Mesoscopic predictions of the effective thermal conductivity for microscale random porous media.
TL;DR: By using the present lattice Boltzmann algorithm along with the structure generating tool QSGS, the effective thermal conductivities of porous media with multiphase structure and stochastic complex geometries are predicted, without resorting to any empirical parameters determined case by case.
Abstract: A mesoscopic numerical tool has been developed in this study for predictions of the effective thermal conductivities for microscale random porous media. To solve the energy transport equation with complex multiphase porous geometries, a lattice Boltzmann algorithm has been introduced to tackle the conjugate heat transfer among different phases. With boundary conditions correctly chosen, the algorithm has been initially validated by comparison with theoretical solutions for simpler cases and with the existing experimental data. Furthermore, to reflect the stochastic phase distribution characteristics of most porous media, a random internal morphology and structure generation-growth method, termed the quartet structure generation set (QSGS), has been proposed based on the stochastic cluster growth theory for generating more realistic microstructures of porous media. Thus by using the present lattice Boltzmann algorithm along with the structure generating tool QSGS, we can predict the effective thermal conductivities of porous media with multiphase structure and stochastic complex geometries, without resorting to any empirical parameters determined case by case. The methodology has been applied in this contribution to several two- and three-phase systems, and the results agree well with published experimental data, thus demonstrating that the present method is rigorous, general, and robust. Besides conventional porous media, the present approach is applicable in dealing with other multiphase mixtures, alloys, and multicomponent composites as well.
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01 Jan 1937
1,390 citations
TL;DR: In this article, a review of the existing major analytical approaches dealing with material properties modeling is presented, with a focus on some recent advances in numerical methodology that are able to predict more accurately and efficiently the effective physical properties of multiphase materials with complex internal microstructures.
Abstract: Theoretical prediction of effective properties for multiphase material systems is very important not only to analysis and optimization of material performance, but also to new material designs. This review first examines the issues, difficulties and challenges in prediction of material behaviors by summarizing and critiquing the existing major analytical approaches dealing with material property modeling. The focus then shifts to some recent advances in numerical methodology that are able to predict more accurately and efficiently the effective physical properties of multiphase materials with complex internal microstructures. A random generation-growth algorithm is highlighted for reproducing multiphase microstructures, statistically equivalent to the actual systems, based on the geometrical and morphological information obtained from measurements and experimental estimations. Then a high-efficiency lattice Boltzmann solver for the corresponding governing equations is described which, while assuring energy conservation and the appropriate continuities at numerous interfaces in a complex system, has demonstrated its numerical power in yielding accurate solutions. Various applications are provided to validate the feasibility, effectiveness and robustness of this new methodology by comparing the predictions with existing experimental data from different transport processes, accounting for the effects due to component size, material anisotropy, internal morphology and multiphase interactions. The examples given also suggest even wider potential applicability of this methodology to other problems as long as they are governed by the similar partial differential equation(s). Thus, for given system composition and structure, this numerical methodology is in essence a model built on sound physics principles with prior validity, without resorting to ad hoc empirical treatment. Therefore, it is useful for design and optimization of new materials, beyond just predicting and analyzing the existing ones.
585 citations
TL;DR: This review summarizes recent progress in developments of the electrospun nanomaterials with applications in some predominant sensing approaches such as acoustic wave, resistive, photoelectric, optical, amperometric, and so on, illustrate with examples how they work, and discuss their intrinsic fundamentals and optimization designs.
547 citations
TL;DR: In this paper, a random generation-growth method was used to reproduce the microstructures of open-cell foam materials via computer modeling, and then solved the energy transport equations through the complex structure by using a high-efficiency lattice Boltzmann method.
233 citations
Cites methods from "Mesoscopic predictions of the effec..."
...For the insulated boundary, a specula reflection treatment is implemented to avoid energy leak along the surfaces [24]....
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...Since our lattice Boltzmann solver has been validated by several theoretical solutions and experimental data for granular porous media in our previous work [24,25], we are comparing our present numerical results for open-cell foam materials with the existing experimental data directly....
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TL;DR: In this paper, a more realistic three-dimensional distribution of fibers dispersed in a matrix phase is reproduced by a developed random generation-growth method to eliminate the overrated inter-fiber contacts by the two-dimensional simulations.
186 citations
Cites background or methods or result from "Mesoscopic predictions of the effec..."
...The temperature and the heat flux can then be calculated according to [18,27]...
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...Similar to other types of porous media [18], the porous structures thus generated exhibit realistic stochastic features, thus leading to fluctuations around an averaged result of each trail with given parameters....
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...For the insulated boundary, a specula reflection treatment is implemented to avoid energy leak along the surfaces [18]....
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...Since the present lattice Boltzmann solver has been validated for predictions of effective thermal conductivities of granular porous media by comparing with the available theoretical solutions and experimental data in our previous work [18,19], we employ it here directly for three-dimensional carbon fiber composites and compare the numerical results with the existing experimental data....
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...For solving the energy transport governing equations in a threedimensional multiphase system, the energy evolution equation can be generally given as [18]...
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References
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TL;DR: An overview of the lattice Boltzmann method, a parallel and efficient algorithm for simulating single-phase and multiphase fluid flows and for incorporating additional physical complexities, is presented.
Abstract: We present an overview of the lattice Boltzmann method (LBM), a parallel and efficient algorithm for simulating single-phase and multiphase fluid flows and for incorporating additional physical complexities. The LBM is especially useful for modeling complicated boundary conditions and multiphase interfaces. Recent extensions of this method are described, including simulations of fluid turbulence, suspension flows, and reaction diffusion systems.
6,565 citations
Book•
19 Oct 2001TL;DR: In this article, a unified approach for the characterization of 2-dimensional (2-3D) moduli is presented. But the approach is not suitable for 3-dimensional moduli.
Abstract: Motivation and overview * PART I Microstructural characterization * Microstructural descriptors * Statistical mechanics of particle systems * Unified approach * Monodisperse spheres * Polydisperse spheres * Anisotropic media * Cell and random-field models * Percolation and clustering * Some continuum percolation results * Local volume fraction fluctuation * computer simulation and image analysis * PART II Microstructure property connections * Local and homogenized equations * Variational Principles * Phase-interchange relations * Exact results * Single-inclusion solutions * Effective medium approximations * Cluster expansions * Exact contrast expansions * Rigorous bounds * Evaluation of bounds * Cross-property relations * Appendix A Equilibrium Hard disk program * Appendix B Interrelations among 2-3D moduli* References * Index
3,021 citations
TL;DR: In this paper, Chen et al. used the half-way wall bounceback boundary condition for the 2-D Poiseuille flow with forcing to obtain second-order accuracy for the 3-D square duct flow.
Abstract: Pressure (density) and velocity boundary conditions inside a flow domain are studied for 2-D and 3-D lattice Boltzmann BGK models (LBGK) and a new method to specify these conditions are proposed. These conditions are constructed in consistency of the wall boundary condition based on an idea of bounceback of non-equilibrium distribution. When these conditions are used together with the improved incompressible LBGK model by Zou et al., the simulation results recover the analytical solution of the plane Poiseuille flow driven by pressure (density) difference with machine accuracy. Since the half-way wall bounceback boundary condition is very easy to implement and was shown theoretically to give second-order accuracy for the 2-D Poiseuille flow with forcing, it is used with pressure (density) inlet/outlet conditions proposed in this paper and in Chen et al. to study the 2-D Poiseuille flow and the 3-D square duct flow. The numerical results are approximately second-order accurate. The magnitude of the error of the half-way wall bounceback is comparable with that using some other published boundary conditions. Besides, the bounceback condition has a much better stability behavior than that of other boundary conditions.
2,001 citations
TL;DR: The half-way wall bounceback boundary condition is also used with the pressure ~density! inlet/outlet conditions proposed in this article to study 2-D Poiseuille flow and 3-D square duct flow.
Abstract: Pressure ~density! and velocity boundary conditions are studied for 2-D and 3-D lattice Boltzmann BGK models ~LBGK! and a new method to specify these conditions is proposed. These conditions are constructed in consistency with the wall boundary condition, based on the idea of bounceback of the non-equilibrium distribution. When these conditions are used together with the incompressible LBGK model @J. Stat. Phys. 81 ,3 5 ~1995!# the simulation results recover the analytical solution of the plane Poiseuille flow driven by a pressure ~density! difference. The half-way wall bounceback boundary condition is also used with the pressure ~density! inlet/outlet conditions proposed in this paper and in Phys. Fluids 8, 2527 ~1996! to study 2-D Poiseuille flow and 3-D square duct flow. The numerical results are approximately second-order accurate. The magnitude of the error of the half-way wall bounceback boundary condition is comparable with that of other published boundary conditions and it has better stability behavior. © 1997 American Institute of Physics. @S1070-6631~97!03406-5#
1,854 citations