过热蒸汽预处理对落叶松方材高频/真空干燥质量的影响

对落叶松髓心方材采用不同温度的过热蒸汽预处理,再利用前期试验得出的高频/真空干燥参数进行试验。结果表明,采用常压105℃过热蒸汽预处理31 h,高频/真空干燥后试材的表裂明显减少,且终含水率分布更加均匀;过热蒸汽预处理工艺使高频/真空干燥周期有所延长,但综合考虑干燥周期和干燥质量,认为此工艺具有可行性。     

人工林落叶松髓心方材的高频真空干燥(英文)

对截面尺寸为100mm×100mm的人工林落叶松髓心方材进行系列高频真空干燥试验,分析研究不同高频真空干燥条件下干燥质量和干燥速度的变化规律,获得合理的高频真空干燥工艺基准;为了进一步减少试材表裂,干燥前对试材进行切口和过热蒸汽预处理。结果表明:沿试材长度方向的中心位置切口和过热蒸汽预处理都能有效减少试材表裂,提高干燥质量。     

人工林落叶松髓心方材高频/真空干燥工艺研究

对人工林落叶松含髓心方材进行高频真空干燥试验,以确定高频真空干燥工艺参数。结果表明,适宜的高频真空干燥工艺,不但能保证落叶松髓心方材干燥质量,而且能大幅度提高干燥速度。试验得出较佳的干燥工艺条件为:电流0.4A,输入电压2kV;高频开启3min停1min,控制温度50℃;干燥初期真空度为13.33kPa,干燥后期真空度为6.67kPa。     

切口处理对落叶松方材高频/真空干燥质量的影响

对兴安岭落叶松髓心方材采用纵向切口处理后,进行高频/真空干燥试验。结果表明,落叶松髓心方材切口处理,能明显减少表面开裂,总表裂长度降低了39%~50%;对干燥速度、含水率分布以及干燥收缩均无显著影响。     

高频真空干燥中压缩载荷对落叶松长方形髓心方材表面裂纹的影响

探究了高频真空干燥中压缩载荷对有纵向槽的落叶松长方形髓心方材表面裂纹的影响。研究结果如下:与正方形方材相比,由于压缩载荷作用和长方形方材宽度的增加,长方形方材宽度与厚度干缩率比大大减少了;因为高频加热和干缩差异应力的减少,长方形方材表面裂纹减少了许多,尤其没有纵向槽的长方形方材表面裂纹明显减少。     

人工林杨木的高频真空干燥工艺

在人工林杨木的高频真空干燥系列试验中,通过不断改变干燥工艺参数并分析总结试验结果,从而确定杨木高频真空干燥适宜的工艺基准。结果表明,在本试验确定的高频真空干燥工艺下,初含水率较高的杨木不仅能保证干燥质量,而且干燥速度可比常规蒸汽干燥法和高温蒸汽干燥法提高数倍。     

木材真空-过热蒸汽干燥的预热特性

在真空状态下，分别对过热蒸汽和空气为干燥介质时木材干燥预热阶段进行对比试验，探讨了木材在真空－过热蒸汽干燥中预阶段的工艺特性。结果表明：过热蒸汽干燥的预热阶段进行得非常迅速，同时其表面水分的凝结量也较以空气为介质时表面水分的凝结量大。     

木材高频真空干燥及其应用前景

一、国内外发展概况及特点木材高频真空干燥是七十年代初首先在前苏联、美国、日本等国研究发展起来的一项先进的干燥技术,八十年代初开始应用于生产。美国的一家动力公司和日本的制造厂商,已推出高频真空干燥机的系列化产品,在欧、美及包括中国台湾在内的很多国家和地区推广应用。高频真空干燥的最大特点是木材干燥极为迅速。由于采用高频介电加热和在连续真空条件下作业,木材可在很短的时间内获得充分的热量,并在较低的温度下迅速干燥。一些用常规窑干法需要干燥数天乃至数十天的木料,采用高频真空干燥,仅需数小时或数十小时即可,干燥周期可缩短17     

成材（板、方材）过热蒸汽-真空干燥技术

木材干燥是在热力作用下以蒸发或沸腾的汽化方式排除木材水分的处理过程。木材干燥是保存木材的优良特性、增强材质、合理利用木材的重要措施之一。 目前国内外普遍应用的木材干燥设备是蒸汽干燥和除湿干燥设备,拥有量占整个干燥设备的８０％以上,而过热蒸汽－真空干燥设备是近几年发展起来的一种新型木材干燥设备,用此种设备干燥的木材质量好,木材颜色变色小,是一种较为理想的木材干燥设备。１工艺理论基础 木材属于植物有机体,含有一定的水分。其作为原材料在加工利用时,水分的存在在大多数情况下是极为不利的,因为木材的物理力学…     

新式高效节能木材蒸汽干燥窑系列产品

木材蒸汽干燥,无论过去、现在和将来,都是主要的,应用普遍的木材干燥方法,其干燥工艺参数易控制和调整;便于消除木材干燥过程中的应力和变形,质量有保证;可集中操作、统一管理,投资少,能耗低,干燥成本也较低。辽中林业机械厂研制的     

杉木人工林木材的高频真空干燥工艺

对人工林杉木25mm和50mm厚板材进行了系列高频真空干燥试验.结果表明:干燥后的板材变形小,表面平整,表芯层含水率差异较小.尽管试板的初始含水率差异较大,但根据高频真空干燥靠近正极板的木材比靠近负极板的干燥速度快的特点,试板的初始含水率由低至高在负极板至正极板之间进行顺序摆放码垛,干燥后的板材含水率可达到均匀一致.     

Effect of EMC and air in wood on the new in-process moisture content monitoring concept under radiofrequency/vacuum (RF/V) drying

To improve the accuracy of the new in-process moisture content (MC) monitoring concept under radiofrequency/vacuum (RF/V) drying, equilibrium moisture content (EMC) tests were carried out under various ambient pressures, and pressure curves in wood were analyzed during chamber evacuation and heating phases. The results showed that EMC increased with a decrease in ambient pressure regardless of temperature, relative humidity (RH), and species. The accuracy of MC estimation for Hinoki under RF/V drying was improved from 1.5% maximum absolute errors to 0.6% after EMC modification. The pressure curves for Hinoki and Sugi under RF/V drying showed similar tendencies to an idealized process. Russian larch showed different curves, indicating that the pressure in the wood did not reach the ambient pressure because of its low permeability. Therefore, MC could not be estimated using this monitoring concept because of the presence of much air in the wood of Russian larch.     

Mass and heat transfer mechanism in wood during radio frequency/vacuum drying and numerical analysis

The mass and heat transfer mechanisms during radio frequency/vacuum(RF/V) drying of square-edged timber were analyzed and discussed in detail, and a new one-dimensional mathematical model to describe the transport phenomena of mass and heat during continuous RF/V drying was derived from conservation equations based on the mass and heat transfer theory of porous materials. The new model provided a relatively fast and efficient way to simulate vacuum drying behavior assisted by dielectric heating. Its advantages compared with the conventional models include:(1) Each independent variable has a separate control equation and is solved independently by converting the partial differential equation into a difference equation with the finite volume method;(2) The calculated data from different parts of the specimen can be displayed in the evolution curves, and the change law of the parameters can be better described. After analyzing the calculated results, most of the important phenomena observed during RF/V drying were adequately described by this model.     

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     

Effect of pretreatment with high temperature and low humidity on drying time and prevention of checking during radio-frequency/vacuum drying of Japanese cedar pillar

This study investigated the effect of pretreatment with high temperature and low humidity (HT-LH) on characteristics of radio-frequency/vacuum (RF/V) drying of boxed heart timber of Japanese cedar (150 × 150 mm in cross section, 3600 mm long). From green to approximately 15% moisture content, the drying times including HT-LH treatment were 170 h for the nonkerfed control, 190 h for the kerfed control, and 150 h for both the kerfed and nonkerfed HT-LH specimens. Surface checks were effectively prevented by the HT-LH treatment while the kerfed HT-LH specimens were free from surface checks. In order to prevent the formation of internal checking during RF/V drying, it is suggested that HT-LH treatment should finish around the fiber saturation point.     

Effect of compressive load on the dimensional changes of the Japanese larch dried in a radio-frequency/vacuum drier

This study investigated the effect of a compressive load of 0.092 MPa on the dimensional changes of Japanese larch in a humidity chamber after continuous radio-frequency/vacuum drying. The dimensional changes in the loading directions were significantly increased while those perpendicular to the loading directions were decreased. The shrinkages showed higher values in continuous drying than in intermittent drying. For the specimens loaded on their tangential sections, the radial shrinkages were even higher than the tangential shrinkages; thus, the tangential/radial shrinkage ratio was decreased by 0.27. The transverse hygroscopicity was reduced for the specimens loaded on their cross sections, but increased for the specimens loaded on their tangential sections.     

STEAMING-HIGH TEMPERATURE DRYING OF LARCH LUMBER

A series of drying tests on Larch Lumber and a theoretical analysis led to the follow-ing conclusions:1.Steaming pretreatment is a very powerful means to decrease defects induced by the drying processand increases the drying velocity of the lumber.2.The steaming—high一temperature drying schedule had resulted in fast drying and good quality ofthe dried lumber.     

菲律宾桃花芯木锯材干燥工艺初探

以菲律宾桃花芯木为研究对象,探索30 mm厚菲律宾桃花芯木锯材干燥工艺。通过百度试验法得知其初期开裂为3级、内裂为2~3级、截面变形为1级;通过密度测定实验得知其气干密度为0.562 g/cm^3、全干密度为0.517 g/cm^3和基本密度为0.465 g/cm^3。根据该木材密度和干燥特性制定3种30 mm厚菲律宾桃花芯木锯材干燥基准并分别进行常规干燥工艺试验。通过对3次工艺试验结果的综合分析表明：在3次工艺实验所用执行基准均能满足2级干燥指标。其中,第一次工艺实验所用执行干燥基准为本研究中最佳干燥基准。第一次工艺实验的初始温度为60℃,末期温度为80℃、初含水率为66.97%、终含水率为7.79%的锯材干燥周期为185 h。     

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.     

25mm厚进口桃花心木干燥基准的优化

采用实验室干燥试验设备,按企业生产干燥基准进行25 mm厚桃花心木干燥试验,并通过锯材干燥质量检测和分析,制定出常规干燥基准的优化方案。结果表明:采用优化的干燥基准,干燥周期由企业原基准的12 d缩短为6 d,干燥效率提高一倍,残余干燥应力值显著降低,锯材综合干燥质量由3级提升至2级,可满足家具、地板等实木制品对锯材质量的要求。