木材微波干燥内部压力对水分移动的影响

在微波干燥过程中,能量是以电磁波的形式直接渗透到木材的内部,并通过微波电磁场与水分子及木材中极化分子(羟基)的相互作用而迅速产生大量的热,导致木材内水分移动机理与常规干燥很大的不同。实验结果表明:微波干燥过程中,存在内高外低的压力场,内中蒸汽压力是水分移动的驱动力。     

落叶松干燥过程水分扩散性的研究-Crank方法与Dincer方法的使用

采用两种改进的多孔固体材料水分扩散偏微分方程分析求解方法,即Dincer方法与Crank方法,分析并计算落叶松干燥过程的水分扩散系数(D)与水分传递系数(k)。使用扩散型微分方程对落叶松干燥过程进行数学模拟,木材试件被理想化为无限大平板状材料,假定木材内部水分的扩散过程是一维的。实验测定了不同干燥介质条件下木材干燥动力曲线。基于取得的实验数据,通过Dincer方法计算了木材水分扩散系数(D)与水分传递系数(k);使用传统的Crank方法分析计算了木材动态水分扩散系数(D)。研究表明,使用Dincer方法计算的木材水分扩散系数(D)均大于相应实验条件下Crank方法计算数值,接近1个数量级。这种结论应该是由于两种分析求解方法间的差异以及水分扩散与热量传递数学求解间的差异。因此相关的水分扩散微分方程的分析求解方法有待改进。随干燥介质温度的升高,木材水分扩散系数(D)与水分传递系数k均显著增大,可以采用Arrhenius方程与木材结合水传递理论来分析解释实验条件下的扩散系数(D)与干燥介质温度(T)间的变化趋势。图2表3参6。     

除湿干燥的节能分析

着重阐述了除湿干燥与蒸汽干燥的区别。单热源与双热源干燥的区别，以及除湿干燥的节能原理，提出了评价热泵节能效果的指标，列举了评价热泵节能率的分析方法。     

花椒叶片水分生理指标量化分析研究

秦安一号花椒是临夏州1995年从天水秦安引进的优良品种.为了进一步弄清该品种在本州的适生范围以及对水分的需求差异,我们将其同当地品种比较,于2001年8月对3个品种的蒸腾强度、含水量、饱和亏、需水程度等生理指标进行了测定.     

木材干燥窑的技术经济分析

在分析木材干燥窑技术经济性能的基础上，提出干燥窑的技术经济指标及其可比性换算的方法。     

可燃物鲜枝水分逸出率的测试与分析

可燃物鲜枝水分逸出率的测试与分析西北林学院张景群马骐＊１前言植物含水率是防火林带树种选择的一个重要指标。近几年，在森林防火的理论研究和应用研究方面，我国学者提出了一些有价值的植物水分指标新概念，如水分逸出速度（浙江大学燃烧与传热学教研室，１９８７）、...     

木材干燥轨道车的应力分析及改进设计

本文为了减轻木材干燥轨道车的重量,对车体进行了较全面的应力分析,证明在γ<1.3时“KS”型木材干燥轨道车是最佳设计。     

木蓼属6种植物水分生理特征的主成分分析

本文用主成分分析法研究了木蓼属6种植物7个主要水分关系指标的生理意义,并对这些种进行了耐旱性排序。结果表明:蒸腾强度、水势、水分饱和亏和持水力4个指标可综合反映该属植物的水分代谢过程;束缚水和自由水比,相对含水率和细胞液浓度三指标可粗略反映该属植物水分与物质的比率关系。6种植物耐旱力从大到小的顺序为布尔津木蓼、拳木蓼、刺木蓼、额河木蓼、东北木蓼、沙木蓼。     

基于小波分析的木材干燥过程的声发射信号的去噪研究

指出了木材结构的各向异性导致了木材声发射信号的提取的困难性。小波分析作为信号和信息的处理工具由于其优越性已经被大家所认可,特别是在去噪方面,小波的多分辨分析、相关性、低墒性使其在去噪领域有着独特的优势。声发射技术是一种动态的无损检测技术,它不仅能对缺陷进行实时的动态监测,还能对发展趋势进行预测。     

人面子木材干燥特性及干燥工艺初探

采用百度试验法研究人面子木材的干燥特性,根据百度试验结果和企业的实际情况,拟定了相对偏软的24 mm和50 mm 2种厚度规格家具用材干燥工艺基准,进行了生产试验。24 mm厚人面子木材从初含水率85%干燥至12%,共用时506h,干燥质量良好,达到预期要求。针对50 mm厚毛边板材干燥速度慢,干燥不均匀,同一块板材内局部区域含水率异常偏高的现象,拟定了气干/窑干联合干燥工艺和相应的半波动窑干基准。     

Moisture flow characteristics during radio frequency vacuum drying of thick lumber

Summary Thick specimens of two softwoods were dried in a laboratory radio frequency/vacuum (RF/V) kiln in order to investigate the internal moisture flow patterns. The spatial moisture distributions in the longitudinal arid transverse directions were monitored as a function of time in a number of runs. The results indicated that both longitudinal and transverse moisture transfer modes contribute on the overall moisture flow occurring within wood, but there was no distinction as to the percentage contribution of each to the overall flux. There were no abrupt drying front changes and no moisture discontinuities observed during drying. A second group of runs was also carried out using end-matched specimens to study its length effects on drying characteristics, such as drying rate, and internal vapor pressure and temperature profiles. The results demonstrated that short specimens dried faster than long ones at moisture contents above the fiber saturation point.The financial support for this work from NSERC/Canada through a Strategic Grant (STR0167393) and the lumber contribution from MacMillan-Bloedel are greatfully acknowledged.     

木材微波干燥缺陷产生原因及其预防措施分析

从木材介电特性、微波穿透深度、微波设备、干燥工艺等方面分析了木材微波干燥缺陷产生的主要原因,并从优化干燥器设计,改善微波场分布均匀性,控制微波辐射功率和辐射时间,改变微波辐射方式等方面探讨了预防干燥缺陷产生的主要措施,以期为木材微波干燥技术的研究和应用提供参考。     

Numerical and experimental analysis of a wood drying process

 Experimental investigation and computational analysis were performed to evaluate the influence of the ambient air parameters during the drying process on the temperature, moisture and resulting deformations and stresses in wood samples. The numerical procedure uses the Finite Volume Method to discretise the equations governing heat, mass and momentum balance and takes into account the anisotropic nature of wood. The comparison of the numerical and experimental results shows very good agreements, implying that the proposed numerical algorithm can be used as a useful tool in designing wood drying schedules. Received 31 March 1999     

蕨菜真空冷冻干燥加工工艺研究

主要以长白山野生蕨菜为原料 ,采用真空冷冻干燥技术制得冻干蕨菜。实验研究表明 ,在干燥室压力2 0Pa、物料的预冻速度为 1 .5℃ /min ,装载量 7.8kg/m2 、加热温度 40～ 5 5℃时的条件下进行加工 ,可获得具有良好品质并较为经济的冻干蕨菜产品。所生产的冻干蕨菜产品的干燥率为 1 4.4、复水比为 1 3 .8、水分活度为0 .48。经实验得出了冻干蕨菜的冻干曲线 ,确定了冻干蕨菜的最佳工艺流程     

两种木材干燥窑窑型结构的分析

本文介绍了两种顶吹型干燥窑的结构特征,测定了通过材堆的气流速度、空气再循环比、壳体与环境温度差和对主要技术经济指标等资料的分析,评估它们结构的优缺点。也探讨了橡胶木的干燥基准和过程自动控制问题。     

Moisture content gradient in a softwood board during drying: simulation from a 2-D model and measurement

Summary A 2-D mathematical model was developed to simulate moisture movement and heat transfer in width and thickness directions within a softwood board during drying. The model is based on wood physiological features and behaviour observed during drying. In sapwood, liquid water movement is assumed to be a consequence of capillary action between liquid and gas phases inside the cell lumens. However, liquid flow does not occur in wood close to the exposed surfaces because at timber surfaces the wood cells are damaged during the sawing process and consequently the liquid column is broken. In heartwood, liquid flow is negligible since the pits are normally aspirated during the formation of heartwood in the growing tree. Water vapour moves under a partial vapour pressure gradient while bound water diffuses within the wood material due to differences in chemical potential. The model was solved numerically to predict moisture-content profiles. Experiments were undertaken to measure the moisturecontent gradient. Samples were removed from a tunnel dryer at intervals throughout drying, frozen overnight and then cut into slices for moisture-content determination. The experimental results were used to verify the model.This work is supported by the New Zealand Foundation of Research, Science and Technology under contract CO4415     

白桦材尿素改性前后干燥特性的研究

对白桦材尿素改性前后的干缩性和干燥特性的研究结果表明,尿素改性材的干燥特性明显好于素材和水煮改性材,干燥速度快,干燥质量好。并探讨了尿素改善白桦材干燥特性的机理。     

刺嫩芽加工前后营养成份分析

通过对牡丹江林区刺嫩芽原料和加工成的即食刺嫩芽罐头产品进行营养成份检测，获得部分数据，为资源开发及产品加工提供参考。     

Diffusion and the drying of wood

Summary Fick's laws, stating that diffusion rate is proportional to the concentration gradient, have traditionally been used to describe the drying of wood. The author contends that they have been used inappropriately, since according to Fick's laws the rate varies as the concentration gradient of diffusing molecules, whereas many wood scientists use the concentration gradient of non-diffusing molecules —the bound water. When the temperature-dependent component of the diffusion coefficient is combined with the concentration gradient of diffusing molecules, the resulting driving force is proportional to the vapour pressure, and the diffusion coefficient is independent of temperature.