Lattice Boltzmann Modeling of the Effective Thermal Conductivity for Complex Structured Multiphase Building Materials

2015 ◽  
Vol 1119 ◽  
pp. 694-699 ◽  
Author(s):  
Mazhar Hussain ◽  
Shakeel Ahmad ◽  
Wen Quan Tao
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Lattice Boltzmann ◽  
Building Materials ◽  
Present Model ◽  
High Efficiency ◽  
Theoretical Models ◽  
Random Generation ◽  
Proposed Model ◽  
Experimental Values

The effective thermal conductivity is an important parameter used to predict the thermal performance analysis of complex structured porous building materials. The observation of porous structure of building materials on REV (representative elementary volume) scale showed that pores can be classified into meso and macro pores. In contrast to the traditional models usually used for the (macro-meso) pore connection , a new numerical random generation macro-meso pores (RGMMP) method, based on geometrical and morphological information acquired from measurements or experimental calculations, is proposed here. Along with proposed structure generating tool RGMMP a high efficiency LBM, characterized with the energy conservation and appropriate boundary conditions at numerous interfaces in the complex system, for the solution of the governing equation is described which yields a powerful numerical tool to obtain accurate solutions. Then present model is validated with some theoretical and experimental values of effective thermal conductivity of typical building materials. The comparison of present model and experimental results shows that the proposed model agrees much better with the experimental data than the traditional theoretical models. Therefore, the present model is not limited to the described building materials but can also be used for predicting the effective thermal conductivity of any type of complex structured building materials.

On the Effective Thermal Conductivity of Nanofluids With Fractal Aggregation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
C. G. Subramaniam
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Effective Medium Theory ◽  
Functionally Graded ◽  
Fractal Aggregates ◽  
Medium Theory ◽  
Analytical Approximations ◽  
Proposed Model ◽  
Dispersing Medium ◽  
Dilute Limit

A generalized effective medium theory (EMT) is proposed to account for the fractal structure of the dispersed phase in a dispersing medium under the dilute limit. The thermal conductivity of nanofluids with fractal aggregates is studied using the proposed model. Fractal aggregates are considered as functionally graded spherical inclusions and its effective thermal conductivity is derived as a function of its fractal dimension. The results are studied for self-consistency and accuracy within the limitations of the analytical approximations used.

Lattice Boltzmann Simulations for Thermal Conductivity Estimation in Heterogeneous Materials

2009 ◽  
Vol 283-286 ◽  
pp. 364-369 ◽  
Author(s):  
M.R. Arab ◽  
Bernard Pateyron ◽  
Mohammed El Ganaoui ◽  
Nicolas Calvé
Keyword(s):  
Thermal Conductivity ◽  
Porous Medium ◽  
Lattice Boltzmann ◽  
Numerical Study ◽  
Theoretical Models ◽  
Short Description ◽  
Physical Parameters ◽  
Two Dimensional ◽  
Lattice Boltzmann Simulations ◽  
Boltzmann Method

For simulating flows in a porous medium, a numerical tool based on the Lattice Boltzmann Method (LBM) is developed with regards to the classical D2Q9 model. A short description of this model is presented. This technique, applied to two-dimensional configurations, indicates its ability to simulate phenomena of heat and mass transfer. The numerical study is extended to estimate physical parameters that characterize porous materials, like the so-called Effective Thermal Conductivity (ETC) which is of our interest in this paper. Obtained results are compared with those which could be found analytically and by theoretical models. Finally, a porous medium is considered to find its ETC.

Porosity and Effective Thermal Conductivity of Wire Screens

1990 ◽  
Vol 112 (1) ◽  
pp. 5-9 ◽  
Author(s):  
Won Soon Chang
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Theoretical Model ◽  
Effective Thermal Conductivity ◽  
Present Model ◽  
Model Based ◽  
Wire Screen ◽  
Simple Theoretical Model ◽  
Parallel Conduction ◽  
The Wire

A simple theoretical model based on combined series and parallel conduction for the effective thermal conductivity of fluid-saturated screens has been developed. The present model has been compared with the existing correlations and experimental data available in literature, and it has been found that the model is effective in predicting thermal conductivity. The study also demonstrates that it is important to include the actual thickness of the wire screen in order to calculate the porosity accurately.

Size and Interface Effects on Thermal Conductivity of Superlattices and Periodic Thin-Film Structures

1997 ◽  
Vol 119 (2) ◽  
pp. 220-229 ◽  
Author(s):  
G. Chen
Keyword(s):  
Thin Film ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Amorphous Materials ◽  
High Efficiency ◽  
Interface Roughness ◽  
Atomic Scale ◽  
Diffuse Interface ◽  
Boltzmann Transport ◽  
Diffuse Interfaces

Superlattices consisting of alternating layers of extremely thin films often demonstrate strong quantum size effects that have been utilized to improve conventional devices and develop new ones. The interfaces in these structures also affect their thermophysical properties through reflection and transmission of heat carriers. This work develops models on the effective thermal conductivity of periodic thin-film structures in the parallel direction based on the Boltzmann transport equation. Different interface conditions including specular, diffuse, and partially specular and partially diffuse interfaces, are considered. Results obtained from the partially specular and partially diffuse interface scattering model are in good agreement with experimental data on GaAs/AlAs superlattices. The study shows that the atomic scale interface roughness is the major cause for the measured reduction in the superlattice thermal conductivity. This work also suggests that by controlling interface roughness, the effective thermal conductivity of superlattices made of bulk materials with high thermal conductivities can be reduced to a level comparable to those of amorphous materials, while maintaining high electrical conductivities. This suggestion opens new possibilities in the search of high efficiency thermoelectric materials.

scholarly journals INVESTIGATION OF THERMAL CONDUCTIVITY OF LUFFA AND LUFFA-COIR REINFORCED EPOXY COMPOSITES

2020 ◽  
Vol 8 (12) ◽  
pp. 69-79
Author(s):  
K. Anbukarasi ◽  
S. Imran Hussain ◽  
S. Kalaiselvam
Keyword(s):  
Thermal Conductivity ◽  
Volume Fraction ◽  
Hybrid Composites ◽  
Theoretical Models ◽  
Epoxy Composites ◽  
Coir Fiber ◽  
Fiber Volume ◽  
Experimental Values ◽  
Thermal Stability Of ◽  
Guarded Heat Flow Meter

Thermal behavior of luffa and coir reinforced epoxy composites have been evaluated for a constant total fiber volume fraction 0.4Vf by varying the ratio of luffa and coir fiber. Thermal conductivity of luffa-epoxy and luffa-coir reinforced epoxy composite was studied experimentally and analytically in terms of fiber size and fiber volume. Thermal conductivity of composites was investigated experimentally by a guarded heat flow meter method. The experimental results at different volume fraction were compared with three theoretical models. The composite C has the lowest thermal conductivity of 0.206 W/mk with 0.81 % of voids. The experimental values of thermal conductivity of hybrid composites are the good correlation with the Maxwell and Maxwell-Eucken models. As in a case of 0.4 Vf of luffa-epoxy composites these values are closer to the rule of mixture models. The thermal stability of the composites was investigated by thermogravimetric analysis. This result reveals that the hybridization of luffa and coir with epoxy allows a significantly improved insulation ability of the composites.

scholarly journals A 3D model to predict the influence of nanoscale pores or reduced gas pressures on the effective thermal conductivity of cellular porous building materials

2019 ◽  
Vol 43 (4) ◽  
pp. 277-300 ◽  
Author(s):  
Wouter Van De Walle ◽  
Hans Janssen
Keyword(s):  
Thermal Conductivity ◽  
Porous Materials ◽  
Effective Thermal Conductivity ◽  
Building Materials ◽  
Full Range ◽  
Advanced Materials ◽  
Future Application ◽  
High Porosity ◽  
Pore Sizes ◽  
Gas Pressures

Cellular porous materials are frequently applied in the construction industry, both for structural and insulation purposes. The progressively stringent energy regulations mandate the development of better performing insulation materials. Recently, novel porous materials with nanopores or reduced gas pressures have been shown to possess even lower thermal conductivities because of the Knudsen effect inside their pores. Further understanding of the relation between the pore structure and the effective thermal conductivity is needed to quantify the potential improvement and design new optimized materials. This article presents the extension of a 3D numerical framework simulating the heat transfer at the pore scale. A novel methodology to model the reduced gas-phase conductivity in nanopores or at low gas pressures is presented, accounting for the 3D pore geometry while remaining computationally efficient. Validation with experimental and numerical results from the literature indicates the accuracy of the methodology over the full range of pore sizes and gas pressures. Combined with an analytical model to account for thermal radiation, the framework is applied to predict the thermal conductivity of a nanocellular poly(methyl methacrylate) foam experimentally characterized in the literature. The simulation results show excellent agreement with less than 5% difference with the experimental results, validating the model’s performance. Furthermore, results also indicate the potential improvements when decreasing the pore size from the micrometre to the nanometre range, mounting up to 40% reduction for such high-porosity low-matrix-conductivity materials. Future application of the model could assist the design of advanced materials, properly accounting for the effect of reduced pore sizes and gas pressures.

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