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Gudmundsson, Kjartan. An approach to determining the water vapour transport properties of building materials. Nordic Journal Of Building Physics: Acta Physica Aedificiorum, p. 1 -1, 2003.
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Abstract

An analytical model, based on the literature, is used to show how the material parameters that rule the transport of water vapour in porous building materials can be evaluated by tracer gas measurements. A distinction is made between viscous flow, Knudsen diffusion and continuum diffusion. Each transport mechanism is formulated by explicit functions of the textural properties of the material and the thermodynamic properties of the gas. Tracer gas measurements can therefore be used to reveal the textural properties of a material, from which the potential water vapour transport, in gas phase, can be derived from the thermodynamic properties of water vapour. The well known concentration dependency of the diffusion coefficient is explained with the random hopping model. The random hopping describes how the surface diffusion of adsorbed molecules relates to the amount adsorbed and the energies involved in adsorption. It is also described how the activation energies of surface migration can be obtained from sorption measurements and how the constant parameters of the surface diffusion coefficient can be determined by stationary or transient wet-cup measurements.
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