共查询到18条相似文献，搜索用时 468 毫秒
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研究了竹材热压干燥过程中的水分迁移特性.结果表明:在整个干燥过程中,前期含水率降低较快,后期含水率降低较慢.竹材平均干燥速度与次表层竹材的干燥速度相近;在含水率较高的干燥初期,水分迁移的阻力在竹材表面,水分迁移主要靠毛细管张力作用;在含水率较低的干燥后期,水分迁移的阻力在竹材内部,水分迁移主要以扩散方式进行,干燥速度取决于木材内部水分移动的速度.竹材热压干燥过程中的水分移动,主要受温度梯度和含水率梯度的共同作用. 相似文献
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木材干燥过程中,介质循环速度是一个影响木材干燥的重要工艺参数.在木材各含水率阶段,通过试验分析研究不同介质循环速度对木材干燥速度的影响.结果表明,介质循环速度对干燥速度的影响显著,但其影响随木材含水率（MC）的降低而减弱.在低介质循环速度条件下,试件MC大于45％时,表现为木材干燥速度和木材含水率偏差（△MC）随循环风速的增加而增加,呈显著正相关关系;试件MC介于35％ ～ 45％之间时,正相关关系存在但不显著;试件MC小于35％时,干燥室内循环风速的大小不影响木材的干燥速度和木材含水率偏差（△MC）.对试件表层含水率分析,试件表层含水率大于25％时,试件表面循环风速对试件表层含水率的影响显著;试件表层含水率小于25％时,试件表面循环风速对试件表层含水率的影响很小,不同循环风速下试件表层含水率基本一样. 相似文献
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以黑胡桃木材为对象,采用X射线扫描含水率分布测试方法,分析、比较了微波干燥与常规热风干燥过程中木材内部含水率动态分布规律.结果表明:在微波干燥和常规热风干燥过程中,木材内层含水率均高于表层,存在着整体性的内高外低的含水率梯度场;在接个微波干燥过程中,木材内部虽然出现了部分内层含水率低于外层的情况,存在着含水率分布的局部不均匀,但并未出现与常规热风干燥相反的含水率梯度;在微波干燥中,木材内部各层与表层含水率的差值随着干燥时间的延长逐渐降低.随着干燥过程的进行,常规热风干燥中木材芯层与表层含水率差呈现出先增加后减小的变化趋势. 相似文献
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短周期工业材干燥过程中木材内部水分迁移特点的研究 总被引：8，自引：0，他引：8
研究了短周期共业材新伐材和气干材在干燥过程中木材厚度方向含水率分布和水分迁移特点,考察了干燥过程中介质温度变化及其对表层产中心层干燥速度的影响。研究表明,原木初含水率径向、从向存在变异、导致板材初含水率分布无规律。在非稳态干燥中,逐渐呈外低内高近似抛物线分布,直至平衡处理后,内外层含水率才接近一致。平均干燥速度随介质温度的提高而增加,不同干燥阶段介质温度的影响也不同,在相同的平衡含量水率条件下,提 相似文献
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赤桉材干燥终了调湿处理中的流变行为 总被引：1，自引：0，他引：1
在实验室的小型调温调湿箱中对25 mm厚赤桉干燥材进行终了调湿处理,并以切片法分析调湿过程中的弹性应变和机械吸附应变特性.结果表明:经24 h的处理,表层的吸湿效果显著,含水率上升达5%,而板材的平均含水率上升2.5%～3.0%;表层压缩弹性应变在经历处理开始3 h内的短暂上升后迅速下降,而整个处理过程中心层的拉伸弹性应变变化不大;处理9 h后,次表层的压缩弹性应力比表层的大,产生反向的应力梯度;处理中,木材表层吸湿软化发生了补充收缩,缩小了内外各层长度差异,应力减小;表层软化有效地减小乃至消除机械吸附应变,但由于干燥历史的影响,机械吸附应变的变化滞后于含水率的变化,在处理的第3～9 h间下降幅度最大. 相似文献
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短周期工业材干缩率和干燥应变规律的研究 总被引：1，自引：0，他引：1
研究了短周期工业材在干燥过程中木材表层和内部各层干缩率及弹性和塑性应变的变化规律。结果表明,基准硬度水平对应变值的大小和最大变就值的到达时间有显著影响。干燥前期,木材表层伸张弹性应变最大值随着温度和平衡含水率的增加而减少,木材表层塑性应变则随平衡含水率的增加而增加。正确调节基准初期阶段的平衡含水率水平,能有效地控制干燥前期应变最大值,从而达到控制干燥质量的目的。 相似文献
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研究小径木白桦锯材在连续加热方式和间歇加热方式(间歇2 h和间歇6 h)干燥过程中表层应力的产生、发展变化规律.结果表明:3种加热方式下锯材表层应力的变化趋势基本一致,但无论是干燥前期或干燥中期,间歇加热锯材的表层应力明显小于连续加热锯材的表层应力,间歇6 h锯材的表层应力最小.间歇阶段使干燥过程中木材的干燥应力得到了释放,延长间歇时间有利于降低锯材表层应力.同一含水率水平下,弦切板的表层应力比径切板的表层应力大. 相似文献
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Li Xian-jun Li Wen-jun Zhang Bi-guang 《中国林学(英文版)》2007,9(1):63-67
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... 相似文献
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Björn A. Källander 《Wood Science and Technology》2002,36(6):477-486
The European Drying Group (EDG) proposal on a wood drying quality standard defines demands on final moisture content variation of the dried wood. The final moisture content variation will depend on material parameters as well as the production process and the wood will always show a “natural” moisture content variation after drying. Thus the drying process has to be defined well enough to allow for the natural moisture content variation in order to fulfil the demands of the drying standards. As the average equilibrium moisture content of the wood in a vacuum drying kiln with pure steam atmosphere is determined by the pressure and the temperature, the demands on the climate control system to fulfil the demands of the drying standard can be calculated with regard to the natural moisture content variation of the wood. In the first part of this contribution the demands on climate control in vacuum dryers are calculated based on the EDG-standard and the natural moisture content variation. In the second part of the contribution the demands on climate control are compared with climate and moisture content measurements from industrial production in vacuum kilns. Critical factors in kiln design and climate control system design necessary to maintain a controlled drying climate are listed. 相似文献
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小径级柞木干燥试验结果表明:在干燥初期干球温度为35℃、干燥末期干球温度为70℃、干燥周期中进行两次中间处理和末期终了处理、干燥周期为15 d的工艺条件下,板材干燥前总平均含水率41.6%,干燥结束后总平均含水率11.7%,板材厚度上含水率偏差<3%;干燥结束后伸长应力和压缩应力甚微,板材表面的颜色轻微变暗,除髓心材和水纹材有少数裂纹和轻微变形外,其余木材并没有发生翘曲、变形、开裂等干燥缺陷,干燥质量满足了GB6491—86《国家锯材干燥质量标准》二级以上的指标要求。本次试验确定的干燥工艺满足了小径级柞木板材的干燥工艺要求。 相似文献
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Elissavet Konstantinidou Ioannis Takos Theodora Merou 《European Journal of Forest Research》2008,127(2):125-131
The effect of seed moisture content (m.c.) and seed storage conditions of bay laurel (Laurus nobilis L.) was investigated in relation to seed viability. In the first experiment, the effect of drying rate on seed moisture and
seed germination was investigated. Fresh seeds, with their original moisture content displayed a germination percentage of
55.1%. When the seed moisture content was reduced by 2.0% in an oven, the germination percentage rose to 81.0%. When the seed
moisture content was reduced even more by using the same method, the germination percentages decreased dramatically. Reducing
the seed moisture content to 28.7 and 23.5% by drying the seeds in alternating room conditions resulted in an increase of
seed germinability to 84.3 and 90.9%, respectively. The drying of the seeds for 45, 60 and 75 days reduced their seed germination
to 66.8, 49.4 and 48.0%, respectively. Reducing seed moisture content below 15.0% resulted in practically nullifying seed
germinability. The fact that bay laurel seeds cannot retain their germinability at lower moisture contents demonstrates that
it is a species with recalcitrant seeds. In the second experiment, moist and dry storage conditions were tested under different
temperatures and moisture contents. The storage experiment showed that the most effective way of conserving the bay laurel
seeds is moist storage at 0 ± 1°C for 4 months without previous drying of the seeds. 相似文献
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Summary The transport of heat and moisture during the convective drying of southern pine was examined experimentally. Moisture distribution within the wood samples was measured using gamma attenuation. The accuracy of these measurements was found to be moisture content dependent with estimated uncertainties ranging from 29.5% at 10% moisture content to 6.8% at 120% moisture content. Local moisture content measurements reveal large inflections at high moisture contents. Peaks in moisture content are closely correlated with low fwood density and vice versa. Above the fiber saturation point the measured drying rate is not a well defined function of the moisture content. This is perhaps due to the biological variability of wood as well as grain orientation, although no definite conclusions could be drawn from the data with regard to the effect of grain orientation. The drying rate does not appear to be highly temperature dependent at high moisture contents. Below the fiber saturation point where diffusion is expected to be the dominant transport mechanism, the drying rate is less affected by biological variability and grain orientation, however, the effects of temperature are evident.The authors wish to acknowledge the support of this work by the National Science Foundation under Grant Number CME-7906367. We must also express our appreciation to staff members at Weyerhaeuser Technology Center who supplied us with wood samples. In addition to the authors, Mr. T. R. Brown, S. H. Moen, and D. Chow played a critical role in gathering much of the data 相似文献