木材流体渗透性研究的发展与趋势

The Development and Tendency in the Research on Fluid Permeability of Wood

介绍了木材流体渗透性研究领域中的主要理论和常用的木材结构模型；简述了我国木材流体渗透性研究的发展和现状，以及自６０年代以来所取得的主要成果。木材渗透性研究的理论主要包括线性粘滞液体流的Ｈａｇｅｎ－Ｐｏｉｓｅｕｉｌｅ方程，非线性粘滞液态流的Ｅｒｋ或Ｂａｒ方程，气体滑流效应的线性气体流Ａｄｚｕｍｉ方程；常用于木材渗透性研究的木材结构模型有：均匀并联毛细管模型、Ｓｅｂａｔｉａｎ针叶材模型、Ｐｅｔｙ串联流导模型、Ｃｏｍｓｔｏｃｋ针叶材模型，以及Ｂｒａｍｈａｌ提出由Ｂｏｌｔｏｎ改进的渗透截面随长度衰减模型；

Abstract This paper reviews the development of the research on the fluids permeability of wood abroad in the twentieth century. The introduction is made towards the theories and structural models of wood concerning the research on the fluid permeability of wood. Meanwhile, it is shown that the progress and development have been made in studying the fluids permeability of wood and the achievement have been gained in China. The major theories which are applied to the research on the fluid permeability of wood include: 1)the Hagen Poiseuille equation for linear flow of viscous fluid, 2) the Erk equation as well as its expression with Couette correction Barr equation for non linear flow of viscous fluid, 3) the Adzumi equation and Klinkenberg equation for non linear gas flow. In order to apply these theories to flow through wood, four kinds of permeability models of wood in common use are made up and they are:simple uniform parallel capillary model, Sebatian model for softwoods, Petty model for conductance in series, and Comstock model for softwoods. There are two kinds of correction in the above liquid and gas flow equations for short capillaries, respectively. One is the Couette correction for liquid flow due to viscous losses at the ends and the other is the Clausing correction for gas flow by accounting for the decreased skip flow. In addition, Bramhall put forward a model, which was modified by Bolton later, to explain the exponential decreased in the cross section area for conduction. The results of research on fluids permeability of wood that are obtained by Chinese scientists are as follows: 1) The examining and measuring permeability of wood to gas was first made with microscopy in conjunction with apparatus of gas permeability in 1965. It expanded the measurement of permeability of wood to fluid from macro level to micro level. 2) The conclusion was first reached that permeabilities of earlywood and latewood to fluid varied with different species of wood other than the permeability of latewood was always higher than that of earlywood. 3) By theoretical analyzing and experimental studying, it is demonstrated that paulownia wood is permeable and diffusion, and there is inherent channel through which fluid can transfer inside paulownia wood. This result corrects the viewpoint that paulownia wood itself has the ability to resist moisture. 4) In hygroscopical moisture content, there is a maximum for permeability of wood to water in the transverse direction and a minimum in axial and transverse direction near fiber saturation point.