木材非对称单侧表层压缩热质耦合迁移机理

Compressing wood surface on one side can improve the mechanical properties and wear resistance of fast-growing plantation wood to meet the high mechanical requirements of wood products such as solid wood flooring and furniture, with the least loss of wood volume. This project starts with the research on the formation conditions of one-sided wood surface layer by compressing the fast-growing plantation wood with the so-called one-step technology of “heating-softening-compressing”. In the compressing process, the modified X-ray instrument is used to detect the variation and distribution of density profile and moisture content of surface compressed wood, and the thermocouple temperature measuring instrument is used to detect the variation and distribution of temperature inside wood; through this it can establish the formation theory of one-sided wood surface layer and the theory of reconstruction of uniform temperature and moisture content field of the asymmetric wood under the asymmetric heating, and determine the characteristic of heat transfer and the moisture diffusion during one-sided wood surface compressing process. This project then gives the mathematical description of heat and mass transfer during one-sided wood surface compressing process, and studies on its fast computational solution and visual presentation, aiming to illustrate the law the coupling heat and mass transfer during such process and provide new idea and evidence to solve the technical problem for one-sided wood surface compression. Therefore, this project can not only enrich the contents of wood physics, heat and mass transfer and other disciplines, but also guide the production of one-sided surface compressed wood, which is of great theoretical and practical significance for promoting the high value-added utilization of fast-growing plantation wood.

木材单侧表层压缩能改善速生软材的力学性能和耐磨性，使其满足实木地板、家具等木制品的使用强度要求，并最大限度地减少木材体积损失。本项目从速生木材单侧表层密化层形成条件入手，利用加热、软化、压缩一步法快速形成表层密化层。采用改进的X射线仪检测木材剖面密度和含水率的分布和变化，采用热电偶温度仪检测木材温度分布和变化，探索木材单侧表层密化层的形成原理和木材在加热非对称、材质非对称状态的温、湿度场平衡重构原理，研究木材单侧表层压缩过程的传热特性和水分扩散特性；建立木材单侧表层压缩过程传热传质数学模型，研究模型的快速数值解法和可视化表述，可望阐明木材非对称单侧表层压缩过程热质耦合传递规律，为解决木材单侧表层压缩存在的技术问题提供新的思路和理论依据。因此，本项目研究可丰富木材物理学、传热传质学等学科内容，指导速生木材单侧表层压缩的实际生产，对于推动速生林木材实木化利用具有十分重要的理论意义和实际意义。

我国人工林面积稳居世界首位，速生木材蓄积量世界第一，但速生木材材质疏松、力学强度低、稳定性差，多应用于人造板、纸浆等领域。木材实木利用可以保持木材最好的天然属性，如能采用有效的木材功能性改良技术，提高速生木材的力学强度、尺寸稳定性，使速生材应用于实木地板、实木家具等领域，拓宽速生材的使用范围，将可以很好的解决我国实木制品原材料供应不足的局面。木材单侧表层压缩能改善速生软材的力学性能和耐磨性，使其满足实木地板、家具等木制品的使用强度要求，并最大限度地减少木材体积损失。本项目从速生木材单侧表层密化层形成条件入手，利用加热、软化快速形成表层密化层，具体开展了木材单侧表层动态压缩过程传热特性和水分扩散特性研究，建立及求解单侧表层压缩热质耦合传递数学模型，并对传热传质数学模型进行试验验证、修正及可视化。通过本项目研究，确定热压工艺即温度、压缩率、压缩速度等参数对单侧表层压缩木密实层形成的影响，并通过试验证明表层密实化杨木的有效密实层的位置和厚度对压缩处理材的力学性能具有显著的影响；开发了在线检测木材含水率的电测法模型，有效提高木材分层含水率检测精度，为模型验证提供技术支撑；运用N-S完全性运动方程描述木材多相流体的输运过程，建立木材单侧表层压缩过程中木材的热-湿耦合传递数学模型，利用Matlab软件和COMSOL Multiphysics进行热质耦合方程组求解和仿真分析，同时通过对比在线测量木材压缩过程中的温度场和水分场变化结果，证实了所提出的热-湿耦合数学模型的正确性，进而揭示木材单侧表层压缩过程的热质耦合迁移机理；采用高温蒸汽热处理和热压板表面处理等方式，有效固定单侧表层压缩木的回弹，为后续研究奠定基础。本项目研究可丰富木材物理学、传热传质学等学科内容，指导速生木材单侧表层压缩的实际生产，对于推动速生林木材实木化利用具有十分重要的理论意义和实际意义。