   The thermal Grashof number Gr indicates the existence of convection so Gr > 0, generates the heating system. Increasing of Gr, causes the surge in buoyancy force which increases the temperature through convection as demonstrated by Fig. 23. It has been noticed in Fig. 24, that the temperature θ(ζ ) is reduced at γ = π 2 , π 3 , π 4 , π 5 . It is observed that the thermal boundary layer thickness is decreased. For γ = 0 o , there is no increasing or decreasing   www.nature.com/scientificreports/ effect in the temperature. Figure 25 specifies the effect of stretching parameter on temperature θ(ζ ). For > 0, the thickness of thermal boundary layer is low due to which heat transfer is minimum. Prandtl number influence on temperature θ(ζ ) is examined in Fig. 26. The energy of the nanoparticles is transferred to the environment which cause to decrease the temperature. It leads to low heat transfer and the thickness of thermal boundary layer.
Pr << 1 signifies that the thermal diffusivity prevails while Pr >> 1 corresponds to the momentum diffusivity     Figure 27 shows that the Eckert number Ec boosts the thermal boundary layer and hence heat transfer. The concentration of homogeneous chemical reactions ϕ(ζ ) and Hall parameter m 1 role are shown through Fig. 28. It is revealed that ϕ(ζ ) tends to minimum on the different values of m 1 . The reason is that due to strong      www.nature.com/scientificreports/ susceptibility to rise the concentration of homogeneous chemical reaction ϕ(ζ ) . Figure 32 illustrates the performance of leading accretion/ablation parameter γ and concentration of homogeneous chemical reaction ϕ(ζ ) . With the given values of γ , ϕ(ζ ) is amplified. Stretching/shrinking parameter and ϕ(ζ ) are depicted in Fig. 33.
There is a very high change in the concentration. Figure 34 elucidates that the Schmidt number Sc proceeds to enhance the species concentration. The effect of strength of heterogeneous chemical reaction parameter k 2 and concentration of homogeneous chemical reaction ϕ(ζ ) are shown in Fig. 35. It is depicted that the different values of k 2 decline the ϕ(ζ ). Entropy generation rate N G (ζ ) and Reynolds number Re are projected in Fig. 36. Due to increasing values of Re, viscosity of the nanoparticles increases which generate more resistive force to the flow and hence enhances the kinetic energy. It is reported that the irreversibility of the system increases with the Reynolds number Re which complement figure 4 of study 18 with respect to increasing behavior. Similar increasing behavior of entropy generation rate N G (ζ ) has been shown for the Brinkman number Br in Fig. 37. The temperature difference parameter θ w has the same increasing behavior for entropy generation rate N G (ζ ) in Fig. 38 which is already reported in figure 5 of study 18 . The progress of diffusion constant parameter γ 1 due to nanoparticle concentration of hybrid nanofluid Cu-Fe 3 O 4 /water is represented in Fig. 39 which has the same increasing behavior like the entropy behavior in Figs. 4 and 5 of the study 18 .

Conclusions
The heat and mass transfer flow of hybrid nanofluid Cu-Fe 3 O 4 /water with Hall current and ion-slip effects as well as entropy generation is analyzed. The main subject is how the strong and uniform magnetic field convert the two dimensional flow in (x, y) coordinates into three dimensional flow in (x, y, z) coordinates. Homotopy analysis method is used to compute the solution of the problem. Effects of all the parameters on different profiles are discussed in detail. The authors have intended to investigate the effect of a non-uniform magnetic field in future on the results which has rarely been investigated using an analytical solution. The summary of the results is presented as