Natural convection unsteady magnetohydrodynamic mass transfer flow past an infinite vertical porous plate in presence of suction and heat sink

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I
NTERNATIONAL
J
OURNAL OF

E
NERGY AND
E
NVIRONMENT



Volume 3, Issue 2, 2012 pp.209-222

Journal homepage: www.IJEE.IEEFoundation.org


ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.
Natural convection unsteady magnetohydrodynamic mass
transfer flow past an infinite vertical porous plate in
presence of suction and heat sink


S. S. Das
1
,

S. Parija
2
, R. K. Padhy
3
, M. Sahu
4

1
Department of Physics, K B D A V College, Nirakarpur, Khurda-752 019 (Orissa), India.
2
Department of Physics, Nimapara (Autonomous) College, Nimapara, Puri-752 106 (Orissa), India.
3
Department of Physics, D A V Public School, Chandrasekharpur, Bhubaneswar-751 021 (Orissa),
India.
4
Department of Physics, Jupiter +2 Women’s Science College, IRC Village, Bhubaneswar-751 015
(Orissa), India.


Abstract
This paper investigates the natural convection unsteady magnetohydrodynamic mass transfer flow of a
viscous incompressible electrically conducting fluid past an infinite vertical porous flat plate in presence
of constant suction and heat sink. Using multi parameter perturbation technique, the governing equations
of the flow field are solved and approximate solutions are obtained.

The effects of the flow parameters on
the velocity, temperature, concentration distribution and also on the skin friction and rate of heat transfer
are discussed with the help of figures and table. It is observed that a growing magnetic parameter or
Schmidt number or heat sink parameter leads to retard the transient velocity of the flow field at all points,
while the Grashof numbers for heat and mass transfer show the reverse effect. It is further found that a
growing Prandtl number or heat sink parameter decreases the transient temperature of the flow field at all
points while the heat source parameter reverses the effect. The concentration distribution of the flow field
suffers a decrease in boundary layer thickness in presence of heavier diffusive species (growing S
c
) at all
points of the flow field. The effect of increasing Prandtl number P
r
is to decrease the magnitude of skin-
friction and to increase the rate of heat transfer at the wall for MHD flow, while the effect of increasing
magnetic parameter M is to decrease their values at all points.
Copyright © 2012 International Energy and Environment Foundation - All rights reserved.

Keywords: Natural convection; Magnetohydrodynamic; Mass transfer; Suction; Heat sink.



1. Introduction
The phenomenon of natural convection flow with heat and mass transfer in presence of magnetic field
has been given much importance in the recent years in view of its varied applications in science and
technology. The study of natural convection flow finds innumerable applications in geothermal and
energy related engineering problems. Such phenomena are of great theoretical as well as practical
interest in view of their applications in diverse fields such as aerodynamics, extraction of plastic sheets,
cooling of infinite metallic plates in a cool bath, liquid film condensation process and in major fields of
glass and polymer industries.
International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

210
In view of the above interests, Hashimoto [1] discussed the boundary layer growth on a flat plate with
suction or injection. Sparrow and Cess [2] analyzed the effect of magnetic field on a free convection heat
transfer. Gebhart and Pera [3] studied the nature of vertical natural convection flows resulting from the
combined buoyancy effects of thermal and mass diffusion. Soundalgekar and Wavre [4] investigated the
unsteady free convection flow past an infinite vertical plate with constant suction and mass transfer.
Hossain and Begum [5] estimated the effect of mass transfer and free convection on the flow past a
vertical plate. Bestman [6] analyzed the natural convection boundary layer flow with suction and mass
transfer in a porous medium. Pop et al. [7] reported the conjugate MHD flow past a flat plate.
Singh [8] discussed the effect of mass transfer on free convection MHD flow of a viscous fluid. Raptis
and Soundalgekar [9] analyzed the steady laminar free convection flow of an electrically conducting
fluid along a porous hot vertical plate in presence of heat source/sink. Na and Pop [10] explained the free
convection flow past a vertical flat plate embedded in a saturated porous medium. Takhar et al. [11]
discussed the unsteady flow and heat transfer on a semi-infinite flat plate in presence of magnetic field.
Chowdhury and Islam [12] developed the MHD free convection flow of a visco-elastic fluid past an
infinite vertical porous plate. Raptis and Kafousias [13] analyzed the heat transfer in flow through a
porous medium bounded by an infinite vertical plate under the action of a magnetic field. Sharma and
Pareek [14] described the steady free convection MHD flow past a vertical porous moving surface. Das
and his co-workers [15] estimated numerically the effect of mass transfer on unsteady flow past an
accelerated vertical porous plate with suction. Recently, Das and his associates [16] investigated the
hydromagnetic convective flow past a vertical porous plate through a porous medium in presence of
suction and heat source.
In the present problem, we analyze the natural convection unsteady magnetohydrodynamic mass transfer
flow of a viscous incompressible electrically conducting fluid past an infinite vertical porous flat plate in
presence of constant suction and heat sink. Approximate solutions are obtained for the velocity,
temperature, concentration distribution, skin friction and the rate of heat transfer using multi parameter
perturbation technique and the effects of the important parameters on the flow field are analyzed with the
help of figures and a table.

2. Formulation of the problem
Consider the unsteady natural convection mass transfer flow of a viscous incompressible electrically
conducting fluid past an infinite vertical porous plate in presence of constant suction and heat sink and a
transverse magnetic field B
0
. The x′-axis is taken in vertically upward direction along the plate and the y′-
axis is chosen normal to it. Neglecting the induced magnetic field and the Joulean heat dissipation and
applying Boussinesq’s approximation the governing equations of the flow field are given by:
Continuity equation:
0
y
v
'
'
=
∂
∂
⇒
'
0
'
vv −=
(constant), (1)

Momentum equation:

()( )
u
B
CCgTTg
y
u
y
u
v
t
u
2
0
*
2
2
′
−
′
−
′
+
′
−
′
+
′
∂
′
∂
=
′
∂
′
∂
′
+
′
∂
′
∂
∞∞
ρ
σ
ββν
, (2)

Energy equation:

()
∞
−
′
+
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
′
∂
′
∂
+
′
∂
′
∂
=
′
∂
′
∂
′
+
′
∂
′
∂
'T'TS
y
u
C
y
T
k
y
T
v
t
T
2
p
2
2
ν
, (3)

Concentration equation:

2
2
y
C
D
y
C
v
t
C
′
∂
′
∂
=
′
∂
′
∂
′
+
′
∂
′
∂
. (4)

International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

211
The initial and boundary conditions of the problem are:

() ( )
ti
ww
ti
ww0
eCCCC,eTTTT,vv,0u
′′
∞
′′
∞
′
−
′
+
′
=
′′
−
′
+
′
=
′′
−=
′
=
′
ωω
εε
at
0y =
′
,
,0u →
′

∞
′
→
′
TT
,
∞
′
→
′
CC
as
∞→
′
y
. (5)

Introducing the following non-dimensional variables and parameters,

,,
v
u
u,
v
4
,
4
vt
t,
vy
y
0
0
2
0
2
00
ρ
η
ν
ων
ω
νν
=
′
′
=
′
′
=
′′
=
′′
=

,
TT
TT
T
w ∞
∞
′
−
′
′
−
′
=

,
CC
CC
C
w ∞
∞
′
−
′
′
−
′
=
2
0
2
0
v
B
M
′
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
ν
ρ
σ
,
( ) ( )
()
∞
∞∞
′
−
′
′
=
′
′
=
′
′
−
′
=
′
′
−
′
===
TTC
v
E,
v
S4
S,
v
CCg
G,
v
TTg
G,
D
S,
k
P
wp
2
0
c
2
0
3
0
w
*
c
3
0
w
rcr
ν
βνβν
νν
. (6)

in Eqs. (2)-(4) under boundary conditions (5), we get

MuCGTG
y
u
y
u
t
u
4
1
cr
2
2
−++
∂
∂
=
∂
∂
−
∂
∂
, (7)

2
c
2
2
r
y
u
EST
4
1
y
T
P
1
y
T
t
T
4
1
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∂
∂
++
∂
∂
=
∂
∂
−
∂
∂
, (8)

2
2
c
y
C
S
1
y
C
t
C
4
1
∂
∂
=
∂
∂
−
∂
∂
, (9)

where
g
is the acceleration due to gravity,
ρ

is the density,
σ

is the electrical conductivity,
ν
is the
coefficient of kinematic viscosity,
β

is the volumetric coefficient of expansion for heat transfer,
β
*
is the
volumetric coefficient of expansion for mass transfer,
ω
is the angular frequency,
η
0
is the coefficient of
viscosity,
k
is the thermal diffusivity,
T
is the temperature,
T'
w
is the temperature at the plate,
T'
∞
is the
temperature at infinity
,
C
is the concentration,
C'
w
is the concentration at the plate,
C'
∞
is the
concentration at infinity
,
C
p
is the specific heat at constant pressure,
D
is the molecular mass diffusivity,
G
r
is the Grashof number for heat transfer,
G
c
is the Grashof number for mass transfer,
M
is the magnetic
parameter,
P
r
is the Prandtl number, ,
S
is the heat sink parameter,
c
S
is the Schmidt number and
E
c
is the
Eckert number.
The corresponding boundary conditions are:

titi
e1C,e1T,0u
ωω
εε
+=+==
at
0y =
,
0T,0u →→
,
0C →
as
∞→y
. (10)

3. Method of solution
To solve Eqs. (7)-(9), we assume
ε
to be very small and the velocity, temperature and concentration
distribution of the flow field in the neighbourhood of the plate as

() () ()
yueyut,yu
1
ti
0
ω
ε
+=
, (11)

( ) () ()
yTeyTt,yT
1
ti
0
ω
ε
+=
, (12)

( ) () ()
yCeyCt,yC
1
ti
0
ω
ε
+=
. (13)

International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

212
Substituting Eqs. (11) - (13) in Eqs. (7) - (9) respectively, equating the harmonic and non-harmonic terms
and neglecting the coefficients of
2
ε
, we get
Zeroth order:

0c0r000
CGTGMuuu −−=−
′
+
′′
, (14)

2
0
cr0
r
0r0
y
u
EPT
4
SP
TPT
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∂
∂
−=+
′
+
′′
, (15)

0CSC
0c0
=
′
+
′′
. (16)

First order:

1c1r111
CGTGuM
4
i
uu −−=
⎟
⎠
⎞
⎜
⎝
⎛
+−
′
+
′′
ω
, (17)

()
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∂
∂
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∂
∂
−=−ω−
′
+
′′
y
u
y
u
EPTSi
P
TPT
cr
r
r
1
0
111
2
4
, (18)

0C
4
Si
CSC
1
c
1c1
=−
′
+
′′
ω
. (19)

The corresponding boundary conditions are

1101100
111000
======= C,T,u,C,T,u:y
,
000000
111000
======∞→ C,T,u,C,T,u:y
. (20)

Solving Eqs. (16) and (19) under boundary condition (20), we get

,eC
yS
c
−
=
0
(21)

,eC
ym
1
1
−
=
(22)

Using multi parameter perturbation technique and assuming
c
E
<<
1, we assume

01000
uEuu
c
+=
, (23)

01000
TETT
c
+=
, (24)

11101
uEuu
c
+=
, (25)

11101
TETT
c
+=
. (26)

Now using Eqs. (23)-(26) in Eqs. (14), (15), (17) and (18) and equating the coefficients of like powers of
c
E
and neglecting those of
2
c
E
, we get the following set of differential equations:
Zeroth order:

0c00r000000
CGTGMuuu −−=−
′
+
′′
, (27)

International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

213
1c10r101010
CGTGu
4
i
Muu −−=
⎟
⎠
⎞
⎜
⎝
⎛
+−
′
+
′′
ω
, (28)

0T
4
SP
TPT
00
r
00r00
=+
′
+
′′
, (29)

()
0TSi
4
P
TPT
10
r
10r10
=−−
′
+
′′
ω
. (30)

The corresponding boundary conditions are,

10100
10100000
===== T,u,T,u:y
;
0000
10100000
====∞→ T,u,T,u:y
. (31)

First order:

01r010101
TGMuuu −=−
′
+
′′
, (32)

11r111111
TGu
4
i
Muu −=
⎟
⎠
⎞
⎜
⎝
⎛
+−
′
+
′′
ω
, (33)

()
2
00r01
r
01r01
uPT
4
SP
TPT
′
−=+
′
+
′′
, (34)

()
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∂
∂
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∂
∂
−=−−
′
+
′′
y
u
y
u
P2TSi
4
P
TPT
1000
r11
r
11r11
ω
. (35)

The corresponding boundary conditions are,

00000
11110101
=====
T,u,T,u:y
;
0000
11110101
====∞→
T,u,T,u:y
. (36)

Solving Eqs. (27)-(30) subject to boundary condition (31) we get,

y
1
n
3
y
c
S
2
y
3
m
100
eAeAeAu
−
−−
−+=
, (37)

y
3
m
00
eT
−
=
, (38)

y
3
n
6
y
1
m
5
y
5
m
410
eAeAeAu
−
−
−
−+=
, (39)

ym
eT
5
10
−
=
. (40)

Solving Eqs. (32)-(35) subject to boundary condition (36) we get,

( ) ( ) ( )
y
3
m
7
y
1
n
3
m
6
y
c
S
1
n
5
y
c
S
3
m
4
y
5
m2
3
y
3
m2
2
y
c
S2
101
eaeaeaeaeaeaeaT
−+−+−+−−−−
−+++++=
, (41)

( ) ( ) ( ) ( ) ( ) ( )
y
c
S
3
n
6
y
c
S
1
m
5
y
c
S
5
m
4
y
3
n
3
m
3
y
3
m
1
m
2
y
5
m
3
m
111
eBeBeBeBeBeBT
+−+−+−+−+−+−
+++++=


()
()
( )
y
5
m
10
y
3
n
1
n
9
y
1
n
1
m
8
y
1
n
5
m
7
eBeBeBeB
−+−
+−
+−
−+++
, (42)

International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

214
( ) ( )
y
c
S
1
n
5
y
c
S
3
m
4
y
1
n2
3
y
3
m2
2
y
c
S2
101
ebebebebebu
+−+−
−
−−
++++=


()
y
1
n
8
y
3
m
7
y
1
n
3
m
6
ebebeb
−
−+−
−++
, (43)

() () ( ) ( ) ( )()
y
c
S
3
n
6
y
c
S
1
m
5
y
c
S
5
m
4
y
3
n
3
m
3
y
3
m
1
m
2
y
5
m
3
m
111
eDeDeDeDeDeDu
+−+−+−+−+−+−
+++++=


()
()
( )
y
3
n
11
y
5
m
10
y
3
n
1
n
9
y
1
n
1
m
8
y
1
n
5
m
7
eDeDeDeDeD
−−+−
+−
+−
−++++
. (44)

Substituting the values of
C
0
and
C
1
from Eqs. (21) and (22) in Eq. (13) the solution for concentration
distribution of the flow field is given by

ym
ti
yS
eeeC
c
1
−
ω
−
ε+=
. (45)

3.1 Skin friction
The skin friction at the wall is given by

0=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∂
∂
=τ
y
w
y
u


( ) ( )
[
c15c341332c1c312c13
SnbSmbnb2mb2Sb2EAnASAm ++++++−+−−=


()
]
( )
[
{
153c635145
ti
1837136
DmmEAnAmAmenbmbnmb +−+−−+−+++
ω
ε


()()()( ) ( )
6c35c14c5333231
DSnDSmDSmDnmDmm ++++++++++


()()()
]
}
113105931811715
DnDmDnnDnmDnm −+++++++
. (46)

3.2 Heat flux

The heat flux at the wall in terms of Nusselt number is given by

0y
u
y
T
N
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
∂
∂
=


( ) ( ) ( )
[]
37136c15c345332c1c3
manmaSnaSmama2ma2Sa2Em −+++++−++−−=


()( ) ( ) ( )( )
[
{
5c14c5333231153c5
ti
BSmBSmBnmBmmBmmEme +++++++++−−+
ω
ε


()( )()( )
]
}
1059318117156c3
BmBnnBnmBnmBSn −++++++++
, (47)

where
⎥
⎦
⎤
⎢
⎣
⎡
++=
c
2
cc1
SiSS
2
1
m
ω
,
⎥
⎦
⎤
⎢
⎣
⎡
++−=
c
2
cc2
SiSS
2
1
m
ω
,
⎥
⎦
⎤
⎢
⎣
⎡
−+=
r
2
rr3
SPPP
2
1
m
,
⎥
⎦
⎤
⎢
⎣
⎡
−+−=
r
2
rr4
SPPP
2
1
m
,
()
⎥
⎦
⎤
⎢
⎣
⎡
−−+=
ω
iSPPP
2
1
m
r
2
rr5
,
()
⎥
⎦
⎤
⎢
⎣
⎡
−−+−=
ω
iSPPP
2
1
m
r
2
rr6
,
[ ]
M411
2
1
n
1
++=
,
[]
M411
2
1
2
n ++−=
,
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
+++=
4
i
M411
2
1
3
n
ω
,
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟
⎠
⎞
⎜
⎝
⎛
+++−=
4
i
M411
2
1
4
n
ω
,
()()
3231
r
1
mnmn
G
A
+−
=
,
()()
c2c1
c
2
SnSn
G
A
+−
=
,
213
AAA +=
,
()()
5453
r
4
mnmn
G
A
+−
=
,
()()
1413
c
5
mnmn
G
A
+−
=
,
546
AAA +=
,
()()
c4c3
2
2
2
cr
1
S2mS2m
ASP
a
+−
=
,
()
34
2
13r
2
m2m
AmP
a
+
−
=
,
()()
1413
2
3
2
1r
3
n2mn2m
AnP
a
+−
=
,
()
c43
r321
4
Smm
PmAA2
a
++
−=
,
()()
c14c13
132cr
5
SnmSnm
nAASP2
a
++−−
−=
,
()
143
321r
6
nmm
mAAP2
a
++
=
,
6543217
aaaaaaa +++++=
,
()
653
61r
1
mmm
AAP2
B
++
−=
,
()()
136135
3151r
2
mmmmmm
mmAAP2
B
++−−
=
,
()
c56
542r
4
Smm
mAAP2
B
++
−=
,
()()
363353
3361r
3
mmnmmn
nmAAP2
B
+++−
=
,
()()
c16c15
152cr
5
SmmSmm
mAASP2
B
++−−
=
,
()()
c63c53
362cr
6
SmnSmn
nAASP2
B
+++−
=
,
()
561
543r
7
mmn
mAAP2
B
++
=
,
()()
611511
1153r
8
mmnmmn
nmAAP2
B
++−+
=
,
International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

215
()()
613513
3163r
9
mnnmnn
nnAAP2
B
++++
=
,
98765432110
BBBBBBBBBB ++++++++=
,
()()
c2c1
1r
1
S2nS2n
aG
b
+−
=
,
()()
3231
2r
2
m2nm2n
aG
b
+−
=
,
()
121
3r
3
n2nn
aG
b
+
−
=
,
()()
c32c31
4r
4
SmnSmn
aG
b
++−−
=
,
()
c12c
5r
5
SnnS
aG
b
++
−
=
,
()
3123
6r
6
mnnm
aG
b
++
−
=
,
()()
3213
7r
7
mnnm
aG
b
+−
=
,
76543218
bbbbbbbb ++++++=
,
()()
354353
1r
1
mmnmmn
BG
D
++−−
=
,
()()
134133
2r
2
mmnmmn
BG
D
++−−
=
,
()
3343
3r
3
mnnm
BG
D
++
−
=
,
()()
c54c53
4r
4
SmnSmn
BG
D
++−−
=
,
()()
c14c13
5r
5
SmnSmn
BG
D
++−−
=
,
()
c34c
6r
6
SnnS
BG
D
++
−
=
,
()()
514513
7r
7
mnnmnn
BG
D
++−−
=
,
()()
114113
8r
8
mnnmnn
BG
D
++−−
=
,
()
1341
9r
9
nnnn
BG
D
++
−
=
,
()()
5453
10r
10
mnmn
BG
D
+−
=
,
1098765432111
DDDDDDDDDDD +++++++++=
.

4. Results and discussions
The problem natural convection unsteady magnetohydrodynamic mass transfer flow of a viscous
incompressible electrically conducting fluid past an infinite vertical porous flat plate in presence of
constant suction and heat sink has been investigated. The governing equations of the flow field are
solved employing multi parameter perturbation technique and the effects of the flow parameters on the
velocity, temperature, concentration distribution and also on the skin friction and rate of heat transfer in
the flow field are analyzed and discussed with the help of velocity profiles 1-5, temperature profiles 6-7,
concentration distribution 8 and Table 1 respectively.

4.1 Velocity field
The velocity of the flow field suffers a substantial change in magnitude with the variation of the flow
parameters. The important parameters affecting the velocity of the flow field are magnetic parameter
M
,
Grashof numbers for heat and mass transfer
G
r
,
G
c
; heat sink parameter
S
and Schmidt number
S
c
.
Figures 1-5 discuss the effects of these parameters on the velocity of the flow field.

0
1
2
3
4
5
6
7
012345
y
u
M=0
M=0.5
M=5
M=10


Figure 1. Velocity profiles against
y
for different values of
M
with
G
r
=3,
G
c
=3,
S
= -0.1,
S
c
=0.60,
P
r
=0.71,
E
c
=0.002,
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2

International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

216
The effect of magnetic parameter
M
on the velocity field is discussed in Figure 1. Curve with
M
=0
corresponds to the case of non-MHD flow. Comparing the curves of Figure 1, it is observed that a
growing magnetic parameter retards the velocity of the flow field at all points due to the dominant effect
of the Lorentz force acting on the flow field. In Figures 2 and 3, we observe the effect of Grashof
numbers for heat and mass transfer
G
r
,
G
c
respectively on the velocity field. Curves with
G
r

<0
correspond to heating of the plate, while those with
G
r
>
0 correspond to cooling of the plate. Analyzing
the curves of Figures 2 and 3, we come to a conclusion that both the parameters
G
r

and
G
c
enhance the
velocity of the field at all points. Figure 4 elucidates the effect of heat sink/source parameter
S
on the
velocity of the flow field. Curves with
S
<0 and S>0 correspond to the presence of heat sink and heat
source respectively in the flow field. The heat source parameter (S>0) is found to accelerate the velocity
of the flow field at all points while the presence of heat sink (
S
<0) reverses effect. The effect of Schmidt
number
S
c
on the velocity field is discussed in Figure 5. The heavier diffusive species (growing
S
c
) has a
decelerating effect on the velocity of the flow field at all points.





Figure 2. Velocity profiles against
y
for different values of
G
r
with
G
c
=3,
M
=1,
S
= -0.1,
S
c
=0.60,
P
r
=0.71,
E
c
=0.002,
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2


0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
012345
y
u
G
r
=
5
G
r
=
3
G
r
=
1
G
r
=
-1
G
r
= -3
G
r
=
-5
International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

217



Figure 3. Velocity profiles against
y
for different values of
G
c
with
G
r
=3,
M
=1,
S
= -0.1,
S
c
=0.60,
P
r
=0.71,
E
c
=0.002,
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2

0
1
2
3
4
5
012345
y
u
S=0.5
S=0
S= -0.05
S= -0.2
S= -0.5


Figure 4. Velocity profiles against
y
for different values of
S
with
G
r
=3,
G
c
=3,
E
c
=0.002,
M
=1,
S
c
=0.60,
P
r
=0.71,
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2

-4
-3
-2
-1
0
1
2
3
4
5
012345
y
u
G
c
=
5
G
c
=
3
G
c
=
1
G
c
=
-1
G
c
=
-3
G
c
=
-5
International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

218


Figure 5. Velocity profiles against
y
for different values of
S
c
with
G
r
=3,
G
c
=3,
E
c
=0.002,
M
=1,
S
= -0.1,
P
r
=0.71,
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2

4.2 Temperature field
The temperature field is found to change appreciably with the variation of Prandtl number
P
r
and heat
sink parameter
S
. These variations have been shown in Figures 6 and 7 respectively. On close
observation of the curves of both the figures, we notice that the effect of increasing the magnitude of heat
sink parameter and the Prandtl number is to decrease the temperature of the flow field at all points; while
the heat source parameter reverses the effect.



Figure 6. Temperature profiles against
y
for different values of
P
r
with
G
r
=3,
G
c
=3,
M
=1,
S
= -0.1,
E
c
=0.002,
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2

0
1
2
3
4
5
6
7
012345
y
u
S
c
=0.22
S
c
=0.3
S
c
=0.6
S
c
=0.78
S
c
=1.004
0
0.2
0.4
0.6
0.8
1
1.2
0 0.4 0.8 1.2 1.6 2
y
T
P
r
=
1
P
r
=
2
P
r
=
7
P
r
=
9
P
r
=
11
International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

219
0
0.2
0.4
0.6
0.8
1
1.2
00.511.52
y
T
S=0.5
S= 0
S= -0.05
S= -0.2
S= -0.5


Figure 7. Temperature profiles against
y
for different values of
S
with
G
r
=3,
G
c
=3,
M
=1,
E
c
=0.002,
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2,
P
r
=0.71

4.3 Concentration distribution
Figure 8 depicts the concentration distribution in presence of foreign species such as
H
2
,
He
,
H
2
O

vapour,
NH
3

and
CO
2
in the flow field with
S
c
= 0.22, 0.30, 0.60, 0.78 and 1.004 respectively. The
concentration distribution of the flow field suffers a decrease in boundary layer thickness in presence of
heavier diffusive species (growing
S
c
) at all points of the flow field. It is further observed that heavier the
diffusive species, the sharper is the reduction in the concentration boundary layer thickness of the flow
field.

0
0.2
0.4
0.6
0.8
1
1.2
0 0.4 0.8 1.2 1.6 2
y
C
Sc=0.22
Sc=0.30
Sc=0.60
Sc=0.78
Sc=1.004


Figure 8. Concentration profiles against
y
for different values of
S
c
with
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2


International Journal of Energy and Environment (IJEE), Volume 3, Issue 2, 2012, pp.209-222
ISSN 2076-2895 (Print), ISSN 2076-2909 (Online) ©2012 International Energy & Environment Foundation. All rights reserved.

220
4.4 Skin friction and rate of heat transfer
Variations in the values of skin friction
τ
and the heat flux i. e. rate of heat transfer
N
u
against the Prandtl
number
P
r
for different values of magnetic parameter
M
are entered in Table 1 keeping other parameters
of the flow field constant. A growing Prandtl number
P
r
increases the skin friction for non-MHD flow
and decreases it at the wall in case of MHD flow. On the other hand, a growing magnetic parameter
M
decreases the effect at all points. The effect of increasing Prandtl number
P
r
is to increase the rate of heat
transfer at the wall, while a growing magnetic parameter
M
leads to decrease its value at all points.

Table 1. Variation in the values of skin friction
τ
and the rate of heat transfer
N
u
against
P
r

for different
values of
M
with
S
= -0.1,
G
r
=3,
G
c

=3,
S
c
=0.60,
E
c
=0.002,
ω
=5.0,
ε
=0.2,
ω
t
=
π
/2

M
=0
M
=0.1
M
=5.0
M
=20.0

P
r
τ

N
u
τ

N
u

τ

N
u

τ

N
u

0.71 11.6271 1.6423 11.3191 1.4287 6.8552 -0.3046 4.1016 -0.2363
2 12.1139 3.2345 8.1317 2.3879 5.4092 1.7626 3.5516 -1.5804
7 16.1056 -9.1989 5.9856 -8.9066 4.2561 -5.4226 2.8680 -4.9101
9 18.1481 -10.812 5.5672 -10.508 4.0844 -6.8703 2.7593 -6.2451


8. Conclusion
We present below the following results of physical interest on the velocity, temperature, concentration
distribution, skin friction and the rate of heat transfer at the wall of the flow field.
1. A growing magnetic parameter
M
or Schmidt number
S
c
or heat sink parameter
S
leads to retard
the transient velocity of the flow field at all points.
2. The effect of increasing Grashof number for heat transfer
G
r
and mass transfer
G
c
is to enhance
the transient velocity of the flow field at all points.
3. An increase in Prandtl number
P
r
decreases the transient temperature of the flow field at all
points while a growing heat sink parameter
S
reverses the effect.
4. A heavier diffusive species (growing
S
c
) has a sharper reduction in the concentration boundary
layer thickness at all points of the flow field.
5. A growing Prandtl number
P
r
increases the skin friction for non-MHD flow and decreases it at
the wall in case of MHD flow. On the other hand, a growing magnetic parameter
M
decreases the
effect at all points.
6. The effect of increasing Prandtl number
P
r
is to enhance the magnitude of rate of heat transfer at
the wall, while a growing magnetic parameter
M
leads to decrease its value at all points.

References
[1] Hashimoto H. Boundary layer growth on a flat plate with suction or injection. J. Phys Soc. Japan.
1957, 22, 7-21.
[2] Sparrow, E. M., Cess R. D. The effect of a magnetic field on a free convection heat transfer. Int. J.
Heat Mass Trans. 1961, 4, 267-274.
[3] Gebhart B., Pera L. The nature of vertical natural convection flows resulting from the combined
buoyancy effects of thermal and mass diffusion. Int. J. Heat Mass Trans. 1971, 14 (12), 2025-
2050.
[4] Soundalgekar V. M., Wavre P. D. Unsteady free convection flow past an infinite vertical plate
with constant suction and mass transfer. Int. J. Heat Mass Trans.1977, 20, 1363-1373.
[5] Hossain M. A., Begum R. A. Effect of mass transfer and free convection on the flow past a vertical
plate. ASME J. Heat Trans. 1984, 106, 664-668.
[6] Bestman A.R. Natural convection boundary layer with suction and mass transfer in a porous
medium. Int. J. Ener. Res. 1990, 14(4), 389-396.
[7] Pop I., Kumari M., Nath G. Conjugate MHD flow past a flat plate. Acta Mech. 1994, 106 (3-4),
215-220.
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[8] Singh N. P. Mass transfer effects on free convection in MHD flow of a viscous fluid. Proc. Math.
Soc. 1994, 10, 59-62.
[9] Raptis A. A, Soundalgekar V.M. Steady laminar free convection flow of an electrically conducting
fluid along a porous hot vertical plate in presence of heat source/sink. ZAMM, 1996, 10, 59-62.
[10] Na T. Y., Pop I. Free convection flow past a vertical flat plate embedded in a saturated porous
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[11] Takhar H.S., Chamkha A.J., Nath G. Unsteady flow and heat transfer on a semi-infinite flat plate
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[12] Chowdhury M.K., Islam M.N. MHD free convection flow of visco elastic fluid past an infinite
vertical porous plate. Heat Mass Trans. 2000, 36, 439-447.
[13] Raptis A.A., Kafousias N. Heat transfer in flow through a porous medium bounded by an infinite
vertical plate under the action of a magnetic field. Int. J. Ener. Res. 2000, 6, 241-245.
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Ind. J. Theo. Phys. 2002, 50, 5-13.
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S. S. Das did his M. Sc. degree in Physics from Utkal University, Orissa (India) in 1982 and obtained his
Ph. D degree in Physics from the same University in 2002. He started his service career as a Faculty o
f
Physics in Nayagarh (Autonomous) College, Orissa (India) from 1982-2004 and presently working as
the Head of the faculty of Physics in KBDAV College, Nirakarpur, Orissa (India) since 2004. He has 29
years of teaching experience and 12 years of research experience. He has produced 2 Ph. D scholars and
presently guiding 15 Ph. D scholars. Now he is carrying on his Post Doc. Research in MHD flow
through porous media. His major fields of study are MHD flow, Heat and Mass Transfer Flow through
Porous Media, Polar fluid, Stratified flow etc. He has 51 papers in the related area, 42 of which are
published in Journals of International repute. Also he has reviewed a good number of research papers of
some International Journals. Dr. Das is currently acting as the honorary member of editorial board of
Indian Journal of Science and Technology and as Referee of AMSE Journal, France; Central European Journal of Physics;
International Journal of Medicine and Medical Sciences, Chemical Engineering Communications, International Journal of Energy
and Technology, Progress in Computational Fluid Dynamics etc. Dr. Das is the recipient of prestigious honour of being selecte
d
for inclusion in Marquis Who’s Who in Science and Engineering of New Jersey, USA for the year 2011-2012 (11
th
Edition) for
his outstanding contribution to research in Science and Engineering.
E-mail address: drssd2@yahoo.com



S. Parija did her M. Sc. degree in Physics from Utkal University, Orissa (India) in 1986 and obtained
her M. Phil degree in Physics from the same University in 1988. She served as a Faculty of Physics in A.
S. College, Tirtol, Orissa from 1987-1997 and presently working as the Senior faculty of Physics in
Nimapara (Autonomous) College, Orissa since 1997. She has 24 years of teaching experience and 3
years of research experience. Presently she is engaged in active research. Her major fields of study are
magnetohydrodynamic flow with or without heat transfer and the related problems. She has published 1
paper in the related area
E-mail address: sephaliparija@yahoo.com




R. K. Padhy obtained his M. Sc. degree in Physics from Berhampur University, Orissa (India) in 2002.
He served as a Faculty of Physics in Little Angel Public School, Nizampatnam, Andhra Pradesh (India)
from 2002-2003 and in Jupiter +2 Science College, Bhubaneswar, Orissa from 2003-2005. Presently he
is working as Head of the faculty of Physics in DAV Public School, Chandrasekharpur, Bhubaneswar
since 2005. He has 9 years of teaching experience and presently he is engaged in active research. His
major field of study is flow and heat transfer in viscous incompressible fluids with or without mass
transfer.
E-mail address: rajesh_pip@ rediffmail.com