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1.
T. Takemura 《Journal of Wood Science》2003,49(1):0011-0017
In recent years a microwave transmission-type moisture meter has been developed in Japan. Its purpose is to measure the average
moisture content of thick woods. Since its development I have realized that there is a negative correlation between the moisture
content of wood and the power voltage of the meter. This realization suggests that an invisible stress has an effect on the
attenuation constant of the wood. The presence of such a stress in the wood could easily be proven by the slicing technique.
In this article a theory is presented to explain further the effect of this stress on the attenuation constant. The theory
was applied to softwood specimens in various states of moisture. It was concluded that the calculated strain distributions
of the various specimens approximated those of the experimental results. Thus, the proposed theory presented herein has validity
or adaptability with regard to qualitatively understanding the stress. Future research efforts would also be expected to detect
the stress in wood due to moisture.
Received: November 30, 2001 / Accepted: March 18, 2002
Acknowledgments The author thanks Mr. K. Hayashida and Mr. T. Taniguchi (former students of Fukui University of Technology) for their assistance
in the experiment. The author also thanks Dr. Okada of the Kawasaki Kiko Co. and Prof. Dr. Sobue of Shizuoka University for
their valuable discussions and suggestions.
Part of this report was presented at the Annual Meeting of the Central District of the Japan Wood Research Society, Gifu,
September 2000
Correspondence to:T. Takemura 相似文献
2.
A microwave applicator for on line wood drying: Temperature and moisture distribution in wood 总被引:7,自引:0,他引:7
Summary An especially designed open microwave applicator was analysed using wood as the material to be heated and dried. The idea
was to develop an on line microwave construction consisting of several small open applicators, each fed by a small standard
magnetron (for example 1.4 kW main power). The process was analysed by measuring the wood temperature during heating using
an IR-camera and detecting the moisture distribution during drying by CT-scanning. Pine and birch wood samples were used in
the experiments, mainly 40 mm in thickness. The experiments show that the power distribution differs between dry wood and
moist wood. The analysis of the temperature fields captured by the IR-camera during the first minutes allows a rather accurate
determination of the MW power. Consequently, the drying proceeds unevenly in the wood specimens, especially in the longitudinal
direction. The dimensions of the applicator and its relation to the wood dimension are very important. However, the wood was
not destroyed, the temperature and moisture gradients did not affect the wood in terms of checks or deformations. The drying
rate in different positions of the specimen varied between 0.30 and 0.80 percentage moisture content/min. The uneven energy,
meaning temperature and field distribution, is to be compensated in the future by a moving wood load and by alternating the
position of each applicator in a larger scale microwave pilot plant.
Received 25 February 1997 相似文献
3.
《Wood material science & engineering》2013,8(3-4):118-129
Abstract Twist in wood, being closely related to spiral grain, may cause serious problems in building structures, furniture and joinery. It is therefore of great interest to sort out, at an early stage in the manufacturing process, trees, logs and boards that have an excess of spiral grain. The spiral grain pattern is described by a helical deviation of the fibre direction in relation to the longitudinal direction of a living tree or a log and seems to be an indicator for other defects such as compression wood. Remote microwave sensing of spiral grain has received a lot of interest during the past two decades. Its development has been impeded by the large variation with moisture content of the microwave properties of wood and by the complexity in modelling the electromagnetic field in a log with spiral grain. A review is presented of a direct method with no requirement for information on moisture content for boards. This procedure has recently been generalized to cylindrical logs and trees having a constant slope of the grain. A further generalization is presented here to allow for the normal spiral grain pattern with radially changing slope of grain in wood under bark. Based on this theory, a measurement procedure is proposed for the detection of wood grain angle with radial dependence, requiring no information on moisture content in the sapwood, which is also applicable to completely or partially frozen wood. A suitable application would be an instrument to use in the forest for measurements on living trees or logs. 相似文献
4.
The purpose of this study was to use images from a microwave sensor on a pixel level for simultaneous prediction of moisture
content and density of wood. The microwave sensor functions as a line-scan camera with a pixel size of 8mm. Boards of Scots
pine (Pinus sylvestris), 25 and 50mm thick, were scanned at three different moisture contents. Dry density and moisture content for each pixel were
calculated from measurements with a computed tomography scanner. It was possible to create models for prediction of density
on a pixel level. Models for prediction of moisture content had to be based on average values over homogeneous regions. Accuracy
will be improved if it is possible to make a classification of knots, heartwood, sapwood, etc., and calibrate different models
for different types of wood. The limitations of the sensor used are high noise in amplitude measurements and the restriction
to one period for phase measurements. 相似文献
5.
较之传统加热方法,微波加热是一种新型加热技术,在简述木材微波加热的机理上,阐述了影响木材介电特性的因素,指出其中木材含水率和温度是影响木材节电性质的两个最重要的因素.通过理论计算确定微波在木材中的穿透深度.计算表明:随着木材含水率和微波工作频率的增加,微波在木材中的穿透深度减少;当用频率为915 MH z和2 450 MH z的微波加热或干燥具有高含水率的木材时,木材的最大厚度应分别控制在16 cm和6 cm左右. 相似文献
6.
Charalampos Lykidis Katerina Kotrotsiou Antonios Tsichlakis 《Wood material science & engineering》2020,15(5):269-277
ABSTRACT Densification of resin impregnated wood under hot-pressing is a method that along with the potential for the reduction of set-recovery could additionally increase the density of wood and further improve other technical properties. In this study, the effect of the methylated melamine-formaldehyde modification on the shape memory effect of densified Populous nigra wood at various compression ratio levels was investigated. Furthermore, the effects on moisture content and compression ratio were also assessed. The most important conclusion drawn was that MF can act as a means for reducing set-recovery of compressed poplar wood since it is obvious that the use of MF significantly improved the stability of densified wood due to the formation of new bonds between cell wall components and MF. In the case of densification under stress of 10?kg/cm2, the stabilization was improved by the use of MF to about 50% compared to water-treated specimens. The effect of MF on the stabilization of densified wood was not very clear for stresses higher than 10?kg/cm2 since due to the outflow of MF solution during the first minutes of compression. 相似文献
7.
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。 相似文献
8.
The aim of this study was to use finite element modeling (FEM) as a tool to analyze microwave scattering in wood and to verify
the model by measurements with a microwave scanner. A medical computed tomography scanner was used to measure distribution
of density and moisture content in a piece of Scots pine (Pinus sylvestris). Dielectric properties were calculated from measured values for cross sections from the piece and used in the model. Images
describing the distribution of the electric field and phase shift were obtained from the FEM simulation. The model was verified
by measurements with a scanner based on a microwave sensor. The results show that simulated values correspond well to measured
values. Furthermore, discontinuities in the material caused scattering in both the measured and the simulated values. The
greater the discontinuity in the material, the greater was the need for computational power in the simulation. 相似文献
9.
Numerical modelling was used to follow the evolution of the moisture content gradient and the stress field resulting from
the restrained differential dimensional response across a wooden cylinder, simulating sculptures, in response to variations
in temperature (T) and relative humidity (RH). Material properties of lime wood (Tilia sp.) were used in the modelling as this wood species was historically widely used. The allowable RH variations, below which mechanical
damage will not occur, were derived as functions of the amplitude, time period and starting RH level of the variation. Lime
wood can endure step RH variations of up to 15% in the moderate RH region, but the allowable domain narrows when RH levels
shift from the middle range. The allowable amplitude of the variations increases when time allowed for the change increases.
The stress field does not vanish even for slow, quasi-static changes in RH due to structural internal restraint resulting
from the anisotropy in the moisture-related dimensional change. 相似文献
10.
Variation in density and moisture content of wood and bark among twenty Eucalyptus grandis progenies
Summary Variation in density and moisture content of Eucalyptus grandis wood and bark is described utilizing the trees established for a half-sib progeny test in southern Florida. Differences in density and moisture content among progenies were significant. Variations in wood properties were largely due to the genetic differences. No relationship was found between wood density and wood moisture content. Implications for genetic manipulation of wood quality for this species were discussed. 相似文献
11.
Research on the effect of microwave pretreatment on moisture diffusion coefficient of wood 总被引:4,自引:0,他引:4
Based on the pathway of moisture diffusion in wood below FSP, an improved moisture diffusion model has been proposed. The
theoretical solution of the mathematic model shows that the diffusion coefficient for microwave pretreated wood was increased
no more than 3% compared with that of wood without being treated even under extreme condition. Experiments indicate that the
pit membrane structure can be effectively destroyed during microwave pretreatment, but the moisture diffusion coefficient
can not be significantly improved. In practice, the effect of microwave pretreatment on moisture diffusion coefficient can
be ignored. The drying rate of wood during the sequent conventional drying can not be significantly improved by microwave
pretreatment. 相似文献
12.
A new method for nondestructive evaluation of solid wood moisture content based on dual-energy X-ray absorptiometry 总被引:1,自引:0,他引:1
This paper presents a new method to determine the moisture content of solid wood based on the principle of dual-energy X-ray absorptiometry. The study investigates the theoretical relationship between X-ray wavelength and mass attenuation coefficients of wood, water, and reference substance. In accordance with this relationship, a theoretically obtained equation is proposed to calculate the moisture content in wood. The proposed equation is compared to experimental results using small blocks of sugi wood, which showed that the change in mass attenuation coefficient of wood with X-ray tube voltage increased with increasing moisture content as expected from the theoretical equation. A regression equation for moisture content estimation was determined based on the experimental results, and the standard error of estimate in the 0–120 % dry-basis moisture content range using the regression equation was determined to be 21.9 % with the most appropriate pair of tube voltages, 15 and 40 kVp. The accuracy of the method will be improved by reducing the duration of X-ray radiography and by increasing the disparity between paired tube voltages. This method has the potential to determine moisture content of solid wood using X-ray without oven-drying or assuming oven-dry density. 相似文献
13.
14.
J. S. Rasmussen C. Felby S. Prasad H. Schmidt G. A. Eiceman 《Wood Science and Technology》2011,45(2):205-214
The durability of wood is improved by wood preservatives. Due to new environmental legislation, commonly used active ingredients
such as chromium and arsenate are being replaced by alternative and more environmentally friendly preservatives. However,
the alternative wood preservatives are more difficult to detect in the wood. Detection of the preservatives is necessary in
order to monitor millwork production for qualitative assessment of the wood preservative uptake. The aim of this study is
to examine the use of solid phase desorption-ion mobility spectrometry (SPD-IMS) can be used for rapid detection of the wood
preservatives propiconazole and tebuconazole in Scots pine (Pinus sylvestris). The findings proved that SPD-IMS is capable of detecting and distinguishing wood preservatives directly from treated wood
shavings. SPD-IMS requires no additional sample preparation or extraction of the wood sample. The findings show that SPD-IMS
is a fast and easily applied method for direct detection of propiconazole and tebuconazole in small wood samples. 相似文献
15.
Oleg V. Startsev Alexey Makhonkov Vladimir Erofeev Sergei Gudojnikov 《Wood material science & engineering》2017,12(1):55-62
The dynamic shear modulus and the loss modulus of Betula alba, Ulmus parvifolia, Quercus robur, Acer platanoides, Tilia cordata, Fraxinus excelsior and Pinus sylvestris wood were measured using an inverted torsion pendulum within a wide temperature range. The glass transition temperature of the lignin–carbohydrate complex and the decomposition temperature of the wood cellulose were estimated. The temperature band from 170°C to 240°С shows the transition of the lignin–cellulose complex from the glassy to the rubbery state. Mechanical properties of different types of wood are affected by moisture and anatomical differences, but glass transition and decomposition temperatures are the same. More than 5% of moisture in the wood stored at normal conditions were found. After drying, the increase of dynamic shear modulus of wood over the entire region of the glassy state was observed. The intensity of maximum peak of dynamic loss modulus is also increased due to activation of the segmental motion of macromolecules of the ligno-carbon complex. The decomposition temperature of the cellulose crystallites was unchanged for specimens containing moisture and for dried specimens. 相似文献
16.
Soichi Tanaka Yuko Fujiwara Yoshihisa Fujii Shogo Okumura Hiroyoshi Togo Naoya Kukutsu Shoji Mochizuki 《Journal of Wood Science》2013,59(5):367-374
To evaluate the dielectric anisotropy caused by wood structure at a millimeter wave frequency of 100 GHz, the dielectric parameters for flat-sawn specimens of nine wood species at 0 and 11 % moisture content (MC) were measured using a free space method devised for reducing the multiple reflections under an electric field of millimeter waves parallel to longitudinal and tangential directions of wood, and those in radial direction were estimated using a conventional approximation theory. The dielectric parameters in the tangential and radial directions were almost identical and constantly smaller than those in the longitudinal direction. All the dielectric parameters increased with wood density and were larger at 11 than 0 % MC. The dielectric parameters in the longitudinal and transverse directions and the dielectric anisotropy between them were well fitted to the regression lines based on a dielectric mixture model composed of pores and dielectric isotropic wood substance, and a parallel capacitor and Lichtenecker’s exponential formulas were employed to represent the dielectric parameters of the mixture in the longitudinal and transverse directions, respectively. It was concluded that the dielectric anisotropy at 100 GHz is caused by the pore alignment and that the dielectric parameters are almost unaffected by anatomical structures, such as the rays. It was also confirmed that the free space method was effective for the measurement of the dielectric parameters for the flat-sawn specimens. 相似文献
17.
In this study,the effects of microwave radiation intensity,radiation time and initial wood moisture content (MC) on the properties of temperature development in Eucalyptus urophylla wood samples during the microwave explosion pretreatment have been investigated using a new microwave pretreatment equipment.The results show that 1) with the increase of microwave radiation intensity and a decrease in initial wood MC,both the average temperature and its rate of increase in wood rise rapidly;2) with an increase ... 相似文献
18.
Pinewood nematode, Bursaphelenchus xylophilus, is an inhabitant of native pine species of North America, where its presence in trees is non‐pathogenic. By contrast, the introduction of this nematode to forests overseas has devastated some pine stands and is recognized as a pest of phytosanitary concern by some countries' National Plant Protection Organizations. The ability to detect B. xylophilus in internationally traded wood products is crucial to reduce the spread of this organism. Current molecular techniques for the detection of B. xylophilus rely on the presence of genomic DNA and thus will detect both living and dead nematodes without differentiation. The detection of dead nematodes could lead to unnecessary trade disruption. Therefore, accurate techniques for the detection of and differentiation between live and dead B. xylophilus are critical. We have developed an endpoint RT‐PCR assay and a SYBR Green 1 real‐time RT‐PCR assay, both of which selectively identify living pinewood nematode by detecting the presence of Hsp70 mRNA as a viability marker. Both of these assays may help overcome or resolve disputes involving the detection of pinewood nematode at the port of entry and can also be used to evaluate the efficiency of wood treatment procedures. 相似文献
19.
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