Description of mass-exchange processes in porous media at low values of the Peclet number

1986 ◽  
Vol 51 (1) ◽  
pp. 825-831 ◽  
Author(s):  
A. I. Moshinskii
Keyword(s):  
Porous Media ◽  
Mass Exchange ◽  
Peclet Number ◽  
Péclet Number ◽  
Exchange Processes

Nanofluid Impinging Jets in Porous Media

2016 ◽  
Vol 7 ◽  
pp. 84-113
Author(s):  
Bernardo Buonomo ◽  
Oronzio Manca ◽  
Sergio Nardini ◽  
D. Ricci
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Rayleigh Number ◽  
Peclet Number ◽  
Pure Water ◽  
Particle Diameter ◽  
Target Surface ◽  
Impinging Jets ◽  
Local Thermal Equilibrium ◽  
Péclet Number

Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications in the fields of automotive, aerospace, electronics and process industry. A possible solution to obtain efficient cooling systems is represented by the use of confined impinging jets. Moreover, the introduction of nanoparticles in the working fluids can be considered in order to improve the thermal performances of the base fluids. In this paper a numerical investigation on mixed convection in confined slot jets impinging on a porous media by considering pure water or Al2O3/water based nanofluids is described. A two-dimensional model is developed and different Peclet numbers and Rayleigh numbers were considered. The particle volume concentrations ranged from 0% to 4% and the particle diameter is equal to 30 nm. The target surface is heated by a constant temperature value, calculated according to the value of Rayleigh number. The distance of the target surface is five times greater than the slot jet width. A single-phase model approach has been adopted in order to describe the nanofluid behaviour while the hypothesis of non-local thermal equilibrium is considered in order to simulate the behaviour in the porous media which is featured by a porosity value of 0.87. The aim consists into study the thermal and fluid-dynamic behaviour of the system. Results show increasing values of the convective heat transfer coefficients for increasing values of Peclet number and particle concentration. This behaviour is more evident at low Peclet number values and Rayleigh number ones.

Solidification With a Throughflow in a Porous Medium

1992 ◽  
Vol 114 (3) ◽  
pp. 675-680
Author(s):  
T. Banerjee ◽  
C. Chang ◽  
W. Wu ◽  
U. Narusawa
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Analytical Solutions ◽  
Peclet Number ◽  
Flow In Porous Media ◽  
Circular Pipe ◽  
Parallel Plates ◽  
Péclet Number ◽  
Solid Interface

A steady throughflow in a porous medium is studied in the presence of a solidified layer due to cooling of the walls. Under the assumption of a moderately sloped melt-solid interface, analytical solutions are obtained for both a flow between parallel plates and a circular pipe. Differences and similarities are examined between the Darcian and the Brinkman porous media, as well as the effects of various parameters, such as the Peclet number, the ratio of diffusivities in the longitudinal and the lateral directions, and a parameter indicating the degree of wall cooling and flow heating, on thermofluid structure of a flow in porous media accompanied by solidification.

Effect of Diffusion on Dispersion

SPE Journal ◽  
2010 ◽  
Vol 16 (01) ◽  
pp. 65-77 ◽  
Author(s):  
Raman K. Jha ◽  
Steven L. Bryant ◽  
Larry W. Lake
Keyword(s):  
Porous Media ◽  
Peclet Number ◽  
Plug Flow ◽  
Nonlinear Dependence ◽  
Hydrodynamic Dispersion ◽  
Direction Transverse ◽  
Péclet Number ◽  
Wide Range ◽  
And Diffusion ◽  
Stream Splitting

Summary It is known that dispersion in porous media results from an interaction between convective spreading and diffusion. However, the nature and implications of these interactions are not well understood. Dispersion coefficients obtained from averaged cup-mixing concentration histories have contributions of convective spreading and diffusion lumped together. We decouple the contributions of convective spreading and diffusion in core-scale dispersion and systematically investigate interaction between the two in detail. We explain phenomena giving rise to important experimental observations such as Fickian behavior of core-scale dispersion and power-law dependence of dispersion coefficient on Péclet number. We track movement of a swarm of solute particles through a physically representative network model. A physically representative network model preserves the geometry and topology of the pore space and spatial correlation in flow properties. We developed deterministic rules to trace paths of solute particles through the network. These rules yield flow streamlines through the network comparable to those obtained from a full solution of Stokes’ equation. Paths of all solute particles are deterministically known in the absence of diffusion. Thus, we can explicitly investigate purely convective spreading by tracking the movement of solute particles on these streamlines. Then, we superimpose diffusion and study dispersion in terms of interaction between convective spreading and diffusion for a wide range of Péclet numbers. This approach invokes no arbitrary parameters, enabling a rigorous validation of the physical origin of core-scale dispersion. In this way, we obtain an unequivocal, quantitative assessment of the roles of convective spreading and diffusion in hydrodynamic dispersion in flow through porous media. Convective spreading has two components: stream splitting and velocity gradient in pore throats in the direction transverse to flow. We show that, if plug flow occurs in the pore throats (accounting only for stream splitting), all solute particles can encounter a wide range of independent velocities because of velocity differences between pore throats and randomness of pore structure. Consequently, plug flow leads to a purely convective spreading that is asymptotically Fickian. Diffusion superimposed on plug flow acts independently of convective spreading (in this case, only stream splitting), and, consequently, dispersion is simply the sum of convective spreading and diffusion. In plug flow, hydrodynamic dispersion varies linearly with the pore-scale Péclet number when diffusion is small in magnitude compared to convective spreading. For a more realistic parabolic velocity profile in pore throats, particles near the solid surface of the medium do not have independent velocities. Now, purely convective spreading (caused by a combination of stream splitting and variation in flow velocity in the transverse direction) is non-Fickian. When diffusion is nonzero, solute particles in the low-velocity region near the solid surface can move into the main flow stream. They subsequently undergo a wide range of independent velocities because of stream splitting, and, consequently, dispersion becomes asymptotically Fickian. In this case, dispersion is a result of an interaction between convection and diffusion. This interaction results in a weak nonlinear dependence of dispersion on Péclet number. The dispersion coefficients predicted by particle tracking through the network are in excellent agreement with the literature experimental data for a broad range of Péclet numbers. Thus, the essential phenomena giving rise to hydrodynamic dispersion observed in porous media are (1) stream splitting of the solute front at every pore, causing independence of particle velocities purely by convection; (2) velocity gradient in pore throats in the direction transverse to flow; and (3) diffusion. Taylor's dispersion in a capillary tube accounts only for the second and third of these phenomena, yielding a quadratic dependence of dispersion on Péclet number. Plug flow in the bonds of a physically representative network accounts only for the first and third phenomena, resulting in a linear dependence of dispersion on Péclet number. When all the three phenomena are accounted for, we can explain effectively the weak nonlinear dependence of dispersion on Péclet number.

scholarly journals A closer look: High-resolution pore-scale simulations of solute transport and mixing through porous media columns

2021 ◽  
Author(s):  
Guillem Sole-Mari ◽  
Diogo Bolster ◽  
Daniel Fernandez-Garcia
Keyword(s):  
Grain Size ◽  
Porous Media ◽  
Peclet Number ◽  
Reactive Transport ◽  
Hydrodynamic Dispersion ◽  
Local Concentration ◽  
Péclet Number ◽  
Incomplete Mixing ◽  
Size Variability ◽  
The Impact

Abstract Mixing is pivotal to conservative and reactive transport behaviors in porous media. Methods for investigating mixing processes include mathematical models, laboratory experiments and numerical simulations. The latter have been historically limited by the extreme computational resources needed for solving flow and transport at the microscopic scale within the complex pore structure of a three-dimensional porous medium, while dealing with a sufficiently large domain in order to generate meaningful emergent continuum-scale observables. We present the results of such a set of virtual column experiments, which have been conducted by taking advantage of modern High-Performance Computing infrastructure and Computational Fluid Dynamics software capable of massively parallel simulations. The computational approach has important advantages such as full control over the experimental conditions as well as high spatial and temporal resolution of measurements. We study the roles of Péclet number and grain size variability on emergent conservative and reactive transport behaviors. Hydrodynamic dispersion results agree with the empirical and theoretical literature and link dispersivity to median grain size, while elucidating the impact of grain-size variability on the critical Péclet number. Reactive transport results also indicate that the relative degree of incomplete mixing is related to the granular material's mean hydraulic radius, and not to the median grain size. When compared to a well-known laboratory experiment with similar configuration, less incomplete mixing is observed in our simulations. We offer a partial explanation for this discrepancy, by showing how an apparent non-linear absorbance-concentration relationship may induce laboratory measurement error in the presence of local concentration fluctuations.

scholarly journals How to use solutions of Advection-Dispersion Equation to describe reactive solute transport through porous media

2021 ◽  
Vol 60 (3) ◽  
pp. 229-240
Author(s):  
Jetzabeth Ramírez Sabag ◽  
Dennys Armando López Falcón
Keyword(s):  
Boundary Condition ◽  
Porous Media ◽  
Solute Transport ◽  
Dispersion Equation ◽  
Analytical Solutions ◽  
Peclet Number ◽  
Reactive Solute Transport ◽  
Péclet Number ◽  
Advection Dispersion ◽  
Outlet Boundary Condition

ResumenLas soluciones de la Ecuación de Advección-Dispersión son usadas frecuentemente para describir el transporte de solutos a través de medios porosos, considerando adsorción en equilibrio, de tipo lineal y reversible. Para indicar algunas sugerencias acerca de este tema, se hizo una revisión de las soluciones analíticas disponibles. Hay soluciones para Problemas con Condiciones de Frontera, de primer y tercer-tipo en la entrada así como de primer y segundo-tipo a la salida. Se analiza el comportamiento de las soluciones equivalentes, para sistemas finitos y semi-infinitos, observando que las soluciones de los sistemas semi-infinitos se aproximan a las correspondientes de los sistemas finitos conforme la condición de frontera de salida en el infinito se aproxima a la ubicación de medición del sistema finito. Solamente se presentan las soluciones analíticas con condiciones de frontera de segundo-tipo a la salida, ya que son iguales a las correspondientes soluciones analíticas con frontera de primer-tipo a la salida, para ambos tipos de condiciones de frontera de entrada usadas. Un análisis paramétrico, basado en el número de Peclet, muestra que todas las soluciones convergen cuando el número de Peclet es mayor que veinte. Los sistemas investigados deben tener un número de Peclet mayor que cinco para usar con confianza las soluciones de la Ecuación de Advección-Dispersión para describir el transporte de soluto en medios porosos.Palabras Clave: Ecuación de Advección-Difusión, Soluciones Analíticas, Transporte de Solutos Reactivos, Medios Porosos.AbstractThe solutions of Advection-Dispersion Equation are frequently used to describe solute transport through porous media when considering lineal and reversible equilibrium adsorption. To notice some warnings about this item, a review of analytical solutions available was done. There are solutions for Boundary Value Problems with first and third-type inlet boundary conditions as well as first and second-type outlet boundary condition. The behavior of equivalent solutions for finite and semi-infinite systems are analyzed, observing that semi-infinite system solutions approximates to the corresponding finite ones as the “infinite” outlet boundary condition approach to the finite measurement location. Because the analytical solutions with a first-type outlet boundary condition are equal to the corresponding analytical solutions with a second-type one, for both inlet boundary condition type used, only the latter is presented. A parametric analysis based on Peclet number shows that all solutions converge for Peclet number greater than twenty. Systems under research must have Peclet number greater than five to use confidently the solutions of Advection-Dispersion Equation to describe reactive solute transport through porous media.Keywords: Advection-Diffusion Equation, Analytical solutions, Reactive Solute Transport, Porous Media.

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