Transverse thermal dispersion and wall channelling in a packed bed with forced convective flow

Cheng, Ping; Vortmeyer, D.

doi:10.1016/0009-2509(88)85186-8

Cited by 106 publications

(55 citation statements)

References 16 publications

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“…Thermal dispersion effects are intimately related to eddy convection (Kandula 20 I 0), and were treated by Cheng and Vortmeyer (1988) along with wall channeling effects (existence of a peak velocity in a region close to the external boundary, analogous to a wall jet in single-phase flow). Convection in variable porosity media, including channeling effects were considered by Vafai (1984).…”

Section: Comparison With the Data Ofmentioning

confidence: 99%

Correlation of Water Frost Porosity in Laminar Flow Over Flat Surfaces

Kandula

2012

Special Topics Rev Porous Media

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A dimensionless correlation has been proposed for water frost porosity expressing its dependence on frost surface temperature and Reynolds number for laminar forced flow over a flat surface. The correlation is presented in terms of a dimensionless frost surface temperature scaled with the cold plate temperature, and the freezing temperature. The flow Reynolds number is scaled with reference to the critical Reynolds number for laminar-turbulent transition. The proposed correlation agrees satisfactorily with the simultaneous measurements of frost density and frost surface temperature covering a range of plate temperature, ambient air velocity, humidity, and temperature. It is revealed that the frost porosity depends primarily on the frost surface and the plate temperatures and the flow Reynolds number, and is only weakly dependent on the relative humidity. The results also point out the general character of frost porosity displaying a decrease with an increase in flow Reynolds number.

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Section: Comparison With the Data Ofmentioning

confidence: 99%

Correlation of Water Frost Porosity in Laminar Flow Over Flat Surfaces

Kandula

2012

Special Topics Rev Porous Media

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Section: Greek Symbolsmentioning

confidence: 99%

“…In their model, Amiri and Vafai (1994) [24] have shown that the thermal diffusivity of the fluid is also proportional to the free stream Reynolds number based on the porous medium pore diameter. Other works dealing with thermal dispersion effects in porous media can be found in the papers by Hunt and Tien (1988) [25] and Cheng and Vortmeyer (1988) [26].In certain porous media applications such as those involving heat removal from nuclear fuel debris, underground disposal of radioactive waste material, storage of food stuffs, and exothermic chemical reactions and dissociating fluids in packed-bed reactors, the working fluid heat generation (source) or absorption (sink) effects are important. Representative studies dealing with these effects have been reported previously by such authors as Acharya and Goldstein (1985) [27], Vajravelu and Nayfeh (1992) [28] and Chamkha (1997) [29].…”

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confidence: 99%

Double-Diffusive Convective Flow of a Micropolar Fluid Over a Vertical Plate Embedded in a Porous Medium with a Chemical Reaction

Chamkha

Al-Mudhaf

Al-Yatama

2004

Inter J Fluid Mech Res

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The problem of steady, laminar, double-diffusive natural convection boundary-layer flow of a micropolar fluid over a vertical permeable semi-infinite plate embedded in a uniform porous medium in the presence of non-Darcian and thermal dispersion effects is investigated. Also, the model problem allows for possible heat generation or absorption and first-order chemical reaction effects. Both the wall temperature and wall concentration are assumed to have linear variations with the distance along the plate. Appropriate transformations are employed to transform the governing differential equations into a non-similar form that can be solved as an initial-value problem. The resulting equations are solved numerically by an efficient implicit, iterative, finite-difference scheme. The obtained results are checked against previously published work on special cases of the problem and are found to be in good agreement. A parametric study illustrating the influence of the microrotation material parameter, concentration to thermal buoyancy ratio, chemical reaction parameter, Schmidt number, heat generation or absorption and the surface suction or injection effects on the fluid velocity, microrotation, temperature and solute concentration as well as the local skin-friction coefficient, local wall microrotation coefficient and the local wall heat and mass transfer coefficients is conducted. The results of this parametric study are shown graphically and the physical aspects of the problem are highlighted and discussed. Greek Symbolseffective thermal diffusivity of the porous medium; α d thermal diffusivity of the porous medium due to thermal dispersion;Introduction Double-diffusive convection is referred to buoyancy-induced flow due to the combined effects of both temperature and concentration gradients. Double-diffusive convection from different geometries embedded in porous media has a wide range of engineering and geophysical applications such as geothermal reservoirs, drying of porous solids, thermal insulation, enhanced oil recovery, packed-bed catalytic reactors, cooling of nuclear reactors, and underground energy transport. Most early studies on porous media have used the Darcy law which is a linear empirical relation between the Darcian velocity and the pressure drop across the porous medium and is limited to relatively slow flows. However, for relatively higher velocity flow situations, the Darcy law becomes inadequate for representing the flow behavior correctly since it does not account for the resulting inertia effects of the porous medium. In this situation, the pressure drop has a quadratic relationship with the volumetric flow rate. The high flow situation is established when the Reynolds number based on the pore size is greater than unity. Vafai and Tien (1981) [1] discussed the importance of inertia effects for high velocity flows in porous media. Double-diffusive convection flow of a Newtonian fluid along a vertical surface embedded in a uniform porous medium was considered by Bejan (1984) [2] based on scale ...

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“…According to the data of various investigators compiled by From a more fundamental consideration, the eddy convection in porous media is intimately related to the phenomenon of thermal dispersion (see Cheng and Vortmeyer, 1988;Hsu and Cheng, 1990). Thermal dispersion is manifested on account of microscopic fluid velocity and temperature deviations from the corresponding average values, and results in enhanced heat transport.…”

Section: Effect Of Eddy Convectionmentioning

confidence: 99%

“…The effect of tortuous flow paths on the constant DI for high Reynolds number flow was reported by Yu and Li (2004) with the aid of a fractal model. Transverse thermal dispersion and wall channeling effects (existence of peak velocity in a region close to the external boundary) were treated by Cheng and Vortmeyer (1988). Convection in variable porosity media, including channeling effects, were considered by Vafai (1984).…”

Section: Effect Of Eddy Convectionmentioning

confidence: 99%

Effective Thermal Conductivity of Frost Consideringmass Diffusion and Eddy Convection

Kandula

2010

Special Topics Rev Porous Media

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A physical model for the effective thermal conductivity of water frost is proposed for application to the full range of frost density. The proposed model builds on the ZehnerSchlunder one-dimensional formulation for porous media appropriate for solid-to-fluid thermal conductivity ratios less than about 1000. By superposing the effects of mass diffusion and eddy convection on stagnant conduction in the fluid, the total effective thermal conductivity of frost is shown to be satisfactorily described. It is shown that the effects of vapor diffusion and eddy convection on the frost conductivity are ofthe same order. The results also point out that idealization ofthe frost structure by cylindrical inclusions offers a better representation of the effective conductivity of frost as compared to spherical inclusions. Satisfactory agreement between the theory and the measurements for the effective thermal conductivity of frost is demonstrated for a wide range of frost density and frost temperature.

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Transverse thermal dispersion and wall channelling in a packed bed with forced convective flow

Cited by 106 publications

References 16 publications

Correlation of Water Frost Porosity in Laminar Flow Over Flat Surfaces

Correlation of Water Frost Porosity in Laminar Flow Over Flat Surfaces

Double-Diffusive Convective Flow of a Micropolar Fluid Over a Vertical Plate Embedded in a Porous Medium with a Chemical Reaction

Effective Thermal Conductivity of Frost Consideringmass Diffusion and Eddy Convection

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