Moisture movement in porous materials under temperature gradients

Abstract--The mathematical formulation of mass transfer in drying processes is often based on the diffusion equation. In principle the diffusion coefficient as a function of moisture content has to be determined experimentally. The most direct approach is to derive the diffusion coefficient from experimental moisture concentration profiles in the material during drying. In this work, the diffusion coefficient determined in this way is called the actual diffusion coefficient. Very often, however, an indirect method is used based on drying curves (average moisture content of a sample vs time). Since the diffusion coefficient is determined indirectly from the macroscopic behaviour of the sample, this coefficient will be called the apparent diffusion coefficient. A comparison of diffusion coefficients as a function of moisture content using both methods shows that for porous materials such as clays, the apparent diffusion coefficient depends on experimental conditions. This can be explained by the fact that the apparent diffusion coefficient is in agreement with the actual diffusion coefficient over a limited range of moisture content only. For materials such as clays, drying curves are not suited to derive diffusion coefficients as a function of moisture content in a satisfactory and consistent way.

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“…Philip and de Vries (1957)]. A more fundamental basis for this equation was later given by Bear (1990) and Whitaker (1977).…”

Section: Introductionmentioning

confidence: 99%

Drying kinetics: A comparison of diffusion coefficients from moisture concentration profiles and drying curves

Ketelaars

Pel

Coumans

et al. 1995

Chemical Engineering Science

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“…In ROCMAS, the Biot (1941) formulation is extended to partially saturated media through Philip and de Vries' (1957) theory for heat-and moisture-flow in soil. This results in a comprehensive coupled THM formulation for partially saturated geological media that includes the coupled processes shown in Figure 2.…”

Section: Rocmasmentioning

confidence: 99%

A Fully Coupled Three-Dimensional THM Analysis of the Febex in Situ Test with the Rocmas Code: Prediction of THM Behavior in a Bentonite Barrier

Rutqvist

Tsang

2004

Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems - Fundamentals, Modelling, Experiments and Applications

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This paper presents a fully coupled thermal-hydrological-mechanical analysis of FEBEX-a large underground heater test conducted in a bentonite and fractured rock system. System responses predicted by the numerical analysis-including temperature, moisture content, and bentonite-swelling stress-were compared to field measurements at sensors located in the bentonite. An overall good agreement between predicted and measured system responses shows that coupled thermal-hydrological-mechanical processes in a bentonite barrier are well represented by the numerical model. The most challenging aspect of this particular analysis was modeling of the bentonite's mechanical behavior, which at FEBEX turned out to be affected by gaps between prefabricated bentonite blocks. At FEBEX, the swelling pressure did not develop until a few months into the experiment when moisture swelling of bentonite blocks had closed the gaps completely. Moreover, the wetting of the bentonite took place uniformly from the rock and was not impacted by the permeability difference between the Lamprophyres dykes and surrounding rock.

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“…) with the transport of mass and energy in the soil. The transport of mass and energy in the soil (and consequently evaporation of water from the soil surface) has been intensively studied, and various formulations and numerical solutions based on the general theory of Philip and de Vries [1957] have been presented [e.g., Milly, 1982[e.g., Milly, , 1984Kondo et al, 1990;Scanlon and Milly, 1994;Parlange et al, 1998;Qin et al, 2002]. The use of such detailed descriptions is not appropriate for large-scale modeling due to the vast amount of field data required [Yang et al, 1998] and the intense computational efforts involved.…”

Section: Introductionmentioning

confidence: 99%

Soil water evaporation during the dry season in an arid zone

Agam¹

2004

J. Geophys. Res.

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[1] The objective of this study was to assess the relative magnitude of latent heat flux density over a bare loess soil in the Negev desert throughout the dry season, during which the atmospheric models usually assume the lack of latent heat flux. The measurements were carried out in the northern Negev, Israel, over a bare loess soil, during nine 24-hour field campaigns throughout the dry season of 2002. In addition to a micrometeorological station that was set up in the research site, an improved microlysimeter was installed. The representativity of the microlysimeter was assessed by comparing its surface temperature to that of the surrounding surface using thermal images acquired on an hourly basis during several campaigns. It was found that although the water content of the uppermost soil is significantly lower than the wilting point, for which most of the commonly used meteorological models would assume no latent heat flux, the latter was $20% of the net-radiation during the night and 10-15% during the day. It is therefore concluded that latent heat flux plays a major role in the dissipation of the net radiation during the dry season in the Negev desert.

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Moisture movement in porous materials under temperature gradients

Cited by 2,032 publications

References 19 publications

Drying kinetics: A comparison of diffusion coefficients from moisture concentration profiles and drying curves

Drying kinetics: A comparison of diffusion coefficients from moisture concentration profiles and drying curves

A Fully Coupled Three-Dimensional THM Analysis of the Febex in Situ Test with the Rocmas Code: Prediction of THM Behavior in a Bentonite Barrier

Soil water evaporation during the dry season in an arid zone

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