双向侧风木材干燥窑内流场的数值模拟与优化

为适配海运木材干燥特点，提出双向侧面通风的干燥方法。应用Fluent软件对不同送风速度下的干燥窑内流场进行模拟，并在此基础上改变干燥窑结构，研究木材堆与墙壁间的气道宽度对干燥窑内流场的影响。结果表明：双向侧风干燥窑流场均匀性良好，但干燥窑中间层和循环末端的木材堆风速偏低。通过对比8 m/s和12 m/s送风速度下干燥窑内部流场，得出当送风速度为12 m/s时，干燥窑内风速满足1～3 m/s这个理想区间，加大送风风速可改善流场均匀性。此外，加宽气道可使中间层风速变大，并提高整体风速，但这种变化趋势存在拐点。研究得到的相关结果可为海运木材干燥窑的搭建提供设计参考。     

顶风机型木材干燥窑气流循环的优化设计

对顶风机型木材干燥窑气流循环不均匀的原因进行了分析,为解决这一问题,在干燥窑顶部气流转向处,安装水平-垂直导流装置,同时在垂直风道一侧设置水平可调导流装置.利用Sc/Tetra软件进行模拟分析的结果表明,窑内气流速度提高,速度场分布的均匀性改善,锯材间隙的平均风速及干燥均匀性提高,提高了生产效率.     

基于Fluent的节能型干燥窑内部结构优化研究

为使设计的节能型干燥窑内部结构能够满足锯材干燥生产时具有较为均匀的流场分布和较大的风速,本研究利用Fluent软件,对不同配气道宽度和不同进排气道结构参数下的节能型干燥窑内速度场进行数值模拟分析。结果表明,节能型干燥窑内材堆中下两层气流分布较为均匀,材堆顶层气流低流速区域随进排气道高度和配气道宽度的增加而有所减少,材堆内部的高流速区域随进排气道高度和配气道宽度的增加而略有加大。从气流在材堆内部整体流速和均匀性的角度出发,结合生产实际,设计节能型干燥窑内部结构时以进排气道高度为1 000 mm,配气道宽度为1 000 mm为最佳。     

基于热流耦合的木材干燥窑风速温度分布解算

为构建木材干燥窑内部循环风速和温度合理分布,采用二维数值模拟方法,利用Fluent软件对试验型小型干燥窑进行仿真模拟,对比安装导流板前后干燥窑内温度和分布情况。木材干燥窑的设计,风速、温度分布是关键问题。首先利用ICEM CFD软件对结构简化的试验型小型干燥窑进行参数化建模,将简化的模型进行网格划分,利用Fluent软件对木材干燥窑内的流动与传热耦合环境进行数值模拟,得出风速分布云图和温度分布云图,研究干燥窑内热流耦合系统,得出其内部速度和温度的具体状态,通过导流板安装前后数值对比,找到导流板合理性的参数。采用二维数值的模拟方法,不能代表实际干燥窑工作状况,具有一定的局限性。     

EWS新一代高效火花探测熄除系统

正德国EWS公司推出了新一代火花探测熄除系统,可探测和熄除工业气力输送管道和高温干燥区域的火花,避免火灾和爆炸事件发生,对于安全生产至关重要,现已广泛应用于人造板和木材加工及其他众多行业。目前,新一代系统已在德国EWS的工厂完成了测试,管道的气流速度高达36 m/s。新系统的改进提升,主要体现在以下方面:     

基于林木病虫害防治的移动喷雾参数对雾滴穿透性影响分析

林木病虫害防治过程中,常采用皮卡搭载喷雾系统进行移动喷雾,以达到快速高效的目的。为了研究移动喷施农药过程中喷雾技术参数对雾滴穿透性的影响,本研究构建了由供液模块、喷雾压力调控和速度实时显示模块、喷头高度和角度调节模块、速度控制调节模块和防冲撞限位模块5大部分组成的移动喷雾测试系统。通过研制的移动喷雾测试开展试验分析,分别设置了3种喷施压力、4种搭载平台行驶速度、国产和进口不同的多个喷头,对仿真树靶标进行了喷雾试验,在仿真树冠层内设置8个采样点铺放卡纸来测定雾滴沉积覆盖率,采用iDASPRO雾滴沉积分析数据,以此来测试喷雾技术参数对雾滴穿透规律的影响。经过统计分析,得到影响喷头穿透效果大小的因素次序:喷雾压力>搭载平台移动速度>喷头孔径,采用Design Expert试验分析软件,建立以喷头孔径、搭载平台移动速度和喷雾压力为自变量、以雾滴覆盖率为应变量的多元非线性回归模型。结果表明:雾滴沉积量随着喷雾压力的增加呈现增加的趋势,当移动速度为最小的0.25m/s时,雾滴沉积量明显高于移动速度为0.50m/s和0.75m/s时的值,研究结果对于植保作业中移动喷雾参数确定和器械选择提供了理论依据与应用参考。     

西北型日光温室内不同风速对甜瓜叶片光合、呼吸等生理指标的影响

试验以优选早蜜甜瓜为试材,研究了不同风速对甜瓜叶片光合、呼吸、蒸腾速率的影响规律。结果表明,从气孔导度来看：1．5m／s时对甜瓜新叶生长最有利,0．7m／s时对甜瓜老叶生长最有利;从胞间CCh浓度来看：0．7m／s时对甜瓜新叶生长最有利,0．7m/s时对甜瓜老叶生长最有利;从净光合速率来看：0．7m/s时对甜瓜新叶生长最有利。0．9m／s时对甜瓜老叶生长最有利;从蒸腾速率来看：0．5m／s时对甜瓜新叶生长最有利,0．7m／s时对甜瓜老叶生长最有利。鉴于0．7rids风速对实验中10项指标中的5项有利。因此：甜瓜温室栽培的风速应以0．7m／s为宜。     

黑龙江省夏季林火蔓延特点

通过对2001-2007年黑龙江省夏季森林火灾调查研究发现,该地区夏季林火种类有地表火、地下火、树冠火3种,这3种蔓延方式之间相互演变,多数为地表火与地下火同时存在。夏季林火蔓延速度普遍较慢,地表火蔓延速度大多在0.05m/s以下;浅层地下火在有林地的燃烧速度为2-4m/h、草甸为1-3m/h,深层地下火在有林地的燃烧速度为0.2m/h以下、草甸为0.05m/h以下;树冠火蔓延速度一般为180-600m/h。     

工艺因子对MDI制备无醛纤维板性能的影响

采用异氰酸脂胶(MDI)制备中密度纤维板,探讨在施胶量不变情况下固化剂、防水剂施加量及热压因子对无醛纤维板性能的影响。结果表明:当MDI施胶量为25 kg/m3,固化剂施加量1.3 kg/m3,防水剂施加量4 kg/m3,热压因子15 s/mm时,所制无醛纤维板物理性能均优于GB/T 11718—2009《中密度纤维板》中干燥状态下使用的家具型中密度纤维板(MDF-FN REG)性能要求。     

热电阻测控仪表误差的调整

木材干燥是木材加工过程中的关键环节，木材干燥质量的好坏直接影响到木材加工后的最终产品。木材干燥对干燥窑的窑内温度要求很高，如果控制仪表所控制的不是干燥窑内的真实温度，将给被干燥木材质量带来很大影响，最终使产品造成很大缺陷。在木材干燥过程中，一般采用热...     

改善顶风机型木材干燥室空气流动特性研究

采用升降式导流装置通过布置在气道中的多级导流板,把顶风机型木材干燥室中的材堆两侧空气循环气道分隔成若干小气道,并通过导流板导向作用使通过每个小气道的介质气流单独对材堆不同高度进气口一侧供风,在一定程度上改善了干燥室内沿材堆高度方向空气气流循环动力学特征。经过测试,该装置可使空气气流在材堆进气口和出气口的风速均方差均低于0.15 m/s,大幅降低风速变异系数。升降式导流装置结构简单,生产成本低,易于操作控制和维护,适用于叉车装卸材堆方式的顶风机木材干燥室。     

Liberation of Heterobasidion annosum conidia by airflow

The effect of speed and humidity of the airflow and the míst sprayed with airflow on the liberation of conidia of Heterobasidion annosum from pure cultures was studied in a small windtunnel. The conidia were liberated more easily in humid than in dry airflow. Liberation was most abundant when mist was added to the airflow. Threshold speed for the liberation of conidia was calculated to vary between 1.8 m/s and 3.9 m/s. According to the results, conidia of H. annosum may be liberated into the air by wind gusts associated with high humidity or mist and thus the conidia may have a role in aerial dispersal, although this is probably small compared with basidiospores.     

杨木太阳能干燥工艺特性

应用一种带有石蜡储热的新型太阳能干燥室干燥杨木,分析该干燥室的温、湿度变化对木材内外温度差和木材干燥速率的影响,并检测了杨木木材的干燥质量,结果表明:太阳能干燥室的温、湿度呈周期性变化规律,在一个温度变化周期内,干燥速度亦呈周期性.建议在升温段控制干燥速度,在降温段加快干燥速度.     

Influence of fan speed on airflow distribution in a batch kiln

Abstract

This study reports experimental data of airflow distribution as a function of fan speed in an industrial batch kiln. Measurements were conducted with 20 hot-film anemometers distributed throughout the load at two occasions. The main result was that airflow distribution did not change significantly as the fan speed was reduced, and no positions where the air movement stopped were found. It was also found that relatively more air ran in the bolster spaces in comparison to the adjacent packages as the air ran through the load.     

干燥室内材堆循环风速测试与分析

通过对五座有代表性的木材干燥室内的材堆循环风速测试结果的对比分析，结果表明，短轴型木材干燥室介质循环性能较好，采用可逆循环风机对于保证木材干燥的均匀性具有重要意义。     

辐射松与杉木在高温干燥中萜烯类释放浓度研究

以40 mm厚的辐射松(Pinus radiata)和人工林杉木(Cunninghamia lanceolat)锯材为对象,研究高温干燥过程中干燥温度和锯材含水率对萜烯类产物释放浓度的影响,并与辐射松常规干燥中的萜烯类释放浓度作比较。高温和常规干燥过程中采抽气样次数均为5次,抽气速度为1.0 L/min,采样时间为30 min,采用Tenax管收集干燥过程中萜烯类产物,用气相色谱仪分析其成分及浓度。结果表明:高温干燥辐射松萜烯类释放浓度高于常规干燥辐射松与高温干燥人工林杉木,但萜烯类挥发物的组分有所差别。常规干燥辐射松锯材萜烯类释放浓度对环境是安全的,然而在高温干燥过程中,尤其在干燥中后期,当萜烯类挥发物浓度大于1.5 mg/m3时,对辐射松和人工林杉木释放萜烯类挥发物应采取回收措施,以确保对环境的安全。     

Evaluation of drag coefficients of poplar-tree crowns by a field test method

To estimate the wind force that causes windthrow damage to a tree, the drag coefficients of actual-sized trees were evaluated by a field test method. In this method, wind velocity and stem deflection were monitored simultaneously. The wind force acting on a tree crown was calculated from stem deflection; stem stiffness was evaluated by conducting tree-bending tests. The results of tests conducted on three poplar trees showed that drag coefficient decreased with an increase in wind velocity. Although the variation in the drag coefficient was large at low wind velocity because of the vibrating behavior of the stem subjected to variable wind force, the variation at wind velocities above 10 m/s was small. The average drag coefficient at a wind velocity of 30 m/s was estimated by the curve-fitting of a power function to the wind velocity-drag coefficient relationship to be 0.102, which was smaller than that of actual-sized conifers studied in previous wind tunnel experiments. The drag coefficients of these crown areas in the defoliation season were smaller than those measured in the leafy season.     

Lumber Quality Model: The theory

Abstract

A new model for predicting moisture content, distortion and shrinkage distribution after lumber drying has been designed, implemented and tested. The model was implemented using Monte Carlo simulation, and it involves three empirical equations that were developed on the basis of experimental data. The model is referred as the Lumber Quality Model, and it is designed to be calibrated by knowing the initial and final moisture content, distortion and shrinkage distribution for a reference drying run. After calibration, the model can be used to predict the same information for other hypothetical drying scenarios. The present study explains the theoretical aspects of the model and the methodology for implementation. The model was validated with experimental data measured in a laboratory kiln. A full-scale industrial validation will be reported in a future paper.     

Field investigation on Salix psammophila plant morphology and airflow structure

The field investigation was undertaken to determin the characteristics of Salix psammophila plant morphdogy and airflow structure of single-line S. psammophila on the southern edge of the Mu Su sandland. The results showed that artificially cultivated single-line S. psammophila could accumulate sand because the plant decreased the windward and leeward wind velocity. There was a significant correlation (R = 0.696) between accumulated sand volume (V ₂) and plant volume (V ₁). The wind velocity was 6 m/s at a 4 m height of single-line S. psammophilahedge row. The wind velocity decreased at 3 H windward and increased at 2 H to windward. The wind velocity then steeply decreased to leeward and reached its lowest value at 1 H to leeward and gradually recovered to the open field velocity. The protection distance of the single-line S. psammophila was about 17 H′ and the effective protection distance was about 13 H′. Single-line S. psammophila had few effects on the wind velocity when the wind was above the plant height. __________ Translated from Chinese of Applied Ecology, 2005, 16(11) [译自: 应用生态学报, 2005, 16(11)]