Surface In Porous Medium Research Articles

THE INTERACTION BETWEEN DIESEL SPRAYS AND POROUS MEDIA: EFFECT OF MEDIUM PORE DENSITY AND INJECTION PRESSURE

The unique properties of porous structures have been utilized in different applications, such as gaseous and liquid fuel burners, to enhance the rate of fuel-air mixing and to increase the thermal efficiency. There have been attempts to utilize these unique features of porous structures to improve the combustion process in direct injection diesel engines as well. In this article, the characteristics of high-pressure diesel sprays directly impinging on the surfaces of porous media (PM) of different pore densities mounted in a constant-volume steel chamber are experimentally investigated. A high-speed imaging technique, designed to capture impingement and egress events at the highest possible frame rates to ensure adequate temporal and spatial resolution for the captured images, is used throughout. The results show that injection pressure and medium pore density have strong influence on the spray patterns above and below the porous medium, streamwise and spanwise spray penetrations, and spray-projected area. The increased projected spray area coupled with multijet splitting following egress from the porous medium is an indication of increased air entrainment and improved degree of air-fuel mixture homogenization.

The influence of radiofrequency electromagnetic fields on the adsorption processes in porous media

The experimental results of the polar hydrocarbon adsorption in saturated porous media after radio-frequency (RF) electromagnetic (EM) influence and the thermal heating for comparison are presented. Temperature dependences of the extracted volume of hydrocarbons from models are shown. Comparing the obtained data an additional influence of RF EM field on the desorption of asphaltenes from the porous media surface has been found, that leads to an increase of the extraction of hydrocarbons from the models. The thermodynamic substantiation and mathematical modeling of heat and mass transfer in a saturated porous media under RF EM influence are used as the basis of theoretical study. The equation of sorption kinetics based on the Henry’s Law includes a summand that represents the contribution of thermal and EM fields is to be considered. Researches have discovered that the adsorption process slows down under RF EM field influence, which has a positive effect on the filtration ability of the saturated rock. Investigation of the field influence on the asphaltene adsorption process using atomic force microscopy (AFM) was conducted to identify the mechanism of adsorption and desorption of polar components on the surface of the porous medium under the RF EM field influence.

Reflection and Transmission at the Boundary Surface of Thermoelastic Swelling Porous Media

The present investigation is concerned with the propagation of waves and their reflection and transmission from a plane interface between two different swelling porous thermo elastic half-spaces in welded contact. It is shown that there exist two dilatational waves, thermal wave and two transverse waves propagating with different velocities. The amplitude ratios of various reflected and transmitted waves are computed and presented graphically. It is found that amplitude ratios of reflected and transmitted waves are functions of angle of incidence, frequency and swelling porosity of the media. A particular case has also been deduced from the present investigation. The present investigation has immense application in geophysics and manufactured materials.

Influence of fluid saturation on Rayleigh wave propagation

Based on the existing three-phase poroelastic theory, an analytical solution for Rayleigh wave propagation along the traction free, permeable surface of an elastic porous medium, saturated by two immiscible, viscous, compressible fluids, is derived. The analytical expression of the dispersion equation of Rayleigh wave is found to be a cubic polynomial. Through solving the dispersion equation, it is concluded that three different types of Rayleigh wave exist in such medium to be denoted as R1, R2 and R3, respectively. The influences of water saturation on these Rayleigh waves are numerically studied with varying frequencies from 1 Hz to 1 MHz. The results show that water content has significant effects on the velocities and attenuation of the three waves. The amplitudes of the three waves decay in both x - and z - directions, which are parallel to and perpendicular to the propagation direction of the waves, respectively. The R1 wave travels fastest, and the R3 and R2 waves have the second greatest and smallest phase velocities, respectively. The R1 wave is least attenuated, followed by the R2 and R3 waves. The attenuation coefficients of the R2 and R3 waves versus water saturation and excitation frequency have the similar variation trend.

Effect of Variable Viscosity on Vortex Instability of Mixed Convection Boundary Layer Flow Adjacent to a Non-isothermal Horizontal Surface in a Porous Medium

In this article, we study the effect of variable viscosity on the flow and vortex instability of non-Darcian free convection boundary layer flow on a horizontal surface in a saturated porous medium. The wall temperature is a power function of the distance from the origin. The variation of viscosity is expressed as an exponential function of temperature. The transformed boundary layer equations, which are developed using a non similar solution approach, are solved by means of a finite difference method. The analysis of the disturbance flow is based on linear stability theory. The local Nusselt number, critical Rayleigh number and the associated wave number at the onset of vortex instability are presented over a wide range of wall to ambient viscosity ratio parameters μ*= μw/μ∞. The variable viscosity effect is found to enhance the heat transfer rate and destabilize the flow for liquid heating, while the opposite trend is true for gas heating.

Diffusive counter dispersion of mass in bubbly media

We consider a liquid bearing gas bubbles in a porous medium. When gas bubbles are immovably trapped in a porous matrix by surface-tension forces, the dominant mechanism of transfer of gas mass becomes the diffusion of gas molecules through the liquid. Essentially, the gas solution is in local thermodynamic equilibrium with vapor phase all over the system, i.e., the solute concentration equals the solubility. When temperature and/or pressure gradients are applied, diffusion fluxes appear and these fluxes are faithfully determined by the temperature and pressure fields, not by the local solute concentration, which is enslaved by the former. We derive the equations governing such systems, accounting for thermodiffusion and gravitational segregation effects, which are shown not to be neglected for geological systems-marine sediments, terrestrial aquifers, etc. The results are applied for the treatment of non-high-pressure systems and real geological systems bearing methane or carbon dioxide, where we find a potential possibility of the formation of gaseous horizons deep below a porous medium surface. The reported effects are of particular importance for natural methane hydrate deposits and the problem of burial of industrial production of carbon dioxide in deep aquifers.

Influence of the boundary conditions on capillary flow dynamics and liquid distribution in a porous medium

AbstractAfter depositing a wetting liquid onto a porous medium surface, and under the influence of the capillary pressure, the liquid is imbibed into the porous medium creating a wetted imprint. The flow within the porous medium does not cease once all the liquid is imbibed but continues as a secondary capillary flow, where the liquid flows from large pores into small pores along the liquid interface. The flow is solved using the capillary network model, and the influence of the boundary condition on the liquid distribution within the porous medium is investigated. The pores at the porous medium boundaries can be defined as open or closed pores, where an open pore is checked for the potential threshold condition for flow to take place. In contrast, the closed pore is defined as a static entity, in which the potential condition for flow to take place is never satisfied. By defining the pores at distinct porous medium boundaries as open or closed, one is able to obtain a very different liquid distribution within the porous medium. The liquid saturation profiles along the principal flow direction, ranging from constant to steadily decreasing, to the profile with a local maximum, are found numerically. It is shown that these saturation profiles are also related to the geometrical dimension that is perpendicular to the flow principal direction, and changing the boundary type from open to closed allows the liquid distribution within the porous medium to be controlled. In addition to the liquid distribution, the influence of the boundary conditions on capillary pressure and relative permeability is investigated, where both parameters are not influenced by variation of the boundary condition types. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Convective mass transfer from a horizontal rotating large-diameter cylinder

The local and average convective mass transfer coefficients from the porous medium surface of a horizontal rotating large-diameter cylinder were measured at a constant mass transfer state. Characteristics of local and average Sherwood numbers varying with rotational Reynolds numbers were investigated. Further, the critical Reynolds number ( Re r,cri ) was determined and analyzed. Based on the experimental results, equations correlating the average Sherwood number ( Sh) and critical Reynolds number ( Re r,cri ) with the rotational Reynolds number ( Re r ), Schmidt number ( Sc) and Grashof number ( Gr) have been obtained, respectively.

Capillary force driven primary and secondary unidirectional flow of wetting liquid into porous medium

The flow dynamics of a unidirectional, spontaneous capillary flow of a wetting liquid into porous medium is investigated numerically and experimentally. With respect to whether the sessile liquid is present or absent at the porous medium surface, the flow within porous medium is referred to as primary and secondary flow, respectively. The primary flow ends once the sessile liquid is imbibed by porous medium, while the secondary flow ceases once the equilibrium liquid distribution in porous medium is achieved. Hence, the wetted volumes of porous medium at the end of the primary and secondary flow can differ significantly. Both primary and secondary flow are solved numerically using a dynamic capillary network model with a micro-force balance, which utilizes the general definition of liquid potential at the liquid free interface. The instantaneous liquid flow quantities, including saturation, flow rate, pressure and capillary pressure at the network pores, are calculated numerically and later averaged to obtain the macroscopic flow characteristics. Three distinct pairs porous medium/liquid: (i) and (ii) flow of two different liquids into the same porous medium, and (iii) flow of one of the previously used liquids into a new porous medium are studied experimentally, and the spatial and time saturation profiles are measured. The capillary network structure is adjusted such that the corresponding numerical and experimental saturation profiles agree. From the numerical solution, the multiphase flow parameters: capillary pressure and relative permeability dependences on the liquid saturation are deduced and referred to as intrinsic properties of the secondary flow. Throughout the secondary flow duration time, each pair of porous medium/liquid shows unique dependences of both capillary pressure and relative permeability as functions of the saturation. Finally, the changes in capillary pressure and relative permeability are compared for distinct pairs of porous medium/liquid.

Gravitational Settling Effects on Unit Cell Predictions of Colloidal Retention in Porous Media in the Absence of Energy Barriers

Laboratory column experiments for colloidal transport and retention are often carried out with flow direction oriented against gravity (up-flow) to minimize retention of trapped air. However, the models that underlie colloidal filtration theory (e.g., unit cell models such as the Happel sphere-in-cell and hemispheres-in-cell) typically set flow in the same direction as gravity (down-flow). We performed unit model simulations and experimental observations of retention of colloids with different size and density in porous media in the absence of energy barriers under both up-flow and down-flow conditions. Unit cell models predicted very different deposition (e.g., for large or dense colloids with gravity number N(G) > 0.01 at pore water velocity of 4 m/day) under down-flow versus up-flow conditions, which reflect underlying influences of gravity and flow on simulated colloid trajectories that resulted in very different distributions of attached colloids over the model surfaces. The Happel sphere-in-cell model showed greater sensitivity to flow orientation relative to gravity than the hemispheres-in-cell model. In contrast, experimental results were relatively insensitive to orientation of flow with respect to gravity, as a result of the variety of orientations of flow relative to gravity and to the porous media surface that exist in actual porous media. Notably, the down-flow simulations corresponded most closely to the experimental results (for near neutrally buoyant colloids); which justifies the common practice of comparing up-flow experiments to theoretical predictions developed for down-flow conditions.

Improved Solutions for Porosity and Specific Surface of a Uniform Porous Medium with Attached Film

AbstractImproved solutions for the porosity and specific surface of uniform porous media with the attached film are provided for four regular packing arrangements. These solutions overcome the limitations of previous solutions, which did not cover the full range of film thicknesses to complete occlusion of the pore space in the porous media. The void spaces within the clogged porous media are analyzed geometrically. The exact solutions for the volume and surface area of overlapping shapes and isolated void spaces are formulated in terms of integrals. New polynomial solutions are proposed to replace the numerical integration in the complete solutions to allow easy implementation in numerical models. With the new solutions, both the porosity and specific surface gradually decrease from the initial values to zero when the film increases to complete pore occlusion. These solutions have application in numerical modeling of the growth of organic mass and deposition of inorganic mass in leachate collection syste...

Experimental Investigation of Kerosene Spray Flames in Inert Porous Media near Lean Extinction

This paper presents a study of kerosene spray flames in inert porous media near lean extinction to understand stable operating regimes. The porous media are composed of silicon-carbide-coated carbon–carbon foam type with 8–25 pores per centimeter and 87% porosity. Two porous media, one in the evaporation section and the other in the combustion section located downstream, are used in the experiments. Aviation-grade kerosene was injected upstream of the evaporation porous medium with an air-blast atomizer. Stable flames were established both inside and on the downstream surface of the combustion porous medium. Results show that, in interior combustion mode, the flame was completely contained within the porous medium until extinction. In the surface combustion mode, a decrease of the fuel flow rate resulted in partial flame lift and subsequent extinction. The equivalence ratio near lean extinction in each mode was determined. A Damkohler number (tres/tchem)-based analysis was developed to study the combustio...

A finite volume approach with local adaptation scheme for the simulation of free surface flow in porous media

SUMMARYWe present a method for solving steady‐state flow with a free surface in porous media. This method is based on a finite volume approach and is halfway between a fixed and an adaptive mesh method, taking advantage of both approaches: computational efficiency and localization accuracy. Most of the mesh remains fixed during the iterative process, while the cells in contact with the free surface (free surface cells) are being reshaped. Based on this idea, we developed two methods. In the first one, only the volumes of the free surface cells are adapted. In the second one, the computational nodes of the free surface cells are relocated exactly at the free surface. Both adaptations are designed for a better application of the free surface boundary conditions. Implementation details are given on a regular finite volume mesh for the case of homogeneous and heterogeneous rectangular dams in 2D and 3D. Accuracy and convergence properties of the proposed approach are demonstrated by comparison with an analytical solution and with existing references. Copyright © 2011 John Wiley & Sons, Ltd.

A Study of Double Diffusive Free Convection From a Corrugated Vertical Surface in a Darcy Porous Medium Under Soret and Dufour effects

This study examines the influence of Soret and Dufour effects on double diffusive free convection due to wavy vertical surface immersed in a fluid saturated semi-infinite porous medium under Darcian assumptions. A wavy to flat surface transformation is applied, and the resulting coupled nonlinear partial differential equations under Boussinesq approximation are reduced to boundary layer equations. A finite difference scheme based on the Keller-Box approach has been used in conjunction with block-tridiagonal solver for obtaining the solution for boundary layer equations. Results from the current study are compared with those available in literature. The effect of various parameters such as wave amplitude (a), Lewis number (Le), buoyancy ratio (B), and Soret (Sr) and Dufour (Df) numbers are analyzed through local and average Nusselt number, and local and average Sherwood number plots.

Soret and Dufour effects on free convection boundary layers over an inclined wavy surface in a porous medium

The problem of free convection boundary layer flow near an inclined wavy surface in a fluid saturated porous medium with Soret and Dufour effects has been solved using boundary layer approximations. A suitable coordinate transformation is used to transform the complex wavy surface to a smooth surface, and the obtained boundary layer equations are solved by the cubic spline collocation method. Effects of Soret parameter, Dufour parameter, angle of inclination, Lewis number, buoyancy ratio, and wavy geometry on the heat and mass transfer characteristics are studied. Results show that increasing the Soret parameter leads to a greater fluctuation of the local Nusselt number with the streamwise coordinate and a smaller fluctuation of the local Sherwood number with the streamwise coordinate. Moreover, as the Dufour parameter increases, the fluctuation of the local Sherwood number with the streamwise coordinate is enhanced, while the amplitude of fluctuation of the local Nusselt number with the streamwise coordinate is reduced. An increase in the Dufour parameter tends to decrease the dimensionless total heat transfer rate while an increase in the Soret parameter tends to decrease the dimensionless total mass transfer rate.

Drying Experiments in a Hydrophobic Model Porous Medium in the Presence of a Dissolved Salt

AbstractThe evaporation of an aqueous NaCl solution in a hydrophobic two‐dimensional model porous medium was studied experimentally. The process is characterized by the formation of efflorescence at the porous medium surface. It is shown that the onset of efflorescence formation and its growth depends on the initial solution concentration. The experiments show that the invasion patterns are little affected by the presence of salt, but that the efflorescence contributes to gradually increase of the evaporation rate as the initial concentration in salt is increased. Then, a second phase was identified where the efflorescence dries out and drying becomes very slow. Results suggest that there exists an initial concentration marking the transition between the regime with high impact of efflorescence and the regime with low impact of efflorescence.

Effect of mass transfer on the free convective flow through a porous medium with variable permeability in slip flow regime with couple stresses

This paper examines the problem of mass transfer on MHD unsteady free convective flow of a polar fluid through a porous medium of variable permeability bounded by an infinite horizontal porous plate in slip flow regime. The permeability of the porous medium decreases exponentially with time about a constant mean. Using perturbation technique the expressions for the velocity distribution, mean angular velocity of rotation of particles, concentration distribution and skin friction are obtained. The effects of permeability parameter K0, Magnetic parameter M, Prandtl number Pr , Schimdt number Sc ,and Grashof number Gr ,Modified Grashof number Gm entering into the problem on velocity, temperature distribution and concentration distribution are shown graphically and discussed numerically. It can be observed that this velocity decreases with the increase in M, Pr, Sc and increases with the increase in K0, Gr, Gm. Temperature and Concentration decreases with the increase in the value of Pr and Sc respectively. INTRODUCTION The convection problem in a porous medium has important application in geothermal reservoirs and geothermal energy extractions. It is obvious that in order to utilize the geothermal energy to maximum, one should have a complete and precise knowledge about the amount of perturbations needed to generate convection current in geothermal fluids. Also the knowledge of the quantity of perturbation is essential to entreat convection current in mineral fluids that is found in the earth’s crust helps one to utilize minimal energy to extract the minerals. Cheng and Lau[1] and Cheng and Teckchandani [2] obtained numerical solutions for the convective flow in a porous medium bounded by two isothermal parallel plates in the presence of withdrawl of the fluid. All the above mentioned studies treat the permeability and the conductivity or thermal resistance of the medium as constant or neglect the effect of porosity. Lai and Kulacki [6] studied Coupled heat and mass transfer by natural convection from vertical surfaces in porous media. Lin and Wu[7] discussed Coupled heat and mass transfer by laminar natural convection from vertical plate. Malasetty and Gaikwad[8] investigated effect of cross diffusion on double diffusion convection in the presence of horizontal gradients. Yan et. al [11] have discussed Simultaneous heat and mass transfer in laminar mixed convection flows between vertical parallel plate with asymmetric heating. Yan[12] studied Turbulent mixed convection heat and mass transfer past a vertical porous plate. Mazumdar and Deka[9] investigated MHD flow past an impulsively started infinite vertical plate in presence of thermal radiation. In geothermal region situation may arise when the flow becomes unsteady and sliping at the boundary may take place as well. In such situation of slip flow, ordinary continuum approach fails to yield satisfactory results. Many authors have solved problems taking slip conditions at the boundary. Jain and Teneja [3] solved the problem of magnetopolar flow through a porous medium in slip flow regime. Khandelwal et al [5] have studied effect of couple stresses on the flow through a porous medium with variable permeability in slip flow regime. Varshney et. al.[10] have discussed effect of heat transfer on the flow through a porous medium with variable permeability in slip flow regime with couple stress. Our problem under study is an extension of the problem of Varshney et. al.[10] with mass transfer. The effects of different parameter entering into the problem viz. Permeability parameter Ko, Magnetic Am. J. Sci. Ind. Res., 2011, 2(3): 469-477 470 parameter M, Prandtl number Pr , Schimdt number Sc ,and Grashof number Gr ,Modified Grashof number Gm entering into the problem on velocity, temperature distribution and concentration distribution are shown graphically and discussed numerically FORMULATION AND SOLUTION OF THE PROBLEM Let us consider the unsteady flow of a polar fluid through a porous medium of variable permeability in slip flow regime past an infinite horizontal porous plate in presence of a transverse magnetic field. The external velocity of the fluid is assumed as nt 0 U [1 e ] − + e . The flow is chosen to be at small magnetic Reynolds number which enables us to neglect the induced magnetic field. The x-axis is taken along the plate and y-axis normal to it. Under these conditions the equations which govern the flow are: v 0 y ∂ = ∂ (1)

An integral treatment for combined heat and mass transfer by mixed convection along vertical surface in a saturated porous medium

Combined free and forced convection heat and mass transfer over an impermeable vertical surface embedded in a saturated porous medium is considered. A similarity transformation has been used to study the mixed convection boundary-layer flow over a semi-infinite vertical flat plate. Integral solutions are derived for the coupled nonlinear similarity equations of coupled heat and mass transfer in porous media for the case where the free stream velocity and temperature and concentration near the wall are kept constant. The governing parameters for the problem under consideration are the Lewis number Le, the buoyancy ratio N and mixed convection parameter (). The results for the heat and mass transfer coefficients in terms of Nusselt and Sherwood numbers are represented graphically for the various values of governing parameters of the problem. The heat and mass transfer in the boundary layer region has been analyzed for aiding and opposing flows. Key words: Convection in porous media, heat and mass transfer, integral method, boundary layer.

Temporal Changes in Aqu/C60 Physical–Chemical, Deposition, and Transport Characteristics in Aqueous Systems

Little is known about how temporal changes in the physical-chemical properties of C₆₀ aggregates formed in aqueous systems (termed aqu/C₆₀) can impact transport pathways contributing to ecological exposures. In this study three aqu/C₆₀ suspensions of short-term (100 days), intermediate-term (300 days), and long-term (1000 days) water exposure were first characterized for particle size distribution, water/toluene phase distribution, and surface chemistry. Then, aqu/C₆₀ deposition to a model silica surface and transport in porous media were studied by quartz crystal microbalance (QCM) and saturated sand columns. As suspension time increased, aqu/C₆₀ particle size shifted to a larger size range as determined by asymmetric flow field-flow fractionation (AF4) and the aqu/C₆₀ distribution to toluene was reduced, likely due to surface polarization as revealed by nuclear magnetic resonance (NMR) and UV-visible spectroscopy of the aqu/C₆₀ suspensions. Additionally, the deposition to silica surfaces in both QCM and column studies decreased with increased water exposure time. Although a small increase in aqu/C₆₀ aggregate size with time may partially explain the greater transport of the long-term aqu/C₆₀ because of the decreased collector efficiency for larger submicrometer particles, the polarization of the aqu/C₆₀ (thus a more hydrophilic surface) revealed by the toluene/water phase distribution and confirmed by NMR, is considered the determining factor.

Jet impingement cooling of a horizontal surface in an unconfined porous medium: Mixed convection regime

Two-dimensional slot jet impingement cooling of an isothermal horizontal surface immersed in an unconfined porous medium is simulated numerically to gain insight into thermal characteristics under mixed convection conditions with the limitation of the Darcy model. The jet direction is considered to be perpendicular from the top to the horizontal heated element; therefore, the jet flow and the buoyancy driven flow are in opposite directions. The results are presented in the mixed convection regime with wide ranges of the governing parameters: Péclet number (1 ⩽ Pe ⩽ 1000), Rayleigh number (10 ⩽ Ra ⩽ 100), half jet width (0.1 ⩽ D ⩽ 0.5), and the distance between the jet and the heated portion (0.1 ⩽ H ⩽ 1.0). It is found that the average Nusselt number increases with increase in either Rayleigh number or jet width for high values of Péclet number. The average Nusselt number also increases with decrease in the distance between the jet and the heated portion. It is shown that mixed convection mode can cause minimum average Nusselt number at two values of Péclet number and a maximum average Nusselt number occurs in between theses two Péclet numbers at higher Rayleigh number due to counteraction of jet flow against buoyancy driven flow. Hence careful consideration must be given while designing a system of jet impingement cooling through porous medium.