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Theoretical investigation of an unsteady MHD free convection heat and mass transfer flow of a non-Newtonian fluid flow past a permeable
moving vertical plate in the presence of thermal diffusion and heat sink
V. Ravikumar1, a, M. C. Raju2, b* and G. S. S. Raju3,c 1, 2 Department of Humanities and Sciences (Mathematics), Annamacharya Institute of Technology
and Sciences, (Autonomous), Rajampet- 516126, A.P, India
3 Department of Mathematics, JNTUA College of Engineering Pulivendula, Pulivendula, A.P, India.
[email protected], b*[email protected], [email protected] * Corresponding author
Keywords: MHD, Rivlin-Ericksen fluid, heat and mass transfer, source or sink and vertical moving porous plate.
Abstract: The problem of unsteady, two-dimensional, laminar, boundary-layer flow of a viscous,
incompressible, electrically conducting and heat-absorbing Rivlin-Ericksen flow fluid along a semi-
infinite vertical permeable moving plate has been investigated. A uniform transverse magnetic field
is applied in the direction of the flow. The presence of thermal and concentration buoyancy effects
is considered. The plate is assumed to move with a constant velocity in the direction of fluid flow
while the free stream velocity is assumed to follow the exponentially increasing small perturbation
law. Time-dependent wall suction is assumed to occur at the permeable surface. The dimensionless
governing equations for this investigation are solved analytically using two-term harmonic and non-
harmonic functions. Numerical evaluation of the analytical results is performed and some graphical
results for the velocity, temperature and concentration distributions within the boundary layer are
presented. Skin-friction coefficient, Nusselt number and Sherwood number are also discussed with
the help of the graphs. Local skin-friction coefficient increases with an increase in the permeability
parameter, and Soret number whereas reverse effects is seen in the case of dimensionless
viscoelasticity parameter of the Rivlin-Ericksen fluid. Nusselt number decreases in the presence of
heat absorption. The presence of Soret number Sherwood number increases.
1. Introduction:
The problem of boundary layer flow over a continuously moving solid surface is an
important type of flow occurring in many industrial processes, such as heat treated materials
traveling between a feed roll and a wind-up roll or materials manufactured by extension, glass fiber
and paper production. Convection of a heated or cooled vertical plate is one of the fundamental
problems in heat and mass transfer studies in recent times. If the existing free convection is
accompanied by an external flow, the combined mode of free and forced convection exists.
Magneto hydrodynamics (MHD) is important in many engineering applications such as, in MHD
power generators, cooling of nuclear reactors, and the boundary layer control in aerodynamics and
crystal growth. Transport processes in porous media play a significant role in various applications,
such as thermal insulation, energy conservation, petroleum industries, solid matrix heat exchangers,
geothermal engineering, chemical catalytic reactors, and underground disposal of nuclear waste
materials. In many transport processes in nature and in industrial applications, the heat and mass
transfer with variable viscosity is a consequence of buoyancy effects caused by the diffusion of heat
and chemical species. The study of such processes is useful for improving a number of chemical
technologies, such as polymer production and food processing. In nature, the presence of pure air or
water is impossible. Some foreign mass may be presented either naturally or mixed with air or
water. The problem of MHD laminar flow through a porous medium has become very important in
recent years because of its possible applications in many branches of science and technology,
particularly in the field of agricultural engineering to study the underground water resources,
seepage of water in river beds; in chemical engineering for filtration and purification process; in
International Journal of Engineering Research in Africa Vol. 16 (2015) pp 90-109 Submitted: 2014-11-10© (2015) Trans Tech Publications, Switzerland Revised: 2015-04-20doi:10.4028/www.scientific.net/JERA.16.90 Accepted: 2015-04-27
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TransTech Publications, www.ttp.net. (ID: 117.211.106.228-22/06/15,10:26:20)
petroleum technology, to study the movement of natural gas, oil and water through the oil
reservoirs. Kim [1] investigated an unsteady MHD convective heat transfer past a semi-infinite
vertical porous moving plate with variable suction. Later Chamkha [2] extended this work; he
discussed unsteady MHD convective heat and mass transfer past a semi-infinite vertical permeable
moving plate with heat absorption. Pal et al. [3] studied combined effects of Joule heating and
chemical reaction on unsteady magneto hydrodynamic mixed convection of a viscous dissipating
fluid over a vertical plate in porous media with thermal radiation. Chen [4] discussed heat and mass
transfer in MHD flow by natural convection from a permeable, inclined surface with variable wall
temperature and concentration. Singh et al. [5] discussed fluctuating heat and mass transfer on
unsteady MHD free convection flow of radiating and reacting fluid past a vertical porous plate in
slip- flow regime. Guedda et al. [6] discussed analytical and ChPDM analysis of MHD mixed
convection over a vertical flat plate embedded in a porous medium filled with water at 4℃. Israel-
Cookey et al. [7] discussed MHD oscillatory Couette flow of a radiating viscous fluid in a porous
medium with periodic wall temperature. Ahamed et al. [8] discussed, the combined heat and mass
transfer by mixed convection MHD flow along a porous plate with chemical reaction in presence of
heat source. Chaudhaury et al. [9] addressed combined heat and mass transfer effects on MHD free
convection flow past an oscillating plate embedded in porous medium. Ravikuamr et al. [10]
considered heat and mass transfer effects on MHD flow of viscous fluid through non-homogeneous
porous medium in presence of temperature dependent heat source. Ravikumar et al. [11]
investigated a problem of MHD three dimensional coquette flows past a porous plate with heat
transfer. Mbeledogu et al. [12] considered, an unsteady MHD free convection flow of a
compressible fluid past a moving vertical plate in the presence of radioactive heat transfer. Israel-
Cookey et al. [13] discussed influence of viscous dissipation on unsteady MHD free convection
flow past an infinite heated vertical plate in porous medium with time-dependent suction. The
density of sea water is determined by both its temperature and its salt content or salinity. Whereas
added heat makes water lighter, added salt makes it denser, so both must be considered when
evaluating the gravitational stability of the water column. That is why, a given column of water will
‘convert’ or overturn if dense waters overlie lighter waters. In many parts of the world ocean, the
distributions of temperature and salinity are opposed in their effects on density. This arises because
of the tendency of warm water to evaporate easily in low latitudes, the predominance of rainfall in
cold, high latitude regions, and the deep circulation patterns that bring the cold waters to lower
latitudes. The opposing effects of temperature and salinity on density, and the fact that the
molecular conductivity of heat is about 100 times as large as the diffusivity of salt in water, makes
possible a variety of novel convective motions that have come to be known as double diffusive
convection. In the following, the oceanic double-diffusive mixing phenomena: ‘salt Rngers’,
‘diffusive convection’, and ‘intrusions’, are discussed in turn. Observational evidence suggests their
importance in all the oceans, and models indicate a substantial impact on water mass structure and
the thermohaline circulation. Awad et al. [14] examined the linear stability analysis of a Maxwell
fluid with double-diffusive convection. Patil et al. [15] considered a double diffusive mixed
convection flow over a moving vertical plate in the presence of internal heat generation and a
chemical reaction. Chamkha et al. [16] discussed a double-diffusive convection in an inclined orous
enclosure with opposing temperature and concentration gradients. Ravikumar et al. [17] studied
analytically MHD double diffusive and chemically reactive flow through porous medium bounded
by two vertical plates. Israel-Alam et al. [18] discussed effects of variable suction and
thermophoresis on steady MHD combined free-forced convective heat and mass transfer flow over
a semi-infinite permeable inclined plat in the presence of thermal radiation. Rahman et al. [19]
discussed numerical study of the combined free forced convection and mass transfer flow past a
vertical porous plate in a porous medium with heat generation and thermal diffusion.
A Newtonian fluid is considered in the above studies. Motivated by the previous
investigations, we have considered a well known non Newtonian fluid, namely Rivlin-Ericksen
fluid in this paper. The Rivlin-Ericksen elastic –viscous fluid has relevance and importance in
geophysical fluid dynamics, chemical technology and industry (e.g. manufacture of various items
International Journal of Engineering Research in Africa Vol. 16 91
mentioned above). Sunil et al. [20] considered, Hall effects on thermal instability of Rivlin-Ericksen
fluid. Gupta et al. [21] discussed on Rivlin-Erickson Elastico-Viscous fluid heated and solution
from below in the presence of compressibility, rotation and hall currents. Uwanta et al. [22]
addressed the effects of mass transfer on hydro magnetic free convective Rivlin-Ericksen flow
through a porous medium with time dependent suction. Rana et al. [23] studied, thermal instability
of compressible Rivlin-Ericksen rotating fluid permeated with suspended dust particles in porous
medium. Noushima Humera et al. [24] discussed hydromagnetics free convective Rivlin-Ericksen
flow through a porous medium with variable permeability. Takhar et al. [25] examined, dissipation
effects on MHD free convection flow past a semi-infinite vertical plate. Ravikumar et al. [26]
studied, combined effects of heat absorption and MHD on convective Rivlin-Ericksen flow past a
semi-infinite vertical porous plate with variable temperature and suction. Raju et al. [27] discussed
MHD convective flow through porous medium in a horizontal channel with insulated and
impermeable bottom wall in the presence of viscous dissipation and joule heating. In this research,
we have considered an unsteady magneto hydrodynamic, double diffusive, mixed convective
Rivlin-Ericksen fluid flow past a moving porous plate. The dimensionless governing equations are
solved by using a regular perturbation technique. The obtained results are compared with the
existing results and found good agreement with the results of Chamkha [2] in the absence of
Revlin–Ericksen fluid.
2. Problem formulation:
We have considered a viscous incompressible electrically conducting non Newtonian fluid,
namely Rivilin-Ericksen fluid past a semi infinite vertical permeable moving porous plate. A
transversely applied magnetic field of uniform strength Bo is applied perpendicular to the plate in
the direction of the flow. Because of the absence of the electrical field, it is assumed that there is no
applied voltage. Since, it is assumed that the transversely applied magnetic field and magnetic
Reynolds number are very small, so that the induced magnetic field and as well as the Hall Effects
are negligible.
Concentration Boundary Layer
g Thermal Boundary Layer
Momentum Boundary Layer
*v
O
Fig.1 Physical model and coordinate system of the problem
Considering the above assumptions, the governing equations for this investigation are based on the
balances of conservation of mass, conservation of momentum, energy and species concentration is
as follows.
y∗
B0
( ) ( ),n t n t
T T T T e C C C C ew ww wε ε
∗ ∗ ∗ ∗∗ ∗ ∗ ∗= + − = + −∞ ∞
,pU x∗ ∗
oo
oo
oo
oo
oo
oo
oo
oo
oo
oo
oo
, ,U T C∗ ∗ ∗∞ ∞ ∞
92 International Journal of Engineering Research in Africa Vol. 16
Equation of Continuity
0v
y
∗
∗
∂=
∂ (1)
Equation of Momentum
( ) ( )2
2 3
2
2 3 3
01 *
1T c
u u p uv v g T T g c c
t y x y
Bu u uv u v
K t y y
β βρ
σβ
ρ
∗ ∗ ∗ ∗∗ ∗ ∗ ∗ ∗
∞ ∞∗ ∗ ∗ ∗
∗ ∗ ∗∗ ∗
∗ ∗ ∗
∂ ∂ ∂ ∂+ = − + + − + −
∂ ∂ ∂ ∂
∂ ∂− − − +
∂ ∂ ∂
(2)
Equation of Energy
( )2
2
0
p
QT T Tv T T
t y cyα
ρ
∗ ∗ ∗∗ ∗ ∗
∞∗ ∗ ∗
∂ ∂ ∂+ = − −
∂ ∂ ∂ (3)
Equation of Mass diffusion
2 2
2 2
1
c c c Tv D D
t y y y
∗ ∗ ∗ ∗∗
∗ ∗ ∗ ∗
∂ ∂ ∂ ∂+ = +
∂ ∂ ∂ ∂ (4)
where ,x y∗ ∗ and t∗ are the dimensional distance along and perpendicular to the plate and
dimensional time, respectively. u∗and v∗ are the components of dimensional velocities along x∗
and y∗ directions, respectively, ρ is the fluid density, ν is the kinematic viscosity, pc is the specific
heat at constant pressure , σ is the fluid electrical conductivity, 0B is the magnetic induction , K ∗ is
the permeability of the porous medium, T ∗ is the dimensional temperature, Q0 is the dimensional
heat absorption coefficient, c∗ is the dimensional concentration, α is the thermal diffusivity , D is
the mass diffusivity, g is the gravitational acceleration and βT and βc are the thermal and
concentration expansion coefficients, respectively. The magnetic and viscous dissipations are
neglected in this study. The third and fourth terms on the RHS of the momentum Eq. (2) denote the
thermal and concentration buoyancy effects, respectively. Also, the last term of the energy Eq. (3)
represents the heat absorption effect. It is assumed that the permeable plate moves with a constant
velocity in the direction of fluid flow, and the free stream velocity follows the exponentially
increasing small perturbation law. In addition, it is assumed that the temperature and the
concentration at the wall as well as the suction velocity are exponentially varying with time.
Under these assumptions, the appropriate boundary conditions for the velocity, temperature and
concentration fields are
pu U∗ ∗= , ( ) n t
w wT T T T eε∗ ∗∗ ∗
∞= + − , ( ) n t
w wc c c c eε∗ ∗∗ ∗
∞= + − at y*=0 (5)
( )0 1 n tu U U eε∗ ∗∗ ∗
∞→ = + , T T∞→ , c c∞→ as y*→∞
where pU ∗ , cw and Tw are the wall dimensional velocity, temperature and concentration,
respectively. U ∗∞ , c∞ and T∞ are the free stream dimensional velocity, concentration and
temperature respectively. U0 and n* are constants. It is clear from Eq. (1) that the suction velocity at
the plate surface is a function of time only. Assuming that it takes the following exponential form:
0 (1 )n tv V Aeε∗ ∗∗ = − + (6)
where A is a real positive constants, ε and εA are small less than unity, and V0 is a scale of suction
velocity which has non-zero positive constant. Outside the boundary layer Eq. (2) gives
2
0
1 dU vU B U
x dt K
ρ σρ ρ
∗∗∗ ∗∞∞ ∞∗ ∗ ∗
∂− = + +
∂ (7)
International Journal of Engineering Research in Africa Vol. 16 93
It is convenient to employ the following dimensionless variables: 2
0 0
0 0 0
, , , , , ,p
p
U uV y t Vu vu v U U t
U V v U U vη ∞
∗ ∗∗ ∗∗ ∗
∞∗
= = = = = =
0
2 2
0
, , , ,p
w w
v cK VT T c c n v vC n K Pr
T T c c V v k
ρθ
α
∗ ∗∗ ∗ ∗ ∗ ∗∞ ∞
∗ ∗ ∗ ∗∞ ∞
− −= = = = = =
− − (8)
( ) ( )2
0 0
2 2 2 2
0 0 0 0 0 0
, , , ,T w c w
p
v g T T v g c cB v vQM Gr Gc Q
V U V U V pc V
β βσρ
∗ ∗ ∗ ∗∞ ∞− −
= = = =
( )( )
2*1 0 1
2 2
0
4 1, , , ,Sc ,
w
w
T TV Dvw vRm w N M So
v V K v Dc c
β∗ ∗
∞
∗ ∗∞
−= = = + = =
−
In view of Eq. (6) - (8), Eq. (2) - (4) reduce to the following dimensionless form:
( ) ( )
( )
2
2
3 3
2 3
1
1
nt
nt
dUu u uAe Gr GcC N U u
t dt
u uRm Ae
t
ε θη η
εη η
∞∞
∂ ∂ ∂− + = + + + + −
∂ ∂ ∂
∂ ∂− − + ∂ ∂ ∂
(9)
( )2
2
11 ntAe Q
t Pr
θ θ θε θ
η η∂ ∂ ∂
− + = −∂ ∂ ∂
(10)
( )2 2
2 2
11 ntC C C
Ae Sot Sc
θε
η η η∂ ∂ ∂ ∂
− + = +∂ ∂ ∂ ∂
(11)
where 1
N MK
= + and Gr, Gc, Pr, and Q are the solutal Grashof number, thermal Grashof
number , Prandtl number, dimensionless heat absorption coefficient, and the Schmidt number ,
respectively. By setting Rm and So equal to zero, Eqs. (9) - (11) reduce to those reported by
Chamkha [2].
The dimensionless form of the boundary conditions (5) become
, 1 , 1 , 1 0
, 0, 0, 0
nt nt nt
pu U e C e U e at
u U C U as
θ ε ε ε η
θ η∞
= = + = + = + =
→ → → → →∞ (12)
3. Solution of the problem
Eq. (9), (10) and (11) represent a set of partial differential equations that cannot be solved in
closed form. However, it can be reduced to a set of ordinary differential equations in dimensionless
from that can be solved analytically. This can be done, by representing the velocity and temperature
and concentration in terms of harmonic and non harmonic functions as follows:
( ) ( ) ( )2
0 1 .............ntU f e fη ε η ε= + + +○ (13)
( ) ( ) ( )2
0 1 .............ntg e gθ η ε η ε= + + +○ (14)
( ) ( ) ( )2
0 1 .............ntC h e hη ε η ε= + + +○ (15)
Substituting Eq. (13) - (15) into eq. (9) - (11), equating the harmonic and non-harmonic terms, and
neglecting and higher- order terms of ( )2ε○ , one obtains the following pairs of equations for
( )0 0 0, ,f g h and ( )1 1 1, ,f g h .
/ / / / / /
0 0 0 0 0 0Rmf f f Nf Grg Gch N+ + − = − − − (16)
( )/ / / / / / / / / /
1 1 1 1 1 1 1 0 01Rmf nRm f f Nf nf n Grg Gch N RmAf Af+ − + − − = − − − − − − (17)
/ / /
0 0 0Pr Pr 0g g Q g+ − = (18)
94 International Journal of Engineering Research in Africa Vol. 16
/ / / /
1 1 1 1 0Pr Pr Pr Prg g n g Q g A g+ − − = − (19)
/ / / / /
0 0 oh Sch ScSog+ = − (20) / / / / / /
1 1 1 1oh Sch nSch ASch ScSog+ − = − − (21)
where a prime denotes ordinary differentiation with respect to η. The corresponding boundary
conditions can be written as
0 1 0 1 0 1
0 1 0 1 0 1
, 0, 1, 1, 1, 1 0
1 , 1, 0, 0 , 0, 0
pf U f g g h h at
f f g g h h at
η
η
= = = = = = =
= = → → → → →∞ (22)
Without going into detail, the solution of Eqs. (16)- (21) subject to Eq. (22) can be shown to be 2
0
mg e η−= (23)
4 2
1 2 1
m mg k e k eη η− −= + (24)
6 2
0 4 3
m mh k e k eη η− −= + (25)
8 6 2 4
1 10 5 11 7
m m m mh k e k e k e k eη η η η− − − −= + + + (26)
Equations (16) and (17) are third order D.Es when Rm≠ 0 and we have two boundary conditions, so
we follow bears and Walters as
( )2
0 01 02mf f R f Rm= + +○ (27)
( )2
1 11 12mf f R f Rm= + +○ (28)
Substituting Esq. (27) and (28) into (16) and (18), equating different powers of Rm and
neglecting ( )2Rm○ .
The corresponding boundary conditions are
01 02 11 12
01 02 11 12
, 0, 0, 0 0
1, 0, 1, 0
pf U f f f at
f f f f as
η
η
= = = = =
= = = = →∞ (29)
We get zeroth order and first order equations of Rm. 10 62
01 17 15 13 1m mmf k e k e k e
η ηη− −−= + + + (30)
10 612 2
02 21 18 19 20
m mm mf k e k e k e k eη ηη η− −− −= − + + + (31)
8 6 1014 4 2
11 36 33 25 34 27 35 30
m m mm m mf k e k k e k e k e k e k eη η ηη η η − − −− − −= − + + + + + + (32)
16 10 6 812 2 14 4
12 51 44 45 46 47 48 49 50
m m m mm m m mf k e k e k e k e k e k e k e k eη η η ηη η η η− − − −− − − −= − + + + + + + + (33)
In view of the above solutions, the velocity ,temperature and concentration distributions in the
boundary layer become
( )10 6 10 62 12 2
8 6 10 1614 4 2
1012
0 1
17 15 13 21 18 19 20
36 33 25 34 27 35 30 51
44 45
, ( ) ( )
[( 1) ( )]
[( ) (
nt
m m m mm m m nt
m m m mm m m
mm
U t f e f
k e k e k e Rm k e k e k e k e e
k e k k e k e k e k e k e Rm k e
k e k e
η η η ηη η η
η η η ηη η η
ηη
η η ε η
ε− − − −− − −
− − − −− − −
−−
= +
= + + + + − + + + +
− + + + + + + + − +
+ + 6 82 14 4
46 47 48 49 50 )]m mm m mk e k e k e k e k eη ηη η η− −− − −+ + + +
(34)
( )2 4 2
0 1
2 1
, ( ) ( )
[ ]
nt
m m mnt
t g e g
e e k e k eη η η
θ η η ε η
ε− − −
= +
= + + (35)
( )
( )6 8 62 2 4
0 1
4 3 10 5 11 7
, ( ) ( )
[ ]
nt
m m mm m mnt
C t h e h
k e k e e k e k e k e k eη η ηη η η
η η ε η
ε− − −− − −
= +
= + + + + + (36)
The skin-friction coefficient and Nusselt number are important physical parameters for this type of
boundary-layer flow. These parameters can be defined and determined as follows:
( )52 53 54 55
0
( )ntuk Rmk e k Rmk
η
τ εη
=
∂= = + + + ∂
(37)
International Journal of Engineering Research in Africa Vol. 16 95
56 57
0
( )ntNu k e kη
θε
η=
∂= = + ∂
(38)
58 59
0
( )ntCSh k e k
η
εη
=
∂= = + ∂
(39)
Where
2
1
4
2
pr pr Qprm
− + += ,
2
2
4
2
pr pr Qprm
+ += ,
( )2
3
4
2
pr pr Qpr nprm
− + + += ,
( )2
4
4
2
pr pr Qpr nprm
+ + += ,
( )2
1 2
2 2
P r
P r P r P r
A mk
m m n Q=
− − +, 2 11k k= − , 5 0m = ,
6m Sc= − , 2
23 2
2 2
ScSomk
m Scm
−=
−, 4 31k k= − ,
2
7
4
2
Sc Sc nscm
− + += ,
2
8
4
2
Sc Sc nscm
+ += ,
6 45 2
6 6
AScm kk
m m Sc nSc=
− −, 2 3
6 2
2 2
AScm kk
m m Sc nSc=
− −,
2
4 27 2
4 4
SoScm kk
m m Sc nSc
−=
− −,
2
2 18 2
2 2
SoScm kk
m m Sc nSc
−=
− −
9 5 6 7 8k k k k k= + + + , 10 91k k= − , 11 6 8k k k= + , 9
1 1 4
2
Nm
− + += , 10
1 1 4
2
Nm
+ += ,
12 2
2 2
G rk
m m N
−=
− −, 4
13 2
6 6
Grkk
m m N
−=
− −, 3
14 2
2 2
Gckk
m m N
−=
− −, 15 12 14k k k= + , 16 13 15 1k k k= + + ,
17 16k Up k= − ,11
1 1 4
2
Nm
− + += ,
12
1 1 4
2
Nm
+ += ,
3
1 0 1 71 8 2
1 0 1 0
m kk
m m N=
− −,
3
2 1519 2
2 2
m kk
m m N=
− −,
3
6 1320 2
6 6
m kk
m m N=
− −, 21 18 19 20k k k k= + + , 22 2 7k Grk Gck= + , 23 1 11k Grk Gck= + ,
( )13
1 1 4
2
N nm
− + + += ,
( )14
1 1 4
2
N nm
+ + += , 24
nk
N n=
+,
( )22
25 2
4 4
kk
m m N n
−=
− − +,
( )23
26 2
2 2
kk
m m N n
−=
− − +,
( )10
27 2
8 8
Gckk
m m N n
−=
− − +,
( )5
2 8 2
6 6
G ckk
m m N n
−=
− − +,
2 9
Nk
N n=
+,
( )10 17
30 2
10 10
Am kk
m m N n=
− − +,
( )2 15
31 2
2 2
Am kk
m m N n=
− − +,
( )6 13
32 2
6 6
Am kk
m m N n=
− − +, 33 24 29k k k= + , 34 26 31k k k= + , 35 28 32k k k= + ,
36 33 25 34 27 35 30k k k k k k k= + + + + + , 37 21 12k Ak m= − , 3 3 2
38 18 10 17 10 30 10 30 10k Ak m Ak m k m nk m= + + + , 3 3 2
39 19 2 15 2 34 2 34 2k Ak m Ak m k m nk m= + + + , 3 3 2
40 20 6 13 6 35 6 35 6k Ak m Ak m k m nk m= + + + ,
3 2
41 36 14 36 14k k m nk m= − − , 3 2
42 25 4 25 4k k m nk m= + , 3 2
43 27 8 27 8k k m nk m= + , ( )
3744 2
12 12
kk
m m N n=
− − +,
( )38
45 2
10 10
kk
m m N n=
− − +,
( )39
46 2
2 2
kk
m m N n=
− − +,
( )40
47 2
6 6
kk
m m N n=
− − +,
( )41
48 2
14 14
kk
m m N n=
− − +,
( )42
49 2
4 4
kk
m m N n=
− − +,
( )43
50 2
8 8
kk
m m N n=
− − +, 51 44 45 46 47 48 49 50k k k k k k k k= + + + + + +
52 17 10 15 2 13 6k k m k m k m= − − − , 53 21 12 18 10 19 2 20 6k k m k m k m k m= − − − ,
54 36 14 25 4 34 2 27 8 35 6 30 10k k m k m k m k m k m k m= − − − − − ,
55 51 16 44 12 45 10 46 2 47 6 48 14 49 4 50 8k k m k m k m k m k m k m k m k m= − − − − − − − , 56 2k m= − , 57 2 4 1 2k k m k m= − − ,
58 4 6 3 2k k m k m= − − , 59 10 8 5 6 11 2 7 4k k m k m k m k m= − − − − .
96 International Journal of Engineering Research in Africa Vol. 16
4. Result and discussion
The non-linear coupled Equations (13) - (21) subject to the boundary condition (22), which
describe, heat and mass transfer flow past an infinite vertical plate immersed in a porous medium in
the presence of heat-absorbing Rivlin-Ericksen flow past a semi-infinite vertical porous moving
plate, under the influence of magnetic field and thermal diffusion are solved analytically by
perturbation technique. In order to get physical insight into the problem, the effects of various
parameters encountered in the equations of the problem are analyzed on velocity, temperature and
concentration fields with the help of figures. These results show the influence of the various
physical parameters such as Grashof number Gr, dimensionless viscoelasticity parameter of the
Rivlin-Ericksen fluid Rm, solutal Grashof number Gc, Magnetic parameter M, Schmidt number Sc,
permeability parameter K, heat absorption parameter Q, Scalar constant ε, Soret number So and
Prandtl number Pr on the velocity, temperature and the concentration distributions. We have also
analyzed the effects of these physical parameters on skin friction coefficient, Nusselt number and
Sherwood number. We can extract interesting insight regarding the influence of all parameters that
govern the problem.
0 1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
3
3.5
η
U
K=0.1,0.2,0.3,0.4,0.5
Fig. 2. Effects of K on velocity profiles.
0 1 2 3 4 5 6 7 8 9 100
1
2
3
4
5
6
η
U
So=0.5,1,1.5,2,2.5,3
Fig. 3. Effects of So on velocity profiles
Pr=0.71; Q=0.001; A=0.5;
n=0.1; Sc=0.22; So=0.1;
M=1; Gr=5; Up=0.5;
Gc=5; Rm=0.05; ε=0.2; t=1;
Pr=0.71; Q=0.001; A=0.5;
n=0.1; Sc=0.22; M=1;
K=0.5; Gr=5; Up=0.5;
Gc=5; Rm=0.05; ε=0.2; t=1;
International Journal of Engineering Research in Africa Vol. 16 97
The velocity profiles are plotted in Fig. 2 for various values of permeability parameter K.
From this figure, it is noticed that the velocity increases with the increase in the values of the
permeability parameter K. Physically, an increase in the permeability of porous medium leads to
rise, in the flow of fluid through it. When the holes of the porous medium become large, the
resistance of the medium may be neglected. A similar approach is noticed with Raju et al. [27]. Fig.
3 shows the velocity profiles against span wise direction for different values of the Soret number
So. It was found that an increase in the value of So leads to an increase in the velocity distribution
across the boundary layer. This is true, as the Soret number increases, small light molecules and
large heavy molecules get separated under a temperature gradient, which intern increases the
velocity of a fluid. Fig. 4 illustrates the variation of velocity function with span wise coordinate’s η
for several values of dimensionless visco-elastic parameter of a Revlin-Ericksen fluid Rm. It is
found that an increase in Rm leads to a decrease in the velocity distribution across the boundary
layer because; it is due to variability in viscosity. Fig. 5 shows the velocity profiles for different
values of magnetic parameter M. It is observed that the increase in the value of M results a decrease
in the velocity profiles. This is due to the application of a magnetic field to an electrically
conducting fluid which produces a dragline force that causes reduction in the fluid velocity. Similar
approach is noticed in the results of Kim [1], Chamkha [2] and Raju et al. [27]. Fig. 6 shows the
velocity profiles for different values of heat absorption parameter Q. From this graph we observe
that the velocity decreases with an increase in the heat absorption parameter Q. Because, in the
presence of heat absorption, the buoyancy force decreases the velocity profiles. Physically, the
presence of heat absorption coefficient has the tendency to reduce the fluid velocity. This cause the
thermal buoyancy effects to decrease resulting in a net reduction in the fluid velocity (see
Ravikumar et al. [26]). Fig. 7 illustrates the temperature profiles for different values of Prandtl
number Pr. It is observed that the temperature decrease as an increase in the values of Prandtl
number. The reason is that smaller values of Pr are equivalent to increase in the thermal
conductivity of the fluid and therefore heat is able to diffuse away from the heated surface more
rapidly for higher values of Pr. Hence, in the case of smaller Prandtl number the thermal boundary
layer is thicker and the rate of heat transfer is reduced.
0 1 2 3 4 5 6 7 8 9 100.5
1
1.5
2
2.5
3
η
U
Rm=1,2,3,4,5
Fig. 4. Effects of Rm on velocity profiles
Pr=0.71; Q=0.001; A=0.5;
n=0.1; Sc=0.22; So=0.1;
M=1; K=0.5; Gr=5;
Up=0.5; Gc=5; ε=0.2;
t=1;
98 International Journal of Engineering Research in Africa Vol. 16
0 1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
3
3.5
η
U
M=1,2,3,4,5
Fig. 5. Effects of M on velocity profiles
Fig. 8 shows the temperature profile for different values of heat absorption parameter Q. From this
figure it is noticed that increase in the value of Q results a decrease in the temperature profiles as
expected. It is observed that increase in the heat absorption parameter is to decrease the temperature
in the boundary layer. This effect is more prominent for fluid closer to the porous plate. This is due
to the fact that heat from the fluid will be absorbed by the porous plate and hence, higher the value
of heat absorption parameter, lower the value of temperature profile in the boundary layer ( see Pal
et al. [3], S. Harinath Reddy et al. [29]). The effects of increasing the Soret number So on the
species concentration profiles have been shown in Fig. 9. From this figure it is noticed that increase
in So result in increase in the concentration profiles.
0 1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
3
3.5
η
U
Q=0.0,0.1,0.3,0.5,0.7
Fig. 6. Effects of Q on velocity profiles
Pr=0.71; Q=0.001; A=0.5;
n=0.1; Sc=0.22; So=0.1;
K=0.5; Gr=5; Up=0.5;
Gc=5; Rm=0.05; ε=0.2;
t=1;
Pr=0.71; A=0.5; n=0.1;
Sc=0.22; So=0.1; M=1;
K=0.5; Gr=5; Up=0.5;
Gc=5; Rm=0.05; ε=0.2;
t=1;
International Journal of Engineering Research in Africa Vol. 16 99
0 1 2 3 4 5 6 7 8 9 100
0.2
0.4
0.6
0.8
1
1.2
1.4
η
T
Pr=0.71,1.0,5.0,7.0
Fig. 7. Effects of Pr on temperature profiles
Figs. 10-15 present the variation of the skin friction coefficient τ against the suction velocity
parameter A for various values of, K, So, Rm, M and Q. Fig.10 shows the skin friction on the
porous plate for different values of permeability parameter K. The results display that an increase in
the value of K results in increase in the skin friction profiles. Fig. 11 shows the skin friction profiles
for different values of Soret number So. From this figure it is noticed that an increase in So results
an increase in the skin friction profile. Fig. 12 depicts the variations in dimensionless viscoelasticity
parameter of the Rivlin-Ericksen fluid Rm against the suction velocity parameter A. It has been
observed that the effects of increase in the values of Rm decrease in the skin friction profile. As
shown in Fig. 13, the surface skin friction for different values of Magnetic parameter M, it is
noticed that an increase in M results a decrease in the skin friction profile. Fig. 14 depicts the
surface skin friction for different values of dimensionless heat absorption coefficient Q. From this
figures it is noticed that an increase in Q results a decrease in the skin friction. Fig. 15 shows the
skin friction on the porous plate for the different values constant plate moving velocity Up against
the suction velocity parameter A. It has been observed that the effects of increase in the value of
Up decrease in the skin friction coefficient.
0 1 2 3 4 5 6 7 8 9 100
0.2
0.4
0.6
0.8
1
1.2
1.4
η
T
Q=0.0.0.1,0.3,0.5,0.7
Fig. 8. Effects of Q on temperature profiles.
Q=0.001; n=0.1; Sc=0.22;
So=0.1; M=1; K =0.5;
Gr=5; Up=0.5; Gc=5;
Rm=0.05; ε=0.2 ; t=1;
Pr=0.71; A=0.5; n=0.1;
Sc=0.22; So=0.1; M=1;
K =0.5; Gr=5; Up=0.5;
Gc=5; Rm=0.05; ε=0.2 ;
t=1;
100 International Journal of Engineering Research in Africa Vol. 16
0 1 2 3 4 5 6 7 8 9 100
0.5
1
1.5
2
2.5
η
C
So=0.5,1,1.5,2,2.5,3
Fig. 9. Effects of So on concentration profiles
0 1 2 3 4 5 6 7 8 9 108
10
12
14
16
18
20
22
A
τ
K=0.1
K=0.2
K=0.3
K=0.4
Fig. 10. Variation of the surface skin friction with the suction velocity parameter A for various
values of K
Fig. 16 presents the variation of the Nusselt number Nu against the suction velocity
parameter A for various values of Q. From this figure we notice that Nusselt number decreases
when the values of dimensionless heat absorption Q increase. Fig. 17 shows the Sherwood number
on the porous plate for different values of Soret number So. The result display that an increase in
the value of So results an increase in the Sherwood number. Fig. 18 depicts the variation of
Sherwood number in the presence of Schmidt number against the suction velocity parameter A. It
has been observed that the effect of increase in the values of Sc decreases the value of Sherwood
number coefficient for all values of suction velocity parameter A.
Pr=0.71; Q=0.001; A=0.5;
n=0.1; Sc=0.22; M=1;
K =0.5; Gr=5; Up=0.5;
Gc=5; Rm=0.05; ε=0.2;
t=1;
Pr=0.71; Q=0.001; n=0.5;
Sc=0.22; So=0.1; M=1;
Gr=5; Up=0.5; Gc=5;
Rm=0.05; ε=0.2; t=1.
International Journal of Engineering Research in Africa Vol. 16 101
0 1 2 3 4 5 6 7 8 9 106
7
8
9
10
11
12
13
14
15
A
τ
So=0.5,1,1.5,2,2.5,3
Fig. 11. Variation of the surface skin friction with the suction velocity parameter A for various
values of So
0 1 2 3 4 5 6 7 8 9 105
6
7
8
9
10
11
A
τ
Rm=0.01,0.03,0.05,0.07
Fig. 12. Variation of the surface skin friction with the suction velocity parameter A for various
values of Rm
Pr=0.71;Q=0.001; n=0.1; Sc=0.22; M=1; K=0.5;
Gr=5; Up=0.5; Gc=5; Rm=0.05; ε=0.2; t=1;
Pr=0.71;Q=0.001; n=0.1; Sc=0.22; So=0.1;
M=1;K =0.5; Gr=5; Up=0.5; Gc=5; ε=0.2; t=1;
102 International Journal of Engineering Research in Africa Vol. 16
0 1 2 3 4 5 6 7 8 9 108
10
12
14
16
18
20
22
A
τ
M=1,2,3,4,5
Fig. 13. Variation of the surface skin friction with the suction velocity parameter A for various
values of M
5. CONCLUSIONS
We have examined theoretically the problem of an unsteady, incompressible MHD
double diffusive convection Rilvin-Ericksen boundary layer flow past a semi-infinite vertical
moving porous plate. The computed values obtained from analytical solutions of velocity,
temperature, concentration fields as well as for the skin friction coefficient, Nusselt number and
Sherwood number are presented graphically. After a suitable transformation, the governing partial
differentiation equations were transformed to ordinary differential equations. These equations were
solved analytically by using perturbation technique. Thus we conclude the following after analyzing
the graphs.
0 1 2 3 4 5 6 7 8 9 103
4
5
6
7
8
9
10
11
A
τ
Q=0.0,0.1,0.3,0.5,0.7
Fig. 14. Variation of the surface skin friction with the suction velocity parameter A for various
values of Q
Pr=0.71;Q=0.001; n=0.1;
Sc=0.22; So=0.1; K =0.5;
Gr=5; Up=0.5; Gc=5;
Rm=0.05; ε=0.2; t=1;
Pr=0.71; n=0.1; Sc=0.22;So=0.1;
M=1; K =0.5;
Gr=5; Up=0.5; Gc=5; Rm=0.05;
ε=0.2; t=1;
International Journal of Engineering Research in Africa Vol. 16 103
0 1 2 3 4 5 6 7 8 9 10-8
-6
-4
-2
0
2
4
6
8
10
12
A
τUp=0.0
Up=0.5
Up=2.0
Up=5.0
Fig. 15. Variation of the surface skin friction with the suction velocity parameter A for various
values of Up
The velocity increases with an increase in permeability parameter, Soret number, whereas reverse
trend is seen with dimensionless viscoelasticity parameter of the Rivlin-Ericksen fluid, Magnetic
parameter, heat absorption parameter. The temperature increases with decrease in the value of
Prandtl umber and heat absorption parameter. The concentration is increasing with increase in the
values of Soret number. The value of the local skin-friction coefficient increases with increase in
the permeability parameter, and Soret number whereas reverse effects is seen dimensionless
viscoelasticity parameter of the Rivlin-Ericksen fluid, Magnetic parameter, heat absorption
parameter and constant plate moving velocity Up. The values of the local Nusselt number decreases
in the presence of heat absorption. The values of the local Sherwood number increases with increase
in Soret number whereas reverse effects is seen in the case of Schmidt number.
0 1 2 3 4 5 6 7 8 9 10-2
-1.8
-1.6
-1.4
-1.2
-1
-0.8
-0.6
A
Nu
Q=0.0
Q=0.1
Q=0.3
Q=0.5
Q=0.7
Fig. 16. Variation of the surface heat flux with the suction velocity parameter A for various values
of Q
Pr=0.71; Q=0.001; n=0.1; Sc=0.22; So=0.1;
M=1; K=0.5; Gr=5; Gc=5; Rm=0.05; ε=0.2;
t=1;
Pr=0.71; n=0.1; Sc=0.22; So=0.1; M=1; K=0.5;
Gr=5; Up=0.5; Gc=5; Rm=0.05; ε=0.2; t=1;
104 International Journal of Engineering Research in Africa Vol. 16
0 1 2 3 4 5 6 7 8 9 10-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
A
Sh
So=0.5,1,1.5,2,2.5,3
Fig. 17. Variation of the surface mass flux with the suction velocity parameter A for various values
of So
0 1 2 3 4 5 6 7 8 9 10-40
-35
-30
-25
-20
-15
-10
-5
0
A
Sh
Sc=0.60
Sc=0.78
Sc=0.96
Sc=0.22
Fig. 18. Variation of the surface mass flux with the suction velocity parameter A for various values
of Sc
Table
Comparison of our results with the existing results of Chamkha [2] in the absence of Rivlin-
Ericksen fluid: Effects of Gc on τ, Nu and Sh for A=0.5,Pr=0.71, Q=0.6, n=0.1, Sc=0.22, So=0,
M=0, K=0.1, Gr=1, Up=0.5, Rm=0, ε=0.2 and t=2.
Results of Chamkha [2] Results of present study
Gc Τ Nu Sh Gc τ Nu Sh
0
1
2
3
4
2.7200
3.3772
3.8343
4.3915
4.9487
-1.7167
-1.7167
-1.7167
-1.7167
-1.7167
-0.8098
-0.8098
-0.8098
-0.8098
-0.8098
0
1
2
3
4
2.9740
3.3247
3.8507
4.0261
4.7274
-1.7190
-1.7190
-1.7190
-1.7190
-1.7190
-0.8151
-0.8151
-0.8151
-0.8151
-0.8151
Pr=0.71; Q=0.001; n=0.1; Sc=0.22; M=1;K=0.5;
Gr=5; Up=0.5;Gc=5; Rm=0.05; ε=0.2; t=1;
Pr=0.71; Q=0.001; n=0.1; So=0.1; M=1;K=0.5;
Gr=5; Up=0.5; Gc=5; Rm=0.05; ε=0.2; t=1;
International Journal of Engineering Research in Africa Vol. 16 105
6. Nomenclature
A suction velocity parameter
B0 magnetic induction
c concentration
Cp specific heat at constant pressure
C dimensionless concentration
D mass diffusion coefficient
Gc solutal Grashof number
Gr Grashoff number
g acceleration due to gravity
K Permeability of the porous medium
M magnetic field parameter
N dimensionless material parameter
n dimensionless exponential index
Nu Nusselt number
Sc Schmidt number
So Soret number
Sh Sherwood number
Pr Prandtl number
Q0 heat absorption coefficient
T temperature
t dimensionless time
U0 scale of free stream velocity
U*, v
* components of velocities along and Perpendicular to
the plate, respectively
V0 scale of suction velocity
x*, y
* distances along and perpendicular to the plate, respectively
Q dimensionless heat absorption coefficient
Rm dimensionless viscoelasticity parameter of the
Rivlin-Ericksen fluid
Up constant plate moving velocity
Greek symbols
α fluid thermal diffusivity
βc coefficient of volumetric concentration expansion
βT coefficient of volumetric thermal expansion
β1 coefficient of volumetric expansion of the working fluid
ε scalar constant (<<1)
η dimensionless normal distance
σ electrical conductivity
ρ fluid density
µ fluid dynamic viscosity
ν fluid kinematic viscosity
τ friction coefficient
θ dimensionless temperature κ Thermal conductivity
τ skin-friction coefficient
Superscripts
/ Differentiation with respect to η
106 International Journal of Engineering Research in Africa Vol. 16
* Dimensional properties
Subscripts
p plate
w wall condition
∞ Free stream condition
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