An approach to determining the water vapour transport properties of buildingmaterials
2003 (English)In: Nordic Journal of Building Physics: Acta Physica Aedificiorum, ISSN 1402-5728, Vol. 3Article in journal (Refereed) Published
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 transportmechanism 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 amaterial, 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 hoppingmodel. 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 surfacemigration can be obtained from sorption measurements and how the constant parameters of the surface diffusioncoefficient can be determined by stationary or transient wet-cup measurements.
Place, publisher, year, edition, pages
2003. Vol. 3
Diffusion, tracer gas, surface diffusion, Random Hopping Model, surface diffusion, porous building materials, time lag method.
IdentifiersURN: urn:nbn:se:kth:diva-13308OAI: oai:DiVA.org:kth-13308DiVA: diva2:323515
QC 201006112010-06-112010-06-112010-06-11Bibliographically approved