Isothermal Vapour and Liquid Transport Inside Clay During Drying

A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally oblained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms.     

Isothermal Vapour and Liquid Transport Inside Clay During Drying

A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally obtained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms.     

Isothermal Vapour and Liquid Transport Inside Clay During Drying

ABSTRACT

A model is presented to describe the moisture transport inside a partially saturated porous material. The transport is caused by vapour diffusion and liquid diffusion. The evaporation inside the porous material is described with a mass transfer coefficient and a specific evaporating surface. Predictions of the model for moisture profiles are compared to experimentally oblained profiles found in the literature. The model needs further extension in the form of incorporating sorption isotherms.     

Isothermal Moisture Transport in Partially Saturated Porous Media

ABSTRACT

The prediction of a hydrodynamic model for the isothermal transport of liquid in partially saturated porous media is compared with experimentally obtained values of water transport in clay. The transport obeys the diffusion equation, The diffusion coefficient is described as a function of porosity, permeability and pore size distribution. The comparison indicates that the model needs some refinement.     

Isothermal Moisture Transport in Partially Saturated Porous Media

The prediction of a hydrodynamic model for the isothermal transport of liquid in partially saturated porous media is compared with experimentally obtained values of water transport in clay. The transport obeys the diffusion equation, The diffusion coefficient is described as a function of porosity, permeability and pore size distribution. The comparison indicates that the model needs some refinement.     

石灰调质污泥恒温干燥特性及动力学模型研究

对添加石灰的市政污泥进行恒温干燥实验,研究在不同的石灰添加量和不同的温度条件下污泥干燥特性、有效水分扩散系数和干燥活化能。结果表明:高温干燥时,石灰添加量的增加对平均干燥速率以及有效扩散系数的提高影响显著,低温干燥时影响不显著;石灰的添加可以降低干燥活化能;基于Modified Page模型建立的通用干燥模型能准确地描述石灰调质污泥的干燥特性;模型方程预测值和实验值吻合,均方根误差为0.32%。     

Diffusion During the Supercritical Drying of Silica Gels

Drying is the most critical elaboration step of large monolithic and crack-free silica aerogel plates. In the present work, we are studying the supercritical CO₂ drying and more precisely the first step, here called the supercritical washing step. This phase consists of replacing the liquid phase contained in the nanopores with supercritical CO₂. Within this study, this step is governed by molecular diffusion through the gels. These phenomena were investigated experimentally in order to estimate the duration of the washing step. The experimental results were then fitted with an analytical mass transfer model to identify the effective diffusion coefficient.     

A Numerical Study of Transient Deformation and Stress Behavior of a Clay Slab During Drying

A transient three-dimensional analysis was carried out on internal strain-stress as well as heat and the moisture transfer in a ceramic slab during drying. A model was developed to analyze viscoelastic behavior, heat conduction and moisture diffusion. The basic equations were solved by the finite element method. The effects of several dimensionless parameters are discussed to find an optimum drying process and a precise design of molds in ceramic production. The stress and the gradient of moisture content were influenced significantly by the Biot or Lewis number. When the moisture diffusion is enhanced or the drying is controlled well so as to form only gentle gradients of moisture content in the slab, the maximum tensile stress can be reduced. Nonuniform drying results in the develoment of warp and increase in the maximum tensile stress. The drying characteristics were not appreciably influenced by shrinkage.     

Diffusion During the Supercritical Drying of Silica Gels

Drying is the most critical elaboration step of large monolithic and crack-free silica aerogel plates. In the present work, we are studying the supercritical CO₂ drying and more precisely the first step, here called the supercritical washing step. This phase consists of replacing the liquid phase contained in the nanopores with supercritical CO₂. Within this study, this step is governed by molecular diffusion through the gels. These phenomena were investigated experimentally in order to estimate the duration of the washing step. The experimental results were then fitted with an analytical mass transfer model to identify the effective diffusion coefficient.     

Experimental Investigation of Hydromechanical Coupling During Clay Drying

Boom clay is studied as a potential host rock for underground nuclear waste storage. This experimental work analyzes its response under the convective drying conditions that may be applied in case of contact with the ambient atmosphere (during disposal drilling, for instance) or with gallery ventilation (because of damage in gallery lining). The drying kinetics is first established. In a second phase, the cracking and shrinkage onset and development are focused on, thanks to an X-ray microtomography device. The results show a phase of ideal shrinkage and a phase of shrinkage with desaturation, which are closely related to the kinetics. Cracking and shrinkage progressively develop from the drying surface, up to values representing about 3 and 12% of the cross section area, respectively.     

A Mass Transport Model for Drying Wood under Isothermal Conditions

Mass transport in wood during drying can have different mechanisms at different periods of drying. Depending on the current moisture content (MC) and the structure of the wood, the driving forces for the mass transport are essentially different. Above the fiber saturation point (FSP), the lumens are partially saturated and the transport of liquid (free) water occurs as a consequence of capillary action. On the other hand, below the FSP, bound water within the cell walls is conveyed by diffusion, and water vapor in the lumens moves under influence of pressures gradient. Based on these considerations, a unified model is presented that takes into account the transport of the different moisture phases. Simulation of the drying of a Norway spruce sample at 50°C from about 135 to 7% MC is carried out using the finite element method (FEM). Comparison between the simulated average MC and the experimental observations obtained from X-ray computed tomography (CT) shows reasonable agreement. Possible simplifications in the model are briefly discussed as well as some aspects of the numerical implementation. Finally, the influence of absolute permeability on the average MC is studied.     

A Mass Transport Model for Drying Wood under Isothermal Conditions

Mass transport in wood during drying can have different mechanisms at different periods of drying. Depending on the current moisture content (MC) and the structure of the wood, the driving forces for the mass transport are essentially different. Above the fiber saturation point (FSP), the lumens are partially saturated and the transport of liquid (free) water occurs as a consequence of capillary action. On the other hand, below the FSP, bound water within the cell walls is conveyed by diffusion, and water vapor in the lumens moves under influence of pressures gradient. Based on these considerations, a unified model is presented that takes into account the transport of the different moisture phases. Simulation of the drying of a Norway spruce sample at 50°C from about 135 to 7% MC is carried out using the finite element method (FEM). Comparison between the simulated average MC and the experimental observations obtained from X-ray computed tomography (CT) shows reasonable agreement. Possible simplifications in the model are briefly discussed as well as some aspects of the numerical implementation. Finally, the influence of absolute permeability on the average MC is studied.     

Mass Transport Through PDMS/Clay Nanocomposite Membranes

Poly(dimethylsiloxane)/clay nanocomposite membranes have been synthesized and mass transport properties through those nanocomposite membranes have been investigated. The effect of mechanical deformation on the transport properties of the PDMS (nanocomposite) membranes has also been studied. With the introduction of clay particles into the polymer matrix, mass transport is reduced, likely due to the longer diffusion path, which slows the diffusion process. The effect of membrane extension on diffusion is more complicated. Under small deformation, the permeation flux decreases, but under high deformation, it shows an enhanced diffusion. As the clay particle concentration increased, the effect of external deformation is reduced, and an enhanced diffusion is observed.     

苯－噻吩－二甲基甲酰胺大沸点差体系的汽液平衡

用鼓泡平衡釜在不同温度下测定了苯－噻吩－ＤＭＦ（Ｎ，Ｎ－Ｄｉｍｅｔｈｙｌｆｏｒｍａｍｉｄｅ，二甲基甲酰胺）体系的二元和三元体系的汽液平衡（ＶＬＥ）数据，所测数据均通过热力学一致性检验，并用多种模型作了关联，其结果令人满意。根据Ｃｏｎｄｅｒ和Ｐｕｒｎｅｌｌ提出的有限浓度普遍化保留理论导出了有限稀释活度系数工作方程，用色谱仪测定了苯－ＤＭＦ和噻吩－ＤＭＦ两个二元体系在稀浓度区的活度系数，结果证明在全浓度范围内Ｗｉｌｓｏｎ模型对本研究体系是完全适用的。     

Moisture Profiles Determination During Convective Drying Using X‐Ray Microtomography

The knowledge of internal moisture profiles which develop during drying is essential for model validation purposes, but they are difficult to determine experimentally. This paper shows that X‐ray microtomography, together with image analysis, provides an accurate, non destructive and easy to use technique to determine moisture profiles. Results reported concern the drying of wastewater sludges whose management is becoming a real environmental challenge. An analysis of the development of moisture gradients at the sample external wall shows an influence of drying operating conditions. Finally, mass diffusion coefficients are estimated from the knowledge of both the moisture gradients and the drying flux.     

色谱法测定葡萄糖果糖在制备柱上的传质和扩散系数

色谱模型对研究色谱分离过程中的传质动力学具有重要的意义。根据物料守恒原理,结合传质扩散模型推导色谱分离连续方程。假设吸附过程相平衡是线性,连续性方程推导出理论板数与流速和色谱模型参数有关。在多组不同流速条件下测定色谱柱参数,计算得到两组分的传质系数和扩散系数。分别用测定模型参数模拟脉冲实验,结果表明拟合较好。