# Unsteady MHD Casson fluid flow through vertical plate in the presence of Hall current

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## Abstract

The problem of unsteady magnetohydrodynamic flow of non-Newtonian fluid through a vertical plate in the presence of Hall current is studied in this paper. Using similarity transformations, the governing coupled partial differential equations of the defined problem are transformed as nonlinear ordinary differential equations which are solved analytically by employing perturbation technique. The core objective of this research is to examine the impact of pertinent physical constraints like magnetic parameter, thermal radiation, and Dufour parameter over the velocity, temperature, and concentration profiles of the fluid. It is noted that Casson fluid has superior heat transfer characteristics compared to Newtonian fluid. Lorentz force which is determined from magnetic field has a proclivity to diminish the flow velocity.

## Keywords

Hall current MHD Casson fluid Dufour effect## 1 Introduction

Continuously flowing material in the presence of additional shear stress is termed as fluid. Flow of fluid caused by infinite vertical pervious plate is a recapitulating topic for researchers, as it has a wide range of applications in many technological and industrial processes. The implications of vertical plate were predominantly analysed by Huang [1]. He explored the outgrowths of non-Darcy and magnetohydrodynamic influence on non-Newtonian fluids with vertical plate in porous medium in the presence of thermal diffusion with diffusion thermoeffects. The study of flow of magnetic nanoparticles was carried out analytically by Ashwinkumar et al. [2] and found that volume friction of magnetic nanoparticles controls the heat transfer rate and wall friction and also deduced that heat transfer rate and flow are maximum for aligned magnetic field than the transverse one.

Basically fluids are categorized as Newtonian and non-Newtonian. Non-Newtonian fluids have viscosity varying according to applied stress or force. In recent days, the study on non-Newtonian fluids has gained the interest of many sundry researchers owing to its considerable implications in mechanical and chemical engineering areas. Casson fluid is the most desired fluid among all non-Newtonian fluids. In 1959, N. Casson investigated the Casson fluid type to forecast the behaviour of flow of pigment oil in printing oil; Casson fluid is considered as the maximum favoured non-Newtonian fluid from its rheological properties, which can be used to examine the rheological character of materials like ketchup, blood, honey, shampoos, flow of plasma as well as mercury amalgams. Raju et al. [3] considered the Casson fluid to examine the significance of magnetic field through a stretching sheet and perceived that the induced magnetic parameter has the propensity to raise the heat transfer rate. Reddy et al. [4] gave detailed description on combined effects of frictional and irregular heat over Casson and Maxwell fluids and concluded that velocity profiles for Casson fluid are maximum than for Maxwell fluid. Numerical results for Casson fluid with the combined influence of heat source and magnetic field over different geometries were carried out by [5, 6, 7] and revealed that the fluid temperature is controlled by Casson parameter. Further, the combined investigation of heat and mass transfer of MHD Casson fluid under the effect of Brownian motion with thermophoresis was carried out by Kumar et al. [8] and concluded that energy and concentration fields of Maxwell fluid are affected by appropriate parameter as compared to Casson fluid.

The interpretation of electrically conducting fluids with magnetic effect is termed as magnetohydrodynamics. The term magnetohydrodynamics was originated by Hannes Alfven in 1942. Flow of fluid towards magnetic field produces the electricity that affects the magnetic flux, and the effect of magnetic intensity upon the electric current implies tensile strength that changes the fluid motion. In present days, working on MHD flow became a topic of great interest as it has several implications in engineering, astrophysics, and geophysics. Recently, Kataria and Patel [9] have accomplished the outflow, thermal, and mass transfer features of magnetohydrodynamic Casson fluid and observed that increased magnetic field declines the fluid velocity as well as boundary layer thickness. Further, the problem of investigating the flow, thermal, and mass transfer performance of flow of MHD past a vertical rotating cone with the impact of radiation, chemical reaction, and thermal diffusion was examined numerically by Sulochana et al. [10]; effect of magnetohydrodynamic flow with heat transfer over distinct materialistic cases like thermal radiation, heat absorption/generation, Joule heating, Hartman number past various geometries was carried out by [11, 12, 13]. Similar study was carried out by Khan et al. [14] with the consideration of Sisko nanomaterial passed over a stretching sheet.

Numerical solutions for heat transfer in ferrofluid with applied magnetic field were illustrated by Javed and Siddiqui [15]. The study of heat transfer holds an imperative role due to its countless applications in environmental, industrial, and engineering processes.

Natural convection motion takes place as buoyancy-induced flow obtained like design of many devices like radiators, solar collectors, various components of power plants, space craft, and many more. Theoretical approach over the motion of Carreau fluid has been carried out by Kumaran et al. [16] and revealed that in parabolic motion, the melting heat transfer rate with buoyancy effect and external heat source have property to increase the thermal energy transfer. Comparatively, Sheikholeslami et al. [17] studied the heat transfer properties of refrigerant-based nanofluid and observed the conduction as well as microconvection in fluid and obtained results. In a while, heat transfer of non-Newtonian fluid using various geometries was examined by [18, 19, 20, 21].

Edwin Hall revealed Hall current in 1879. This phenomenon reports the nature of electrons across the conductor under electric and magnetic field effects due to Lorentz force due to an electric potential difference among both sides of plate. It is observed that if the current across the plate is applied, the electrons move in a direction opposite to that of implemented magnetic field. Again, if enforced flux field is at right angle to the movement of electrons, the motion of electrons takes a curved path, and hence, electrons in motion gather along a side of the plate. It results in voltage development towards both the sides of plate; such an voltage is called ‘Hall voltage’, normal to the flow of magnetic as well as electric current. Hall current is employed in power generators, magnetometers, automotive fuel level indicators, planetary fluid dynamics, etc. In view of a wide range of applications, Biswas and Ahmed [22] examined the effect of radiant heat and chemical reaction with Hall current on variable Casson nanofluid and reported that velocity fall of with growing Casson parameter and as temperature profile decreases the heat generation raises. Further, [23, 24, 25, 26] explored the Hall current effect on MHD.

Radiative heat transfer plays a vital role in the initiation of excessive temperature and hence has gained prominence due its usage in nuclear power plants, aircraft propulsion, space vehicles, and gas turbines. For instance, Sulochana et al. [26] elaborated the study of 3D Casson fluid flow with the influence of thermal radiation and thermodiffusion with unsteady heat source/sink. In one more attempt, Gupta et al. [27] addressed the effect of Brownian motion and thermophoresis in non-Newtonian nanofluid. Further, Hayat et al. [28] considered analytically the outcome of Joule heating and thermal radiation with chemical reaction of first order by considering flow of Maxwell nanofluid. Similar studies related to thermal radiation can be seen in [29].

From the above noted studies towards the boundary of the flow, we further consider the 2D motion of non-Newtonian Casson fluid with Dufour effect and chemical reaction. Sharma et al. [30] elaborated numerically by considering thermal diffusion and diffusion thermoreactions on free connective, heat absorption radiative nanofluid. The stagnation point of Casson fluid was presented by Shaw et al. [29] under the influence of radiation, thermal diffusion, diffusion thermoeffects with chemical reaction.

The study of heat and mass transfer including chemical reaction has influential aspect in various operations and hence gained substantial importance in present days, like evaporation of water body, polymer production, formulation as well as dispersion of fog, heat transfer in moist cooling tower, etc. The flow of magnetic nanofluid using ferrous nanoparticles with an elongated sheet was addressed by Poojari et al. [31] while Ibrahim et al. [32] addressed the combined influence of heat and mass transfer in view of Casson fluid with influence of thermal radiation with Soret and Dufour effects and concluded that strength of Dufour number boosts with raise in density of thermal boundary layer.

To the best extent of our knowledge, no work has been carried by the researchers to note the effect of Hall current over an incompressible boundary layer slip motion of Casson fluid over an infinite vertical plate together with heat suction, thermal radiation, and chemical reaction. We made the comparative study for Newtonian and non-Newtonian fluids. Hence, by making use of the above-mentioned results, we attempted to bridge the gaps by extending El-Aziz and Yahya [33] problem. To workout the ordinary differential equations, we speculated an analytical perturbation technique and obtained graphical illustrations with the aid of MATLAB package.

## 2 Formulation of the problem

*i*,

*j*)th element of measure of deformation, critical point of the product depend upon non-Newtonian fluid model is, the plastic absolute viscosity of non-Newtonian fluid is \(\mu_{B}\), and resultant fluid stress is \(\tau_{0}\).

*g*is the gravitational acceleration, \(\bar{T}\) is the spatial fluid temperature close to the plate, \(\bar{T}_{\infty }\) is the free flow spatial temperature, \(\beta\) is the heat expansion factor, \(\mu\) is the fluid viscosity, \(\rho\) is the density of fluid,

*k*is the thermal conductivity, \(\upsilon = \frac{\mu }{\rho }\) is the kinematic viscosity of fluid, \(\xi\) is the Casson fluid constant, \(Q_{0}\) represents the spatial heat exhaustion factor with \(c_{p}\) as definite temperature of the fluid with steady force. From the above suppositions, suitable preconditions for rate of velocity as well as thermal fields are delimited as (24).

- At \(\bar{y} = 0\):$$\bar{u} = \bar{u}_{\text{slip}} = \chi \left( {1 + \frac{1}{\xi }} \right)\frac{{\partial \bar{u}}}{{\partial \bar{y}}},\,\,\bar{w} = \bar{w}_{\text{slip}} = \chi \left( {1 + \frac{1}{\xi }} \right)\frac{{\partial \bar{w}}}{{\partial \bar{y}}},\,\,\bar{T} = \bar{T}_{\text{w}} + \varepsilon \left( {\bar{T}_{\text{w}} - \bar{T}_{\infty } } \right)\exp \left( {i\bar{\omega }\bar{t}} \right).$$
- As$$\bar{y} \to \infty : \bar{u} \to \bar{U}_{\infty } = U_{0} \left[ {1 + \varepsilon \exp \left( {i\bar{\omega }\bar{t}} \right)} \right]\quad \bar{w} \to 0,\quad \bar{T} \to \bar{T}_{\infty }.$$(16)

*A*is a real absolute constant, \(\varepsilon\) as well as \(\varepsilon A\) is insignificant terms not more than one. Here minus symbol expresses the absorption of velocity about the plate. Away from interfacial layer, Eq. (12) implies:

- At \(\bar{y} = 0\):$$\bar{q}_{\text{slip}} = \chi \left( {1 + \frac{1}{\xi }} \right)\frac{{\partial \bar{q}}}{{\partial \bar{y}}},\,\,\,\,\bar{T} = \bar{T}_{\text{w}} + \varepsilon \left( {\bar{T}_{W} - \bar{T}_{\infty } } \right)\exp \left( {i\bar{\omega }\bar{t}} \right).$$
- As \(\bar{y} \to \infty\):$$\bar{q} \to \bar{U}_{\infty } = U_{0} \left( {1 + \varepsilon \exp \left( {i\bar{\omega }\bar{t}} \right)} \right),\,\,\,\,\bar{T} \to \bar{T}_{\infty } .$$(24)

Here Gr is the Grashof number, Pr is the Prandtl number, *M* is the constant of magnetic flux, with \(Q_{\text{H}}\) as the parameter of heat absorption. The non-dimensional mode preconditions of the boundary (24) turn into:

Here \(\delta = \frac{{\left( {\chi V_{0} } \right)}}{\upsilon }\) is the slip parameter. Equations (26), (27) and (28) are PDE’s and cannot be solved directly; however, the set of PDE’s may be reduced into set of ODE’s in non-dimensional form and the solutions can be found analytically. In this,

*q*’ is the velocity, ‘\(\theta\)’ is the temperature, and ‘\(\phi\)’ is the concentration, which are given as follows:

*q*’ from Eq. (30) in (26), we get:

Next solving Eq. (40),

Now solving Eq. (38),

Applying the boundary conditions (47) into Eq. (46) and

now solving Eq. (37),

Solving Eq. (35) analytically,

*Skin friction*

*Nusselt number*

*Sherwood number*

## 3 Results and discussions

*M*, slip variable \(\delta\), Grashof number, Prandtl number, heat absorption parameter \(Q_{\text{H}}\), for both non-Newtonian and Newtonian fluids, are drawn accordingly. We take into account the measures of non-dimensionalized parameters as

*e*= 0.2,

*b*= 0.1, Pr= 0.7,

*M*= 1,

*t*= 0.1, Gr = 5, Du = 2, Sc = 0.6, \(Q_{\text{H}}\) = 5,

*S*= 2, Kr = 0.5,

*R*= 1,

*A*= 1,

*m*= 1,

*w*= 10, as standard values in the entire study except indicated in the graphs (Fig. 1).

*M*over momentum. It is noted that, for rising values of magnetic parameter, velocity profile diminishes, as magnetic parameter owns a propensity to accelerate the resistance which converses towards the flow. This energy is known as Lorentz force that results in lowering the velocity.

*m*over the velocity field for both Newtonian and non-Newtonian fluids. From the graph, it is observed that rising values of Hall parameter lead to greater velocity. Since the effective conductivity decreases with the increase in Hall parameter and which intends decrease in magnetic damping, results the increase in velocity. Figure 4 shows the effect of slip parameters \(\delta\) over momentum field. It is perceived that an escalation in velocity increases the slip parameter \(\delta\) as it has a propensity of lowering the resistance forces that raises the velocity of fluids.

## 4 Conclusions

Fluid velocity rises with the rise in Hall parameter and slip parameter values, whereas it decreases with the increasing value of magnetic parameter.

The velocity of fluid decreases with the rising heat absorption parameter and Prandtl number, whereas increasing Grashof number increases the fluid velocity.

The radiation parameter and Dufour number help to strengthen the fluid velocity and temperatures.

Increasing rates of Prandtl number and heat absorption variable diminish the rate of heat transfer.

Concentration profiles increase due to Schmidt number and decrease due to chemical reaction parameter.

Skin friction factor shows an increment against magnetic parameter and Prandtl number while it declines against Grashof number and radiation parameter.

Nusselt number displays an increasing nature with growing values of magnetic parameter.

Sherwood number decreases with rising Dufour numbers.

## Notes

### Acknowledgements

The authors acknowledge backward classes Government of Karnataka, India, for financial support under OBC-Ph.D. fellowship (No 2017PHD41900).

### Compliance with ethical standards

### Conflict of interest

The authors declare that they have no conflict of interest.

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