Assessment of structure effects on the thermal conductivity of two-phase porous geomaterials

“…Côte and Konrad [13] point out that heat conduction through a two-phase porous media depends on the thermal conductivity as well as the structure of the solid matrix. In terms of thermal behaviour, the structure of the solid matrix determines the contact resistance and the continuity of the solid phase [11].…”

Section: Two-phase Systemsmentioning

confidence: 99%

Calculation of thermal conductivity of gypsum plasterboards at ambient and elevated temperature

Korte

Brouwers

2009

Fire and Materials

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SUMMARYPlasterboard often protects steel structures of buildings because it conducts heat slowly and absorbs the heat of the fire by its volumetric enthalpy. The most important property governing the heat transfer is the thermal diffusion. This property depends on the density, specific heat and thermal conductivity. The first two can be calculated based on the mass composition of the board. The thermal conductivity is more difficult to derive since it is a directional property. This paper will focus on the calculation of the thermal conductivity at ambient and elevated temperatures.It is shown that the thermal conductivity of gypsum plasterboard (i.e. a porous medium) can be assumed to be a three-phase system. Plasterboard consists of a solid phase and a water/air mix in the voids. The differences between different theoretical equations for both dry and moistured plasterboards are presented. The equation proposed by Zehner and Schlunder (Chem. Ing.-Tech. 1972; 44(23):1303-1308) with shape-factor C of 5 gave good agreement with experimental data of the different boards. Furthermore, the influence of the composition of the boards on the thermal conductivity is investigated. This has an influence, especially since the composition is also related to its moisture content. Regression analysis * Correspondence to: A. C. J. points out that the moisture content depends only on the gypsum content. A value of 2.8% absorbed water on the mass of gypsum is found, and this water plays an important role in the thermal conductivity of plasterboard at ambient temperature.Finally, the thermal conductivity of board at elevated temperature is computed. A close fit between computed and experimental values derived from literature is found.

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“…Soil type also affects l. Soils with relatively flat grain surfaces, such as silts and clays, have more contact points between grains and higher l than do more rounded particles like sands and gravels, which have smaller contact area and lower l (Becker et al, 1992). Grain size also affects l where coarse-grained materials often maintain a higher l than fine-grained materials (Al Nakshabandi and Kohnke, 1965;Côté and Konrad, 2009). The increase in l for coarse-grained materials is due to the larger grains' ability to enable a more continuous length of high conductivity material (fewer gaps filled with air or water).…”

mentioning

confidence: 99%

Thermal Conductivity of Binary Sand Mixtures Evaluated through Full Water Content Range

Wallen

Smits

Sakaki

et al. 2016

Soil Science Soc of Amer J

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A soil's grain-size distribution affects its physical and hydraulic properties; however, little is known about its effect on soil thermal properties. To better understand how grain-size distribution affects soil thermal properties, specifically the effective thermal conductivity, a set of laboratory experiments was performed using binary mixtures of two uniform sands tightly packed with seven different mixing fractions over the full range of saturation. For each binary mixture, the effective thermal conductivity, l, capillary pressure, h c , and volumetric water content, q, were measured. Results demonstrated that the l-q relationship exhibited distinct characteristics based on the percentage of fine-and coarse-grained sands. We further compared measured l-q properties with independent estimates from two semi-empirical models (Campbell Model and Lu and Dong Model) to evaluate the models' applicability in relation to physically based parameters associated with changes in soil mixing (e.g., porosity and grain size). Both models were able to fit experimental data but to varying degrees based on the number of physically based parameters used. In general, model improvements are needed to capture the l-q relationship solely on physically based parameters.Abbreviations: SWRC, soil water retention curve. U nderstanding soil thermal properties is important to properly determine the impact of heat transfer on the distribution, circulation, and evaporation of water in soil. Heat transfer within soil influences micrometeorological phenomena (Hanks et al., 1967), engineering efforts such as cooling electronic devices with heat pipes and insulating buildings (Bussing and Bart, 1997;Sakaguchi et al., 2009;Moradi et al., 2015), agricultural production (Al Nakshabandi and Kohnke, 1965;Usowicz et al., 1996;Lipiec et al., 2007), and landmine detection efforts that rely on thermal contrast (e.g., Garcia-Padron et al., 2002;Martínez et al., 2004). Previous studies provide insight into the effect of soil moisture, temperature, and soil physical characteristics on soil thermal properties, specifically the effective thermal conductivity, l (W m -1 K -1 ; e.g., De Vries, 1963;Johansen, 1975;Hopmans and Dane, 1986;Ochsner et al., 2001;Tarnawski and Gori, 2002). However, to our knowledge, none of the studies to date has investigated the effect of mixing differently sized particles on controlling the l behavior under varying soil water contents (q, cm 3 cm -3 ). Knowledge of the l-q relationship for differently sized soil fractions is particularly important in many engineering applications such as soil borehole thermal energy storage (SBTES), landfill covers, and engineered material stabilization.Previous research provides strong evidence that l is affected by a wide range of parameters including q (e.g., Philip and de Vries, 1957;De Vries, 1963;Yadav and Saxena, 1977; Core Ideas• Thermal conductivity and water content relationship based upon mixtures are distinct.• Systematic change in particle fine fraction directly affects thermal cond...

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Assessment of structure effects on the thermal conductivity of two-phase porous geomaterials

Cited by 75 publications

References 39 publications

Experimental study and modeling on effective thermal conductivity of EPS lightweight concrete

Experimental study and modeling on effective thermal conductivity of EPS lightweight concrete

Calculation of thermal conductivity of gypsum plasterboards at ambient and elevated temperature

Thermal Conductivity of Binary Sand Mixtures Evaluated through Full Water Content Range

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