A.J.J. van der Zanden

Isothermal moisture transport in partially saturated porous media

ABSTRACT The prediction of a hydrodynamic model for the isothermal transport of liquid in partially saturated porous media is compared with experimentally obtained values of water transport in clay. The transport obeys the diffusion equation, The diffusion coefficient is described as a function of porosity, permeability and pore size distribution. The comparison indicates that the model needs some refinement.

An iterative procedure to obtain the concentration dependency of the diffusion coefficient from the space-averaged concentration vs time

A numerical method is presented to obtain the dependency of the diffusion coefficient on the concentration when the space-averaged concentration is known as a function of time. The method uses a correction of computed concentration profiles and a successive substitution of a diffusion coefficient dependency to approach the true dependency.

A possible revision of the results of a model for moisture transport in partially saturated porous media

ABSTRACT It is shown that the discrepancy between the prediction of the model of van der Zanden et al. for the diffuslion coefficient of liquid in porous materials and experiments can be explained with inaccuracies in the measurement of the pore size distribution or small cracks in the drying porous material.

Determination of the Diffusion Coefficient of Water in Brick with a Simple Mass Distribution Technique

A method is presented for the determination of the diffusion coefficient of water in brick. A brick is sealed on five sides to ensure one-dimensional water transport. The wet brick is hung with the utmost ends each from a balance. This way, not only the mass of the water in the brick is measured, but some information is obtained about the mass distribution inside the brick. The brick used in this study appears to be quite inhomogeneous. This is incorporated in the model with an inhomogeneity constant. It needs further research if this parameter depends on the water concentration in the brick.

AN EXPERIMENTAL STUDY OF THE MENISCUS SHAPE ASSOCIATED WITH MOVING LIQUID-FLUID CONTACT LINES

Using a new technique involving light reflection, the interfacial curvature of a meniscus formed by a well wetting liquid steadily displacing a gas in a glass capillary has been measured down to about 50 nm from the solid. Within the domain explored, the measured meniscus curvature increases strongly as the wall is approached, in agreement with classical models which make use of the continuum approximation, no slip, etc. The inner length scale, at which such models fail, is inferred from the measurements to be of the order of a molecular dimension, suggesting that non-continuum effects dominate. A comparison of measured dynamic contact angles of liquid-liquid pairs of large viscosity ratio with a model developed earlier by the authors, incorporating such an inner length scale, suggests that the true contact angle in the advancing fluid increases significantly with line speed in one of the cases.

An approximate solution of the hydrodynamic problem associated with moving liquid-liquid contact lines

Abstract The same approach used by the authors in the context of advancing and receding contact lines is applied to the case of liquid-liquid contact lines. The result is an ordinary differential equation whose solution provides an approximate description of the shape of a moving meniscus. It is shown that a system with a viscosity ratio of 103 or more may be regarded as being a purely advancing/receding case. From the comparison of the present model with experimental results a dependence of the true contact angle on the line speed is inferred.

An approximate solution of the hydrodynamic problem associated with receding liquid-gas contact lines

Abstract An ordinary differential equation, derived previously by the authors to describe liquid-gas menisci in the context of advancing contact lines, is applied to the receding case. The existence of a critical capillary number is demonstrated above which no solution of the differential equations exists. This critical capillary number exhibits a strong dependence on the system scale and true contact angle at the wall. Comparison of critical capillary numbers, predicted by the model and obtained from experiments, suggests that at the critical capillary number the true contact angle at the wall is smaller than the (receding) static contact angle.

Heat and mass transfer in heterogeneous media where a phase transition takes place

Heat and mass transport is modelled in a heterogeneous material where convection can take place in the continuous phase and diffusion can take place in both continuous and dispersed phase. The component being transported is in the continuous phase a vapour and in the dispersed phase a liquid. At the phase interface, the component can evaporate or condensate. Derivations are given for the effective material properties (diffusion coefficient and thermal conductivity) and for the transport of heat and mass.

The influence of sorption isotherms on the drying of porous materials

A model is presented for the simultaneous vapour and liquid transport in porous materials. The model describes the evaporation inside a porous material with a mass transfer coefficient and a specific evaporating surface. The model also includes the effect of sorption isotherms. Predictions of the model are compared with experimental results found in the literature.

Simultaneous heat and mass transfer in heterogeneous media

Simultaneous heat and mass transfer can take place in a heterogeneous material in both the continuous and the dispersed phase. Expressions for the effective material properties (diffusion coefficient and thermal conductivity) are given. Thermal diffusion (the Soret-effect) and the diffusion thermoeffect (the Dufour-effect) are included in the model. With the result, the effective heat and mass fluxes can be calculated when the gradients in effective concentration and temperature are given.