Thermal diffusion of bound water in wood

Skaar, Christen; Siau, J. F.

doi:10.1007/bf00367857

Cited by 37 publications

(12 citation statements)

References 3 publications

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“…which relies on a separate description of the movement of free water owing to the action of capillary pressure gradient (according to Darcy's law) and a mechanism of sorption-diffusion of bound water molecules according to a diffusive process supplied by a gradient of bound water [37,38]. This approach has a major shortcoming which relies on a tricky identification of both the transport coefficients related to bound water (diffusion coefficient) and those related to capillary movement of free water according to the Darcy law (permeability, viscosity, etc.).…”

Section: Continuum Approach Of Moisture Transport In Unsaturated Poromentioning

confidence: 99%

Numerical modelling of moisture transfers with hysteresis within cementitious materials: Verification and investigation of the effects of repeated wetting–drying boundary conditions

Zhang

Thiéry²,

Baroghel-Bouny³

2015

Cement and Concrete Research

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a b s t r a c tIn natural environment, the cover layer of reinforced concrete structures is affected by periodic variations of external relative humidity (RH). However, most moisture transport models in the literature only focus on drying of materials. In this study, a method coupling a moisture transport model with any kind of hysteresis modelling is presented. Two hysteresis models (conceptual and empirical) have been implemented and compared. The scope of the study is limited to cyclic variations of RH with no direct contact with liquid water during the wetting steps. Experimental data verifications show that the conceptual approach yields better results than the empirical one. Comparisons of non-hysteresis and hysteresis modellings have been carried out for different cycle durations, RH amplitudes and initial moisture states. All comparisons and investigations enhance the necessity of considering hysteresis to quantify moisture transport under repeated drying-wetting boundary conditions.

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Section: Continuum Approach Of Moisture Transport In Unsaturated Poromentioning

confidence: 99%

Numerical modelling of moisture transfers with hysteresis within cementitious materials: Verification and investigation of the effects of repeated wetting–drying boundary conditions

Zhang

Thiéry²,

Baroghel-Bouny³

2015

Cement and Concrete Research

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“…Bound water movement can be described as a diffusion process driven by differences in concentration of activated water molecules, and the gradient can be expressed in terms of the bound water concentration gradient (Skaar and Siau, 1981). Consequently, the mass flux of the bound water phase can be expressed as…”

Section: V(pbvbmentioning

confidence: 99%

“…Consequently, the findings of the research conducted in wood science can be applied to concrete. As proposed by Skaar and Siau (1981), the bound water coefficient is a function of the activation energy for bound water, and for concrete, it can be described as a function of saturation and temperature in the following way Db = Dr(S,T)= Db,oexp (16.8-2 08 S--~---~T ~ "…”

Section: Materials Parameters and Constitutive Relationsmentioning

confidence: 99%

Moisture transport in initially fully saturated concrete during drying

1996

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Moisture content changes during drying were investigated in the present work. Particular emphasis was placed on the initial stage of drying of saturated concrete, where moisture contents are high: For this stage of drying, experimental data are lacking, and no comprehensive theory exists to describe it.The present investigation was performed experimentally and numerically for drying of cylinders with one exposed end, made of normal weight and lightweight concrete with varying water to cement ratio (w/c). The gravimetric technique was employed to obtain the spatial distribution of moisture content. The experimental results obtained indicate that drying of concrete becomes diffusion controlled when the average moisture content decreases below 70 to 80% of the initial saturation. Typical drying rates are in the order of magnitude of 0.18 kg/day/m 2 and 0.02 kg/day/m 2 for the first and the second stage of drying, respectively.The lightweight concrete cylinders as compared to those made of normal weight concrete exhibited higher levels of moisture content throughout the process. At high w/c ratios, the moisture profiles for both types of cylinders, as expected, show steeper changes with time. Large, constant drying rates were observed both experimentally and numerically in the beginning of the drying.The numerical model developed is based on a generalized mathematical formulation for mass and heat transfer in porous media, and its predictions are in agreement with the experimental data within the uncertainty range of the input data.

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“…The bound water diffusion coefficient is a function of the activation energy of bound water [16] and can be expressed as a function of saturation and temperature.…”

Section: Materials Parameters and Constitutive Relationsmentioning

confidence: 99%

Modeling of multiphase flow with phase change in porous media - a case study

Šelih

Sousa

2005

Mat.-wiss. u. Werkstofftech.

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A general numerical model developed to simulate the time-dependent changes of moisture content, temperature and pore pressures is proposed for a porous material. The model is based on a coupled heat and mass transfer mathematical formulation. The model's validation is conducted using experimental data for concrete. The gravimetric technique is used to obtain the experimental data on moisture content in cylinders made up of fully saturated concrete exposed to drying. Further to demonstrate the applicability of the model, it is also studied the moisture migration, temperature development and thermal stresses in a concrete element exposed to fire. The obtained results indicate that during fire, several degradation phenomena are taking place at the same time. Thermal stresses developed by the temperature differential, especially when temperature-dependent material properties are taken into the account, along with the increase of pore pressures, may contribute to structural failure.

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Thermal diffusion of bound water in wood

Cited by 37 publications

References 3 publications

Numerical modelling of moisture transfers with hysteresis within cementitious materials: Verification and investigation of the effects of repeated wetting–drying boundary conditions

Numerical modelling of moisture transfers with hysteresis within cementitious materials: Verification and investigation of the effects of repeated wetting–drying boundary conditions

Moisture transport in initially fully saturated concrete during drying

Modeling of multiphase flow with phase change in porous media - a case study

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