Multi-phase model for moisture transport in wood supported by X-ray computed tomography data

IF 3.1 2区农林科学 Q1 FORESTRY Wood Science and Technology Pub Date : 2025-02-14 DOI:10.1007/s00226-025-01635-9

Royson D. Dsouza, Tero Harjupatana, Arttu Miettinen, Florian Brandstätter, Anni Harju, Martti Venäläinen, Veikko Möttönen, Marc Borrega, Antti Paajanen, Josef Füssl, Stefania Fortino

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Abstract

This study investigates the dynamics of moisture transport in Scots pine (Pinus sylvestris L.) heartwood and sapwood, under alternating drying and wetting cycles, incorporating interactions between bound water, free water, and water vapor using a multi-phase model. Cylindrical specimens oriented longitudinally, radially, and tangentially were subjected to controlled relative humidity (RH) steps of 33%, 94%, and 64% at 23 \(^\circ\)C. High-resolution X-ray computed tomography (CT) provided detailed, time-resolved measurements of moisture distributions within the wood. A multi-phase model was developed that couples Fickian diffusion (for bound water and vapor) with Darcy’s law (for free water), supplemented by phase-conversion terms that account for evaporation and sorption. Key parameters, including absolute and relative permeabilities, direction-dependent vapor diffusivity reductions, thermal conductivity tensors, and free water transport formulations, were determined by matching predicted moisture profiles to the CT measurements. Among concentration and mixed concentration-pressure formulations for free water model, the mixed approach produced the most accurate match. The CT images revealed a rapid depletion of free water during the initial drying step, followed by distinct variations in bound water content as the RH was raised and lowered. Numerical simulations closely replicated these trends, indicating that the calibrated model effectively represents moisture transport both above and below the fiber saturation point.

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本研究调查了苏格兰松木（Pinus sylvestris L.）心材和边材在交替干燥和湿润循环下的水分传输动力学，并使用多相模型结合了结合水、自由水和水蒸气之间的相互作用。在 23 \(^\circ\)C 温度条件下，将纵向、径向和切向的圆柱形试样置于 33%、94% 和 64% 的受控相对湿度（RH）条件下。高分辨率 X 射线计算机断层扫描（CT）对木材内部的水分分布进行了详细的时间分辨测量。我们建立了一个多相模型，该模型将菲克扩散（用于结合水和水蒸气）与达西定律（用于自由水）结合起来，并辅以考虑蒸发和吸附的相转换项。通过将预测的湿度剖面与 CT 测量结果相匹配，确定了关键参数，包括绝对渗透率和相对渗透率、与方向相关的水汽扩散率降低、热传导张量和自由水传输公式。在自由水模型的浓度公式和浓度-压力混合公式中，混合公式的匹配最为准确。CT 图像显示，在最初的干燥步骤中，自由水迅速耗尽，随后随着相对湿度的升高和降低，结合水的含量发生了明显的变化。数值模拟密切复制了这些趋势，表明校准模型有效地反映了纤维饱和点上下的水分传输。

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来源期刊

Wood Science and Technology 工程技术-材料科学：纸与木材

CiteScore

5.90

自引率

5.90%

发文量

审稿时长

3 months

期刊介绍： Wood Science and Technology publishes original scientific research results and review papers covering the entire field of wood material science, wood components and wood based products. Subjects are wood biology and wood quality, wood physics and physical technologies, wood chemistry and chemical technologies. Latest advances in areas such as cell wall and wood formation; structural and chemical composition of wood and wood composites and their property relations; physical, mechanical and chemical characterization and relevant methodological developments, and microbiological degradation of wood and wood based products are reported. Topics related to wood technology include machining, gluing, and finishing, composite technology, wood modification, wood mechanics, creep and rheology, and the conversion of wood into pulp and biorefinery products.