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A theoretical, numerical and experimental study of heat and mass transfer in wood during drying.

机译：干燥过程中木材传热和传质的理论，数值和实验研究。

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The United States is one of the world's major consumers of wood and wood products. For most applications, green wood must undergo a drying process before it is ready for use. Despite the fact that wood has a complicated structure, most previous drying models have assumed that wood is a homogeneous and isotropic material. This results in significant differences between the experimental data and the numerical predictions.; This dissertation systematically investigates, from the theoretical, numerical, and experimental aspects, the effects of the heterogeneous and anisotropic nature of wood on the heat and mass transfer process during drying. A theoretical model has been derived based on the fundamental equations for thermodynamics and heat, mass and momentum transport. This is the first model which accounts for the heterogeneous and anisotropic wood structure. The model is applicable to both diffusive and capillary moisture transport and to drying in any transverse direction. The model, which has been implemented in a finite difference program, is capable of predicting the heterogeneous and anisotropic effects on the moisture as well as temperature distributions in wood during drying.; In order to verify the model equations, a corresponding experiment has been designed and conducted. The measurement of local moisture content, both internally and at the surface, has been accomplished using a {dollar}gamma{dollar}-ray attenuation system and a near-infrared reflectance analyzer, respectively. In particular, the near-infrared reflectance measurements of the surface moisture are the first of their kind. A series of experimental tests have been conducted for drying in various transverse directions. By showing the significant non-uniform moisture distribution in the radial direction and non-uniform drying on the different sides of the sample, the test results indicate that the heterogeneity and the anisotropy of wood structure have significant impacts on heat and mass transfer in wood during drying. The experimental results also show that the moisture transport undergoes a transition period from capillary transport at moisture content above the fiber saturation point to diffusive transport at moisture content below the fiber saturation point. The model predictions are in good agreement with the experimental results.

机译：美国是世界上木材和木制品的主要消费国之一。在大多数应用中，生木必须经过干燥处理后才能使用。尽管木材具有复杂的结构，但大多数以前的干燥模型都假定木材是均匀且各向同性的材料。这导致实验数据和数值预测之间存在显着差异。本文从理论，数值和实验等方面系统地研究了木材的非均质和各向异性性质对干燥过程中传热传质的影响。基于热力学以及热，质量和动量传递的基本方程式，已经推导出了理论模型。这是第一个解释异质和各向异性木材结构的模型。该模型适用于扩散和毛细管湿气传输以及任何横向干燥。该模型已经在有限差分程序中实现，能够预测干燥过程中木材水分和温度分布的异质和各向异性影响。为了验证模型方程，已设计并进行了相应的实验。内部和表面的局部水分含量的测量已分别使用{γ}γ{射线}射线衰减系统和近红外反射分析仪完成。特别地，表面水分的近红外反射率测量是此类技术中的第一例。已经进行了一系列用于在不同横向上干燥的实验测试。通过显示样品的径向上明显的水分分布不均匀以及样品两侧干燥不均匀的现象，测试结果表明，木材结构的异质性和各向异性对木材在传热过程中的传热和传质有重要影响。烘干。实验结果还表明，水分输送经历了从在纤维饱和点以上的水分含量下的毛细管输送到在纤维饱和点以下的水分含量下的扩散输送的过渡时期。模型预测与实验结果吻合良好。

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作者
Gong, Li.;
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作者单位

Washington State University.;

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授予单位 Washington State University.;
学科 Engineering Mechanical.; Engineering Agricultural.; Agriculture Wood Technology.
学位 Ph.D.
年度 1992
页码 272 p.
总页数 272
原文格式 PDF
正文语种 eng
中图分类机械、仪表工业;农业工程;森林采运与利用;
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1. NUMERICAL AND EXPERIMENTAL VALIDATION OF THE TRANSIENT HEAT AND MASS TRANSFER DURING HEAT TREATMENT OF PINE WOOD [J] . R. Younsi, D. Kocaefe, S. Poncsak, International Journal Of Modelling & Simulation . 2008,第2期

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2. Heat and mass transfer model in wood chip drying. [J] . Souza ME de P, Nebra SA, de P Souza ME Wood and Fiber Science . 2000,第2期

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3. Experimental and theoretical investigation of heat and mass transfer processes during wood pyrolysis [J] . Won Chan Park, Arvind Atreya, Howard R. Baum Combustion and Flame . 2010,第3期

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5. A THEORETICAL AND NUMERICAL INVESTIGATION OF LAMINAR BOUNDARY-LAYER HEAT AND MASS TRANSFER IN NATURAL CONVECTION: I. SIMULTANEOUS HEAT AND MASS TRANSFER. II. MASS TRANSFER IN THE ABSENCE OF HEAT TRANSFER [D] . CARDNER, DAVID VICTOR. 1963

机译：自然对流层流边界层传热和传质的理论和数值研究：I。同时传热和传质。二。没有传热时的传质
6. Experimental and Numerical Investigation into theHeat- and Mass-Transfer Processes of n-ButaneAdsorption on Activated Carbon [O] . Fei Zhao, Ling Zhu, *, 2021

机译：实验和数值调查正丁烷的热量和传质方法对活性炭的吸附
7. This article presents a new numerical model describing the behaviour of a thermally thick wood sample exposed to high solar heat flux (above 1 MW/m2). A preliminary study based on dimensionless numbers is used to classify the problem and support model building assumptions. Then, a model based on mass, momentum and energy balance equations is proposed. These equations are coupled with liquid-vapour drying model and pseudo species biomass degradation model. By comparing to a former experimental study, preliminary results have shown that these equations are not enough to accurately predict biomass behaviour under high solar heat flux. Indeed, a char layer acting as radiative shield forms on the sample exposed surface. In addition to this classical set of equations, it is mandatory to take into account radiation penetration into the medium. Furthermore, as biomass contains water, medium deformation consecutively to char steam gasification must also be implemented. Finally, with the addition of these two strategies, the model is able to properly capture the degradation of biomass when exposed to high radiative heat flux over a range of sample initial moisture content. Additional insights of biomass behaviour under high solar heat flux were also derived. Drying, pyrolysis and gasification fronts are present at the same time inside of the sample. The coexistence of these three thermochemical fronts leads to char gasification by the steam produced from drying of the sample, which it is the main phenomenon behind medium ablation. [O] . Pozzobon, Victor, Salvador, Sylvain, Bézian, Jean Jacques 2018

机译：本文提供了一个新的数值模型，该模型描述了暴露于高太阳热通量（高于1 / MW / m2）的热厚木材样品的行为。基于无量纲数的初步研究用于对问题进行分类并支持模型构建假设。然后，提出了一种基于质量，动量和能量平衡方程的模型。这些方程式与液体蒸汽干燥模型和假物种生物质降解模型耦合。通过与以前的实验研究进行比较，初步结果表明，这些方程不足以准确预测高太阳热通量下的生物量行为。的确，在样品暴露的表面上形成了充当辐射屏蔽层的炭层。除了这套经典的方程式之外，还必须考虑到辐射向介质的渗透。此外，由于生物质中含有水，因此还必须在炭蒸气汽化后进行连续的介质变形。最后，通过添加这两种策略，该模型能够在一定范围的样品初始水分含量下暴露于高辐射热通量的情况下，正确捕获生物质的降解。还得出了在高太阳热通量下生物量行为的其他见解。样品内部同时存在干燥，热解和气化前沿。这三个热化学前沿的共存会导致样品干燥产生的蒸汽产生焦炭气化，这是介质烧蚀的主要现象。

A theoretical, numerical and experimental study of heat and mass transfer in wood during drying.

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