scholarly journals Computational implementation of interfacial kinetic transport theory for water vapour transport in porous media

2014 ◽  
Vol 470 (2161) ◽  
pp. 20130278 ◽  
Author(s):  
Bashar Albaalbaki ◽  
Reghan J. Hill
Keyword(s):  
Porous Media ◽  
Aspect Ratio ◽  
Water Vapour ◽  
Transport Theory ◽  
Effective Diffusivity ◽  
Water Vapour Permeability ◽  
Vapour Transport ◽  
Computational Framework ◽  
Vapour Permeability ◽  
Water Vapour Transport

A computational framework is developed for applying interfacial kinetic transport theory to predict water vapour permeability of porous media. Modified conservation equations furnish spatially periodic disturbances from which the average flux and, thus, the effective diffusivity is obtained. The equations are solved exactly for a model porous medium comprising parallel layers of gas and solid with arbitrary solid volume fraction. From the microscale effective diffusivity, a two-point boundary-value problem is solved at the macroscale to furnish the water vapour transport rate in membranes subjected to a finite RH differential. Then, the microscale model is implemented using a computational framework (extended finite-element method) to examine the role of particle size, aspect ratio and positioning for periodic arrays of aligned super-ellipses (model particles that pack with high density). We show that the transverse water vapour permeability can be reduced by an order of magnitude only when fibres with a high-aspect ratio cross section are packed in a periodic staggered configuration. Maximum permeability is achieved at intermediate micro-structural length scales, where gas-phase diffusion is enhanced by surface diffusion, but not limited by interfacial-exchange kinetics. The two-dimensional computations demonstrated here are intended to motivate further efforts to develop efficient computational solutions for realistic three-dimensional microstructures.

scholarly journals On molecular diffusion in nanostructured porous media: interfacial exchange kinetics and surface diffusion

2012 ◽  
Vol 468 (2146) ◽  
pp. 3100-3120 ◽  
Author(s):  
Bashar Albaalbaki ◽  
Reghan J. Hill
Keyword(s):  
Porous Media ◽  
Surface Diffusion ◽  
Water Vapour ◽  
Molecular Diffusion ◽  
Effective Diffusivity ◽  
Cellulose Fibre ◽  
Vapour Transport ◽  
Moisture Concentration ◽  
Water Vapour Transport ◽  
Exchange Kinetics

Water-vapour transport in nanostructured composite materials is poorly understood because diffusion and interfacial exchange kinetics are coupled. We formulate an interfacial balance that couples diffusion in dispersed and continuous phases to adsorption, absorption and interfacial surface diffusion. This work is motivated by water-vapour transport in cellulose fibre-based barriers, but the model applies to nanostructured porous media such as catalysts, chromatography columns, nanocomposites, cementitious structures and biomaterials. The interfacial balance can be applied in an analytical or a computational framework to porous media with any microstructural geometry. Here, we explore its capabilities in a model porous medium: randomly dispersed solid spheres in a continuous (humid) gas. We elucidate the roles of equilibrium moisture uptake, solid, gas and surface diffusion coefficients, inclusion size and interfacial exchange kinetics on the effective diffusivity. We then apply the local model to predict water-vapour transport rates under conditions in which the effective diffusivity varies through the cross section of a dense, homogeneous membrane that is subjected to a finite moisture-concentration gradient. As the microstructural length scale decreases from micrometres to nanometres, interfacial exchange kinetics and surface diffusion produce a maximum in the tracer flux. This optimal flux is flanked, respectively, by interfacial-kinetic- and diffusion-limited transport at smaller and larger microscales.

scholarly journals A critique on ‘A Boltzmann transformation method for investigation of water vapour transport in building materials’

2020 ◽  
pp. 174425912098004
Author(s):  
Hans Janssen
Keyword(s):  
Transport Properties ◽  
Water Vapour ◽  
Reference Values ◽  
Building Materials ◽  
Transformation Method ◽  
Dynamic Measurement ◽  
Vapour Transport ◽  
Vapour Permeability ◽  
Water Vapour Transport

In 2011, this journal published the paper ‘A Boltzmann transformation method for investigation of water vapour transport in building materials’, proposing a dynamic measurement of building materials’ vapour permeability via the Boltzmann-Matano method. This critique points out that this publication is flawed, since it proposes an invalid approach and presents erroneous results. The analysis first shows that the presented vapour permeability values cannot be reproduced and instead far lower vapour transport properties are obtained. These corrected outcomes are however also much below the dry-cup reference values, and it is established that these deviations stem from the invalidity of the proposed approach, due to disregarding the material’s hygroscopicity. Given its erroneous results and invalid approach, it is finally recommended to have the paper officially retracted by the journal.

scholarly journals Barrier Properties of Footwear Packages against Water Vapour Transport and Thermal Resistance

2021 ◽  
Vol 29 (1(145)) ◽  
pp. 70-74
Author(s):  
Wioleta Serweta ◽  
Małgorzata Matusiak ◽  
Justyna Wójcik
Keyword(s):  
Thermal Resistance ◽  
Water Vapour ◽  
Polyurethane Foam ◽  
Three Dimensional ◽  
Barrier Properties ◽  
Dimensional Structure ◽  
Vapour Transport ◽  
Knitted Fabrics ◽  
Vapour Permeability ◽  
Water Vapour Transport

In this paper the authors focused on the analysis of relations between the material (such as knitted fabrics with a two and three dimensional structure) configurations and hygienic parameters of packages. In order to measure hygienic properties, the water vapour permeability and absorption were both used with the thermal resistance capacity. The connector role in the packages measured was played by air (in the case of two – layered package), polyurethane foam and three – dimensional knitted fabric with similar characteristics to polyurethane foam in respect of the mass per square metre and thickness. On the basis of the results obtained, a statistical model of the barrier was created and the changes in water vapour transport process described.

Effect of Test Methods on Apparent Moisture Vapour Transmission of P/V and P/C Fabrics

2014 ◽  
Vol 18 (1) ◽  
pp. 71-79
Author(s):  
Subhasis Das ◽  
V. K. Kothari
Keyword(s):  
Water Vapour ◽  
Transmission Rate ◽  
Test Methods ◽  
Test Method ◽  
Transport Rate ◽  
Vapour Transport ◽  
Vapour Permeability ◽  
Water Vapour Transport ◽  
Moisture Vapour

The moisture vapour permeability properties of a series of almost similar polyesterviscose (P/V) and polyester-cotton (P/C) blended fabrics are investigated. The water vapour transport rate greatly differs depending on the principle of the test methods, even when other parameters are nearly identical, such as air permeability, areal density, porosity and thickness. The water absorption characteristics of fibre seem to be the most important in determining the overall water vapour transport rate. Substitution of polyester for viscose and cotton in P/V and P/C blended fabrics respectively, reduces the water transport rate of the fabrics in a long term method. It is found that the P/C blended fabrics show greater water vapour transport than the corresponding P/V fabrics when a long term test method is used; however, the P/V fabrics show relatively higher water vapour permeability than the P/C fabrics when short duration tests are carried out by using the Permetest and moisture vapour transmission rate (MVTR) cell methods

Using Control Chart to Detect Abnormal Changes in the Permeability

2013 ◽  
Vol 779-780 ◽  
pp. 319-322
Author(s):  
Ming Hung Shu ◽  
Jui Chan Huang ◽  
Thanh Lam Nguyen ◽  
Bi Min Hsu
Keyword(s):  
Water Vapour ◽  
Average Run Length ◽  
Stable Process ◽  
Critical Factor ◽  
Water Vapour Permeability ◽  
Control Signal ◽  
Process Mean ◽  
Vapour Permeability ◽  
Practical Applications ◽  
Printing Papers

Water-vapour permeability is a critical factor of writing/ printing papers in most of practical applications; but how to monitor the manufacturing process to keep the key characteristic of the paper in control is still understudied. Therefore, in this paper, in order to monitor the water-vapour permeability of writing/ printing papers, MaxGWMA chart is first suggested due to its best effectiveness in terms of average run length performance and its high capability of detecting small shifts in the process mean and variability as well as identifying the source and the direction of an out-of-control signal. By using MaxGWMA chart, assignable causes of any out-of-control signal should be deeply examined so as to have proper corrective actions undertaken to either eliminate them from the process or reduce the variability induced by them to make the papers consistently manufactured under a stable process.

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