Influence of mass transfer on the estimation of the thermal conductivity of a wet material by the hot wire and parallel hot wire methods

Abstract

Biosourced insulating materials can provide an interesting response to climate challenges by reducing the energy consumption of buildings without using petroleum-based products. Compared to traditional insulating materials, they have the particularity of being hydrophilic so that mass transfer by water evaporation and condensation occurs when temperature or humidity boundary conditions change. To estimate the influence of mass transfer on the thermal conductivity estimation in the hot wire and in the parallel hot wire method, a coupled heat/mass transfer 1D model in cylindrical geometry was developed and numerically solved. Its exploitation to perform numerical experiments showed that the hot wire method allows the measurement of the thermal conductivity while the parallel hot wire method allows the measurement of an equivalent conductivity, sum of the thermal conductivity and of a term related to the phase change phenomena of water within the medium. These theoretical results were confirmed by an experimental study carried out on an anisotropic wood wool.