Modelling and simulating simultaneous liquid and vapour transport in partially saturated porous materials

Simultaneous liquid and vapour transport in partially saturated porous materials is modelled with two coupled diffusion equations in which a term accounts for the evaporation. The solution of the differential equation for the vapour diffusion is approximated with the quasi steady solution. The differential equation for the liquid diffusion is solved using the numerical Crank-Nicolson method. The predictions of the model are compared with experimental data of drying clay as found in the litera ture. The influence of sorption isotherms must be included in the model

The measurement of the sorption isotherm of water in paint films

A hygrometric method is presented with which the sorption isotherm of water in paint films can be measured. Only standard laboratory equipment is used. The principle of the technique is that a known amount of water is added to a system of paint and air. The relative humidity in the air is measured. The amount of water in the paint follows from a mass balance. A small leakage is incorporated in the model. The method is used on three alkyd paints and three latex paints

Velocity of long bubbles in oscillating vertical pipes

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Modelling of water and chloride transport in concrete during yearly wetting/drying cycles

\u3cp\u3eThe simultaneous transport of water and chloride in concrete has been modelled. The water transport is described with a concentration dependent diffusion coefficient. The chloride transport is modelled with a convective part, caused by the water transport, and a diffusive part, caused by the chloride concentration gradient in the pore water. Because the water velocity depends on the pore radius, the chloride transport is a complex pore radius dependent process. Modelling this process leads to an expression for the dispersion coefficient, for the chloride diffusion. The model equations are applied on concrete with a yearly variation of the surface water concentration. A few different boundary conditions for the chloride transport are described. The water distribution is almost homogeneous over the samples. The chloride concentration at the surface can rise considerably, when water leaves the concrete sample, while chloride stays behind. Crystallization and a few other possible model extensions are discussed.\u3c/p\u3

A hygroscopic method to measure the adsorption isotherm of porous construction materials

A sorption isotherm is the relationship between the moisture content in a material and the relative humidity of the surrounding atmosphere in an equilibrium situation. Most often, the sorption isotherm is measured with a gravitational method. This work presents a method to measure the adsorption isotherm of a porous construction material (sand-lime) with a hygroscopic method. The set-up of the experiment consists of a glass vessel that contains a humidity and temperature sensor. The measurement starts with drying a sample completely inside the vessel by blowing dry air through the vessel. After injecting a known amount of water into the vessel, the water evaporates and is adsorbed partly by the sample until an equilibrium state is reached. With the known amount of the injected water, the measured humidity inside the vessel and the volume of the vessel, one point of the adsorption isotherm is determined. For measuring the next point, more water is injected into the vessel. The desorption isotherm can also be measured with this technique

The measurement of low air flow velocities

Air flow velocity is measured with an acoustic sensor, which can be used especially for measuring low air flow velocities as well as the temperature of the air simultaneously. Two opposite transducers send a sound pulse towards each other. From the difference of the transit times, the air flow velocity is computed. With this method, it is possible to determine the flow direction even at low velocities. Two calibration methods are carried out. First, a set of calibration experiments is carried out in a wind tunnel, in which a uniform air flow is generated. In the centre of the wind tunnel, the sensor and a reference speedometer of Pitot tube are installed to measure the air flow velocity independently. Second, a set of calibration experiments for low air flow velocity is performed with the acoustic sensor in amoving tube with a controlled velocity. The sensor shows good and accurate results corresponding to the speed of the tube