E.F. Kaasschieter

Saline absorption in calcium-silicate brick observed by NMR scanning

The absorption of a 4 M NaCl solution in calcium-silicate brick was investigated by nuclear magnetic resonance scanning. This method has the advantage that quasi-simultaneously both the moisture and the Na profile can be measured during absorption. It was found that during the absorption process the Na ions clearly stay behind and hardly any Na is present near the wetting front. This is caused by binding of the Na ions to the pore surface. It is shown that both the moisture and the Na profiles during absorption can be scaled using the Boltzmann-Matano transformation.

On the risk of cracking in clay drying

Based on the assumptions related to porous media, the governing equations of mass transfer and static equilibrium are presented. The mechanical stresses generated by the drying strains are expressed according to the linear-elastic model. The von Mises cracking criterion is introduced in order to locate the area where risk for cracking occurs. The model is applied to the drying of Kaolin clay. Moisture and solid displacements results as well as evolutions of the criterion are exposed. The danger of cracking is the highest at the beginning of the drying, since the yield stress is low. The criterion reaches its peak value during the first hour and at a particular point, located on the surface, exactly in-between two corners. Moisture evolution has been measured by means of nuclear magnetic resonance (NMR) imaging, during the drying of a piece of Kaolin clay. The diffusion coefficient is evaluated from these experimental results. Finally, the model is used to reproduce them.

Solving the Buckley–Leverett equation with gravity in a heterogeneous porous medium

Immiscible two‐phase flow in porous media can be described by the fractional flow model. If capillary forces are neglected, then the saturation equation is a non‐linear hyperbolic conservation law, known as the Buckley–Leverett equation. This equation can be numerically solved by the method of Godunov, in which the saturation is computed from the solution of Riemann problems at cell interfaces. At a discontinuity of permeability this solution has to be constructed from two flux functions. In order to determine a unique solution an entropy inequality is needed. In this article an entropy inequality is derived from a regularisation procedure, where the physical capillary pressure term is added to the Buckley‐Leverett equation. This entropy inequality determines unique solutions of Riemann problems for all initial conditions. It leads to a simple recipe for the computation of interface fluxes for the method of Godunov.

Analytic solution for the non-linear drying problem

Recently, Landman, Pel and Kaasschieter proposed an analytic solution for a non-linear drying problem using a quasi-steady state solution. This analytic model for drying is explained here. An important consequence of this model is that the drying front has a constant speed when it is entering the material. This is also observed in experiments. On the basis of this constant drying front speed comparisons are made between the analytic model and numerical simulations. Finally comparisons are made between measured moisture profiles during drying and the analytic model.

The influence of shrinkage on drying behaviour of clays

Abstract A correct description of the evolution of moisture concentration profiles in shrinking materials is complicated by the influence of shrinkage on mass transfer. Shrinkage has to be accounted for in the diffusion equation. Simulations have been performed for three types of shrinkage: isotropic, unidirectional and no shrinkage. Since many materials show isotropic shrinkage behaviour, unidirectional and no shrinkage should be considered as approximations of the actual material behaviour. Various numerical simulations show that for clays the influence of the type of shrinkage on drying curves is small.

Squeezing a sponge : a three-dimensional solution in poroelasticity

A three-dimensional solution is derived for the fluid flow in a deformable porous medium. It is assumed that the deformation of the medium is described by Hookes law and the flow of the fluid by Darcys law, i.e. the theory of poroelasticity applies. The governing equations are completed by suitable boundary conditions such that a compressed saturated cubic sponge is modelled. The solution is a three-dimensional generalisation of the one-dimensional solution of Terzaghi. A two-dimensional plane strain solution is derived also. Both solutions give excellent possibilities to test numerical codes.

Ion transport in porous media studied by NMR

Moisture and salt transport in masonry can give rise to damages. Therefore a detailed knowledge of the moisture and salt transport is essential for understanding the durability of masonry. A special NMR apparatus has been made allowing quasi-simultaneous measurements of both moisture and Na profiles in porous building materials. Using this apparatus both the absorption of a 4 M NaCl solution in a calcium silicate brick and the drying of a 3 M NaCl capillary saturated fired-clay brick have been studied. It was found that during the absorption process the Na ions clearly stay behind, which this is caused by adsorption of these ions to the pore surface. For the drying it was found that at the beginning of the drying process the ions accumulate near the surface. As the drying rate decreases, diffusion becomes dominant and the ion profile levels off again.

Numerical modelling of Cartilage as a Deformable Porous Medium

Soft biological tissues, like cartilage and intervertebral disc tissue, exhibit swelling and shrinking behaviour due to mechanical and chemical loadings. A mixture theory is used to simulate this behaviour.

Numerical Fractional Flow Modelling Of Inhomo- Geneous Air Sparging

Spillage of organic compounds into the subsurface environment can result in costly remediation. As a possibly effective remediation technique, the injection of air into the groundwater (air sparging) has gained attention. The injected air migrates towards the unsaturated zone, volatising contaminants from the groundwater and delivering oxygen to biota for biodegradation (see The two-phase flow of air and water turns out to be predominantly driven by convection. It is modelled using a fractional flow approach, which yields a hyperbolic governing equation for the air saturation. The Godunov method is evaluated for the numerical solution of the one-dimensional problem in an inhomogeneous porous medium. 1 Governing equations Air sparging is a three-dimensional two-phase flow process of air and water, starting in the saturated zone of a porous medium and passing to the unsaturated zone. Transactions on Ecology and the Environment vol 17,