Notes On Steady Natural Convection Heat Transfer by Double Diffusion From A Heated Cylinder Buried in A Saturated Porous Media
Notes On Steady Natural Convection Heat Transfer by Double Diffusion From A Heated Cylinder Buried in A Saturated Porous Media
Notes On Steady Natural Convection Heat Transfer by Double Diffusion From A Heated Cylinder Buried in A Saturated Porous Media
discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/273551919
READS
16
5 AUTHORS, INCLUDING:
Carlos Alberto Chaves
Universidade de Taubat
University of So Paulo
16 PUBLICATIONS 11 CITATIONS
51 PUBLICATIONS 94 CITATIONS
SEE PROFILE
SEE PROFILE
Introduction
Many transport processes presented in environment occur due
to the flow off with a simultaneous occurrence of temperature and
concentration gradients. Some oceanographic phenomena like
salt sources are explained by coupled presence of thermal gradients and saline. There is also an application dissemination control of pollutants contaminators from chemical industrial waste
and radioactive waste that solves the problem in area of radioactive spreading out in ground, in water contamination, and in other
correlates that still ask for solution [1].
A study on transient natural convection promoted by double
diffusion in saturated porous media was done in Ref. [2]. This
study proposed a numerical solution to variations of Rayleigh
number (0 to 1000), Lewis number (0 to 100), and the buoyancy
ratio number (3 to 3) using the control volume method idealized in Ref. [3]. This method has been widely used and its implementation to a bipolar coordinates system was realized.
Patankars method was applied to the case of transient natural
convection heat transfer by double diffusion from heated cylinders
buried in saturated porous media in Ref. [2].
Numerical solutions for transient natural convection heat transfer by double diffusion from a heated cylinder buried in a saturated porous mediawhere both, cylinder and media surfaces,
were kept at constant uniform temperature and concentration
were presented in Ref. [4], where heat and mass transfer were
studied as a function of Rayleigh, Lewis, and buoyancy ratio
numbers.
Reference [5] turned its attention to processes of combined
(simultaneous) heat and mass transfer that were driven by buoyancy. The density gradients that provide the driving buoyancy
force were induced by the combined effects of temperature
and species concentration nonuniformities present in the fluidsaturated medium. This paper was guided by the review of
Ref. [6]. Review articles on double-diffusive convection such as
those given in Refs. [79] are useful in this work.
This paper is guided by a study made previously in Ref. [4]
applied to the case of the problem of steady natural convection
heat transfer by double diffusion from heated cylinders buried in
saturated porous media presented in Ref. [10].
This paper aims to present numerical solutions for the problem
of steady natural convection heat transfer by double diffusion
from a heated cylinder buried in a saturated porous media exposed
to constant uniform temperature and concentration in the cylinder
and in the media surface.
Problem Statement
An infinite cylinder buried in a saturated porous media is considered. The cylinder has a radius r1 and it is buried in depth d
from the porous media superior surface. The cylinder outside
cover is kept at temperature TW and at concentration CW, constant
while the porous media superior surface is kept at temperature TS
and at concentration CS, according to Fig. 1. The hypothesis of
steady state and impermeable wall is considered as well.
C 2015 by ASME
Copyright V
(1)
where To, Co, and qo are references temperature, concentration, and specific mass, respectively, and b and bc are the
coefficients of thermal and chemical expansions, respectively, defined by the following equations:
1 @q
q0
@T p
(2)
bc
1
@q
q0
@C p
(3)
1 cos u cosh v
cosh v
Vu
and G
cos u 2
1 @W
hv @v
hu hv
sinh v sin u
cosh v cos u 2
and V v
1 @W
hu @u
a
cos u
cosh v
@W @T @W @T
r T Ra
@v @u @u @v
2
@W @C @W @C
r2 C RaLe
@v @u
@u @v
(6)
(7)
where
a
sinh v1
r1
d
d cosh v1
r1
T Ts
T
Tw Ts
C Cs
C
Cw Cs
a
W
aRa
(8)
bc DC
BN
b DT
a
D
(10)
K g b DT r 1
a
(11)
Le
Ra
(9)
Dv
@ue
Ai1;j
Dv
@uw
Ai;j1
Du
@vn
Ai;j1
Du
@vs
where
DT T w T s
DC Cw Cs
Methods
To solve the problem numerically, Eqs. (5)(7) were integrated
related to u and v variables, which are already described in dimensionless bipolar coordinates on a generic volume control. Such
dominion is described in Fig. 2, and the integration is done following the volume control method formulation developed in
Ref. [3], where potential law schematic is taken to calculate the
flux term through the limits of each internal control volume.
Integrating Eq. (5) in the control volume VCP in Fig. 2 related
to the variables u and v takes to Eq. (12). After defining these conditions, a computational program is developed in FORTRAN to solve
the problem proposed
@ 2 w
@ 2 w
du dv
du dv
2
2
VCp @u
VCp @v
@T
@T
a
H
G
du dv
du dv
@u
@v
VCp
VCp
@C
@C
BN
H
G
du dv
du dv
@u
@v
VCp
VCp
(12)
Patankars power law [3] was adopted to calculate the flow
terms through the frontier of each internal control volume, and
takes to the equation in the following form:
Journal of Heat Transfer
(13)
where Du, Dv, (@u)w, (@u)e, (@v)n, and (@v)s are values represented in Fig. 2.
Ai;j Ai1;j Ai1;j Ai;j1 Ai;j1
3
2
Dv
H
T
T
i;j
i1;j
i1;j
7
6
2
7
6
7
6
Du
Dv
7
6
Ti;j1
Bi;j a 6 Gi;j
Ti;j1
N Hi;j
7
7
6
2
2
7
6
5
4
Du
Ci;j1 Ci;j1
Ci1;j Ci1;j BNGi;j
2
(14)
To obtain the equations of the chemical constituent and the
energy, in the discrete mode, it proceeds in an analogical way.
For dimensionless terms, the new coordinate system (u,v) is
established following boundary and initial conditions as the
dominion shows in Fig. 1:
For u 0 and v1 < v 0 ) W 0
(15)
@T
@C
0
@v
@v
(16)
v v1 and 0 u p ) W 0;
T C 1 over the buried cylinder
(17)
v 0 and 0 u p ) W 0;
T C 0over floor surface
(18)
For Ra 0.1, the problem is reduced to virtually a cylinder buried in a purely conductive media. In this case, most of the heat is
transported by conduction. When Ra increases, the convective
effects become important.
In case Ra 10, a plume forms between the wall and the heated
cylinder. The very close lines in temperature fields in the vicinity
of the cylinder surface indicate a greater temperature gradient in
this region. The Ra 10 well represents the transition from purely
conductive flow to the highly convective one.
Note that the increase in Rayleigh number intensifies the flow
more and more near to the top of the cylinder buried and the line
of symmetry of the plume that is formed on the cylinder.
In Fig. 3, the influence of Rayleigh on the Nusselt numbers in
the cylinder and the wall is observed. Heat exchange with the
cylinder increases monotonically with the Rayleigh number. This
behavior also occurs for Nusselt in the wall.
Figure 4 shows the influence of Rayleigh and Lewis parameters
on the average Sherwood number of the flow for BN 0, where it
Conclusions
The study of doubly diffusive natural convection for a cylinder
buried in a homogeneous porous and saturated media was investigated numerically.
The equations describing the problem were expressed in bipolar
coordinates according to stream function formulation and numerically solved by the method of control volume.
The program implemented allowed to achieve satisfactory
results and enabled a better understanding of the influence of
Rayleigh and Lewis numbers on flows driven by heat.
The Nusselt and Sherwood numbers as a function of Rayleigh,
Lewis, and the ratio of thrust N were widely analyzed and their
effects relatively explained within the range of values specified in
this work.
The results for the heat driven flow directed allowed basically
demonstrating purely conductive, conductive, and convective, and
strongly convective regions for different values of Rayleigh and
Lewis considered.
A finite volume scheme has been used to predict the flow,
temperature, and concentration distributions at any space from a
heat cylinder buried into a fluid-saturated porous medium for a
bipolar coordinates system.
Examples presented show that the differences in the flow
distribution caused not only when Rayleigh number range is
considered but also when Lewis number range is considered.
Further, increase in the Rayleigh number has a significant influence in the flow distribution when the concentration distribution is
considered.
Steady natural convection heat transfer by double diffusion
from a heated cylinder buried in a saturated porous medium is
studied numerically using the finite volume method. To model
fluid flow inside the porous medium, the Darcy equation is used.
Numerical results are obtained in the form of streamlines, isotherms, and isoconcentrations. The Rayleigh number values range
Acknowledgment
Dr. Wendell de Queiroz Lamas thanks his "Productivity Scholarship in Research," supported by the Brazilian National Council
for Scientific and Technological Development (CNPq), Grant
No. 301260/2013-3.
Dr. Jose Rui Camargo and Dr. Francisco Jose Grandinetti thank
their "Productivity Scholarship in Technological Development
and Innovative Extension," supported by the Brazilian National
Council for Scientific and Technological Development (CNPq),
Grant No. 311795/2012-9.
Nomenclature
a
A
B
BN
C
d
D
F
g
G
g
h
H
K
Le
Nu
Qx
Qy
r1
Ra
Sh
T
u, v
V
V
v1
x, y
Greek Symbols
a
b
bc
D
r
h
l
q
W
@
Subscripts
e
i
j
N
Superscript
* dimensionless parameters
References
[1] Chaves, C. A., and Trevisan, O. V., 1992, Natural Convection Double Diffusion
Around a Cylinder Buried in a Saturated Porous Media, IV Brazilian Congress
of Thermal Sciences and Engineering, Rio de Janeiro, pp. 110 (in Portuguese).
[2] Chaves, C. A., 1990, Natural Convection Double Diffusion Around a Cylinder
Buried in a Saturated Porous Media, Ph.D. thesis, State University of Campinas, Campinas, SP, Brazil (in Portuguese).
[3] Patankar, S., 1980, Numerical Heat Transfer and Fluid Flow, Hemisphere,
New York.
[4] Chaves, C. A., Camargo, J. R., Cardoso, S., and Macedo, A. G., 2005,
Transient Natural Convection Heat Transfer by Double Diffusion From a
Heated Cylinder Buried in a Saturated Porous Media, Int. J. Therm. Sci.,
44(8), pp. 720725.
[5] Nield, D. A., and Bejan, A., 2013, Double-Diffusive Convection, Convection
in Porous Media, Springer, New York.
[6] Trevisan, O. V., and Bejan, A., 1990, Combined Heat and Mass Transfer by
Natural Convection in a Porous Medium, Adv. Heat Transfer, 20,
pp. 315352.
[7] Diersch, H.-J. G., and Kolditz, O., 2002, Variable-Density Flow and Transport
in Porous Media: Approaches and Challenges, Adv. Water Resour., 25(812),
pp. 899944.
[8] Mamou, M., 2002, Stability Analysis of Double-Diffusive Convection in
Porous Enclosures, Transport Phenomena in Porous Media II, D. B. Ingham
and I. Pop, eds., Elsevier, Oxford, UK.
[9] Mojtabi, A., and Charrier-Mojtabi, M. C., 2005, Double-Diffusive Convection
in Porous Media, Handbook of Porous Media, 2nd ed., K. Vafai, ed., Taylor
and Francis, New York.
[10] Bau, H. H., 1984, Convective Heat Losses From a Pipe Buried in a SemiInfinite Porous Media, Int. J. Heat Mass Transfer, 27(11), pp. 20472056.
[11] Bejan, A., 1984, Convection Heat Transfer, Wiley, New York.
[12] Bird, R. B., Stewart, W. E., and Lightfoot, E. N., 1976, Transport Phenomena,
Wiley, New York.
[13] Moon, P., and Spenser, D. E., 1971, Field Theory Handbook, Springer, Berlin.