A Bingham fluid is a category of non-Newtonian fluid that exhibits solid-like behavior at low-stress levels and flows as a viscous liquid under elevated stress levels. They demonstrate yield stress, indicating that the fluid remains static until the applied stress is above a specific critical threshold. Below this yield stress, the material exhibits rigid body behavior. Upon surpassing the yield stress, the flow behavior becomes linear, characterized by a constant viscosity. The linear correlation between stress and strain rate manifests similarly to that observed in Newtonian fluids. Typical instances encompass toothpaste, mayonnaise, and concrete. These materials necessitate a certain force to initiate flow. Bingham fluids are significant in numerous industrial and scientific applications, especially where materials necessitate exact regulation of flow characteristics. Bird et al. ¹ examined the behaviour of a Bingham fluid within a hard circular tube. Kapur ² introduced several mathematical models, such as Cais-son, the Bingham, and Herschel-Bulkley models. Rathy ³ examined the fluid dynamics of a Bingham fluid within a channel and an annulus featuring impermeable barriers. Vajravelu et al. ⁴ conducted an experimented on the flow of Bingham fluid in an annular tube with a porous wall. Ramakrishna et al ⁵ investigated the flow behaviour of a Bingham fluid on a permeable bed in an enclosed channel. Goverdhan ⁶ examined the flow of Bingham fluid in a porous channel. Narahari et al. ⁷ Investigate the movement of a Bingham fluid between two porous substrates, focusing on its unsteady behaviour. Recently, Murthy et al. ⁸ focused on analysing the flow of a Bingham fluid, which is not stable, in contact with a Newtonian fluid within two parallel plates. The objective is to determine the velocity field, mass flow rates, and interface velocity. Tsangaris et al. ⁹ conducted on the movement of a Bingham fluid between two porous walls that are parallel to each other. One wall moves steadily in the same direction as the other wall, which remains stationary. At the same time, there is a pressure difference throughout the length of the wall, and there is a flow of fluid across the walls due to their porous nature. Adnan and Abdulhadi ¹⁰ performed an investigation on the influence of an inclined magnetic field on the flow of incompressible Bingham plastic fluid within an inclined symmetric channel. The study also considered the effects of mass transfer and heat transfer. Slip circumstances are utilised for heat transmission and focus. Lakshminarayana et al. ¹¹ examined the impact of wall slip circumstances, elasticity wall characteristics, and heat transfer on the movement of conducting Bingham fluid in an irregular channel using the presumptions of a lengthy wavelength and low Reynolds number. The current research by Mahabaleshwar et al. ¹² investigates how radiation and chemical reactions affect the two-dimensional boundary layer flow of a bi-viscous Bingham fluid on a thermosolutal Marangoni boundary that is accompanied by a magnetic field and thermal source or sink. A mathematical model is developed using the Navier-Stokes equations to represent the physical flow problem. In order to convert these nonlinear PDEs into a system of nonlinear ODEs, they employed a similarity transformation. The study conducted by Basavarajappa et al. ¹³ examines the multilayer flow of a bi-viscous Bingham fluid within a vertical slab with a hybrid nanofluid, using the nonlinear Boussinesq approximation. Recent studies have continued to examine oscillatory and unsteady MHD convection in thermally active media. Afridi et al. ¹⁴ analyzed entropy generation minimization and heat-transfer enhancement in MHD oscillatory ferrofluid flow, emphasizing the role of magnetic control in thermal transport. Ullah et al. ¹⁵ studied oscillatory mixed convection around a horizontal circular cylinder embedded in a porous medium while considering temperature-dependent density effects. Nandkeolyar et al. ¹⁶ investigated unsteady hydromagnetic natural convection of a dusty fluid past a moving vertical plate with ramped temperature and thermal radiation. These studies show that unsteadiness, magnetic effects, buoyancy, and porous-medium resistance remain important mechanisms in convective transport problems.

Heat transport in Bingham fluids entails intricate interplay between the fluid’s rheological features and thermal aspects. The existence of a yield stress, which regulates flow commencement, profoundly influences heat transfer processes. Vradis et al. ¹⁷ numerically resolved the concurrent evolution of thermal fields and hydrodynamic at the entry region of a cylindrical pipe for a non-Newtonian Bingham-type fluid by employing the completely elliptic mathematical models of continuity, momentum, and energy. Mustafa et al. ¹⁸ conducted a heat transfer simulation for the swirling flow of a Bingham fluid constrained by a permeable rotation disk. The influence of concentration and temperature variations on magnetohydrodynamic (MHD) oscillatory flow in a porous media has numerous practical implications in the fields of engineering, industry, medical research, and issues related to the extraction and transportation of petroleum. Hamza et al. ¹⁹ conducted a study on the impact of slip condition, radiative heat transfer, and transverse magnetic field on the unsteady flow of a conducting optical thin fluid via a channel equipped with a porous media. Khudair and Al-Khafajy ²⁰ proposed a heat transfer model for MHD oscillating flow of Williamson fluid over a porous plate, considering two different forms of flow. Al-Aridhee and Al-Khafajy ²¹ examined the impact of mass and heat transfer on the peristaltic movement of MHD flow of a non-Newtonian Jeffrey fluid via a cylindrical porous media channel. The investigation focuses on the flow within a wave frame of reference that is travelling at the velocity of the wave. Al-Khafajy and Labban ²² conducted a study on the combined impact of concentration and thermo-diffusion on the fluctuating flow of an incompressible Carreau fluid via an angled permeable channel. Liu et al. ²³ investigate the steady flow and thermal transfer of Bingham fluid over a spinning disk of limited radius with radially varying thickness in the boundary layer. Eldabe et al. ²⁴ examined the flow of non-Newtonian Bingham blood fluid down an irregular conduit. The fluid exhibits electrical conductivity, and an external uniform magnetic field is added to this motion. Heat and mass transmission are considered, leading to an examination of the Dufour and Soret effects. Al-Khafajy and Mohammed ²⁵ examined a mathematical model elucidating the effects of thermal transfer on the oscillating flow of Bingham fluid with changing viscosity in a porous channel within the context of magnetohydrodynamics. Salahuddin et al. ²⁶ performed a study analyzing numerical behavior utilizing the Adams-Bashforth predictor-corrector method of numerical analysis for the Williamson fluid model, considering variable viscosity, natural convection, and an angled magnetic field. Additionally, thermal radiation, Joule heating, and heat source/sink effects are incorporated into the thermal considerations. Akram et al. ²⁷ studied the peristaltic flow of Bingham fluids under an inclined magnetic field, while Humnekar and Darbhasayanam ²⁸ investigated variable-viscosity nanofluid flow in inclined porous media. These recent studies highlight the ongoing need for improved formulations that incorporate thermal, magnetic, and viscous variations simultaneously. Recent works have also extended non-Newtonian flow analysis by incorporating advanced thermal and concentration mechanisms. Panda et al. ²⁹ examined Marangoni convection in a tangent hyperbolic fluid with Cattaneo–Christov heat and mass flux, buoyancy, and activation energy effects. Sneha et al. ³⁰ considered MHD Marangoni nano-boundary-layer flow with carbon nanotubes and thermal radiation, highlighting the influence of magnetic and radiative effects on heat transfer. More closely related to yield-stress rheology, Sachhin et al. ³¹ analyzed thermodynamic and viscosity-ratio effects in a non-Newtonian tetra-Bingham nanofluid flow, showing the importance of rheological parameters in controlling transport behavior.

In an inclined channel, the influence of gravity is crucial in propelling the flow. The gravitational force acting along the slope of the channel affects the overcoming of yield stress, allowing the fluid to flow. In the case of Bingham fluids, flow takes place when the shear stress surpasses the yield stress. The angle of inclination in a channel influences the critical shear stress required to initiate flow. Lakshminarayana et al. ³² investigated the concurrent impacts of heated Joules and slip on the peristaltic flow of a Bingham fluid within an inclination tapered permeable channel featuring elastic walls. Mohammed and Al-Khafajy ³³ examined the impact of temperature and concentration on magnetohydrodynamic oscillatory flow of Bingham fluid with varying viscosity in a sloped channel. umbinarasaiah ³⁴ conducted a numerical investigation of entropy generation in an incompressible Casson fluid moving through an inclined permeable channel subjected to magnetic influence. Jha and Aina ³⁵ offered a mathematical model for the complete magnetohydrodynamic mixed convection flow of an electrically conducting, viscous, incompressible fluid in an inclined permeable channel subject to time-periodic boundary constraints.

Although the above studies provide useful insights into oscillatory MHD convection, porous-medium transport, non-Newtonian rheology, and coupled heat and mass transfer, most of them address these mechanisms separately or in different geometrical configurations. Analytical studies combining oscillatory MHD mixed convection, Bingham yield-stress behavior, variable viscosity, porous-medium resistance, inclination effects, and coupled thermal and concentration transport in a single channel-flow formulation remain limited. Therefore, the novelty of the present work lies in developing an analytical model that brings these interacting mechanisms together and clarifies how the competition between buoyancy forces, Lorentz-force damping, yield-stress resistance, viscosity variation, and porous drag controls the velocity, temperature, and concentration fields.

This study comprises five sections. The initial section is the introduction, which encompasses a historical review of the factors being examined. The second involves constructing the mathematical model. The third portion presents the resolution to the issue. The fourth portion encompasses an analysis of the outcomes via the function diagrams we acquired. The investigation was ended with a discussion and conclusions.

Let us consider the flow of a non-Newtonian (Bingham) fluid with variable viscosity under the effects of radioactive heat transfer and electrically-applied magnetic field as depicted through an inclined porous channel with a width of h ( Figure 1). Fluids are supposed to have minimal electromagnetic power produced with a low electrical conductivity. We think of the system of Cartesian coordinates so that is the velocity vector.

The basic equations governing the problem are provided as:

The continuity equation is given by: ∇ . U = 0 (1)

The momentum equations: ρ ( U ¯ . ∇ ) U ¯ = ∇ . S ¯ + J ¯ × B ¯ − μ ( T ¯ ) k U ¯ + ρg B T sin φ ∆ T ¯ + ρg B C sin φ ∆ C ¯ + ρg ( isin ( ϕ ) − jcos ( ϕ ) ) (2)

The concentration equation: ( U ¯ . ∇ ) C ¯ = ∇ . ( D C T d T m ∇ T ¯ + D C ∇ C ¯ ) − K r ∗ ∆ C ¯ (3)

The temperature equation: ρ c T ( U ¯ . ∇ ) T ¯ = ∇ . ( K T ∇ T ¯ ) + ∆ . Q T + Q H ∆ T ¯ (4) where U ¯ = ( u ¯ ( y ¯ , t ¯ ) , 0 , 0 ) is the velocity field, T ¯ = T ¯ ( y ¯ , t ¯ ) “temperature”, C ¯ = C ¯ ( y ¯ , t ¯ ) “concentration”, J ¯ × B ¯ = − σ B s 2 sin 2 φ u i “Lorentz force for inclined magnetic field strength”, ³³ σ is a conductivity of the fluid, k is a permeability, ρ “fluid density”, g “gravity field”, c T “specific heat at constant pressure”, K T “thermal conductivity”, Q H “heat generation”, D C “coefficient of mass diffusivity” and T d “thermal diffusion ratio”, ∆ . Q T = 4 α 2 ( T ¯ − T 0 ) ”radiation heat flux”, ³⁶ α “radiation absorption”, ( 0 ≤ ϕ ≤ π ) is the angle between the centre channel and the ground acceleration. The corresponding boundary conditions are given below: u ¯ = 0 , T ¯ = T 0 , C ¯ = C h at y ¯ = 0 and u ¯ = 0 , T ¯ = T h , C ¯ = C 0 at y ¯ = h (5)

The basic equation for the Bingham fluid, ³² given by: S ¯ = − p ¯ I + s ¯ and s ¯ = { ( μ ( T ¯ ) + τ 0 ( ∂ u ¯ ∂ y ¯ ) ) ( ∇ U ¯ + ( ∇ U ¯ ) T ) for τ ≥ τ 0 0 for τ < τ 0 (6)

Where p ¯ “pressure”, I “unit tensor”, μ c “fluid viscosity”, τ 0 “yield stress”, and γ ̇ ¯ “shear rate”.

When compensating for the velocity vector and the concentration and temperature functions, taking into account the magnetic field generated by the passage of a simple electric current over a porous wall of the inclined flow channel, and by compensating for the shear stress ( Equation 6), and after simplifying, we rewrite the nonlinear partial differential system (1)-(4) as follows: ∂ u ¯ ∂ x ¯ + ∂ v ¯ ∂ y ¯ = 0 (7) ρ ( ∂ u ¯ ∂ t ¯ + u ¯ ∂ u ¯ ∂ x ¯ + v ¯ ∂ u ¯ ∂ y ¯ ) = − ∂ p ¯ ∂ x ¯ + ∂ s ¯ 11 ∂ x ¯ + ∂ s ¯ 12 ∂ y ¯ − σ B s 2 sin 2 φ u ¯ − μ ( T ¯ ) k u ¯ + ρg B T sin φ ( T ¯ − T 0 ) + ρg B C sin φ ( C ¯ − C 0 ) + ρg sin ϕ (8) ρ ( ∂ v ¯ ∂ t ¯ + u ¯ ∂ v ¯ ∂ x ¯ + v ¯ ∂ v ¯ ∂ y ¯ ) = − ∂ p ¯ ∂ y ¯ + ∂ s ¯ 21 ∂ x ¯ + ∂ s ¯ 22 ∂ y ¯ − μ ( T ¯ ) k v ¯ (9) ∂ C ¯ ∂ t ¯ + u ¯ ∂ C ¯ ∂ x ¯ + v ¯ ∂ C ¯ ∂ y ¯ = D C T d T m ( ∂ 2 T ¯ ∂ x ¯ 2 + ∂ 2 T ¯ ∂ y ¯ 2 ) + D C ( ∂ 2 C ¯ ∂ x ¯ 2 + ∂ 2 C ¯ ∂ y ¯ 2 ) − K r ∗ ( C ¯ − C 0 ) (10) c T ρ ( ∂ T ¯ ∂ t ¯ + u ¯ ∂ T ¯ ∂ x ¯ + v ¯ ∂ T ¯ ∂ y ¯ ) = K T ( ∂ 2 T ¯ ∂ x ¯ 2 + ∂ 2 T ¯ ∂ y ¯ 2 ) − 4 α 2 ( T 0 − T ¯ ) + Q H ( T ¯ − T 0 ) (11)

The stress components are given by: s ¯ 11 = s ¯ 22 = 0 and s ¯ 12 = s ¯ 21 = ( μ ( T ¯ ) + τ 0 ( ∂ u ¯ ∂ y ¯ ) ) ∂ u ¯ ∂ y ¯ = μ ( T ¯ ) ∂ u ¯ ∂ y ¯ + τ 0 (12)

By substituting the equation (12) into the governing equations and after simplifying, we obtain: ρ ∂ u ¯ ∂ t ¯ = − ∂ p ¯ ∂ x ¯ + ∂ ∂ y ¯ ( μ ( T ¯ ) ∂ u ¯ ∂ y ¯ + τ 0 ) − σ B s 2 sin 2 φ u ¯ − μ ( T ¯ ) k u ¯ + ρg sin φ ( B T ( T ¯ − T 0 ) + B C ( C ¯ − C 0 ) ) + ρg sin ϕ (13) ∂ p ¯ ∂ y ¯ = 0 (14) ∂ C ¯ ∂ t ¯ = D C T d T m ∂ 2 T ¯ ∂ y ¯ 2 + D C ∂ 2 C ¯ ∂ y ¯ 2 − K r ∗ ( C ¯ − C 0 ) (15) c T ρ ∂ T ¯ ∂ t ¯ = K T ∂ 2 T ¯ ∂ y ¯ 2 + ( 4 α 2 + Q H ) ( T ¯ − T 0 ) (16)

The equation (14) shows that the pressure does not depend on y . To solve the above system of equations, we use its non-dimensional conditions as follows:

By substituting equations from Table 1 into equations (13), (15), (16) and the equations of boundary conditions equation (5), we have the following non-dimensional equations: R e ∂ u ∂ t = − ∂ p ∂ x + μ ( T ) ∂ 2 u ∂ y 2 + ∂ u ∂ y ∂ μ ( T ) ∂ y − ( M 2 sin 2 φ + μ ( T ) Da ) u + sin φ ( G T T + G C C ) + R e F r sin ϕ (17) ∂ C ∂ t = S T ∂ 2 T ∂ y 2 + 1 S C ∂ 2 C ∂ y 2 − K C C (18) Pe ∂ T ∂ t = ∂ 2 T ∂ y 2 + ( K T + Q H ) T (19) u = 0 , T = 0 , C = 1 at y = 0 and u = 0 , T = 1 , C = 0 at y = 1 (20)

This part includes analyzing the solutions we obtained. We start with the temperature function Figures 2 and 3, then the concentration function Figures 4– 7, and then the fluid velocity function Figures 8– 24.

Figure 2 The data indicates that the temperature of the fluid rises as Q H and K T increase. In contrast, Figure 3 shows that temperature fluid decreases by increasing ω and Pe .

Figures 4– 7, Fluid concentration rises with higher values of ω and Pe, but decreases with increased Q H , K T , S C , S T , and K C .

Figures 8– 24, Exhibit that fluid velocity escalates with an increase in Q H , K T , G C , Pe , R e , G T , λ , ϕ , φ , and Da , while diminishing with an increase in S C , S T , K C , M , ω , and F r . It is evident that the velocity fluctuates more significantly in the scenario of changing viscosity compared to that of constant viscosity.

This study analyzed the transient, incompressible magnetohydrodynamic (MHD) oscillatory flow of a non-Newtonian Bingham fluid through an inclined porous channel, considering variable viscosity, heat generation, and concentration effects. The governing nonlinear equations were solved using the separation of variables technique with computational assistance from Wolfram Mathematica 13. The obtained results were interpreted in terms of the influence of several dimensionless parameters on temperature, concentration, and velocity distributions. •

The velocity of the fluid was observed to increase with larger values of the solutal Grashof number G C , Reynolds number Re , thermal Grashof number G T , and pressure gradient constant λ . In contrast, the velocity decreased when the magnetic parameter M , and Froude number Fr were increased. Moreover, the fluid motion was enhanced with a higher channel inclination angle ϕ, as this promotes gravitational acceleration along the channel wall, whereas the effect of the magnetic field inclination φ was relatively minor.