Evaluation of relationships between particle orientation and thermal conductivity in bark insulation board by means of CT and discrete modeling

Abstract

Insulation boards made out of larch bark were pressed and scanned with an industrial X-ray computed tomograph (CT) in order to study the structure of the boards and to allow structure-based thermal modeling. The CT images were segmented using a categorization algorithm based on ANOVA. Apart from gaining knowledge about panel porosity, understanding of the inhomogeneous bark boards was enhanced by finding that two main components are prevalent. That knowledge of the board's inner microstructure enabled the application of a numerical model for thermal conductivity based on the finite difference method (FDM). Contrary to simple cut-ups, the application of CT and subsequent modeling enables the evaluation of the effects of particle orientation on a panel's thermal conductivity. Panels with horizontal particles (oriented parallel to the panel plane) proved to have a significantly lower thermal conductivity than panels with vertical particles (oriented orthogonal to the panel plane). This trend could be confirmed by means of the presented modeling approach, which allows further theoretical ex ante optimization in the production process. These findings give the direction for developments of efficient bark insulation panels with well-defined microstructure.