Finite Element Analysis of Chemical Reaction and Radiation Effects on Isothermal Vertical Oscillating Plate with Variable Mass Diffusion

The objective of this paper is to investigate an unsteady flow of a viscous incompressible flow past an infinite isothermal vertical oscillating plate, in the presence of thermal radiation and chemical reaction. The fluid considered here is a gray, absorbing-emitting radiation but a nonscattering medium. The plate temperature is arised to Tw, and the concentration level near the plate is raised linearly with respect to time. An exact solution to the dimensionless governing equations has been obtained by the finite element method, when the plate is oscillating harmonically in its own plane. The effects of velocity, temperature, and concentration are studied for different physical parameters like thermal Grashof number, mass Grashof number, radiation parameter, prandtl number, chemical reaction parameter, Schmidt number, phase angle, and time are studied graphically. The skin-friction coefficient, the Nusselt number, and the Sherwood number at the plate are discussed, and their numerical values for various values of physical parameters are presented through tables.


Introduction
The present trend in the field of chemical reaction analysis is to give a mathematical model for the system to predict the reactor performance.The effect of a chemical reaction depends on whether the reaction is heterogeneous or homogeneous.This depends on whether they occur at an interface or as a single-phase volume reaction.In most cases of chemical reactions, the reaction rate depends on the concentration of the species itself.A reaction is said to be of the order n, if the reaction rate is proportional to the nth power of the concentration.In particular, a reaction is of first order, if the rate of reaction is directly proportional to concentration itself.Thermal radiation effects on heat and mass transfer play an important role in manufacturing industries for the design of fins, steel rolling, nuclear power plants, gas turbines, and various propulsion devices for air craft, missiles, satellites, and space vehicles are examples of such engineering applications.If the temperature of the surrounding fluid is rather high, radiation effects play an important role, and this situation does exist in space technology.England et al. 1 have studied the thermal radiation effects of a optically thin gray gas bounded by a stationary vertical plate.Radiation effect on mixed convection along a isothermal vertical plate was studied by Hossain and Takhar 2 .Raptis and Perdikis 3 studied the effects of thermal radiation and free convection flow past a moving vertical plate.The governing equations were solved analytically.Das et al. 4 have analyzed radiation effects on flow past an impulsively started infinite isothermal vertical plate.
The effect of a chemical reaction depends on whether the reaction is homogeneous or heterogeneous.This depends on whether they occur at an interface or as a single-phase volume reaction.In well-mixed systems, the reaction is heterogeneous, if it takes place at an interface and homogeneous, if it takes place in solution.Chambré and Young 5 have analyzed a first-order chemical reaction in the neighborhood of a stationary horizontal plate.Das et al. 6 have studied the effect of homogeneous first-order chemical reaction on the flow past an impulsively started infinite vertical plate with uniform heat flux and mass transfer.Again, mass transfer effects on moving isothermal vertical plate in the presence of chemical reaction studied by Das et al. 7 .The dimensionless governing equations were solved by the usual Laplace-trans form technique, and the solutions are valid only at lower time level.
The flow of a viscous, incompressible fluid past an infinite isothermal vertical plate, oscillating in its own plane, was solved by Soundalgekar 2.1 .The effect on the flow past a vertical oscillating plate due to a combination of concentration and temperature differences was studied extensively by Soundalgekar and Akolkar 8 .Radiation effects on the oscillatory flow past vertical in the presence of uniform temperature analyzed by Mansour 9 .The governing were solved by perturbation technique.The effect of mass transfer on the flow past an infinite vertical oscillating plate in the presence of constant heat flux has been studied by Soundalgekar et al. 10 .Muthucumaraswamy 11 studied thermal radiation effects on vertical oscillating plate in the presence of variable temperature and mass diffusion.Mazumdar and Deka 12 considered the MHD flow past an impulsively started inifinite vertical plate in presence of thermal radiation.MHD and radiation with variable mass diffusion were considered by Muthucumaraswamy and Janakiraman 13 .Radiation and chemical reaction effects on isothermal vertical oscillating plate with variable mass diffusion have been studied by Manivannan et al. 14 .It is proposed to study chemical reaction and thermal radiation effects on unsteady flow past infinite isothermal vertical oscillating plate with variable mass diffusion.The dimensionless governing equations are solved using the finite element method.The effects of various governing parameters on the velocity, temperature, concentration, skin-friction coefficient, Nusselt number, and Sherwood number are shown in figures and tables and discussed in detail.

Formulation of the Problem (Figure 1)
Chemical reaction and thermal radiation effects on unsteady flow of a viscous incompressible fluid past an infinite isothermal vertical oscillating plate with variable mass diffusion are studied.Here we discussed the unsteady flow of a viscous incompressible fluid which is initially at rest and surrounds an infinite vertical plate with temperature T ∞ and concentration C ∞ .Here, the x -axis is taken along the plate in the vertically up ward direction and the yaxis is taken normally to the plate.Initially, it is assumed that the plate and the fluid are of the same temperature and concentration.At time t > 0, the plate starts oscillating in its own plane with frequency w and the temperature of the plate is raised to T w , and the concentration level near the plate is raised linearly with respect to time.The fluid considered here is a gray, absorbing-emitting radiation but a nonscattering medium.It is also assumed that there exists a homogeneous first-order chemical reaction between the fluid and species concentration.Then by usual Boussinesq's approximation, the unsteady flow is governed by the following equations: The initial and boundary conditions are as follows:

2.4
The local radiant for the case of an optically thin gray gas is expressed by:

2.5
It is assumed they that the temperature differences within the flow are sufficiently small such that may be expressed as linear function of the temperature.This is accomplished by expanding in a Taylor series about and neglecting higher-order terms, thus: By using 2.5 and 2.6 , 2.2 reduces to The dimensional quantities are defined as

2.8
In view of the 2.1 , 2.2 , and 2.3 reduce to the following dimensionless form: where Gr, Gm, Pr, R, Sc, and K are the thermal Grashof number, mass Grashof number, Prandtl number, radiation parameter, Schmidt number, and chemical reaction parameter, respectively.
The initial and boundary conditions in nondimensional form are 2.12

Solution of the Problem
The linear functional for 2.9 over a typical line segment element e , y j ≤ y ≤ y k is Let u e N j u j N k u k be the linear piecewise approximation solution over the element e , y j ≤ y ≤ y k , where u j , u k are the values of the function u at the ends of the element e and N j y k − y/y k − y j , N k y − y j /y k − y j are the basis functions.One obtains where dot denotes the differentiation with respect tot and l e y k − y j .Assembling the element equations for two consecutive elements y i−1 ≤ y ≤ y i and y i ≤ y ≤ y i 1 , the following is obtained: Now put row corresponding to the node i to zero, the difference schemes with l e his Applying the trapezoidal rule, the following system of equations in Crank-Nicholson method are obtained:

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Here r k/h 2 and h, k are mesh sizes along y-direction and timet-direction, respectively.Index i refers to the space and j refers to the time.In the above equations 3.5 -3.7 taking i 1 1 n and using initial and boundary conditions 2.12 , the following tridiagonal system of equations are obtained: where A, D, and F are tri-diagonal matrices of order-n and whose elements are given by

3.9
Here u, θ, C and B, E, G are column matrices having the n-components u , respectively.The solutions of the above system of equations are obtained by using Thomas algorithm for velocity, temperature and concentration.Also, the numerical solutions for these equations are obtained by C-program.In order to prove the convergence and stability of Ritz finite element method, the computations are carried out for slightly changed values of hand k by running the same C-program.No significant change was observed in the values of u, θ, and C. Hence, finite element method is convergent and stable.The skinfriction, Nusselt number, and Sherwood number are important physical parameters for this type of boundary layer flow.
The skinfriction at the plate, which in the nondimensional form is given by The rate of heat transfer coefficient, which in the nondimensional form in terms of the Nusselt number is given by Nu − ∂θ ∂y y 0 .

3.11
The rate of mass transfer coefficient, which in the nondimensional form in terms of the Sherwood number, is given by Sh − ∂C ∂y y 0 .

Results and Discussion
In order to get a physical insight of the problem numerical calculations are carried out for different physical parameters, namely, thermal Grashof number, mass Grashof number, Prandtl number, radiation parameter, chemical reaction Schmidt number, phase angle and time on the physical flow field, computations are carried out for velocity, temperature, and concentration and they are presented in figures below.In the present study we adopted the following default parameter values of finite element computations: Gr 2.0, Gm 2.0, Pr 0.71, R 5.0, Sc 0.6, K 2.0, wt π/4, t 0.4.All graphs therefore correspond to these values unless specifically indicated on the appropriate figures.
In order to assess the accuracy of the numerical results, the present results are compared with the previous results.The velocity and concentration profiles for t 0.4, wt π/4, Gr 2.0, Gc 2.0, Pr 0.71, R 5.0, Sc 0.6 are compared with the available solution of Manivannan 14 in Figure 2. It is observed that the present results are in good agreement with that of Manivannan 14 .The influence of thermal Grashof number Gr on the velocity is shown in Figure 3.The thermal Grashof number signifies the relative effect of the thermal buoyancy force to the viscous hydrodynamic force.The flow is accelerated due to the enhancement in buoyancy force corresponding to an increase in the thermal Grashof number, that is, free convection effects.The positive values of Gr correspond to cooling of the plate by natural convection.Heat is therefore conducted away from the vertical plate into the fluid which increases the temperature and thereby enhances the buoyancy force.In addition, it is seen that the peak values of the velocity increases rapidly near the plate as thermal Grashof number increase and then decays smoothly to the free stream velocity.
Figure 4 presents typical velocity profiles in the boundary layer for various values of the mass Grashof number Gc.The mass Grashof number Gc defines the ratio of the species buoyancy force to the viscous hydrodynamic force.It is noticed that the velocity increases with increasing values of the mass Grashof number.
Figures 5 and 6 illustrate the velocity and temperature profiles for different values of Prandtl number Pr.The numerical results show that the effect of increasing values of Prandtl number results in a decreasing velocity.It is observed that an increase in the Prandtl number   results in a decrease of the thermal boundary layer thickness and in general lower average temperature with in the boundary layer.The reason is that smaller values of Pr are equivalent to increasing the thermal conductivities, and therefore heat is able to diffuse away from the heated surface more rapidly than for higher values of Pr.Hence in the case of smaller Prandtl numbers as the boundary layer is thicker and the rate of heat transfer is reduced.For different values of the radiation parameter R, the velocity and the temperature profiles are shown in Figures 7 and 8.It is noticed that an increase in the radiation parameter results in a decrease in the velocity and temperature within the boundary layer, as well as decreased the thickness of the velocity and temperature boundary layers.The concentration profiles for different time are shown in Figure 12.The trend shows that the wall concentration increases with increasing values of the time t.The effects of velocity profiles for different time are shown in Figure 13.In this case, the velocity increases gradually with respect to time t.The velocity profiles for different phase angles are shown in Figure 14.It is observed that the velocity increases with decreasing phase angle wt.
The effects of Gr, Gm, Pr, R, Sc, and K on the skin-friction C f , Nusselt number Nu, Sherwood number Sh are shown in Tables 1 to 3. From Table 1, it is observed that as Gr or Gm increases, the skin-friction coefficient increases.From Table 2, it is noticed that as R increases, the skin-friction coefficient decreases, while the Nusselt number decreases and Pr increases, the skin-friction coefficient decreases, while the Nusselt number decreases.From Table 3, it is found that as Sc or K increases, the skin-friction coefficient decreases while the Sherwood number decreases.

Conclusions
An exact analysis is performed to study thermal radiation effects on un steady flow past an infinite isothermal vertical oscillating plate, in the presence of variable wall concentration.The governing equations are solved using finite element method.The conclusions of the study are as follow.
1 The velocity increases with decreasing phase angle wt and radiation parameter R, the wall concentration increases with decreasing Schmidt number.
2 The velocity as well as concentration decreases with an increase in the chemical reaction parameter.
3 The temperature decreases due to high thermal radiation, and the leading edge effect is not affected by the oscillation of the plate.

Figure 1 :
Figure 1: The physical model of the problem and coordinate system.

K = 5 , 10 Figure 2 :
Figure 2: Comparison of concentration profiles at different values of K.

Figure 3 :
Figure 3: Velocity profile for different values of Gr.

Figure 4 :
Figure 4: Velocity profile for different values of Gr values of Gc.

Figure 5 :
Figure 5: Velocity profile for different values of Pr.

Figure 9 : 10 Figure 10 :
Figure 9: Velocity profile for different values of K.

Figure 11 :
Figure 11: Velocity profile for different values of Sc.

Figure 9 Figure 12 :Figure 13 :
Figure 9 represents the velocity profiles for different values of the chemical reaction parameter.The trend shows that the velocity increases with decreasing chemical reaction parameter.Figure 10 demonstrates the effect of the concentration profiles for different values of the chemical reaction parameter.It is observed that the concentration increases with decreasing chemical reaction parameter.

Figure 14 :
Figure 14: Concentration profile for different values of wt.

Figure 11
Figure 11  represents the effect of concentration profiles for different Schmidt number.The effect of concentration is important in concentration field.The profiles have the common feature that the concentration decreases in a monotone fashion from the surface to a zero value far away in the free stream.It is observed that the wall concentration increases with decreasing values of the Schmidt number

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Chemical reaction increases, the skin-friction coefficient decreases, while the Sherwood number decreases.5Radiation parameter increases, the skin-friction coefficient decreases, while the Nusselt number decreases.