Heat Transfer and Unsaturated Flow Phenomena in Rigid Dual- Scale Porous Media (original) (raw)

Evaluation of Effective Thermal Conductivities of Porous Textile Composites

International Journal for Multiscale Computational Engineering, 2008

An uncoupled multi-scale homogenization approach is used to estimate the effective thermal conductivities of plain weave C/C composites with a high degree of porosity. The geometrical complexity of the material system on individual scales is taken into account through the construction of a suitable representative volume element (RVE), a periodic unit cell, exploiting the information provided by the image analysis of a real composite system on every scale. Two different solution procedures are examined. The first one draws on the classical first order homogenization technique assuming steady state conditions and periodic distribution of the fluctuation part of the temperature field. The second approach is concerned with the solution of a transient flow problem. Although more complex, the latter approach allows for a detailed simulation of heat transfer in the porous system. Effective thermal conductivities of the laminate derived from both approaches through a consistent homogenization on individual scales are then compared with those obtained experimentally. A reasonably close agreement between individual results then promotes the use of the proposed multi-scale computational approach combined with the image analysis of real material systems.

A synthesis of tortuosity and dispersion in effective thermal conductivity of porous media

International Journal of Heat and Mass Transfer, 2010

Effects of tortuosity and dispersion on the effective thermal conductivity of fluid-saturated porous media are investigated analytically with help of a volume averaging theory. Firstly, a general expression for the effective stagnant thermal conductivity has been derived using a unit cell model, which consists of rectangular solids with connecting arms in an in-line arrangement. The validity of the expression for the stagnant thermal conductivity has been confirmed comparing the present results with available experimental and theoretical data for packed beds, porous foams and wire screens. Secondly, an general expression for the thermal dispersion conductivity has been sought with help of the two energy equations for solid and fluid phases, derived on the basis of a volume averaging theory. It has been shown that the interstitial heat transfer between the solid and fluid phases is closely associated with the thermal dispersion. The resulting expressions for the longitudinal and transverse thermal dispersion conductivities agree well with available experimental data and empirical correlations.

Modeling heat transfer within porous multiconstituent materials

Journal of Physics: Conference Series, 2012

The purpose of our work has been to determine the effective thermal properties of materials considered heterogeneous at the microscale but which are regarded as homogenous in the macroscale environment in which they are used. We have developed a calculation code that renders it possible to simulate thermal experiments over complex multiconstituent materials from their numerical microstructural morphology obtained by volume segmentation through tomography. This modeling relies on the transient solving of the coupled conductive and radiative heat transfer in these voxelized structures.

The Influence of the Percentage of Porosity on the Thermal Conductivity of a Composite Material, for Example Clay

WSEAS TRANSACTIONS ON ENVIRONMENT AND DEVELOPMENT, 2020

The purpose of this work is to study the influence of the percentage of porosity, that is to say the volume of air compared to total volume on the thermal conductivity of clay at different degrees of temperature, this study is very interesting because clay is used in several fields for example construction, pottery, etc, and also in certain regions of the world as a building material and especially in countries which at a higher temperature, for this we perform together experiments on a mass of clay with a cubic shape of dimensions (10cm * 10cm * 10cm), but with each experiment we varied the percentage of porosity, then we relied on the CT-METRE device to measure the thermal conductivity

A theoretical model for determining thermal conductivity of porous solid materials

2012

In present study a new-developed simple algebraic equation is used to find out the effective thermal conductivity of new–produced composite materials that have nonhomogenous microscopic porosity. Thermal power plant ashes, tragacanth and portland cement are used as binding components of these porous composite materials. By varying the mixing ratio of three components, 24 samples have been produced. Effective thermal conductivity coefficients obtained by the algebraic method is then compared to the ones obtained by experimental measurement techniques. The theoretical results are found to be agreeable with the experimental results.

The effective thermal conductivity of double-reinforced composites

Heat and Mass Transfer, 2020

Polymer based composite materials have a great potential for applications in tribology as dry lubricants since the components comprising the composition may be chosen to fit to various tribological requirements. It is however well known that heat transfer and thermal effects are important for such systems. Systematic experimental studies of temperature effects are time consuming and expensive. In this work, we use a numerical homogenization approach in order to study the principal influence of key composite descriptors of fiber and particle reinforced PEEK on the homogenized heat conductivity. It turns out that the sensitivity of this key parameter on the descriptors can be nicely fitted to a regression model and thus allows for interpolation in the sense of a structure-property-relationship.

A mathematical model for thermal conductivity of homogeneous composite materials

2016

In this paper, a mathematical model to find the thermal conductivity of a large category of polymer homogeneous composite materials is performed. This type of composites contains ideal spherical particles encircled by an inhomogeneous interphase region, whereas the matrix is considered as isotropic. The thermal conductivity of the interphase is formulated as a continuous single-valued function of the radius of a spherical model. In this context, it is evident that the concept of boundary interphase is a useful manner for a quantitative description of the adhesion efficiency between matrix and filler since it is well known that there is a considerable effect of this phase on the thermo-mechanical properties of the composite. On the other hand, the particle distribution which can be considered as the influence of neighboring particles and their possible interaction should affect the thermal conductivity of the overall material.

Modelling of void shape effect on effective thermal conductivity of lotus-type porous materials

Mechanics of Materials, 2020

In this paper, a formula for estimating the effective thermal conductivity of lotus-type porous materials (LTPM) combining an analytical formula with a mean-field homogenisation technique is developed and validated. LTPMs are considered multi-phase materials in which each phase is defined by the pore shape. To estimate the effective thermal conductivities of multi-phase LTPMs, a two-step mean-field homogenisation method is implemented and validated. The validation is applied by comparing the results obtained with those of the representative volume element based finite element homogenisation method, which has been taken as a reference. The proposed formula is applied by replacing the first step of the two-step mean field homogenisation method using a formula for estimating the effective thermal conductivity of two-phase lotus-type materials. The good agreement between the results of the proposed formula and the reference results indicates that the proposed formula ensures an accurate estimation of the effective macroscopic thermal conductivities of multi-phase lotus-type porous materials.