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Similitude criteria for fluid flow in macro-porous materials

Allori, Davide; Bartoli, Gianni; Miguel, Antonio F.
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
67.68884%
In the present paper, the problem of a suitable modelling of porous elements at the wind tunnel scale is addressed. This works involves an experimental study based on macro-porous materials, performed on perforated plates having holes with different geometry, thickness and sizes. The objective of this paper is double fold. At first, it aims at clarifying the effect of configuration of pores (holes) on fluid flow. Secondly, it aims to present a comprehensive similitude criterion for macro-porous structures based on physical insight.

Effect of temperature and humidity on the permeability of porous materials

Serrenho, A.; Miguel, A. F.; Reis, A. H.
Fonte: Pacific Center of Thermal-Fluids Engineering (PCTFE) Publicador: Pacific Center of Thermal-Fluids Engineering (PCTFE)
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
57.57035%
The permeability of a porous material represents the ability of the material to be crossed by a fluid stream. An experimental study in the Darcy regime allows us to measure the permeability of two different porous materials. Measurements were performed by using two gases: air and helium. Experiments were performed at ambient temperatures ranging from 293 to 315 K and humidities ranging from 30 to 96%. The way how the effect of air temperature and humidity on permeability affects the flow within porous media is discussed with the help of the pertinent equations.

Wind tunnel similitude criteria for fluid flow in macro-porous materials

Allori, D; Bartoli; Miguel, A. F.
Fonte: DSL Publicador: DSL
Tipo: Aula
Português
Relevância na Pesquisa
57.49%
A wind tunnel experimental set-up was performed at CRIACIV (Inter – University Research Centre on Building Aerodynamics and Wind Engineering) Boundary Layer Wind Tunnel Laboratory at the University of Florence, with the aim of determining some possible similitude and scaling criteria. The pressure drop and the drag force on the porous material obtained at different air velocities were measured for twenty five porous samples with porosities ranging from 0.2268 to 0.6940

Fluid flow through macro-porous materials: friction coefficient and wind tunnel similitude criteria

Allori, D.; Bartoli, G.; Miguel, A. F.
Fonte: Begell House Inc Publicador: Begell House Inc
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
67.60849%
This work reports the study of airflow fluid through macro-porous materials. Several perforated plates having holes with different geometry, thickness and size were tested in a wind tunnel. The objective of this paper is double fold. At first, it aims at clarifying the effect of configuration of pores (holes) on fluid flow. Friction resistance and drag coefficients are obtained. Secondly, it has the purpose to present a comprehensive similitude criterion for macro-porous structures based on physical insight.

Moisture and heat transport in porous materials: analytical solutions for the case of periodic boundary conditions.

Miguel, A. F.; Silva, A. M.
Fonte: Press of Czech University of Agriculture in Prague Publicador: Press of Czech University of Agriculture in Prague
Tipo: Parte de Livro
Português
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57.371387%
In this chapter, we present approximate analytical solutions for moisture and heat transport equations in porous materials under periodic boundary conditions. The significance of this is threefold: (1) the solutions presented provide results which are comparable with data collected by other authors; (2) the solutions developed serve to gauge the accuracy of any numerical approach such as the finite element and the finite difference techniques when applied to solve this type of equations; (3) finally, these solutions provide an approach not only to predict moisture and temperature distribution but also to evaluate the importance of the transfer coefficients in moisture analysis.

Is Macroporosity Absolutely Required for Preliminary in Vitro Bone Biomaterial Study? A Comparison between Porous Materials and Flat Materials

Lee, Juliana T.Y.; Chow, King L.; Wang, Kefeng; Tsang, Wai Hung
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 08/11/2011 Português
Relevância na Pesquisa
48.139272%
Porous materials are highly preferred for bone tissue engineering due to space for blood vessel ingrowth, but this may introduce extra experimental variations because of the difficulty in precise control of porosity. In order to decide whether it is absolutely necessary to use porous materials in in vitro comparative osteogenesis study of materials with different chemistries, we carried out osteoinductivity study using C3H/10T1/2 cells, pluripotent mesenchymal stem cells (MSCs), on seven material types: hydroxyapatite (HA), α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP) in both porous and dense forms and tissue culture plastic. For all materials under test, dense materials give higher alkaline phosphatase gene (Alp) expression compared with porous materials. In addition, the cell density effects on the 10T1/2 cells were assessed through alkaline phosphatase protein (ALP) enzymatic assay. The ALP expression was higher for higher initial cell plating density and this explains the greater osteoinductivity of dense materials compared with porous materials for in vitro study as porous materials would have higher surface area. On the other hand, the same trend of Alp mRNA level (HA > β-TCP > α-TCP) was observed for both porous and dense materials...

Investigation of shock wave attenuation in porous materials

Boey, Chung Wai.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
Português
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47.925605%
Approved for public release, distribution unlimited; This thesis investigates the use of porous materials in a multi-layered armor concept. The prototype layered structure consists of an initial high-strength material to slow down the projectile and cause significant plastic deformation,, followed by an orthotropic wave-spreading layer to spread shock waves laterally away from the axis of penetration and subsequently attenuate the shock waves by using a porous material to convert kinetic energy into internal energy. Based on the above armor concept, composite plates consisted of an alumina (Al203)-based ceramic, Dyneema® and porous foams were constructed and tested against conventional armor steel of equivalent areal density. This study used two commercially available porous materials, one based on aluminum metal and one a rigid polyurethane foam. This study also investigated the effect of porous initial density of the polymeric foam on ballistic. The author developed a P-a compaction model for the chosen porous materials for use in AUTODYN® simulations to describe their dynamic compaction during an impact event. The author also conducted a ballistic trial to validate the performance of the armor laminate against numerical simulations. Based on the results of this study...

Micromechanical modeling of elastic-plastic porous materials using finite element analysis

Badders, Daniel Christopher
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 77 p.; application/pdf
Português
Relevância na Pesquisa
57.562793%
Elastic-plastic behavior of porous materials is analyzed using a hollow sphere micromodel and the NIKE2D finite element program. Surface average responses are computed for several displacement controlled homogeneous loadings. The data provides simple equations for elastic constants in terms of porosity. Yield surfaces are plotted and approximated by a yield function. The function's shape, hydrostatic strength, and deviatoric strength closely match the data for a wide range of porosities. Most significantly, plotting plastic strain rates relative to this yield function validates the common normality assumption for porous materials.

Micromechanical modeling of elastic-plastic porous materials using finite element analysis

Badders, Daniel Christopher
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 77 p.; application/pdf
Português
Relevância na Pesquisa
57.562793%
Elastic-plastic behavior of porous materials is analyzed using a hollow sphere micromodel and the NIKE2D finite element program. Surface average responses are computed for several displacement controlled homogeneous loadings. The data provides simple equations for elastic constants in terms of porosity. Yield surfaces are plotted and approximated by a yield function. The function's shape, hydrostatic strength, and deviatoric strength closely match the data for a wide range of porosities. Most significantly, plotting plastic strain rates relative to this yield function validates the common normality assumption for porous materials.

Quantitative properties of complex porous materials calculated from X-ray μCT images

Sheppard, Adrian P.; Arns, Christoph H.; Sakellariou, Arthur; Senden, Tim J.; Sok, Rob M.; Averdunk, Holger; Saadatfar, Mohammad; Limaye, Ajay; Knackstedt, Mark A.
Fonte: Society of Photo-optical Instrumentation Engineers (SPIE) Publicador: Society of Photo-optical Instrumentation Engineers (SPIE)
Tipo: Artigo de Revista Científica Formato: 15 pages
Português
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57.70659%
A microcomputed tomography (μCT) facility and computational infrastructure developed at the Department of Applied Mathematics at the Australian National University is described. The current experimental facility is capable of acquiring 3D images made up of 20003 voxels on porous specimens up to 60 mm diameter with resolutions down to 2 μm. This allows the three-dimensional (3D) pore-space of porous specimens to be imaged over several orders of magnitude. The computational infrastructure includes the establishment of optimised and distributed memory parallel algorithms for image reconstruction, novel phase identification, 3D visualisation, structural characterisation and prediction of mechanical and transport properties directly from digitised tomographic images. To date over 300 porous specimens exhibiting a wide variety of microstructure have been imaged and analysed. In this paper, analysis of a small set of porous rock specimens with structure ranging from unconsolidated sands to complex carbonates are illustrated. Computations made directly on the digitised tomographic images have been compared to laboratory measurements. The results are in excellent agreement. Additionally, local flow, diffusive and mechanical properties can be numerically derived from solutions of the relevant physical equations on the complex geometries; an experimentally intractable problem. Structural analysis of data sets includes grain and pore partitioning of the images. Local granular partitioning yields over 70...

Modellization of hydraulic fracturing of porous materials

Tzschichholz, F.; Wangen, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/01/2001 Português
Relevância na Pesquisa
57.297134%
We review microstructural fracture growth models suitable for the study of hydraulic fracture processes in disordered porous materials and present some basic results. It is shown that microstructural models exhibit certain similarities to corresponding theories of continua. These similarities are most easily demonstrated for simple crack geometries, i.e., straight cracks (finite size scalings). However, there exist even scaling relations which are completely independent of the particular employed crack structure. Furthermore it is demonstrated that disorder in cohesional/flow properties can influence the crack growth and the resulting fracture geometry in an essential way.; Comment: 34 pages, 18 figures, Latex

Shock Wave Response of Porous Materials: From Plasticity to Elasticity

Xu, Aiguo; Zhang, Guangcai; Ying, Yangjun; Zhang, Ping; Zhu, Jianshi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 06/05/2010 Português
Relevância na Pesquisa
57.562793%
Shock wave reaction results in various characteristic regimes in porous material. The geometrical and topological properties of these regimes are highly concerned in practical applications. Via the morphological analysis to characteristic regimes with high temperature, we investigate the thermodynamics of shocked porous materials whose mechanical properties cover a wide range from hyperplasticity to elasticity. It is found that, under fixed shock strength, the total fractional area $A$ of the high-temperature regimes with $T \geq T_{th}$ and its saturation value first increase, then decrease with the increasing of the initial yield $\sigma_{Y0}$, where $T_{th}$ is a given threshold value of temperature $T$. In the shock-loading procedure, the fractional area $A(t)$ may show the same behavior if $T_{th}$ and $\sigma_{Y0}$ are chosen appropriately. Under the same $A(t)$ behavior, $T_{th}$ first increases then decreases with $\sigma_{Y0}$. At the maximum point $\sigma_{Y0M}$, the shock wave contributes the maximum plastic work. Around $\sigma_{Y0M}$, two materials with different mechanical properties may share the same $A(t)$ behavior even for the same $T_{th}$. The characteristic regimes in the material with the larger $\sigma_{Y0}$ are more dispersed.; Comment: 6 figures...

Generalization of the adsorption process in crystalline porous materials and its application to Metal-Organic Frameworks (MOFs)

Mendoza-Cortes, Jose L.; Aduenko, Alexander A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
57.869185%
In this paper we present an approach for the generalization of adsorption of light gases in crystalline porous materials. Our approach allows the determination of gas uptake considering only geometrical constrains of the porous framework and interaction energy of the guest molecule with the framework. The derivation of this general equation for the uptake of any crystalline porous framework is presented. Based on this theory, we calculated optimal values for the adsorption enthalpy at different temperatures and pressures. We also present the use of this theory to determine the optimal linker length for a topological equivalent framework series. We validate this theoretical approach by comparing the predicted uptake to experimental values for MOF-5, MOF-14, MOF-177, MOF-200, SNU-77H and Li-metalated MOF-177 and MOF-200. We obtained the universal equation for optimal linker length given a topology of a porous framework. This work applies the general equation to Metal-Organic Frameworks (MOFs) but it can be used for other crystalline materials such as Covalent-Organic Frameworks (COFs) and Zeolitic imidazolate frameworks (ZIFs). These results will serve to design new porous materials that exhibit high net storage capacities, in particular for molecular hydrogen.; Comment: 8 pages

DFT Perspective of Hydrogen Storage on Porous Materials

Venkataramanan, N. S.; Kawazoe, Y.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/02/2011 Português
Relevância na Pesquisa
57.81456%
In this chapter, the physisorption of hydrogen molecules in porous materials as possible hydrogen storage systems has been reviewed. Owing to the weak interaction between H2 molecules and the adsorbent, high storage capacities are typically reached only at cryogenic temperature. Different classes of porous materials possessing different structure and composition have been designed for hydrogen storage applications using computational methods and especially with the aid of DFT methods. The adsorption energies for hydrogen in different porous materials have been increases by the doping of light weight alkali and alkali earth metals. Ab initio molecular dynamics has been carried out to know the stability of the newly functionalized materials. GCMC methods have been employed to know the gravimetric and volumetric uptake percentage of the newly functionalized materials. Therefore, the combined approach provides a better understanding and designing new materials to operate at near room temperature for the reversible hydrogen storage application.; Comment: 10 figures, 7 tables

Extension of the Wu-Jing equation of state (EOS) for highly porous materials: thermoelectron based theoretical model

Geng, H. Y.; Wu, Q.; Tan, H.; Cai, L.; Jing, F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/03/2012 Português
Relevância na Pesquisa
57.48988%
A thermodynamic equation of state (EOS) for thermoelectrons is derived which is appropriate for investigating the thermodynamic variations along isobaric paths. By using this EOS and the Wu-Jing (W-J) model, an extended Hugoniot EOS model is developed which can predict the compression behavior of highly porous materials. Theoretical relationships for the shock temperature, bulk sound velocity, and the isentrope are developed. This method has the advantage of being able to model the behavior of porous metals over the full range of applicability of pressure and porosity, whereas methods proposed in the past have been limited in their applicability.; Comment: 18 pages, 1 figure, appeared at J. Appl. Phys. 92, 5924 (2002)

Extension of the Wu-Jing equation of state (EOS) for highly porous materials: calculations to validate and compare the thermoelectron model

Geng, H. Y.; Wu, Q.; Tan, H.; Cai, L.; Jing, F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/03/2012 Português
Relevância na Pesquisa
57.562793%
In order to verify and validate the newly developed thermoelectron equation of state (EOS) model that is based on the Wu-Jing (W-J) EOS, calculations of shock compression behavior have been made on five different porous metals-iron, copper, lead, tungsten, and aluminum-which are commonly used as standards. The model was used to calculate the Hugoniot, shock temperature, sound velocity, and unloading isentrope for these materials and comparisons were made to previous calculations and available data. Based on these comparisons, it is felt that the model provides information in good agreement with the corresponding experimental and theoretical data published previously. This suggests that the new model can satisfactorily describe the properties of shocked porous materials over a wide range of pressure and porosity.; Comment: 27 pages, 11 figures, appeared at J. Appl. Phys. 92, 5917 (2002)

Effect of electrons on equation of state of porous materials

Nayak, Bishnupriya
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/09/2014 Português
Relevância na Pesquisa
57.48988%
A new equation of state (EOS) is developed for porous materials in which contribution of electrons is considered explicitly. This EOS describes anomalous behaviour of hugoniot of porous substances as observed experimentally. Using this EOS, hugoniot of copper and aluminium are evaluated for different porosities and the agreement with experimental data is good. The present EOS is valid over a wide range of porosities (1 to 10). The contribution of electrons is significant for porosity greater than equal to 2. Also, shock and particle velocity curves obtained using this EOS agree well with experimental data.; Comment: 22 pages, 10 figures

Materiales y técnicas para el acoplamiento mecánico óptimo de piezocerámicas en aire; Techniques and materials for optimum mechanical matching of piezoceramics vibrating in air

Montero de Espinosa Freijo, Francisco; Gómez Álvarez-Arenas, Tomás
Fonte: Sociedad Española de Cerámica y Vidrio Publicador: Sociedad Española de Cerámica y Vidrio
Tipo: Artículo Formato: 591898 bytes; application/pdf
Português
Relevância na Pesquisa
57.45512%
[ES] En los últimos años se están realizando grandes esfuerzos para poder realizar inspecciones de Ensayos no Destructivos por ultrasonidos sin emplear líquidos como medio de acoplo entre los transductores piezoeléctricos y las estructuras a inspeccionar. En este campo compiten dos tecnologías de transducción, los transductores basados en piezocerámicas y los de tipo capacitivo. En el caso de los piezocerámicos, el punto crítico lo constituye la desadaptación de impedancias entre el resonador piezoeléctrico y el aire. Para soslayar este problema es posible utilizar capas de adaptación (λ/4). Para esto es necesario utilizar materiales con muy baja densidad y velocidad de propagación (impedancia acústica específica del orden de 0.1 MRayl), baja atenuación y buena sintonización a la frecuencia de trabajo. Con frecuencia, todas estas propiedades son extremadamente difíciles de conjugar. En el trabajo se presenta la caracterización de materiales con elevada porosidad y su utilización como líneas de transmisión λ/4 para frecuencias en el entorno de 1 MHz. La caracterización – constantes elásticas y coeficiente de atenuación- se realiza con acoplamiento en aire. El uso de estos materiales como línea de adaptación logra mejoras de transmisión de hasta 35 dB y sensibilidad en modo emisión-recepción de hasta –20 dB.; [EN] Great efforts have been made over the last years to avoid the use of coupling agents between ultrasonic transducers and sample materials for NDE applications. Two different technologies compite for this particular application: piezoelectric and electrostatic transducers. In the first case...

Sensitivity analysis and non linear parameters estimation of porous materials from normal sound coefficient absorption measurements

Garoum, M.; Idchabani, R.; Tajayouti, M.; Rhachi, M.; Moreno, Antonio
Fonte: Société française d'acoustique; Acoustical Society of America; European Acoustics Association Publicador: Société française d'acoustique; Acoustical Society of America; European Acoustics Association
Tipo: Comunicación de congreso Formato: 29167 bytes; application/pdf
Português
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67.681406%
Communication presented at: Acoustics '08 (Paris, France, June 29-July 4, 2008), comprising: 5th Forum Acusticum, 155th ASA Meeting, 9e Congrès Français d'Acoustique, 7th European Conference on Noise Control (Euronoise), 9th European Conference on Underwater Acoustics (ECUA).-- Book of abstracts published in Vol. 94 Suppl.1: S1-S1020 (May/June 2008) of Acta Acustica united with Acustica: The Journal of the European Acoustics Association (ISSN 1610-1928).; In literature, various models have been proposed in order to predict characteristic impedance Zc and wave number kc of porous materials. To use these models their involved nonacoustical parameters (i. e. flow resistivity, tortuosity porosityoe) are usually measured. Unfortunately measurements require specialised equipments and are often difficult on loose porous materials leading most often to erroneous values. Moreover, the inverse estimation of theses parameters from experimental data is not an easy task as believed. This is due to the non linearity of models and the presence of some parameters with weak and/or linearly dependent influences. In this work an approach based on the tradeoff between magnitude and linear independence of the sensitivity matrix components is presented in order to achieve an efficient ranking of parameters according to their inherent ease of estimation. Next this approach is associated to Genetic Algorithms to minimize the least squares norm between measured and modelled normal sound absorption coefficient. For five widely used models in literatures...

Three-dimensional Imaging of Multiphase Flow in Porous Media

Turner, Michael; Knuefing, Lydia; Arns, Christoph; Sakellariou, Arthur; Senden, Timothy; Sheppard, Adrian; Sok, Robert; Limaye, Ajay; Pinczewski, Wolf Val; Knackstedt, Mark
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
57.49%
This paper reports progress in the 3D pore-scale micro-CT imaging of multiple fluid phases during drainage experiments in porous materials. Experiments performed on a sintered monodisperse bead pack and a Berea sandstone sample are described. It is observed that the residual (trapped) wetting phase in the sintered bead pack is present as pendular rings, bridges between adjacent grains and lenses within pore throats. Estimates of the residual wetting phase saturation are in accord with previous experiments and predictions on model bead packs. Relative permeabilities computed directly on the digitised images of the fluid phases are in good agreement with experimentally measured values for Berea sandstone. Two simple numerical methods for estimating two phase drainage saturation distributions directly from images are compared. Both methods give good agreement with the bead pack experiment. The match for Berea sandstone is poorer; differences may be due to variable wettability.