Moisture Effective Diffusivity in Porous Media with Different Physical Properties

2006 ◽  
pp. 207-212
Author(s):  
Miranda M.N.N. ◽  
M.A. Silva
Keyword(s):  
Porous Media ◽  
Physical Properties ◽  
Effective Diffusivity ◽  
Moisture Effective Diffusivity

Moisture Effective Diffusivity in Porous Media with Different Physical Properties

2006 ◽  
Vol 258-260 ◽  
pp. 207-212
Author(s):  
Miranda M.N.N. ◽  
M.A. Silva
Keyword(s):  
Porous Media ◽  
Diffusion Coefficient ◽  
Moisture Content ◽  
Mass Transport ◽  
Physical Properties ◽  
Pore Size ◽  
Structural Properties ◽  
Effective Diffusivity ◽  
Nay Zeolite ◽  
Moisture Effective Diffusivity

In the drying of porous media, the mass transport occurs in the pores as well as on the surface of the solid. The mechanisms involved can take place simultaneously, influenced by the predominant one and can change depending on the moisture content. In this work, the moisture effective diffusivity was estimated in solids with distinct structural properties in order to verify the predominant mechanisms according to the moisture content, analyzing the influence of the physical properties. The materials studied were NaY Zeolite, Kaolin, Silica and Alumina. The results of diffusion coefficient present a minimum at low moisture content that can be related to pore size.

Measurement of the Effective Diffusivity in Porous Media by the Diffusion Cell Method

1996 ◽  
Vol 38 (2) ◽  
pp. 189-247 ◽  
Author(s):  
IN-SOO PARK∗ ◽  
DUONG D. DO ◽  
ALIRIO E. RODRIGUES
Keyword(s):  
Porous Media ◽  
Effective Diffusivity ◽  
Diffusion Cell ◽  
Cell Method

A FRACTAL MODEL FOR PREDICTING OXYGEN EFFECTIVE DIFFUSIVITY OF POROUS MEDIA WITH ROUGH SURFACES UNDER DRY AND WET CONDITIONS

Fractals ◽  
2021 ◽  
pp. 2150076
Author(s):  
BOQI XIAO ◽  
QIWEN HUANG ◽  
BOMING YU ◽  
GONGBO LONG ◽  
HANXIN CHEN
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Oxygen Diffusion ◽  
Water Saturation ◽  
Rough Surfaces ◽  
Effective Diffusivity ◽  
Fractal Model ◽  
Relative Roughness ◽  
Oxygen Diffusivity ◽  
Dry And Wet Conditions

Oxygen diffusion in porous media (ODPM) with rough surfaces (RS) under dry and wet conditions is of great interest. In this work, a novel fractal model for the oxygen effective diffusivity of porous media with RS under dry and wet conditions is proposed. The proposed fractal model is expressed in terms of relative roughness, the water saturation, fractal dimension for tortuosity of tortuous capillaries, fractal dimension for pores, and porosity. It is observed that the normalized oxygen diffusivity decreases with increasing relative roughness and fractal dimension for capillary tortuosity. It is found that the normalized oxygen diffusivity increases with porosity and fractal dimension for pore area. Besides, it is seen that that the normalized oxygen diffusivity under wet condition decreases with increasing water saturation. The determined normalized oxygen diffusivity is in good agreement with experimental data and existing models reported in the literature. With the proposed analytical fractal model, the physical mechanisms of oxygen diffusion through porous media with RS under dry and wet conditions are better elucidated. Every parameter in the proposed fractal model has clear physical meaning, with no empirical constant.

Numerical Model of Complex Porous Media

2002 ◽  
Author(s):  
Andre´ Chambarel ◽  
Herve´ Bolvin
Keyword(s):  
Porous Media ◽  
Numerical Model ◽  
Physical Properties ◽  
Space Distribution ◽  
Partial Differential ◽  
Differential Problem ◽  
Classical Models ◽  
Element Approach ◽  
Statistical Approaches ◽  
Percolation Phenomenon

In complex porous media we often notice a percolation phenomenon [KIR 71] [GRI 89]. Usually these media present discontinuous characteristics and a random space distribution [LET 00] [BIR 95]. There results that the classical models based on the resolution of a partial differential problem become inefficient because we have non-derivable function [MAU 01]. Statistical approaches based on the resolution of partial differential problems pose notably the questions concerning the continuity of the functions representing the physical properties of the medium. In this work we propose to study a numerical model of porous media based on a mixture of 2 components in a percolation context. In practice, the main difficulty is based on the complex physical properties. We present also a model of homogenization. Our numerical model is based on the Finite Element approach.

scholarly journals A homogenised model for flow, transport and sorption in a heterogeneous porous medium

2021 ◽  
Vol 932 ◽  
Author(s):  
L.C. Auton ◽  
S. Pramanik ◽  
M.P. Dalwadi ◽  
C.W. MacMinn ◽  
I.M. Griffiths
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Multiple Scales ◽  
Effective Diffusivity ◽  
Rectangular Lattice ◽  
Mathematical Framework ◽  
Anisotropic Flow ◽  
Flow And Transport ◽  
Soft Porous Media ◽  
The Impact

A major challenge in flow through porous media is to better understand the link between microstructure and macroscale flow and transport. For idealised microstructures, the mathematical framework of homogenisation theory can be used for this purpose. Here, we consider a two-dimensional microstructure comprising an array of obstacles of smooth but arbitrary shape, the size and spacing of which can vary along the length of the porous medium. We use homogenisation via the method of multiple scales to systematically upscale a novel problem involving cells of varying area to obtain effective continuum equations for macroscale flow and transport. The equations are characterised by the local porosity, a local anisotropic flow permeability, an effective local anisotropic solute diffusivity and an effective local adsorption rate. These macroscale properties depend non-trivially on the two degrees of microstructural geometric freedom in our problem: obstacle size and obstacle spacing. We exploit this dependence to construct and compare scenarios where the same porosity profile results from different combinations of obstacle size and spacing. We focus on a simple example geometry comprising circular obstacles on a rectangular lattice, for which we numerically determine the macroscale permeability and effective diffusivity. We investigate scenarios where the porosity is spatially uniform but the permeability and diffusivity are not. Our results may be useful in the design of filters or for studying the impact of deformation on transport in soft porous media.

scholarly journals The effect of temperature on the okra drying process: kinetic study and physical properties of powders

2021 ◽  
pp. 649-660
Author(s):  
Francislaine Suelia dos Santos ◽  
Rossana Maria Feitosa de Figueirêdo ◽  
Alexandre José de Melo Queiroz ◽  
Ana Raquel Carmo de Lima ◽  
Thalis Leandro Bezerra de Lima
Keyword(s):  
Free Energy ◽  
Physical Properties ◽  
Gibbs Free Energy ◽  
Effective Diffusion ◽  
Effective Diffusivity ◽  
Effect Of Temperature ◽  
Drying Temperature ◽  
Drying Kinetic ◽  
Drying Models ◽  
The One

This study aimed to evaluate the effect of drying temperature (50, 60, 70 and 80 °C) on okra dehydration by comparing its powder’s physical properties obtained from a sample produced by a lyophilization process. Ten drying models were adjusted to the experimental data of the drying kinetics. As a result, effective diffusivity and activation energy were determined in addition to thermodynamic parameters: entropy, enthalpy and Gibbs free energy. A physical characterization, as well as the pigments and colorimetry analyses of the aforementioned powders were made, by comparing them with samples produced by lyophilization. The powders were characterized for hygroscopicity, solubility, wettability, apparent and compacted density, fluidity and cohesiveness, pigments, colorimetric, morphological analysis (SEM) and X-ray diffraction. Midilli model was the one that best adjusted to the drying kinetic curves. There was a booster in the effective diffusion coefficient with the increase of temperature. Enthalpy and entropy were reduced with the increase of both drying temperature and Gibbs free energy. The powders presented high luminosity, and the lyophilized powder had higher pigments retention and greater solubility. All powders presented poor fluidity and intermediate cohesiveness, with amorphous, irregular and asymmetric particles. Thus, from the present study it was possible to evaluate the best drying method, the one that should be applied for the drying of okra, considering the costs involved, its quality and the final application of the product, meeting the specific needs of each consumer

scholarly journals Drying kinetics of fermented grape pomace: Determination of moisture effective diffusivity

2016 ◽  
Vol 20 (8) ◽  
pp. 763-768 ◽  
Author(s):  
Kricelle M. Deamici ◽  
Lucas C. de Oliveira ◽  
Gabriela S. da Rosa ◽  
Elizangela G. de Oliveira
Keyword(s):  
Experimental Data ◽  
Effective Diffusivity ◽  
Drying Kinetics ◽  
Grape Pomace ◽  
Desorption Isotherms ◽  
Drying Curves ◽  
Gab Model ◽  
Kinetics Of ◽  
Moisture Effective Diffusivity

ABSTRACT The aim of this study was to obtain the equilibrium moisture content of grape (variety ‘Tannat’) pomace through desorption isotherms, to evaluate the drying kinetics, determine the coefficient of effective diffusivity and physico-chemically characterize the grape pomace and the product obtained after drying. The desorption isotherms were determined at 50, 60 and 70 ºC and the experimental data were fitted using the GAB model (Gugghenheim, Anderson and de Boer). Drying was evaluated using a 22 factorial experimental design with three center points and effective diffusivity was obtained through the diffusion model of Fick’s second law. The grape pomace was characterized regarding the contents of moisture, protein, carbohydrates, lipids, ash and dietary crude fiber. The obtained isotherms showed sigmoid shape and the experimental data fitted well to the GAB model. The drying curves showed only a decreasing rate period. The effective diffusivity values were within the range for organic materials. Dry grape pomace showed high contents of protein and fiber and can be used in the development of new products, in order to increase the nutritional content and add value to this byproduct.

scholarly journals Dryout and Replenishment of Bottom-Heated Saturated Porous Media with an Overlying Plain Water Layer

2018 ◽  
Vol 8 (12) ◽  
pp. 2607
Author(s):  
Montserrat Carbonell ◽  
Luis Virto ◽  
Pedro Gamez-Montero
Keyword(s):  
Porous Media ◽  
Physical Properties ◽  
Thermal State ◽  
Water Layer ◽  
Coarse Sand ◽  
Solid Matrix ◽  
Plain Water ◽  
Liquid Phases ◽  
State Evolution ◽  
The Stability

The aim of this paper is to elucidate the influence of the physical properties of both phases—solid matrix and saturating liquid—of bottom-heated porous media with an overlying plain water layer. The dryout, the stability of the system’s water layer-vapor region, and the thermal state evolution are studied. The porous media under study are a bronze powder saturated by water, and a solution of surfactant and coarse sand saturated by the same liquids. From the experimental data obtained, a theoretical approach is carried out to describe the dryout and rewetting process. The influence of the nature and physical properties of the solid and liquid phases is also analyzed, with special attention to the addition of surfactant in the saturating liquid.

Sign in / Sign up

Export Citation Format

Share Document