基于容积密度计算的X射线法测定木材含水率分布

Moisture Content Distribution of Wood via X-Ray Method Based on the Volume Density

针对X射线法计算木材含水率的算法进行理论推导及试验研究。首先,介绍X射线法测量木材密度的基本原理;其次,引入多孔材料容积密度的概念,量化分析木材各相(细胞壁物质与水)在体积变化情况下的容积密度,推导出以纤维饱和点为分界线的含水率计算公式;最后,以杉木为试验材料,利用X射线剖面密度仪测量干燥过程中试样密度的经时变化数据。基于这些密度数据,分别采用Cai计算方法与容积密度计算方法计算木材干燥过程中的含水率分布;同时,以传统切片法测量的含水率分布为对照组,将三者之间得到的含水率分布进行比较。结果表明:在整个含水率范围内,容积密度计算方法计算的含水率与切片法测得的含水率之间无显著性差异;当含水率在纤维饱和点以上时,Cai计算方法计算的含水率与切片法测得的含水率之间有显著性差异,当含水率低于纤维饱和点时,二者之间无显著性差异。试验证明,采用容积密度计算方法得到的含水率更为合理,为运用X射线法测量干燥过程中木材内部的含水率分布提供了一个更为精确的计算方法。

A new algorithm for calculating moisture content （MC） by X-ray scanning was deduced and studied in this paper. Firstly, the principle of the X-ray measuring wood density was presented. Secondly, the volume density of wood components（ cell wall material and water）under volume change were quantitatively analyzed based on the concept of volume density in the porous materials. And then the formulas for calculating the MC were deduced with the fiber saturation point （FSP） as demarcation line. Finally, taking Chinese fir（ Cunninghamia lanceolata）as the experimental material, the density variation with drying time was measured by X-ray scanning during wood drying process. Based on these data, the MC distribution was calculated by Cai method and volume density method, at the same time, taking slicing method as control group, the results from this three method were compared. The results showed that there were no significant differences between volume density method and slicing method in the entire range of MC. When MC was above FSP, the MC distribution based on Cai method was significantly different with the slicing method, when MC was lower than FSP, there were no significant differences between these two methods. It was suggested that the volume density method was reasonable, which could provide an accurate method for calculating MC distribution during wood drying via X-ray scanning method.