Begell House
Journal of Porous Media
Journal of Porous Media
1091-028X
18
10
2015
PREFACE: HEAT AND MASS TRANSFER IN POROUS MEDIA
Moran
Wang
Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084, China
Michel
Quintard
Université de Toulouse; INPT, UPS; IMFT (Institut de Mécanique des Fluides de Toulouse); Allée Camille Soula, F-31400 Toulouse, France and CNRS; IMFT; F-31400 Toulouse, France
Ning
Pan
Biological and Agricultural Engineering and NEAT, University of California, Davis, California 95616, USA
Kambiz
Vafai
Department of Mechanical Engineering, University of California, Riverside, CA 92521-0425 USA
v-vi
LATTICE BOLTZMANN SIMULATION OF EFFECTIVE THERMAL CONDUCTIVITY OF POROUS MEDIA WITH MULTIPHASE
The particle size, distribution, and orientation will decide the heat conduction behavior of porous media, and the trends of different effects can be obtained according to the various model assumptions. With or without consideration of the thermal contact resistance, the effects of the grain size on the thermal conductivity of porous materials may be adverse. The lattice Boltzmann method has microscopic and mesoscopic features that facilitate the processing of irregular boundary conditions for porous media. A corrected heat flux of the thermal lattice Boltzmann model is proposed in this paper, which naturally ensures heat flux continuity at the phase−phase interface. A new equivalent relaxation time is set at the phase−phase interface in the thermal lattice Boltzmann model, and through the use of the thermal energy transport model with series and parallel sets, the reliability of the new method in dealing with the phase−phase interface is verified. Porous media are generated by the quartet structure generation set. The effective thermal conductivity is obtained both with single-phase and multiphase fluid in the porous media. The effective thermal conductivity of porous media increases with increasing particle size. The connectivity of the particles along the heat transfer direction provides a preferential path for heat transfer, which creates higher effective thermal conductivity. When wetting fluid, with lower thermal conductivity, is absorbed on the porous matrix, the predicted effective thermal conductivity is close to the Hashin−Shtrikman lower bound.
Dongdong
Wang
School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Zhichun
Liu
School of Energy and Power Engineering, Huazhong University of Science and Technology,
Wuhan 430074, China
Jun
Shen
School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Wei
Liu
School of Energy and Power Engineering, Huazhong University of Science and Technology,
Wuhan 430074, China
929-939
THERMAL CONDUCTIVITY OF MONODISPERSE SILICA NANOSPHERES
Monodisperse hollow silica nanospheres (HSNSs) with an outer diameter of ~300 nm and shell thickness of ~50 nm were prepared via a spontaneous dissolution−regrowth process of solid silica nanospheres (SSNSs) in NaBH4 aqueous solution. Experimental results indicated that the as-prepared HSNSs have a reduced thermal conductivity of about 0.0519±0.0007 W/(m·K), compared to ~0.082±0.005 W/(m·K) of the corresponding SSNSs. Moreover, a small shell thickness and a small inner pore diameter are, in general, required to achieve HSNSs with low thermal conductivities. A comparison between HSNSs and SSNSs enables calculating the intrinsic solid thermal conductivity of SSNSs, which is about 0.042 W/(m·K) for SSNSs with a mean diameter of 200 nm.
Tao
Gao
Norwegian University of Science and Technology (NTNU), Department of Civil and Transport Engineering, NO-7491 Trondheim, Norway
Bjørn Petter
Jelle
Department of Civil and Transport Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway; Department of Materials and Structures, SINTEF Building and Infrastructure, NO-7465 Trondheim, Norway
Linn Ingunn C.
Sandberg
Department of Civil and Transport Engineering, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
Arild
Gustavsen
Department of Architectural Design, History and Technology, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway
941-947
IMPACT OF ANISOTROPY ON GEOMETRICAL AND THERMAL CONDUCTIVITY OF METALLIC FOAM STRUCTURES
The thermo-physical properties of open cell metal foams depend on their microscopic structure. Various virtual ideal periodic isotropic foam samples having circular, square, hexagon, diamond, and star strut cross sections with various orientations are realized in the porosity range from 60 to 95%. The anisotropy of the original foam sample is then realized by elongating in one direction by a factor Ω, while a factor of 1/√Ω is applied along the two perpendicular directions to conserve the porosity of the original sample. A generalized analytical model of geometrical parameters has been proposed and all results are fully compared with the original measured data. Three-dimensional heat conduction numerical simulations at the pore scale have been performed, which allow determining the macroscale physical properties, such as the effective thermal conductivity, using the volume averaging technique. Two analytical models are derived simultaneously in order to predict the intrinsic solid phase conductivity (λs) and effective thermal conductivity (λeff). A modified correlation term (F) is introduced in the analytical resistor model to take into account the thermal conductivities of constituent phases and a modified Lemlich model is derived. The analytical results of the effective thermal conductivity are compared with the numerical data and excellent agreement is observed.
Prashant
Kumar
IUSTI, CNRS UMR 7343, Aix-Marseille University, Marseille, France
Frederic
Topin
Polytech Marseille, Laboratoire IUSTI, UMR CNRS 7343, Technopole de Chateau Gombert, 5 rue Enrico Fermi, 13453 Marseille Cedex 13, France
949-970
PREDICTION OF THERMAL CONDUCTIVITY OF FIBER/AEROGEL COMPOSITES FOR OPTIMAL THERMAL INSULATION
A numerical model for predicting the effective thermal conductivity of fused silica fiber/aerogel composites by simultaneously considering the effects of the fiber volume fraction and fiber diameter is presented. The predicted effective thermal conductivity of the fiber/aerogel composites agreed well with the existing measured and predicted results. The effects of the volume fraction (0−25%) and diameter (0.3−10 µm) of fibers on the effective thermal conductivity of aerogel composites were investigated under a large range of temperatures (300−1300 K). The results indicated that the minimum effective thermal conductivity of the fiber/aerogel composites by simultaneously considering the optimized fiber volume fraction and diameter was significantly lower than when individually considering the optimized fiber volume fraction and diameter values. For instance, the minimum effective thermal conductivity by simultaneous optimization was 0.0262 W/m−1 K−1 at 1000 K, which was much lower than 0.0327 W/m−1 K−1 by individually optimizing the fiber volume fraction at a diameter of 8 µm and 0.0532 W/m−1 K−1 by individually optimizing the fiber diameter at a volume fraction of 3%. Moreover, the quantitative relations between the minimum effective thermal conductivity of the fiber/aerogel composites and the temperatures are presented, with the aim of identifying the optimal thermal insulation for applications in aeronautics and astronautics, construction, and other industrial fields.
Jianming
Yang
College of Civil Engineering, Guangzhou University, Guangzhou 510006, China
Huijun
Wu
College of Civil Engineering, Guangzhou University, Guangzhou 510006, China
Shiquan
He
College of Civil Engineering, Guangzhou University, Guangzhou 510006, China
Moran
Wang
Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084, China
971-984
ANALYSIS OF IMPROVED-LUMPED MODELS FOR PROPERTY ESTIMATION FROM TEMPERATURE FIELD DATA USING A FIN MODEL
The purpose of this paper is to analyze the application of one-dimensional heat transfer models for estimating material properties from full-field temperature measurements, such as those obtained from thermography experiments. The forward problem is that of heat conduction in a fin; however, simple one-dimensional models are analyzed. The classical fin formulation considers no gradients across the fin cross section, which limits its application to problems that involve low Biot number values. This can become a problem in multi-phase systems that involve a notable amount of a low thermal conductivity phase, as occurs in gas-filled porous media. In such materials, an increase in the porosity reduces the effective thermal conductivity, easily increasing the Biot number to values above the classical 0.1 limit. Besides these cases, the same problem can be found in many composite materials as well. Hence, this paper studies the application of the so-called improved lumped-differential models for the estimation of the thermal conductivity and phase fractions of two-phase systems from a given temperature field. Synthetic data of the surface temperature are employed for assessing models obtained with different approximation levels. These data were generated from the analytical solution of a two-dimensional model of the problem, and in some cases included the addition of a Gaussian error. The results show that the improved-lumped models clearly outperform the classical lumped fin formulation, providing very reasonable estimates for the Biot number and volume fraction of two-phase systems for most cases, the exception being a few cases where the Biot number of the continuous phase alone is high.
Debora Carneiro
Moreira
Thermal Sciences Laboratory & Laboratory of Theoretical and Applied Mechanics, Universidade Federal Fluminense, Rua Passo da Patria 156, Niteroi, RJ 24210-240, Brazil
M.C.
de O. Telles
Thermal Sciences Laboratory & Laboratory of Theoretical and Applied Mechanics, Universidade Federal Fluminense, Rua Passo da Patria 156, Niteroi, RJ 24210-240, Brazil
Luiz Carlos Da Silva
Nunes
Thermal Sciences Laboratory & Laboratory of Theoretical and Applied Mechanics, Universidade Federal Fluminense, Rua Passo da Patria 156, Niteroi, RJ 24210-240, Brazil
Leandro A.
Sphaier
Department of Mechanical Engineering – PGMEC, Universidade Federal Fluminense, Rua
Passo da Patria 156, bloco E, sala 216, Niteroi, RJ, 24210-240, Brazil
985-996
INFLUENCE OF VOLUMETRIC FIBER FRACTION AND HEATING TEMPERATURE ON HEAT TRANSFER CHARACTERISTICS OF LATENT HEAT STORAGE PARAFFIN WITH ALUMINUM FIBER MATERIALS
Paraffin is used as a latent heat energy storage material because it has relatively high latent heat and various melting points. However, the low thermal conductivity of paraffin leads to more time in latent heat storage and release processes. Therefore, it is necessary to improve the latent heat storage and release processes of paraffin. It is noted that metal fiber materials are mixed with paraffin in order to enhance the effective thermal conductivity of paraffin. The present investigation experimentally deals with the heat storage and heat release process of paraffin with metal fiber materials as a function of the volumetric fiber fraction and heating temperature. As a result, the heat release characteristic of paraffin with metal fiber materials was improved by enhanced effective thermal conductivity. On the other hand, the heat storage process of paraffin with metal fiber materials was influenced by the natural convection flow, and the heat storage process was not improved because of the interaction between the enhanced effective thermal conductivity and suppression of the natural convection flow by the metal fiber materials.
Naoto
Haruki
Okayama Prefectural University
Akihiko
Horibe
Okayama University, 3-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530, Japan
Yoshihiko
Sano
Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu, 432-8561, Japan
Kohei
Hachiya
Graduate School of Natural Science and Technology, Okayama University
997-1008
AN OPTIMIZATION STUDY OF HEAT TRANSFER ENHANCEMENT DUE TO JET IMPINGEMENT OVER POROUS HEAT SINKS USING THE LATTICE BOLTZMANN METHOD
In this paper, an optimization study involving five variable parameters that are critical in evaluating the thermal performance of the air jet flow impingement over porous heat sinks in a mixed convection regime is presented. The variable parameters include the porous block height, channel height, jet width, porosity, and Darcy number. The lattice Boltzmann method for porous media is used as the numerical tool to simulate the objective functions in terms of the Nusselt number and pressure drop. The Kriging method combined with a genetic algorithm is used to generate the optimal Pareto plot. Three optimal cases from the Pareto plot showing the maximum, minimum, and optimum Nusselt numbers and the pressure drop are considered. The optimized results show that the porosity and Darcy number are relatively invariant along the Pareto surface. Thus, the geometry of the channel and porous block are the most significant parameters governing the Nusselt number and pressure drop values. The results from optimization corresponding to the three optimal cases are analyzed in detail. The local variation in the Nusselt number for these cases is also plotted to understand the effect of the channel and porous heat sink parameters on heat transfer.
Sampath Kumar
Chinige
Department of Mechanical Engineering, Indian Institute of Technology Madras
Nikhilesh
Ghanta
Department of Mechanical Engineering, Indian Institute of Technology Madras
Arvind
Pattamatta
Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036,
India; Institute for Technical Thermodynamics, Technische Universitat Darmstadt, Darmstadt, 64287, Germany
1009-1020
EFFECTS OF DIELECTRIC PERMITTIVITY OF SOLID STRUCTURE ON ELECTRO-OSMOTIC PERMEABILITY IN POROUS MEDIA
For modeling electro-osmosis in porous media in previous studies, there have been two popular approaches used to obtain the electrostatic force, which is dependent on the local strength of the applied electrical field. One approach was to apply a constant electrical field strength, which actually assumes the dielectric permittivity of the solid structure is the same
as that of liquid. The other method treated solid materials as an ideal dielectric with zero permittivity. However, both approaches are questionable since the solid permittivity, in practice, is neither the same as that of liquid nor is it equal to zero. In this paper, we derive a modified model for electro-osmotic flows in the whole domain based on the Poisson−Boltzmann model and solve the Poisson equation with discontinuous properties in order to acquire the local electrical field strength by the lattice Boltzmann method. The results show that electro-osmotic permeability decreases with the dielectric permittivity of solid structures. Predictions by assuming constant electrical field strength underestimate the electro-osmotic permeability, while it will lead to overestimated values by leaving the solid as an ideal dielectric.
Li
Zhang
Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084, China
Moran
Wang
Department of Engineering Mechanics and CNMM, Tsinghua University, Beijing 100084, China
1021-1029
EVOLUTION OF THE HOMOGENIZED VOLUMETRIC RADIATIVE PROPERTIES OF A FAMILY OF α-SiC FOAMS WITH GROWING NOMINAL PORE DIAMETER
A numerical foam generation method is employed to design open-cell foams with prescribed and realistic textural features
(i.e., porosity, volumetric surface, pore size distribution, and pore−pore distance distribution). The foam generation
is initialized by seeding the centers of the pores. Seeds are first regularly distributed following a tetrahedral compact network
modeling the real cell connectivity observed in samples elaborated with the foam replication method, and their
positions are then randomly perturbed. A fast-marching technique coupled to a watershed algorithm governs the growth
and the segmentation of the pores. The strut shape is finally controlled by a thickness growth method. Afterward, for a
given numerical foam, a numerical tool (iMorph) provides accurate knowledge of the whole set of textural parameters.
The homogenized volumetric radiative properties (i.e., extinction, absorption, and scattering coefficients, denoted by
β, α, and γ, respectively) of the reconstructed three-dimensional foams can then be identified by the radiative distribution
function identification method insofar as they comply with Beerian behavior. In this study, the radiative properties
of a set of numerical α-SiC foams with real textural features are compared at T = 300 K. In particular, a practical
relationship between the extinction coefficient on the one hand and the nominal pore diameter at fixed porosity on the
other hand may be found. Comparisons with previous relationships often used to model heat and mass transfer in high-temperature
industrial applications, such as in concentrated solar power plants, are also proposed. Finally, a generator
is used to study the influence of the porosity on the extinction coefficient.
Simon
Guevelou
UMR CNRS 6607 Laboratoire de Thermocinetique de Nantes
Benoit
Rousseau
PRES LUNAM, CNRS, UMR 6607 LTN, Rue Christian Pauc, 44306 Nantes Cedex 3, France
Gilberto
Domingues
PRES LUNAM, CNRS, UMR 6607 LTN, Rue Christian Pauc, 44306 Nantes Cedex 3, France
Jerome
Vicente
lnstitut Universitaire des Systemes Thermiques Industriels (IUSTI-CNRS-UMR 6595), Aix-Marseille Universite Technopole de Chateau-Gombert
Cyril
Caliot
Laboratoire des Procedes, Materiaux et Energie Solaire, CNRS UPR 8521
Gilles
Flamant
Laboratoire des Procedes, Materiaux et Energie Solaire, PROMES-CNRS UPR 8521, 7 rue du Four solaire, 66120 Font Romeu-Odeillo, France
1031-1045