Begell House Inc.
Computational Thermal Sciences: An International Journal
CTS
1940-2503
6
3
2014
TRANSIENT FREE-CONVECTION FLOW OF A REACTIVE VARIABLE VISCOSITY FLUID IN A VERTICAL TUBE
191-198
10.1615/.2014005412
Saira
Hussnain
Department of Mathematics, Quaid-i-Azam University, Islamabad, Pakistan
Ahmer
Mehmood
Department of Mathematics, International Islamic University, Islamabad, Pakistan
Asif
Ali
Department of Mathematics, Quaid-i-Azam University 45320, Islamabad 44000, Pakistan
transient free-convection flow
variable viscosity
reactive viscous fluid
vertical tube
Transient free-convection flow of a reactive viscous fluid with temperature dependent viscosity effects in a vertical tube has been investigated numerically by using a finite-difference scheme. The study reports the temperature dependent viscosity effects on the flow hydrodynamics and thermal characteristics. Skin friction and Nusselt number at the surface of the tube are determined for different parameters such as reactant consumption parameter λ, activation energy parameter (ε) and Prandtl number (Pr) and are discussed through graphs.
NUMERICAL STUDY OF NATURAL CONVECTION HEAT TRANSFER OF NANOFLUIDS IN PARTIALLY HEATED SEMI-ANNULI
199-217
10.1615/.2014010754
Sonia
Bezi
Laboratory of Mechanic of Fluids, Physics Department, Faculty of Sciences of Tunis, University of Tunis El-Manar, 2092 El-Manar II, Tunis, Tunisia
Antonio
Campo
Department of Mechanical Engineering, The University of Vermont, Burlington, VT 05405, USA
Nader
Ben-Cheikh
Laboratory of Mechanic of Fluids, Physics Department, Faculty of Sciences of Tunis, University of Tunis El-Manar, 2092 El-Manar II, Tunis, Tunisia
Brahim
Ben-Beya
Laboratory of Physics of Fluids, Physics Department, Faculty of Science of Tunis, University of
Tunis El-Manar, 2092 El-Manar 2, Tunis, Tunisia
nanofluids
partially heated outer cylinder
cooled inner cylinder
heat transfer enhancement
heat transfer correlation
semi-annular enclosure
This study addresses a numerical analysis of heat transfer and fluid flow in a partially heated horizontal annulus filled with nanofluids. The conservation equations in cylindrical coordinates are solved using an in-house FORTRAN code based on the finite-volume method coupled with multigrid acceleration. A heat source owing constant temperature is placed along the outer cylinder of the annular region. The temperature of the inner cylinder is lower than that of the outer cylinder, while the remaining parts are kept insulated. The numerical investigation is carried out for a Rayleigh number in the range of 102 ≤ Ra ≤ 106 and for solid volume fraction of nanoparticles limited to 0 ≤ φ ≤ 0.08. Four nanoparticles (Au, Cu, CuO, Al2O3) and three base fluids (water, ethylene glycol, oil) are selected to examine potential heat transfer enhancement in the annulus. In order to investigate the effects of the size and/or location of the heat source on the fluid flow and heat transfer, different configurations are considered. Results are presented in terms of streamline and isotherms plots, as well as the local and average Nusselt numbers at the heat source surface under different conditions. It is found that the average Nusselt number exhibits an increasing trend as dual functions of the Rayleigh number and the solid volume fraction of the nanoparticles. Furthermore, the results reveal that one type of nanoparticle or base fluid is a key factor for improving the heat transfer. In particular, the highest values of enhancement are obtained when using Au nanoparticles or an oil base fluid. Moreover, it is observed that the size, γ, and location, θp, of the heat source significantly affect the resulting convective flow. An optimum size of the heat source is manifested in which the average Nusselt number attains a minimum for a given Rayleigh number. Reliable correlations formulae expressing the average Nusselt number in terms of Ra, φ, γ, and θp are established.
FLOW REVERSAL IN MIXED CONVECTION IN VERTICAL CONCENTRIC ANNULI: WHY IT OCCURS IN BUOYANCY-AIDED FLOWS
219-240
10.1615/.2014005755
Esmail M. A.
Mokheimer
Mechanical Engineering Department King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia
buoyancy-aided flows
buoyancy-opposed flows
concentric vertical annuli
flow reversal
mixed convection
pressure variation
The main purpose of this article is to shed more light on the cause of flow reversal in vertical concentric annular channels for buoyancy-aided flows under isothermal boundary conditions. The concept used to quantify the critical values of the modified buoyancy parameter (Gr/Re)critical at which the adverse pressure gradient first occurs is outlined and applied to analytically estimate these critical values. The conditions for flow reversal are also analytically obtained for buoyancy-aided and buoyancy-opposed flows. The analytical solutions show that pressure buildup takes place only for buoyancy-aided flows while flow reversal occurs for both buoyancy-aided and buoyancy-opposed flows. The analytical solutions reveal also that values of the buoyancy parameter required to initiate the pressure buildup for buoyancy-aided flows in the vertical annuli are smaller than those required to initiate the flow reversal. Thus, for buoyancy-aided flows, pressure buildup would precede the flow reversal. A numerical scheme is developed and used to simulate the development of pressure and pressure gradient in the entrance region of the vertical concentric annuli. The numerical scheme is validated by the analytical solution as well as the previously published pertinent results. Numerical results that show the pressure buildup in the developing entry region of the annuli for values of the modified buoyancy parameter (Gr/Re) greater than its critical values (Gr/Re)critical along with other flow and heat transfer parameters of importance are also presented and discussed. The locations of pressure buildup as well as those of flow reversal have been obtained and reported.
WAVE PROPAGATION IN AN INHOMOGENEOUS ANISOTROPIC GENERALIZED THERMOELASTIC SOLID UNDER THE EFFECT OF GRAVITY
241-250
10.1615/.2014010868
Santosh
Kumar
Department of Mathematics, SRM Institute of Science and Technology,
Kattankulathur-603203, India
P. C.
Pal
Department of Applied Mathematics, Indian School of Mines, Dhanbad-826004, India
plane waves
relaxation time
inhomogeneity parameter
thermal waves
The plane wave propagation in an inhomogeneous anisotropic thermally conducting elastic solid under the effect of gravity is studied with two thermal relaxations times. Three types of plane waves, namely quasi-P, quasi-S, and thermal waves, are shown to exist. The analytical expressions for their velocities of propagation are obtained. The inhomogeneity in elastic coefficients, density, thermal conductivities, and thermal moduli are considered exponential type. It drastically affects the velocity of these waves and also depends on the angle of propagation, frequency, and gravity. The effects of these parameters are shown graphically.
A DISCRETE METHOD TO TREAT HEAT CONDUCTION IN COMPRESSIBLE TWO-PHASE FLOWS
251-271
10.1615/.2014010575
Fabien
Petitpas
Aix-Marseille Universite, CNRS, IUSTIUMR 7343,5 rue Enrico Fermi, 13453 Marseille Cedex 13, France
Sebastien
Le Martelot
Aix-Marseille Universite, CNRS, IUSTIUMR 7343,5 rue Enrico Fermi, 13453 Marseille Cedex 13, France
two-phase compressible flow
heat conduction
discrete method
interface problems
This paper deals with modeling of heat conduction in two-phase compressible flows. This kind of flow is predominant in propulsion, space, or defense applications. A total nonequilibrium model for two-phase compressible flows with heat conduction is first built. Without heat conduction, the Baer and Nunziato model is recovered. When heat conduction terms are present, extra nonconservative terms appear in the flow model and are responsible for interface condition satisfaction with heat conduction. When dealing with interface problems between compressible fluids, this model contains useless effects that may be omitted. That is why simpler models are derived. They are obtained by successive asymptotic reductions in the limit of stiff relaxation effects of velocities, pressures, and eventually temperature from the nonequilibrium model. The presented models respect conservation laws and guarantee entropy production. From a numerical point of view, a specific discrete explicit and implicit numerical method is developed to solve numerically heat conduction terms. Coupled with a suitable numerical method for two-phase compressible flows, an efficient method is obtained to simulate interface problems between compressible fluids with heat conduction. Analytical solutions of steady state problems of heat conduction in compressible single- and two-phase media are also specially derived to validate the numerical strategy.
VISCOSITY AND FLUID SUCTION/INJECTION EFFECTS ON FREE CONVECTION FLOW FROM A VERTICAL PLATE IN A POROUS MEDIUM SATURATED WITH A PSEUDOPLASTIC FLUID
273-283
10.1615/.2014011207
Driss
Achemlal
University of Sidi Mohammed Ben Abdellah, Polydisciplinary Faculty of Taza
M.
Sriti
University of Sidi Mohamed Ben Abdellah, Polydisciplinary Faculty of Taza, LSI, Team of
Numerical Modeling in Mechanics Applied (MNMA), BP.1223, Taza, Morocco
M.
El Haroui
University of Sidi Mohamed Ben Abdellah, Polydisciplinary Faculty of Taza, LIMAO, BP 1223, Taza, Morocco
free convection
pseudoplastic fluid
suction/injection
porous medium
This paper investigates the effects of the fluid viscosity, the fluid suction/injection, and the power law fluid index on the free convection flow from a heated vertical plate in a porous medium saturated with a pseudoplastic fluid in the presence of internal heat generation. The problem is studied for power law fluid exponents between 0 and 1. The governing equations are transformed into an autonomous third-order nonlinear degenerate ordinary differential equation by means of similarity transformations. This equation is then solved numerically by the fifth-order Runge-Kutta scheme associated with the shooting iteration technique. Also, the effects of the governing physical parameters on the velocity and temperature, the local Nusselt number, and the local skin-friction profiles have been computed and studied with the help of graphs.