New monitoring concept of moisture content distribution in wood during RF/vacuum drying

A new method for monitoring moisture content during radio-frequency (RF)/vacuum drying was developed by measurement of temperature and pressure in wood. Temperature and pressure inside the wood were measured simultaneously during RF/vacuum drying at the same point. The relative humidity (RH) and moisture content (MC) below the fiber saturation point (FSP) were calculated based on temperature and pressure, and the relationship between the temperature, RH, and equilibrium moisture content (EMC) at the measurement point. When the moisture content was below the FSP, the calculated MC was slightly greater than the value given by oven drying. The absolute error was within 0.8% near the open cross side, and was within 1.8% at another measurement point. Thus, we concluded that it was practicable to monitor the moisture content below the FSP according to the temperature and pressure inside the wood. Part of this study was presented at the 15th Annual Meeting of the Chugoku Shikoku Branch of the Japan Wood Research Society, Higashi-Hiroshima, Japan, September 2003     

Causes of color changes in wood during drying

The forest industry operates in a dynamic and global market where change and competition are the rule rather than the     

非接触式无损检测木材干燥应力的方法

木材干燥应力是干燥过程中产生干燥缺陷的主要因素。文章根据数字散斑相关方法(DSCM)检测应力的原理设计出了一种非接触式无损检测木材干燥过程中应力的方法,用木材干燥表面测点位移的变化速率即应变速率来表示木材干燥过程中的应力状态,初步提出了建立木材干燥应力评价体系的设想。研究结果表明:木材表面测点位移变化量与时间存在着对数关系,与含水率变化量则呈线性关系。     

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。     

Modelling natural drying of European beech (Fagus sylvatica L.) logs for energy based on meteorological data

A key factor for improving the whole fuel wood supply chain is moisture management. Moisture affects material quality, transport costs and revenue. The aim of this study was to develop a drying model for piled European beech (Fagus sylvatica L.) logs based on meteorological data, employing the continuous weighing approach. Two drying cycles with three piles altogether were conducted. In the first one (February to October 2013) the moisture content of the pile dropped from 43.5% to 22.5%, whereas in the second one (December 2013 to March 2015), the moisture content of the 2 piles dropped from 42.1% and 40.5% to 20.6% and 19.8%, respectively. Model performance (R² adj?=?0.41) was validated by applying the model developed from the second cycle's data on the first cycle's data. Model's mean deviation in moisture content from the observed curve was ?0.41%?±?0.72%. Economic benefits and environmental impact were highlighted. Calorific value increased from 2.65 to 3.57?kWh?kg^–1 from February to October 2013. Truckload volume utilization increased by 25.1% and transported calorific value by 48.0%. The number of truck trips for transportation was reduced from nine to seven.     

浅析传统木材干燥实现节能减排的途径

阐述了我国传统木材干燥节能减排的主要途径。指出,采用除湿机和热管换热器等设备回收干燥室排气余热,是节能减排的主要途径之一;完善干燥室的设备配置和运行管理也有可观的节能潜力。介绍了几种联合干燥技术,提出这将是今后节能减排技术的重要发展方向。最后指出一定规模的集约化经营将有利于保障木材干燥质量和节能。     

24种南方阔叶树材的干燥特性及窑干基准

通过对24种南方阔叶树材进行100℃干燥试验和窑干试验,说明了这些树种的干燥特性,提出了这些树种适宜的干燥基准。试验结果指出,多数树种在实际窑干试验中发生降等的倾向与100℃试验中发生的干燥缺陷是一致的,但少数树种不一致,这些树种的预定干燥条件需要通过多次窑干试验加以修正。     

相思木常规干燥过程中的水分迁移

对相思木干燥过程中水分迁移的研究成果表明 ,在干燥全过程中 ,含水率下降速度由快变慢 ;平均干燥速度与次表层干燥速度相近 ;表层与次表层间的含水率梯度最大。     

Effect of growing site,sampling date,wood location in trunk and drying method on concentration of soluble proanthocyanidins in Betula pendula wood,with special reference to wood colour

Proanthocyanidins (PAs), which are common phenolic compounds in plants, are considered to be mainly defensive compounds against different kinds of stress, e.g. herbivory. In addition to increasing after stress, they may condense and/or oxidize to form coloured compounds when cells die, which may affect both the resistance of xylem to rot and its colour. This is important in the mechanical wood industry. The effects of some biological factors (growing site, sampling date, wood location in the trunk) on the concentration of soluble PAs (sPAs) were studied in fresh and dried birch wood. Those factors that affected sPA concentration most were sampling date and radial location. Drying method also had a great effect on the sPA concentration, which in turn correlated with the colour of the wood.     

水性聚氨酯漆料干燥速率及漆膜性能影响规律研究

以4种水性聚氨酯漆料为研究对象,系统研究了漆料和基材类型、涂饰工艺对水性漆表干、实干时间和漆膜硬度、附着力及耐磨性的影响规律。结果表明:漆料的表实干时间及漆膜性能很大程度受成膜树脂本身性能影响;基材影响漆料表实干时间、漆膜硬度和附着力,对漆膜耐磨性影响不大,漆料涂饰在樱桃木和水曲柳上的干燥速率最快,在樱桃木、沙比利和水曲柳上的硬度最佳,达2 H,在樱桃木、沙比利和红橡上的附着力最佳,达0级;涂饰工艺对漆料的表干、实干时间以及漆膜硬度、附着力、耐磨性的影响都不明显,3种工艺涂饰后漆膜硬度和附着力分别为2 H和0级,漆膜耐磨性差别不大。     

Effect of steam explosion treatments on drying rates and moisture distributions during radio-frequency/vacuum drying of larch pillar combined with a longitudinal kerf

This study was carried out to investigate the effects of steam explosion treatment on drying rates, moisture distribution, shrinking, and checking during radio-frequency/vacuum drying of Korean larch pillar combined with a longitudinal kerf. All the pillars except the nonkerf/control with high initial moisture content (MC) could be dried within 89 h from the green condition to about 15% MC. In pillars with high initial moistures or in the early stage of drying, the drying rates were sharply accelerated by steam explosion treatments. The final moisture gradients along the transverse direction were gentler for the steamexploded pillars and for pillars with a longitudinal kerf, respectively, than for the unexploded pillars and for pillars without a longitudinal kerf. The moisture gradients along the longitudinal direction on all the layers were gentler for the pillars with a longitudinal kerf than for those without the kerf. Formation of checking was significantly controlled in the pillars with a longitudinal kerf. All the steam-exploded pillars except the kerf/1-cycle, however, were more severely damaged by checks than the unexploded pillars. A prong test revealed an extremely low level of residual stress for all the dried pillars.     

常规木材干燥室不同供热状况的 损失分析

着重分析常规木材干燥室蒸汽管道不同供热状态的损失:当蒸汽管道供热温度一定时,干燥室温度越低,传热温差越大,损失越大;当干燥室温度及蒸汽管道外壁温度一定时,蒸汽管道供热温度越高,传热温差越大,损失越大。传热温差对损失的影响很大,当蒸汽管道供热温度110℃时,传热温差由40℃降到30、20、10℃,其损失分别减少46.08%、77.01%和94.48%,所以要根据干燥室需要的温度尽量减少供热温差,以减少损失。压差流动损失随压差增大而增加,而且压力较高时比压力较低时压降的损失大。蒸汽在管道内压差流动的损失数值比温差传热损失大许多,至少要大1～2个数量级。因此,由锅炉向干燥室供热,应该尽量减少降压节流的情况。     

杉木生材含水率分布及其对气干的影响

以人工林杉木为研究对象,研究生材状态下不同厚度锯材含水率的差异,比较含髓心、钝棱与其他类型等3类锯材的含水率差异,建立生长轮宽度与锯材含水率的关系,分析生材状态含水率对锯材气干周期的影响。研究结果显示,25mm和40 mm的锯材含水率差异极显著;含髓心锯材含水率最低,其次是其他类的,最大是含钝棱锯材;随着生长轮宽度减少,锯材含水率增大;生长轮宽度为4 mm时,是生材含水率分界线,即当生长轮平均宽度小于和不小于4.0 mm时,锯材含水率差异极显著;25 mm和40 mm厚不同含水率锯材各2组气干至含水率25%,低含水率锯材较高含水率的气干周期分别缩短57%和66%。     

Microwave vacuum drying characteristics of Pinus massoniana wood

Microwave-vacuum (MV) drying characteristics of plantation Masson pine (Pinus massoniana) were studied experimen-tally for various levels of microwave radiation time, initial moisture content (MC), vacuum level and wood thickness. The results show that the process of MV drying for wood can be significantly divided into a short accelerating rate drying period, a long constant rate drying period and falling rate drying period, and the second drying period can extend to levels of mean MC below the fiber satu-r...     

Kiln drying behavior of lumber from ten fast-growth plantation species in Costa Rica

Abstract

Plantation wood from tropical climate has been introduced rapidly in the national market; however, there is lack of knowledge about the process. The main objective of this study was to investigate the kiln drying behavior of 10 plantation-grown wood species from natural forest in Costa Rica using the recommended drying schedule. Initial moisture content (MCi), final moisture content (MCf), drying rate, drying time, and drying defects were evaluated. The drying schedule applied produced the following results: (1) high MCi (over 110%) in four species and lower values in two species. (2) The largest drying time was found in species with high MCi, and the shortest drying time in species with lower MCi. (3) Significant variations of target MCf were found in some species, despite equalization and conditioning. (4) Exponential relationship MC=a*?^?t*b was used to establish a moisture content (MC) decrease model, which is not a good indicator of drying time for fives species. (5) High incidence of drying defects was found in Alnus acuminata and Vochysia guatemalensis. According to the above results, it is necessary to test other drying schedule oriented to improve lumber quality and to decrease variability of MC in wood from plantation trees.     

木材含水率测定方法的比较研究

为修订国家标准“CB1931—80木材含水率测定方法”提供依据,本文对含树脂和挥发性物质较多的马尾松等5种木材,采用烘干法、真空干燥法和蒸馏法进行含水率测定的比较。结果表明,烘干法简便实用,但所测得的含水率结果比真空干燥法和蒸馏法为高,如果试样含有较多的挥发性物质,应用烘干法测定含水率误差偏大时,可采用真空干燥法。     

基于时延神经网络的木材干燥温湿度建模研究

利用神经网络建立了木材干燥的温湿度模型,给出了其时延神经网络辨识结构。分别提出温、湿度控制模型(控制信号与温、湿度之间的关系模型)和木材干燥基准模型(温、湿度与木材含水率之间的关系模型),并利用实验干燥窑得到的实际数据进行了仿真研究。仿真结果表明,利用此方法建模是可行的,所建模型是有效的。图10参16。     

Changes of decay and termite durabilities of Japanese larch (Larix leptolepis) wood due to high-temperature kiln drying processes

We investigated the effects of high-temperature drying schedules (120°–130°C) on decay and termite feeding of Japanese larch timbers. Thermogravimetric analysis was conducted to investigate changes of the wood components. Decay and termite feeding tests showed that specimens dried under high-temperature schedules were susceptible against a decaying fungus Fomitopsis palustris and attacks from termites Coptotermes formosanus and Reticulitermes speratus. These drying schedules changed chemical components, which were suggested by the thermal analytical result compared to the control sample. The results of this study indicated that the acceleration of termite feeding takes place even under temperatures that are comparatively lower than that used in our previous research in which 170°C steaming treatment was applied to Japanese larch wood. Decay durability against a brown rot fungus also decreased, possibly from production of low molecular weight fragments when hemicellulose decreased during the high-temperature drying processes.     

The influences of log storage and kiln drying climate on the colour of non-steamed beech (Fagus sylvatica L.) wood

Abstract

Discolouration during the drying of non-steamed beech is a major industrial concern. The generally preferred yellow-white colour can easily develop a reddish or dull grey appearance during drying. In this study, the influences of log storage time and kiln drying climate on the colour of non-steamed sawn beech have been investigated and quantified. Samples 27×87 mm in cross section were dried in laboratory kilns and the average colour, in CIELAB colour space was measured on dry planed surfaces using a photoelectric colorimeter. Log storage for 13 weeks under low-temperature conditions had no visible effect. The reddish discolouration is mainly temperature related while the greyish discolouration is mainly controlled by the equilibrium moisture content (EMC) during the initial drying. Within the investigated climate interval, the EMC was twice as important as temperature for the final colour. Regression models developed show that, as long as the EMC is kept below 15%, a temperature of up to 37°C can be allowed without any visually detectable discolouration.     

Analysis of moisture diffusivity of larch timber during convective drying condition by using Crank＇s method and Dincer＇s method

Two analytical procedures （Crank＇s method and Dincer＇s method） for porous solid materials were reevaluated and used to determine moisture diffusion coefficients and moisture transfer coefficients for larch lumber subjected to drying. A diffusion-like equation was used to describe drying process data. The lumber was idealized in the modeling as infinite plates. The moisture transport process inside the board was assumed to be one-dimensional. The macroscopic drying kinetics curves of larch timber at particular conditions were determined experimentally. Based on these data, calculation for both the moisture diffusion coefficients and moisture transfer coefficients by the Dincer＇s analytical procedure were made. The dynamic moisture diffusion coefficients by the traditional Crank＇s method were calculated. In general, diffusion coefficients calculated by the Dincer＇s method were all higher than those by Crank＇s method. These results could be due to the differences between two analytical methods and also different characteristics between solid moisture diffusion process and heat transfer process. Therefore the analysis and solution procedures of moisture diffusion differential equations need to be adapted in the future. With drying temperature＇s increasing moisture diffusion coefficient （D） and moisture transfer coefficient （k） increases accordingly. Also the relationships between diffusion coefficients and temperature as well as material moisture contents were analyzed by using Arrhenius equation and bound water transport theory.