热压干燥中高含水率杨木锯材内水分状态及迁移机制  

Moisture State and Migration Mechanism of High Moisture Content Poplar Lumber during Platen Drying

作　　者：周永东[1] 侯俊峰[2] Zhou Yongdong;Hou Junfeng(Research Institute of Wood Industry,CAF,Beijing 100091;School of Engineering,Zhejiang A&F University,Hhanghzou 311300)

机构地区：[1]中国林业科学研究院木材工业研究所,北京100091 [2]浙江农林大学工程学院,杭州311300

出　　处：《林业科学》2020年第9期104-111,共8页Scientia Silvae Sinicae

基　　金：国家自然科学基金重大项目(31890772);林业公益性行业科研专项(201404502)。

摘　　要：【目的】检测热压干燥中含水率高于纤维饱和点(FSP)的杨木锯材内温度和压力,分析热压板温度对锯材内不同位置温度和压力的影响,探究锯材表层和心层水分状态和变化规律,阐释高含水率杨木锯材内水分迁移机制,为揭示木材热压干燥机制和干燥过程的精准控制提供理论依据。【方法】在热压板温度为120、130和140℃条件下,对400 mm(L)×120 mm(T)×25 mm(R)杨木锯材(含水率40%~60%)进行热压干燥,采用温度-压力集成传感器在线检测锯材表层和心层温度和压力,并依据热力学原理中饱和压力与饱和温度的关系分析锯材内水分状态。【结果】1)热压干燥中杨木锯材表层和心层温度和压力峰值随热压板温度升高而增大,当热压板温度从120℃升至140℃时,锯材表层温度和压力峰值分别从115.4℃、209.3 kPa增至133.0℃、314.5 kPa,心层温度和压力峰值分别从109.4℃、235.5 kPa增至126.4℃、336.9 kPa,但表层和心层温度达到峰值的时间滞后于压力峰值。2)杨木锯材表层水分状态分析表明,在热压板温度为120℃条件下,表层水分处于未饱和水状态,干燥后表层含水率高于FSP可提供佐证;在热压板温度为130和140℃条件下,表层测点位置的自由水转变为水蒸气,随干燥时间增加,由饱和蒸汽状态逐渐转变为过热蒸汽状态,干燥后表层含水率低于FSP证实推测正确。杨木锯材心层水分状态分析表明,虽然含水率高于FSP的锯材内温度高于大气压下水的沸点温度,但由于心层压力较高,水分处于未饱和水状态;在热压板温度为120、130和140℃条件下,干燥后心层含水率均在50%以上,显著高于FSP,证明液态水状态的推测。3)热压板打开期间杨木锯材内水分状态分析表明,热压板打开瞬间锯材表面和内部压力急剧下降,锯材中部分液态水发生闪蒸转变为水蒸气,锯材内水蒸气从表面快速迁出引起锯材含水率降低。【结论】�【Objective】In order to provide theoretical basis for revealing drying mechanisms and precise control of wood platen drying process,the effects of heating platens’temperature on temperature and pressure inside poplar lumber with moisture content(MC)beyond fiber saturation point(FSP)were studied,the moisture state variety in surface layer and center layer of poplar lumber was further analyzed,and the moisture migration mechanisms were explained accordingly.【Method】The dimension of poplar lumber specimen was 400 mm(L)×120 mm(T)×25 mm(R).The wood initial MC range was 40%-60%.The platen drying experiments were conducted under three levels of heating platens’temperatures,i.e.120,130 and 140℃.The temperature and pressure in the surface and center layer of lumber was measured with temperature-pressure integrated sensor in drying process,and the moisture state was further analyzed in accordance with the thermodynamics principle,which is based on the relationships between saturated pressure and saturated temperature of vapor.【Result】1)The peak values of temperature and pressure inside poplar lumber were increased with the increase of heating platens’temperature.As the heating platens’temperature increased from 120℃to 140℃,the peak values of temperature and pressure in the surface layer of lumber were increased from 115.4℃,209.3 kPa to 133.0℃,314.5 kPa,respectively.The peak values of temperature and pressure in the center layer of poplar lumber were increased from 109.4℃,235.5 kPa to 126.4℃,336.9 kPa,separately.However,the peak temperatures’occurrence time lagged behind the related peak pressures.2)The analysis for moisture state in the surface layer of poplar lumber showed that the moisture in poplar lumber was unsaturated water at the heating platens’temperature of 120℃.The final MC of surface layer,which was higher than FSP,provided the evidence for the conclusion.The heat transferred from the heating platens to surface layer of poplar lumber resulted in the large volume vaporiza

关 键 词：热压干燥 热板温度 杨木锯材 水分状态 温度 压力 

分 类 号：S781.71[农业科学—木材科学与技术]