InterPore2026

Fluid–solid–thermal coupling in fibrous porous media: distinct roles of porosity, fiber orientation and relative humidity in cellulose fiber stacks

19 May 2026, 14:20

15m

Oral Presentation (MS16) Complex fluid and Fluid-Solid-Thermal coupled process in porous media: Modeling and Experiment MS16

Speaker

Karen MOURDA

Description

Fibrous bio-based insulation materials are highly porous media in which thermal transport arises from coupled contributions of the solid network, the interstitial gas phase, and moisture stored as bound water within the fibers. In such systems, heat transfer is governed both by the microstructural organization imposed during material processing and by the hygrometric state of the solid phase. Assessing the relative importance of these two contributions remains experimentally challenging, yet is essential for developing predictive descriptions of thermal transport in fibrous porous media. Here, we present a systematic experimental investigation of steady-state thermal conductivity in model cellulose fiber stacks, focusing on the interplay and relative contributions of structure-controlled effects (porosity and compression-induced fiber orientation) and humidity-controlled effects associated with bound water.
The microstructure is imposed during sample preparation by uniaxial compression, which simultaneously sets the porosity and induces a preferred fiber orientation. Thermal conductivity is measured using a heat flow meter in two configurations, defined by the relative orientation between the heat flux and the compression axis. In the dried state, thermal conductivity is governed by this compression–controlled microstructure. As porosity is reduced, two distinct conductivity–porosity trends emerge: in the axial configuration, conductivity increases moderately with decreasing porosity, whereas in the transverse configuration, it exhibits a much steeper dependence. This reflects the progressive reorientation of fibers and the associated evolution of solid-phase connectivity, starting from a common loose reference state. These trends are rationalized using a physically motivated structural framework anchored to the as-poured reference state.
The effect of relative humidity is then investigated. In the axial configuration, thermal conductivity follows distinct linear dependencies on porosity in the two limiting states (RH ≈ 0% and RH ≈ 100%), with higher values in the saturated state due to the contribution of bound water. During drying from saturation, an apparent increase in porosity is observed; this effect is shown to arise from the moisture dependence of the solid-phase density and does not reflect any microstructural rearrangement. The drying trajectory of thermal conductivity can therefore be predicted from porosity alone by interpolation between the two limiting states. In contrast, in the transverse configuration, thermal conductivity exhibits only weak sensitivity to humidity at a given porosity, confirming the dominant role of geometry and packing in this direction.
Overall, these results clarify the respective contributions of structure and moisture to thermal transport in fibrous porous media and provide experimentally grounded insight into fluid–solid–thermal coupling relevant for bio-based insulating materials.