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1.
Mehdi Ghalambaz Faramarz Moattar Abdolreza Karbassi Mikhail A. Sheremet Ioan Pop 《Transport in Porous Media》2017,116(2):473-491
The triple-diffusive mixed convection heat and mass transfer of a mixture is analyzed in an enclosure filled with a Darcy porous medium. The mass transfer buoyancy effects due to concentration gradients of the dispersed components (pollutant components) are taken into account using the Boussinesq approximation model. The governing equations are transformed into a non-dimensional form, and six groups of non-dimensional parameters, including Darcy–Rayleigh number, Peclet number, two Lewis numbers for pollutant components 1 and 2 and two buoyancy ratio parameters for pollutant components 1 and 2, are introduced. The governing equations are numerically solved for various combinations of non-dimensional parameters using the finite element method. The effect of each group of non-dimensional parameters on the pollutant distribution and the heat transfer in the cavity is discussed. The results indicate that the presence of one pollutant component can significantly affect the pollutant distribution of the other component. When the Lewis number of a pollutant component is small, the increase in the bouncy ratio parameter of the proposed component always increases the Nusselt and Sherwood numbers in the cavity. 相似文献
2.
Mohammad Ghalambaz Hossein Hendizadeh Hossein Zargartalebi Ioan Pop 《Transport in Porous Media》2017,116(1):379-392
This work is dealing with the natural convection heat transfer in a square filled with porous medium that has been extended according to the Nield and Kuznetsov model to tridisperse porous medium. Considering impermeable walls which the horizontal ones are insulated and vertical ones are assumed to be isothermal, the governing equations are set as the three equations for momentum and three equations for energy for three phases of porosity and are numerically solved utilizing finite element method. In this study isothermal contours, streamlines and Nusselt number values are foremost criteria which are presented for three levels of porosity. The influence of various governing parameters on the heat transfer is investigated. 相似文献
3.
Steady mixed convection boundary layer flow from an isothermal horizontal circular cylinder embedded in a porous medium filled
with a nanofluid has been studied for both cases of a heated and cooled cylinder. The resulting system of nonlinear partial
differential equations is solved numerically using an implicit finite-difference scheme. The solutions for the flow and heat
transfer characteristics are evaluated numerically for various values of the governing parameters, namely the nanoparticle
volume fraction φ and the mixed convection parameter λ. Three different types of nanoparticles are considered, namely Cu, Al2O3 and TiO2. It is found that for each particular nanoparticle, as the nanoparticle volume fraction φ increases, the magnitude of the skin friction coefficient decreases, and this leads to an increase in the value of the mixed
convection parameter λ which first produces no separation. On the other hand, it is also found that of all the three types
of nanoparticles considered, for any fixed values of φ and λ, the nanoparticle Cu gives the largest values of the skin friction coefficient followed by TiO2 and Al2O3. Finally, it is worth mentioning that heating the cylinder (λ > 0) delays separation of the boundary layer and if the cylinder
is hot enough (large values of λ > 0), then it is suppressed completely. On the other hand, cooling the cylinder (λ < 0) brings
the boundary layer separation point nearer to the lower stagnation point and for a sufficiently cold cylinder (large values
of λ < 0) there will not be a boundary layer on the cylinder. 相似文献
4.
Natural convection in a partially filled porous square cavity is numerically investigated using SIMPLEC method. The Brinkman-Forchheimer
extended model was used to govern the flow in the porous medium region. At the porous-fluid interface, the flow boundary condition
imposed is a shear stress jump, which includes both the viscous and inertial effects, together with a continuity of normal
stress. The thermal boundary condition is continuity of temperature and heat flux. The results are presented with flow configurations
and isotherms, local and average Nusselt number along the cold wall for different Darcy numbers from 10−1 to 10−6, porosity values from 0.2 to 0.8, Rayleigh numbers from 103 to 107, and the ratio of porous layer thickness to cavity height from 0 to 0.50. The flow pattern inside the cavity is affected
with these parameters and hence the local and global heat transfer. A modified Darcy–Rayleigh number is proposed for the heat
convection intensity in porous/fluid filled domains. When its value is less than unit, global heat transfer keeps unchanged.
The interfacial stress jump coefficients β
1 and β
2 were varied from −1 to +1, and their effects on the local and average Nusselt numbers, velocity and temperature profiles
in the mid-width of the cavity are investigated. 相似文献
5.
A fully developed mixed convection flow between inclined parallel flat plates filled with a porous medium is considered through
which there is a constant flow rate and with heat being supplied to the fluid by the same uniform heat flux on each plate.
The equations governing this flow are made non-dimensional and are seen to depend on two dimensionless parameters, a mixed
convection parameter λ and the Péclet number Pe, as well as the inclination γ of the plates to the horizontal. The velocity and temperature profiles are obtained in terms of λ, Pe and γ when the channel is inclined in an upwards direction as well as for horizontal channels. The limiting cases of small and
large λ and small Pe are considered with boundary-layer structures being seen to develop on the plates for large values of λ. 相似文献
6.
Ali J. Chamkha S. Abbasbandy A. M. Rashad K. Vajravelu 《Transport in Porous Media》2012,91(1):261-279
The problem of steady, laminar, mixed convection boundary-layer flow over an isothermal vertical wedge embedded in a porous
medium saturated with a nanofluid is studied, in the presence of thermal radiation. The model used for the nanofluid incorporates
the effects of Brownian motion and thermophoresis with Rosseland diffusion approximation. The wedge surface is maintained
at a constant temperature and a constant nanoparticle volume fraction. The resulting governing equations are non-dimensionalized
and transformed into a non-similar form and then solved by Keller box method. A comparison is made with the available results
in the literature, and our results are in very good agreement with the known results. A parametric study of the physical parameters
is made, and a representative set of numerical results for the velocity, temperature, and volume fraction, the local Nusselt
and Sherwood numbers are presented graphically. The salient features of the results are analyzed and discussed. 相似文献
7.
The steady mixed convection boundary-layer flow over a vertical impermeable surface in a porous medium saturated with water
close to its maximum density is considered for uniform wall temperature and outer flow. The problem can be reduced to similarity
form and the resulting equations are examined in terms of a mixed convection parameter λ and a parameter δ which measures
the difference between the ambient temperature and the temperature at the maximum density. Both assisting (λ > 0) and opposing
flows (λ < 0) are considered. A value δ0 is found for which there are dual solutions for a range λc < λ < 0 of λ (the value of λc dependent on δ) and single solutions for all λ ≥ 0. Another value of δ1 of δ, with δ1 > δ0, is found for which there are dual solutions for a range 0 < λ < λc of positive values of λ, with solutions for all λ≤ 0. There is also a range δ0 < δ < δ1 where there are solutions only for a finite range of λ, with critical points at both positive and negative values of λ, thus
putting a finite limit on the range of existence of solutions. 相似文献
8.
Transport in Porous Media - The article “Quantitative In-situ Analysis of Water Transport in Concrete Completed Using X-ray Computed Tomography”, written by “Tyler Oesch, Frank... 相似文献
9.
10.
A numerical study of mixed convection in a vertical channel filled with a porous medium including the effect of inertial forces
is studied by taking into account the effect of viscous and Darcy dissipations. The flow is modeled using the Brinkman–Forchheimer-extended
Darcy equations. The two boundaries are considered as isothermal–isothermal, isoflux–isothermal and isothermal–isoflux for
the left and right walls of the channel and kept either at equal or at different temperatures. The governing equations are
solved numerically by finite difference method with Southwell–Over–Relaxation technique for extended Darcy model and analytically
using perturbation series method for Darcian model. The velocity and temperature fields are obtained for various porous parameter,
inertia effect, product of Brinkman number and Grashof number and the ratio of Grashof number and Reynolds number for equal
and different wall temperatures. Nusselt number at the walls is also determined for three types of thermal boundary conditions.
The viscous dissipation enhances the flow reversal in the case of downward flow while it counters the flow in the case of
upward flow. The Darcy and inertial drag terms suppress the flow. It is found that analytical and numerical solutions agree
very well for the Darcian model.
An erratum to this article is available at . 相似文献
11.
Mixed Convection in a Vertical Porous Channel 总被引:1,自引:1,他引:0
12.
Unsteady Natural Convection Flow in a Square Cavity Filled with a Porous Medium Due to Impulsive Change in Wall Temperature 总被引:1,自引:0,他引:1
Unsteady natural convection flow in a two-dimensional square cavity filled with a porous material has been studied. The flow
is initially steady where the left-hand vertical wall has temperature T
h and the right-hand vertical wall is maintained at temperature T
c (T
h > T
c) and the horizontal walls are insulated. At time t > 0, the left-hand vertical wall temperature is suddenly raised to which introduces unsteadiness in the flow field. The partial differential equations governing the unsteady natural convection
flow have been solved numerically using a finite control volume method. The computation has been carried out until the final
steady state is reached. It is found that the average Nusselt number attains a minimum during the transient period and that
the time required to reach the final steady state is longer for low Rayleigh number and shorter for high Rayleigh number. 相似文献
13.
Calculated free convection flows and heat transfer are presented for concentric spherical annular sectors, filled with a porous medium. Two isothermal walls and an adiabatic radial wall at the sector angle define the sectors. The governing equations (in the stream function and temperature formulation) are solved numerically using ADI (alternative direction implicit) finite-difference method. Over the range of geometric parameters examined, the obtained results for spherical annuli and low Rayleigh number Ra. As Ra increases, multicellular flows develop for small values of the aspect ratio parameter . In addition, analytical solutions of the governing equations were obtained for small values of Ra (1) and it was shown that these solutions agree well with those obtained numerically. Significant differences in the local heat transfer rates on the inner and outer walls of the spherical annuli were observed from these solutions. 相似文献
14.
Azizah Mohd Rohni Syakila Ahmad John H. Merkin Ioan Pop 《Transport in Porous Media》2013,96(2):237-253
The steady mixed convection boundary-layer flow on a vertical circular cylinder embedded in a porous medium filled by a nanofluid is studied for both cases of a heated and a cooled cylinder. The governing system of partial differential equations is reduced to ordinary differential equations by assuming that the surface temperature of the cylinder and the velocity of the external (inviscid) flow vary linearly with the axial distance x measured from the leading edge. Solutions of the resulting ordinary differential equations for the flow and heat transfer characteristics are evaluated numerically for various values of the governing parameters, namely the nanoparticle volume fraction ${\phi}$ , the mixed convection or buoyancy parameter ?? and the curvature parameter ??. Results are presented for the specific case of copper nanoparticles. A critical value ?? c of ?? with ?? c <?0 is found, with the values of | ?? c| increasing as the curvature parameter ?? or nanoparticle volume fraction ${\phi}$ is increased. Dual solutions are seen for all values of ?? >??? c for both aiding, ?? >?0 and opposing, ?? <?0, flows. Asymptotic solutions are also determined for both the free convection limit ${(\lambda \gg 1)}$ and for large curvature parameter ${(\gamma \gg 1)}$ . 相似文献
15.
The effect of surface melting on the dual solutions that can arise in the problem of the mixed convection boundary-layer flow past a vertical surface embedded in a non-Darcian porous medium is considered. The problem is described by M, melting parameter, \(\lambda \), mixed convection parameter, and \(\gamma \), the flow inertia coefficient, numerical results being obtained in terms of these three parameters. It is seen that the melting phenomenon reduces the heat transfer rate and enhances the boundary-layer separation at the solid–liquid interface. Asymptotic solutions for the forced convection, \(\lambda =0\), and free convection, large \(\lambda \), limits are derived. 相似文献
16.
Dahani Youssef Hasnaoui Mohammed Amahmid Abdelkhalek Hasnaoui Safae 《Transport in Porous Media》2022,143(1):195-223
Transport in Porous Media - In the present study, a multiple-relaxation-time lattice-Boltzmann method is considered to investigate double-diffusive natural convection in a cavity with heating and... 相似文献
17.
Adopting a two-temperature and two-velocity model, appropriate to a bidisperse porous medium (BDPM) proposed by Nield and
Kuznetsov (2008), the classical steady, mixed convection boundary layer flow about a horizontal, isothermal circular cylinder
embedded in a porous medium has been theoretically studied in this article. It is shown that the boundary layer analysis leads
to expressions for the flow and heat transfer characteristics in terms of an inter-phase momentum parameter, a thermal diffusivity
ratio, a thermal conductivity ratio, a permeability ratio, a modified thermal capacity ratio, and a buoyancy or mixed convection
parameter. The transformed partial differential equations governing the flow and heat transfer in the f-phase (the macro-pores)
and the p-phase (the remainder of the structure) are solved numerically using a very efficient implicit finite-difference
technique known as Keller-box method. A good agreement is observed between the present results and those known from the open
literature in the special case of a traditional Darcy formulation (monodisperse system). 相似文献
18.
Transport in Porous Media - This paper investigates a peculiar case of thermal convection in a vertical porous prism with impermeable and partially conducting walls. We facilitate the analysis in... 相似文献
19.
Mixed convection flow in a two-sided lid-driven cavity filled with heat-generating porous medium is numerically investigated.
The top and bottom walls are moving in opposite directions at different temperatures, while the side vertical walls are considered
adiabatic. The governing equations are solved using the finite-volume method with the SIMPLE algorithm. The numerical procedure
adopted in this study yields a consistent performance over a wide range of parameters that were 10−4 ≤ Da ≤ 10−1 and 0 ≤ Ra
I
≤ 104. The effects of the parameters involved on the heat transfer characteristics are studied in detail. It is found that the
variation of the average Nusselt number is non-linear for increasing values of the Darcy number with uniform or non-uniform
heating condition. 相似文献
20.
B. Straughan 《Journal of Mathematical Fluid Mechanics》2014,16(4):727-736
We show that for many classes of convection problem involving a porous layer, or layers, interleaved with finite but non-deformable solid layers, the global nonlinear stability threshold is exactly the same as the linear instability one. The layer(s) of porous material may be of Darcy type, Brinkman type, possess an anisotropic permeability, or even be such that they are of local thermal non-equilibrium type where the fluid and solid matrix constituting the porous material may have different temperatures. The key to the global stability result lies in proving the linear operator attached to the convection problem is a symmetric operator while the nonlinear terms must satisfy appropriate conditions. 相似文献