Theoretical modeling of the effects of temperature and moisture content on the acoustic velocity of Pinus resinosa wood

To investigate the effects of temperature and moisture content(MC) on acoustic wave velocity(AWV)in wood,the relationships between wood temperature,MC,and AWV were theoretically analyzed.According to the theoretical propagation characteristics of the acoustic waves in the wood mixture and the differences in velocity among various media(including ice,water,pure wood or oven-dried wood),theoretical relationships of temperature,MC,and AWV were established,assuming that the samples in question were composed of a simple mixture of wood and water or of wood and ice.Using the theoretical model,the phase transition of AWV in green wood near the freezing point(as derived from previous experimental results) was plausibly described.By comparative analysis between theoretical and experimental models for American red pine(Pinus resinosa) samples,it was established that the theoretically predicted AWV values matched the experiment results when the temperature of the wood was below the freezing point of water,with an averageprediction error of 1.66%.The theoretically predicted AWV increased quickly in green wood as temperature decreased and changed suddenly near 0 °C,consistent with the experimental observations.The prediction error of the model was relatively large when the temperature of the wood was above the freezing point,probably due to an overestimation of the effect of the liquid water content on the acoustic velocity and the limited variables of the model.The high correlation between the predicted and measured acoustic velocity values in frozen wood samples revealed the mechanisms of temperature,MC,and water status and how these affected the wood(particularly its acoustic velocity below freezing point of water).This result also verified the reliability of a previous experimental model used to adjust for the effect of temperature during field testing of trees.

Determination of Wood Moisture Properties Using a CT-Scanner in a Controlled High-Temperature Environment

Theaim of the present work wasto analyze moisture flow and moisture content data for high-temperature drying by usingan advanced image- processing algorithm.Since wood starts to shrink below the fibre saturation point during drying, the size and shape of wood will change. The dry wood image was thoroughly transformed to the shape of the wet wood image prior to calculating the dry weight moisture content. The use of the image- processing algorithm for the dry weight moisture content on density data from the CT-scanning during drying in a controlled high-temperature environment showed that this method is a powerful tool for analyzing the moisture flow inside the wood piece. Furthermore, the new CT-scanner together with the climate chamber gave unique results, as it has not been possible to study high-temperature drying with this method before.

External Heat Transfer in Moist Air and Superheated Steam for Softwood Drying

In kiln drying of softwood timber, external heat and moisture mass transfercoefficients are important in defining boundary temperature and moisture content at the woodsurface. In addition, superheated steam drying of wood is a promising technology but this has notbeen widely accepted commercially, partially due to the lack of understanding of the dryingphenomena occurred during drying. In this work, experimental investigation was performed to quantifythe heat transfer between wood surface and surrounding moist air or superheated steam. In theexperiment, saturated radiata pine sapwood samples were dried using dry-bulb/wet-bulb temperaturesof 60℃/50℃, 90℃/60℃, 120℃/70℃, 140℃/90℃, 160℃/90℃, 140℃/100℃ and 160℃/100℃. The lasttwo schedules were for superheated steam drying as the wet-bulb temperature was set at 100℃. Thecirculation velocity over the board surface was controlled at 4.2m·s^(-1). Two additional runs(90℃/60℃) using air velocities of 2.4 m·s^(-1) and 4.8 m·s^(-1) were performed to check theeffect of the circulation velocity. During drying, sample weight and temperatures at wood surfaceand different depths were continuously measured. Prom these measurements, changes in woodtemperature and moisture content were calculated and external heat-transfer coefficient wasdetermined for both the moist air and the superheated steam drying.

System Identification of Wood Drying Process Based on ARMAX Model

This article presents system identification of wood drying process based on ARMAX model. Temperature and equivalent moisture content are considered as inputs, and moisture content of the wood sample during drying is taken as output of the system. The comparative study of RLS and FF-RLS to identify the system parameters is presented. Simulation results are presented to val-idate the efficacy of the ARMAX model for wood drying process.

Development and Evaluation of an All Weather-Type Solar Drying House to Make for Wood Pellet Material

To suppress the global environment pollutions, we tried to develop a new-type solar drying house by improving a typical agricultural green-house, so that an all weather-type solar drying house was invented ultimately. This house is capable to dry raw wood materials (Ogako) into suitable moisture content (Mc) to make a wood pellet. The all weather-type solar Ogako drying house is covered with a triple transparent film, and an open/close free-type shield sheet is spread along with house’s inner surface with a small space, which is opened when solar radiation is incident on the house in daytime and closed to prevent heat loss from the house while out of sun shining in night. Inside of the all weather-type solar Ogako drying house, there are four belt-conveyors over which four top radiation panels are hanged, and on which four Ogako agitators are touched, a turn-table, two hoppers, four small fans, and besides, a floor heating is molded in concrete floor. Also on the north wall outside the house, two insulated cylinders (chimney) are stood up vertically to exhaust inside moist air passively. Then, to make clearly the operation performance of the house, the drying tests for the proof examination were conducted nineteen times at first test site in Ashoro where is located east-central part of Hokkaido, Japan. As a result of the drying test for the proof examination, it was made clear that the all weather-type solar Ogako drying house is practically useful as a supplementary apparatus to produce the dried Ogako, and consequently to suppress CO2 exhaustion.

Mechanical behaviour of wood compressed in radial direction:Part II.Influence of temperature and moisture content

This study investigated the influence of pressing temperature and moisture content on the me-chanical properties of wood compressed in radial direction.Jack pine(Pinus banksiana)and bal-sam poplar(Populus balsamifera)specimens were tested under a combination of pressing temper-ature(20℃,55℃,90℃,and 125℃)and wood moisture content(2%,7%,12%,and 17%).The yield stress(_(δ)y)and modulus of elasticity(MOE)of the specimens were determined from the stress-strain response.It was found that an increase in either pressing temperature or moisture content of wood generally caused a decrease in the mechanical properties for both species.The t-test results revealed that jack pine specimens are more sensitive to changes in pressing tem-perature and wood moisture content than balsam poplar.For jack pine specimens,at any of the pressing temperatures,the moisture content of 12%was found to be a crucial level to start a significant decrease in𝜎y and MOE,while at any of the moisture content,a change in temper-ature from 55℃to 90℃exhibited a significant change in𝜎y and MOE.The regression models developed can be used to predict𝜎y and MOE as a function of temperature and moisture content.

Study on drying rate in contact drying with flexible screen

The moisture contents (MC) of popular veneers were tested in Composition Board Laboratory of Northeast Forestry University by contact drying with flexible screen. The influence factors considered included temperature, initial moisture contents (IMC), and veneer thickness. Veneer-drying laws under different hot press conditions were analyzed. The results showed that the drying rate increased with temperature rising. 160°C was considered to be more efficient than 140°C and 180°C because excessive high temperature has no significant contribution to drying rate. IMC had significant effect on drying rate. The veneer with high IMC had a higher drying rate at above fiber saturation point (FSP) and a lower drying rate at below FSP, compared to the veneer with low IMC. Average drying rate also varied with thickness in power law.

Hot Air Drying and Quality of Red and White Varieties of Onion (Allium cepa)

This study was undertaken to investigate the drying characteristics of red and white varieties of onion (Allium cepa) in a convective dryer. The drying characteristics of onion slices were examined at air temperatures of 50℃, 60℃ and 70℃ and sample thicknesses of 2 mm. During the drying experiments, air velocity was held stable at 0.9 m/s. The effects of air temperature on the drying characteristics and quality parameters such as vitamins C and D, macro minerals (Mg, Na, P, Ca and K), non-enzymatic browning and thiolsulphinate of the dried onion slices were determined. For each of the plots of the drying curves from the mechanical drying tests, there was an absence of or just a very brief appearance of a constant rate period because onions are hygroscopic and hygroscopic foods tending to quickly enter the falling rate period;drying time decreased considerably with increased temperature. The time required to reduce the moisture content to any given value was dependent on the drying conditions, being the longest at an air temperature of 50℃, 0.9 m/s and the shortest at an air temperature of 70℃ and air velocity of 0.9 m/s. The loss of vitamin C, which is a thermo-sensitive compound, was the least at an air temperature of 50℃.

Image processing analysis to track colour changes on apple and correlate to moisture content in drying stages

Colour and moisture content are two most important attributes of the commercial food product.Estimation of moisture content is very important to know the storability of the food product.It also relates to the process of drying in a fruit or vegetable.Extra drying and shrinkage deteriorates the quality of food product.The goal of the experiment was to examine the changes in RGB values of an apple during drying at different temperatures.In this study,emphasis was given on how the colour changes when there is a significant change in the moisture content of the apple.Three randomly chosen varieties of apples were sliced to 8 mm thickness and dried in vacuum oven at 60°C,70°C,and 80°C.The loss of moisture was recorded for every 30 min interval and corresponding digital images were taken to determine the change in RGB value.The images that were captured during the study was analysed in MATLAB image analysis computer software.The analysis of moisture content and average colour share with respect to time showed that average colour share value decreases with time at all three temperatures.More than 50 per cent of variation in moisture content was explained by average colour share.There is a significant linear relationship between moisture content and colour changes in RGB and can be used to predict the moisture content of apple during drying process.

干燥处理木材动态黏弹性的含水率依存性

采用高温干燥、低温干燥和真空冷冻干燥方法对杉木人工林木材进行干燥处理,测定3种干燥处理材在不同含水率平衡态的动态黏弹性质。测定的温度范围为-120～40℃,频率范围为0.5～10 Hz。结果表明：1）随着含水率增加,木材的贮存模量E′随温度升高而降低的程度增大,其中高温干燥处理材的贮存模量降低程度最小;2）在测定温度范围内观察到2个力学松弛过程,较高温度域的α力学松弛过程是由低分子质量的半纤维素发生玻璃化转变引起的,低温域的β力学松弛过程是基于木材细胞壁无定型区中伯醇羟基的回转取向运动与吸着水分子的回转取向运动两者叠加而成的;3）力学松弛过程的损耗峰温度随着含水率的增加而降低,随着测量频率的增加而向高温方向移动;4）力学松弛过程的表观活化能随着含水率的增加而减小,对于α力学松弛过程,高温和低温干燥处理材的表观活化能低于真空冷冻干燥处理材的表观活化能。

考古木材降解评价的物理指标

为寻找一种能较为科学、方便地反映木材降解程度的指标,共收集不同地方出土的13种木材,8个树种,对这些树种的考古木材与新鲜木材的含水率、干缩性、基本密度、气干密度、综纤维素等指标进行对比分析。实验表明,基本密度和最大含水率(饱水含水率)基本上能够反映古木的降解程度,可以作为反映古木降解程度的物理评价指标。

低温环境下桦木顺纹抗压强度的研究

为揭示不同水分状态木材在低温环境下的力学强度变化规律,研究了5种水分状态(饱水、生材、纤维饱和点、气干、绝干)桦木木材在0^-196℃低温环境下的顺纹抗压强度,并与室温环境下(20℃)的5种水分状态木材顺纹抗压强度进行比较。结果表明,在低温(0^-196℃)环境下,随着测试环境温度的降低,木材顺纹抗压强度增加,在-196℃环境下,5种水分状态的桦木顺纹抗压强度比室温环境下分别增加821.24%,718.05%,632.87%,223.75%和95.28%。木材顺纹抗压强度与温度呈线性关系,其斜率代表了顺纹抗压强度随温度变化的增加率,即木材含水率越高,随着低温温度的降低,顺纹抗压强度增速越大。在低温环境下,木材细胞中水分形成的冰柱,是木材顺纹抗压强度增加的主要原因。对绝干材而言,木材细胞壁上纤维和纤维胶着物质发生硬化,是其顺纹抗压强度增加的主要原因。

超高温热处理对水曲柳板材尺寸稳定性的影响

分别采用窑式常压和罐式带压过热蒸汽对水曲柳板材进行超高温热处理,研究了两种热处理方式对木材平衡含水率、尺寸稳定性、吸湿滞后及干缩系数的影响,分析了两种热处理方法使木材稳定性提高的原因。结果表明:两种热处理均可降低木材的平衡含水率,但罐式带压热处理可以更有效地降低木材在使用中的平衡含水率,减小木材使用环境的相对湿度变化对木材含水率的影响,降低木材干缩系数,更有利于提高木材的尺寸稳定性。提高处理温度可以减小热处理材的吸湿滞后,罐式带压热处理材比窑式常压热处理材的吸湿滞后小。

干燥过程中木材温度的变化规律以及与含水率关系的研究

通过对高温和常规温度干燥过程中木材温度及含水率变化与分布的测定,研究木材温度变化的特点和木材温度与含水率的变化关系。分析自由水蒸发面移动、水分状态改变对温度变化的影响。在此基础上,探讨利用木材温度控制干燥过程的可能性和实施方法,

木材干燥过程含水率和温度变化的数学模型研究

木材干燥过程存在着热质互换和能量的转移,这为从热力学的角度研究木材干燥过程提供了前提条件,因此提出利用热力学原理分析木材干燥过程含水率和温度变化规律的数学模型。首先建立描述含水率和温度变化的高阶非线性偏微分方程组,然后采用有限元分析原理将方程组离散化,再经过一系列数学运算得到方程的收敛解,具体方法为牛顿迭代法,最后通过对木材含水率和温度变化情况仿真结果的分析,验证该方法的可行性及数学模型的准确性。

木材解吸过程中含水率及温度变化的研究

以尺寸20 mm ×20 mm× 10 mm的杨木为试材,利用自行研制的恒温箱、配合红外热像仪考察了在25℃,从相对湿度100％调节至22％、47％和75％3种条件下解吸过程中试材的含水率、温度变化及其顺纹方向上的温度梯度分布情况.结果表明：在解吸初期,试材的含水率迅速下降,其整体平均温度也明显降低1～5℃;随着解吸过程的进行,木材含水率和整体平均温度逐渐趋向平衡;在顺纹方向上,试材的温度呈现出表面温度低、中间温度高的分布形态,表层与芯层之间的温度差在解吸过程初期5 min内达到最大值,约为0.7℃,当达到解吸平衡时二者之间的温差约降至0.2℃.

温度及水分状态对美国红松弯曲弹性模量的影响

应用温度控制系统,对美国红松小试样规格材进行测试,检验木材温度及水分状态对木材弯曲弹性模量的影响。结果表明:温度对木材的抗弯性能具有显著影响,随着温度的升高,木材的抗弯性能逐渐减弱;相同承载条件下,含水率越高,冻结木材的抗弯曲性能越强。对于纤维饱和材,冰点以下其弹性模量随着温度的降低而迅速增加,在冰点以上则增加缓慢;对于非纤维饱和材,其弹性模量受温度影响变化幅度在冰点两侧区别不明显。冻结木材弹性模量相对于常温(20℃)情况下(相对弹性模量)受温度和含水率变化的影响十分显著,而非冻结木材的相对弹性模量对温度变化均表现不敏感。通过建立的相对弹性模量-温度试验模型,能较好地预测不同温度及含水率下的木材弯曲弹性模量相对于常温的变化幅度。该研究为不同温度条件下尤其是低温时的木材弹性模量测量结果修正提供了试验依据。

栓皮栎板材的降温干燥试验

采用了一种新的干燥方法──降温干燥法对栓皮栎板材进行了于燥试验。试验结果表明，在降温干燥过程中，木材内部含水率梯度和温度梯度方向相一致，加速了木材内部水分的迁移，提高了干燥速度。同时由于木材表层温度较内部温度低，表面水分蒸发的速度减慢，降低了木材内应力，使木材干燥质量与常规干燥相比有所提高。这种干燥方法为难干材的干燥提供了一条新的途径。

木材干燥机理和应用的研究

通过对木材干燥机理和应用的研究,提高木材的干燥速度并选择合理的干燥方法,从而实施科学的木材干燥作业。

烘丝控制模式的建立与实现

通过对烘丝过程的分析 ,针对现有烘丝控制系统的不足 ,提出了新的控制模式。正常工作时稳定进入烘丝筒内烟丝的脱水量以及烘丝筒的筒壁温度 ,从而稳定烘后烟丝的含水率。在热风管道上增加一个由电磁阀控制的低压蒸汽喷射装置 ,“模拟”正常烘丝过程中筒内的环境 ,以减少“干头”和“干尾”烟丝量。使用新的控制模式 ,提高了烘后烟丝含水率的稳定性 ,“干头”和“干尾”