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1.
为研究植物层传热特性,选取校园内十种常见园林植物测定其叶片导热系数、叶片与周边空气对流换热系数,拟合导热系数与叶片含水量的近似关系式,对比实验测定对流换热系数与通过经验公式理论计算所得对流换热系数,比较与叶片接触前后空气的相对湿度。结果表明,叶片存在降温增湿作用,在5~25 ℃下叶片导热系数随温度变化较小;叶温20 ℃时,叶片导热系数随叶片含水量降低而减小;实验测试对流换热系数与理论计算结果吻合度较高。  相似文献   

2.
对拟赤杨(Alniphyllum fortunei Makino)纯林、拟赤杨-马尾松(Pinus massoniana Lamb.)混交林和拟赤杨-杉木[Cunninghamia lanceolata(Lamb.)Hook.]混交林中拟赤杨木材的物理力学性质和化学组分进行了测定和比较分析。结果表明,混交林中拟赤杨的木材密度、干缩系数和力学强度均大于纯林,且拟赤杨-马尾松混交林中拟赤杨木材的各指标值均最高。拟赤杨-杉木混交林中拟赤杨木材的热水抽出物、1%NaOH抽出物、苯醇抽出物、硝酸-乙醇纤维素和Klason木素含量分别为2.31%、18.63%、2.52%、45.74%和21.59%,均高于纯林;拟赤杨-马尾松混交林中拟赤杨木材的戊聚糖含量(22.98%)高于纯林。说明拟赤杨-马尾松混交林中拟赤杨木材的材性总体上最优,在拟赤杨木材品质培育过程中宜选择马尾松作为伴生树种。  相似文献   

3.
油杉木材物理力学性质研究   总被引:1,自引:0,他引:1  
对油杉Keteleeria fortunei木材的物理与力学性质进行测定与比较,结果表明,油杉木材的气干密度为0.576 g·cm~(-3),全干密度为0.544 g·cm~(-3),属中密度木材。油杉木材的气干径向、弦向和体积干缩系数分别为4.408%、3.272%和7.892%,气干差异干缩为1.347,油杉木材具有不易开裂和变形的特征。油杉木材的抗弯强度、顺纹抗压强度分别为92.701、57.217 Mpa,端面、弦面和径面硬度分别为4635.9、3420.8和3606.8 N,其抗弯强度、顺纹抗压强度和硬度均属中等。50年生油杉木材的物理力学性质优于22年生马尾松Pinus massoniana、湿地松Pinus elliottii和28年生杉木Cunninghamia lanceolata、秃杉Taiwania cryptomerioides。  相似文献   

4.
香椿人工林和天然林木材纤维形态和化学成分比较研究   总被引:7,自引:0,他引:7  
通过对香椿人工林和天然林木材纤维形态和化学成分的比较分析,揭示了香椿人工林木材纤维形态的特征及径向变化规律,以及人工林和天然林木材纤维形态和化学成分的差异。结果表明,香椿人工林的工艺成熟期为10年左右,其木材纤维长度和长宽比小于天然林,宽度大于天然林;纤维素、戊聚糖和木素含量均稍高于天然林;灰分和抽出物含量均低于天然林。香椿木材可作为林产工业纤维材料使用。  相似文献   

5.
有机废弃物是重要的待开发利用的生物质资源,特别是发展生物炼制。文中针对林业剩余物第二级分类的全部10个类型,根据1993–2017年间报道的有关林业剩余物系数研究,首先在前人研究结果的基础上,完善了系数体系及其定义。然后,对以前的取值通过文献溯源甄别其合理性,对于没有明确依据的取值和迄今未取值的系数,通过相关研究获得数据并进行实地调研,确定了计算林木苗圃剩余物、林木修枝剩余物、木材采伐剩余物、木材造材剩余物、木材加工剩余物、竹材加工剩余物、薪材、废旧竹材和废旧木材、香蕉和菠萝残体所需系数的合理取值。  相似文献   

6.
植物温度是森林生态系统能量平衡和植被呼吸估算的重要参数.采用T型热电偶监测树皮和木材特性各异的2个阔叶树种(白桦和水曲柳)不同深度、高度和方位的树干温度(Ts),探索Ts日变化的空间变异及其影响因素.结果表明: Ts月平均日变化格局与空气温度呈相似的正弦曲线,但Ts变化滞后于空气温度,时滞从树皮表面处的0 h增加到6 cm深度处的4 h.随测定深度的增加和高度的降低,Ts日变化的峰值和日较差均逐渐减小.Ts周向差异不大,休眠季节白天南向、西向Ts日峰值略高.两树种树皮和木材的热学特性(比热容和导热系数)的差异,会通过影响树干表面与外界的热交换和树干内部热扩散而造成Ts径向变化的种间差异.白桦树皮较高的反射率削弱了太阳辐射对Ts的影响.多元逐步回归分析表明,环境因子可以很好地估测Ts日动态(R2>0.85),影响程度依次为空气温度>水汽压>净辐射>风速.估算生物量热储和树干表面CO2通量时应考虑Ts径向、纵向和种间差异.  相似文献   

7.
不同生态条件对人工林杨树木材物理力学性质的影响   总被引:2,自引:1,他引:1  
在施肥与未施肥、淹水与未淹水两种生态条件下,以杨树人工林木材I?69杨为对象,对木材年轮宽度、基本密度、干缩性质、主要力学性质进行了测试,并对数据进行了统计、对比和分析.结果表明,施肥处理后,木材年轮宽度、静态抗弯弹性模量和顺纹抗压强度分别增大0.99%、2.73%和1.06%;全干时和气干时的径向、弦向、体积全干干缩率分别降低了4.2%、7.7%、6.6%、15.6%、6.3%和11.1%;木材密度、抗弯强度、动态抗弯弹性模量则分别降低了2%、1.79%、8.13%.与未淹水相比,季节性淹水对I?69杨木材密度、木材干缩率和力学性质的影响较大,二者差异显著(P<0.05).其中木材密度、全干时和气干时的径向、弦向、体积干缩率、抗弯强度、抗弯弹性模量以及顺纹抗压强度分别降低了5.5%、11.1%、9.2%、9.6%、16.7%、10.9%、8.5%、24.29%、18.18%和16.81%.  相似文献   

8.
农田防护林木材材质物理特性研究   总被引:7,自引:0,他引:7  
对早柳和小青杨的年轮宽度、年轮密度、木材纤维长度和干缩率及其径向变异进行了研究.结果表明,木材物理特性受年轮年龄的影响显著,而纤维长度不受年轮宽度影响.综合材质物理特性的径向变异规律,可将旱柳和小青杨整个生长期划分为4个时期:幼林期、速生期、成熟期和更新期,确定了各生长期的年龄值.  相似文献   

9.
吴树明   《广西植物》1987,(3):210-210
<正> 所用木材标本采自福建省太宁县。树干胸径为10.5厘米。在横切面上,从中心向外连续选取木材样品两个,照一般方法作横向、径向和弦向三种切片租离析,均用番红染色,供显微研究使用。  相似文献   

10.
赤霉素对米老排苗木生长的影响   总被引:1,自引:0,他引:1  
米老排(Mytilaria laoensis Lecomte.)属金缕梅科的一种常绿高大乔木,树高30余米,胸径80厘米以上。木材为散孔材,结构细致,纹理直,木材容重0.525(含水量15%)体积干压系数为0.473%,木质中等,色泽美观,加工容易,是建筑、造船、枕木、家俱及胶合板的良好用材,属优良、速生、珍贵阔叶用材树种。米老排原系野生,从1958年开始人工引种,现已在南方各省山地、丘陵及低丘陵等  相似文献   

11.
In the present study, the radial thermal rectification and thermal conductivity of the graphene were investigated by non-equilibrium molecular dynamics simulation and then corrected by quantum correction to make it closer to the fact. The Optimised three-body Tersoff potential is employed in order to simulate the interactions between the carbon atoms in the graphene sheet. A circular region in the centre and the one at the graphene edge are selected as hot and cold bath to generate radial temperature gradient. It is observed that the heat current passes through radially inward direction than outward with the same temperature gradient and hence there is a radial thermal rectification in graphene. Also, temperature distribution and heat flux are theoretically introduced as a function of distance from the graphene centre and then it is confirmed by the molecular dynamics simulation data. Finally, the influence of temperature gradient and size of graphene on radial thermal rectification and the impact of size on the radial thermal conductivity is investigated.  相似文献   

12.
Solar steam generation, combining the most abundant resources of solar energy and unpurified water, has been regarded as one of the most promising techniques for water purification. Here, an artificial tree with a reverse‐tree design is demonstrated as a cost‐effective, scalable yet highly efficient steam‐generation device. The reverse‐tree design implies that the wood is placed on the water with the tree‐growth direction parallel to the water surface; accordingly, water is transported in a direction perpendicular to what occurs in natural tree. The artificial tree is fabricated by cutting the natural tree along the longitudinal direction followed by surface carbonization (called as C‐L‐Wood). The nature‐made 3D interconnected micro‐/nanochannels enable efficient water transpiration, while the layered channels block the heat effectively. A much lower thermal conductivity (0.11 W m?1 K?1) thus can be achieved, only 1/3 of that of the horizontally cut wood. Meanwhile, the carbonized surface can absorb almost all the incident light. The simultaneous optimizations of water transpiration, thermal management, and light absorption results in a high efficiency of 89% at 10 kW m?2, among the highest values in literature. Such wood‐based high‐performance, cost‐effective, scalable steam‐generation device can provide an attractive solution to the pressing global clean water shortage problem.  相似文献   

13.
Among many other requirements, energy efficient building materials require effective daylight harvesting and thermal insulation to reduce electricity usage and weatherization cost. The most commonly used daylight harvesting material, glass, has limited light management capability and poor thermal insulation. For the first time, transparent wood is introduced as a building material with the following advantages compared with glass: (1) high optical transparency over the visible wavelength range (>85%); (2) broadband optical haze (>95%), which can create a uniform and consistent daylight distribution over the day without glare effect; (3) unique light guiding effect with a large forward to back scattering ratio of 9 for a 0.5 cm thick transparent wood; (4) excellent thermal insulation with a thermal conductivity around 0.32 W m?1 K?1 along the wood growth direction and 0.15 W m?1 K?1 in the cross plane, much lower than that of glass (≈1 W m?1 K?1); (5) high impact energy absorption that eliminates the safety issues often presented by glass; and (6) simple, scalable fabrication with reliable performance. The demonstrated transparent wood composite exhibits great promise as a future building material, especially as a replacement of glass toward energy efficient building with sustainable materials.  相似文献   

14.
On the Lamellar Structure of the Tracheid Cell Wall   总被引:2,自引:0,他引:2  
Abstract: It is clear that cross sections of wood cells show a lamellar structure. This paper investigates the orientation of this lamellar structure of spruce (Picea abies) tracheids using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross sections of spruce wood were produced through fracturing in longitudinal bending and tensile testing. When investigated with SEM, the fracture surfaces show a structure of mostly larger radial lamellae, in the order of 30 - 100 nm, i.e., agglomerations of a few cellulose aggregates. Thin transverse sections of the fracture zones investigated with atomic force microscopy show concentric lamellae with a width in the order of a single cellulose aggregate, i.e., 15 - 25 nm. No structural connection to the splinters in the radial direction can be seen. It is suggested that the radial lamellar structure is a consequence of the energy released during fracturing of the wood samples and that the undistorted wood has a concentric lamellar structure on a smaller structural level.  相似文献   

15.
The formations of compression wood and eccentric radial increment are two phenomena that are so closely associated that they cannot be readily discussed separately. However, various studies suggest that their formation is stimulated by different mechanisms and that there is no functional relationship. While the formation of compression wood is a reaction of coniferous trees to negative gravitroptic scenarios which enables the trees to recover from displacement, one-sided radial growth promotion is stimulated by unilateral mechanical strain on the cambium for lowering stress peaks. This study offers an approach to quantify the relation of both phenomena in stem cross-sections and single growth rings.Samples of 56 Norway spruces (Picea abies [L.] Karst.) from sites differing in slope and exposure to the prevailing wind direction were examined for their cross-sectional compression wood distribution and eccentricity in radial increment. The assessment of both phenomena on stem cross-sections was based on their spectral properties in reflected light. Hyperspectral image analysis allowed detection of compression wood distribution as well as measurement of annual radial increment along eight radii, oriented by compass direction.Since the distributions of both phenomena comprise both a directional component as well as amplitude in annual reference, these data were handled as vectors. Circular statistics were applied to describe and quantify their relationship and to test both phenomena for the inducing environmental factor that stressed the tree.The direction of compression wood formation and eccentric growth is significantly positively correlated. In the majority of observations a unimodal distribution of both phenomena is given. Mostly strong one-sided compression wood formation is associated with a coincident direction of eccentric radial increment. However, stem cross-sections with a distinct direction of compression wood were observed without a dominating direction of eccentric growth, and vice versa.Bivariate statistics that consider vector direction as well as vector length have proved to be very helpful in retrospectively identifying possible initiating environmental factors for both phenomena at a given site. The location of standard and confidence ellipses in relation to the assumed direction of action is a strong indication for or against an assumed environmental factor.  相似文献   

16.
Based on the theories of tissue optics and artificial neural network, the relationship between the optical properties and biological parameters was studied, and a new experimental method was derived. The properties of the organism were obtained indirectly by a black-box model derived by self-study of the artificial neural network between optical parameters and thermo-physical properties without using the heat transfer equation. In this method, the energy of light in diffuse radiation, diffuse transmission and collimated transmission was absorbed by a dual-integrating sphere experimental system of a spectrometer, and the spectrogram of the energy was obtained. Combining these spectral data of the energy, the diffuse-reflecting power, the diffuse transmissivity and the collimated transmissivity were calculated. The calculated results were taken as the input parameters of a black-box model. The experimental results show that there are apparent differences between the spectrogram of the energy on the diffuse radiation, the diffuse transmission and the collimated transmission of different matters, while there is a little difference in the same matter. Each spectrogram has its own characteristic. The values of the four thermal properties including the density, the constant pressure specific heat, the thermal diffusivity and the viscosity were calculated using the black-box model. Compared with the real values the calculated one has an average relative error between −5% and 5%. The conductivity of the tongue is 0.68 W/(m K) that calculated from the value of the density, the constant pressure specific heat and the thermal diffusivity. The results also show that there is a little difference on the conductivities in the longitudinal cross-section and the transverse section, but the effect of temperature on the conductivity of the tongue is not apparent. The difference implies the anisotropy of the properties of the organism, which cannot be easily obtained by a conventional experimental method.  相似文献   

17.
18.
A biphasic, anisotropic model of the aortic wall   总被引:4,自引:0,他引:4  
A biphasic, anisotropic elastic model of the aortict wall is developed and compared to literature values of experimental measurements of vessel wall radii, thickness, and hvdraulic conductivity as a function of intraluminal pressure. The model gives good predictions using a constant wall modulus for pressures less than 60 mmHg, but requires a strain-dependent modulus for pressures greater than this. In both bovine and rabbit aorta, the tangential modulus is found to be approximately 20 times greater than the radial modulus. These moduli lead to predictions that, when perfused in a cylindrical geometry, the aortic volume and its specific hydraulic coonductivity are relatively independent of perfusion pressure, in agreement with experimental measurements. M, the parameter that relates specific hydraulic conductivy, to tissue dilation, is found to be a positive quantity correcting a previous error in the literature.  相似文献   

19.
Acoustic emission (AE) and radial shrinkage were compared between fully saturated fresh and pre-dried Norway spruce sapwood during dehydration at ambient temperature. Hydraulic conductivity measurements, anatomical investigations on bordered pits and X-ray computed tomography (CT) scans were done to search for possible AE sources other than the breakage of the water columns inside the tracheids. Both fresh and pre-dried specimens showed radial shrinkage due to drying surface layers right from the beginning of dehydration, which induced almost no AE. Whereas no dimensional changes occurred in pre-dried wood thereafter, fresh wood showed a rapid shrinkage increase starting at 25% relative water loss. This dimensional change ceased when further moisture got lost and was even partially reversed. AE of fresh wood showed much higher activity and energy, which is a waveform feature that describes the strength of the acoustic signal. Extremely high single AE energy events were detected at this critical stage of dehydration. After partial recovery from shrinkage, neither dimensional changes nor AE activity showed differences between fresh and pre-dried wood after more than 80% relative moisture loss. Our results suggested that fresh sapwood is more prone to dehydration stresses than pre-dried sapwood. Differences in AE and shrinkage behavior might be due to the weakening or distortion of the pit membranes (cavitation fatigue), pit aspiration, structural changes of the cell walls and micro-checks, which occurred during the first dehydration cycle.  相似文献   

20.
红松种源材质性状研究   总被引:4,自引:0,他引:4  
对帽儿山地区17年生26个红松种源试验林进行了材质性状研究,主要包括材质性状在不同种源间遗传变异情况以及从髓心到树皮径向变异模式研究.结果表明:红松各项材质在不同种源间均存在着极显著差异.各项材质均存在着一定的径向变异模式,主要表现在:红松各种源的管胞长度、管胞直径、木材密度和晚材率总体趋势是从髓心向外呈迅速增加趋势,而年轮宽从髓心向外呈递减趋势.本项研究为红松材性早期选择和预测提供依据.  相似文献   

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