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The resistance to air flow of porous materials suitable for boundary-layer-control applications using area suction

Description: "Measurements were made of the resistance to air flow of commercially available porous materials. Three general types of porous media were tested - granular (sintered materials), fibrous (felt cloths and filter papers), and perforated. The flow-resistance characteristics of the porous materials tested are presented in a form intended to assist in the selection of materials for applications to boundary-layer control using area suction" (p. 1).
Date: January 1954
Creator: Dannenberg, Robert E.; Weiberg, James A. & Gambucci, Bruno J.
Partner: UNT Libraries Government Documents Department

Rocks as poroelastic composites

Description: In Biot's theory of poroelasticity, elastic materials contain connected voids or pores and these pores may be filled with fluids under pressure. The fluid pressure then couples to the mechanical effects of stress or strain applied externally to the solid matrix. Eshelby's formula for the response of a single ellipsoidal elastic inclusion in an elastic whole space to a strain imposed at infinity is a very well-known and important result in elasticity. Having a rigorous generalization of Eshelby's results valid for poroelasticity means that the hard part of Eshelby' work (in computing the elliptic integrals needed to evaluate the fourth-rank tensors for inclusions shaped like spheres, oblate and prolate spheroids, needles and disks) can be carried over from elasticity to poroelasticity - and also thermoelasticity - with only trivial modifications. Effective medium theories for poroelastic composites such as rocks can then be formulated easily by analogy to well-established methods used for elastic composites. An identity analogous to Eshelby's classic result has been derived [Physical Review Letters 79:1142-1145 (1997)] for use in these more complex and more realistic problems in rock mechanics analysis. Descriptions of the application of this result as the starting point for new methods of estimation are presented.
Date: April 30, 1998
Creator: Berryman, J G
Partner: UNT Libraries Government Documents Department

Pore compressibility in rocks

Description: The unjacketed core compressibility in a porous rock is the change in pore volume due to change in pore pressure for constant differential pressure. This parameter affects how the saturated bulk modulus of a rock is related to the drained frame modulus and the pore fluid compressibility. Recent measurements of poroelastic constants and effective medium theories are used to estimate how the pore compressibility depends on effective stress and how uncertainty in the pore compressibility affects uncertainty in Gassmann' equation estimates of the saturated bulk modulus. Results for Berea sandstone and for models of sand-clay mixtures show that the estimate of the change in the saturated bulk modulus due to substitution of different fluids in the rock may differ in size by a factor of two or more if the pore compressibility is approximately equal to the fluid compressibility instead of the grain compressibility. In general, the order of magnitude and sign of the pore compressibility cannot be determined from solid and fluid compressibility information alone.
Date: June 5, 1998
Creator: Berge, P A
Partner: UNT Libraries Government Documents Department

Numerical Methods for a Porous Medium Equation

Description: The degenerate parabolic equation has been used to model the flow of gas through a porous medium. Error estimates for continuous and discrete time finite element procedures to approximate the solution of this equation are proved and a new regularity result is described.
Date: August 1978
Creator: Rose, Michael Edward
Partner: UNT Libraries Government Documents Department

Scaling Equation for yield strength of nanoporous open-cell foams

Description: A comprehensive study on the relationship between yield strength, relative density and ligament sizes is presented for nanoporous Au foams. Depth-sensing nanoindentation tests were performed on nanoporous foams ranging from 20 to 42% relative density with ligament sizes ranging from 10 to 900 nm. The Gibson and Ashby yield strength equation for open-cell macro-cellular foams is modified in order to incorporate ligament size effects. This study demonstrates that at the nanoscale, foam strength is governed by ligament size, in addition to relative density. Furthermore, we present the ligament length scale as a new parameter to tailor foam properties and achieve high strength at low densities.
Date: May 25, 2006
Creator: Hodge, A M; Biener, J; Hayes, J R; Bythrow, P M; A.Volkert, C & Hamza, A V
Partner: UNT Libraries Government Documents Department

Ensemble phase averaging equations for multiphase flows in porous media, part I: the bundle-of-tubes model

Description: A bundle-of-tubes construct is used as a model system to study ensemble averaged equations for multiphase flow in a porous material. Momentum equations for the fluid phases obtained from the method are similar to Darcy's law, but with additional terms. We study properties of the additional terms, and the conditions under which the averaged equations can be approximated by the diffusion model or the extended Darcy's law as often used in models for multiphase flows in porous media. Although the bundle-of-tubes model is perhaps the simplest model for a porous material, the ensemble averaged equation technique developed in this paper assumes the very same form in more general treatments described in Part 2 of the present work (Zhang 2009). Any model equation system intended for the more general cases must be understood and tested first using simple models. The concept of ensemble phase averaging is dissected here in physical terms, without involved mathematics through its application to the idealized bundle-of-tubes model for multiphase flow in porous media.
Date: January 1, 2008
Creator: Yang, Dali; Zhang, Duan & Currier, Robert
Partner: UNT Libraries Government Documents Department

Porous ceramic scaffolds with complex architectures

Description: This work compares two novel techniques for the fabrication of ceramic scaffolds for bone tissue engineering with complex porosity: robocasting and freeze casting. Both techniques are based on the preparation of concentrated ceramic suspensions with suitable properties for the process. In robocasting, the computer-guided deposition of the suspensions is used to build porous materials with designed three dimensional (3-D) geometries and microstructures. Freeze casting uses ice crystals as a template to form porous lamellar ceramic materials. Preliminary results on the compressive strengths of the materials are also reported.
Date: March 15, 2008
Creator: Saiz, Eduardo; Munch, Etienne; Franco, Jaime; Deville, Sylvain; Hunger, Phillip; Saiz, Eduardo et al.
Partner: UNT Libraries Government Documents Department

Laboratory experiments on dispersive transport across interfaces: The role of flow direction

Description: We present experimental evidence of asymmetrical dispersive transport of a conservative tracer across interfaces between different porous materials. Breakthrough curves are measured for tracer pulses that migrate in a steady state flow field through a column that contains adjacent segments of coarse and fine porous media. The breakthrough curves show significant differences in behavior, with tracers migrating from fine medium to coarse medium arriving significantly faster than those from coarse medium to fine medium. As the flow rate increases, the differences between the breakthrough curves diminish. We argue that this behavior indicates the occurrence of significant, time-dependent tracer accumulation in the resident concentration profile across the heterogeneity interface. Conventional modeling using the advection-dispersion equation is demonstrated to be unable to capture this asymmetric behavior. However, tracer accumulation at the interface has been observed in particle-tracking simulations, which may be related to the asymmetry in the observed breakthrough curves.
Date: April 1, 2009
Creator: Berkowitz, B.; Cortis, A.; Dror, I. & Scher, H.
Partner: UNT Libraries Government Documents Department

X-ray absorption spectroscopy from H-passivated porous Si and oxidized Si nanocrystals

Description: Quantum confinement in nanoscale Si structures is widely believed to be responsible for the visible luminescence observed from anodically etched porous silicon (por-Si), but little is known about the actual size or shape of these structures. Extended x-ray absorption fine structure data from a wide variety of por-Si samples show significantly reduced average Si coordination numbers due to the sizable contribution of surface-coordinated H. (The IUSI ratios, as large as 1.2, were independently confirmed by ir-absorption and {alpha}-recoil measurements.) The Si coordinations imply very large surface/volume ratios, enabling the average Si structures to be identified as crystalline particles (not wires) whose dimensions are typically <15 {Angstrom}. Comparison of the size-dependent peak luminescence energies with those of oxidized Si nanocrystals, whose shapes are known, shows remarkable agreement. Furthermore, near-edge x-ray absorption fine structure measurements of the nanocrystals shows the outer oxide and interfacial suboxide layers to be constant over a wide range of nanocrystal sizes. The combination of these results effectively rules out surface species as being responsible for the observed visible luminescence in por-Si, and strongly supports quantum confinement as the dominant mechanism occurring in Si particles which are substantially smaller than previously reported or proposed.
Date: November 1, 1994
Creator: Schuppler, S.; Marcus, M.A. & Friedman, S.L.
Partner: UNT Libraries Government Documents Department

Ambient-pressure silica aerogel films

Description: Very highly porous (aerogel) silica films with refractive index in the range 1.006--1.05 (equivalent porosity 98.5--88%) were prepared by an ambient-pressure process. It was shown earlier using in situ ellipsometric imaging that the high porosity of these films was mainly attributable to the dilation or `springback` of the film during the final stage of drying. This finding was irrefutably reconfirmed by visually observing a `springback` of >500% using environmental scanning electron microscopy (ESEM). Ellipsometry and ESEM also established the near cent per cent reversibility of aerogel film deformation during solvent intake and drying. Film thickness profile measurements (near the drying line) for the aerogel, xerogel and pure solvent cases are presented from imaging ellipsometry. The thickness of these films (crack-free) were controlled in the range 0.1-3.5 {mu}m independent of refractive index.
Date: December 31, 1994
Creator: Prakash, S.S.; Brinker, C.J. & Hurd, A.J.
Partner: UNT Libraries Government Documents Department

Characterization of microenvironment polarity and solvent accessibility of polysilsesquioxane xerogels by the fluorescent probe technique

Description: Poly (1, 4 bis(triethoxysilyl)benzene) (PTESB), a representative of a new type of organic-inorganic hybrid polysilsesquioxane material, was characterized by fluorescence spectroscopy for both microenvironmental polarity and solvent accessibility. A dansyl fluorescent molecule was incorporated into the bulk as well as onto the surface of both PTESB and silica materials. Information about the microenvironment polarity and accessibility of PTESB to various organic solvents was determined and compared to that of silica gel. This study found that both the bulk and surface of PTESB are less polar than that of the silica material. The silica material is accessible to polar solvents and water, while YMB is accessible to polar solvents but not to water. The hydrophobicity of PTESB differentiates these new materials from silica gel.
Date: May 1, 1995
Creator: Shea, K.J.; Zhu, H.D. & Loy, D.A.
Partner: UNT Libraries Government Documents Department

Synthesis of surfactant-templated mesoporous materials from homogeneous solutions

Description: Mesoporous is defined as 20{le}d{le}500{angstrom}. Mesoporous materials with narrow pore size distributions may be useful as hosts, supports, catalysts, or separation media for small molecules. An ensemble of organic molecules to create a larger template has been used to synthesize ordered mesoporous materials. The silicon alkoxide precursors TEOS and TMOS were examined. Cosolvents were used to control pore size and the structure of the mesophase. Effects of anions (salts) on mesophase formation were examined. Properties of mesophases made from homogeneous solutions are discussed.
Date: August 1, 1995
Creator: Anderson, M.T.; Martin, J.E.; Odinek, J. & Newcomer, P.
Partner: UNT Libraries Government Documents Department

Effects of Spatially Heterogeneous Porosity on Matrix-Diffusion as Investigated by X ray Absorption Imaging

Description: Laboratory experiments were performed to investigate the effects of spatial variation in porosity on matrix-diffusion processes. Four centimeter-scale slabs of Culebra dolomite taken from the Waste Isolation Pilot Plant site were used in the tests. Experiments involved the simple diffusion of iodine into a single edge of each rock slab while X ray absorption imaging was used to measure the resulting two-dmensional solute concentration field as a function of time. X ray imaging was also used to quantify the two-dimensional porosity field of each rock slab. Image analysis provided a unique opportunity to both visuake and quantifj the effects of the spatially variable porosi~ on matrixdMusion. Four key results were obtained. First, significant variation in rates of diffusion were realized over the relatively small length (centimeter) and time scales (months) investigated. Second, clear evidence of diffusion preferentially following zones of relatively higher porosity was noted. Third, rate of difhion was found to vary as tracer diffused into the rock slabs encountering changing porosity conditions. Fourth, strong correlation between porosi~ and the calculated diffusion coefficients was found. In fact, the nature of the correlation can be related to the geometry, position, and orientation of the heterogeneous porosity features populating each rock slab.
Date: October 20, 1998
Creator: Boney, C.; Christian-Frear, T.; Meigs, L. C. & Tidwell, V. C.
Partner: UNT Libraries Government Documents Department

ARDISC (Argonne Dispersion Code): Computer Programs to Calculate the Distribution of Trace Element Migration in Partially Equilibrating Media

Description: A computer program (ARDISC, the Argonne Dispersion Code) is described which simulates the migration of nuclides in porous media and includes first order kinetic effects on the retention constants. The code allows for different absorption and desorption rates and solves the coupled migration equations by arithmetic reiterations. Input data needed are the absorption and desorption rates, equilibrium surface absorption coefficients, flow rates and volumes, and media porosities.
Date: April 1979
Creator: Strickert, Richard; Friedman, Arnold M. & Fried, Sherman
Partner: UNT Libraries Government Documents Department

Analyze and Rebuild an Apparatus to Gauge Evaporative Cooling Effectiveness of Micro-Porous Barriers.

Description: The sample used for evaporative cooling system is Fabric defender 750 with Shelltite finish. From the experimental data and equations we have diffusion coefficient of 20.9 ± 3.71 x 10-6 m2/s for fabric with one layer with 17%-20% fluctuations from the theory, 27.8 ± 4.5 x 10-6 m2/s for fabric with two layers with 6%-14% fluctuations from the theory and 24.9 ± 4.1 x 10-6 m2/s for fabric with three layers with 13%-16% fluctuations from the theory. Since the thickness of the fabric increases so the mass transport rate decreases so the mass transport resistance should be increases. The intrinsic mass resistances of Fabri-1L, Fabri-2L and Fabri-3L are respectively 104 ± 10.2 s/m, 154 ± 23 s/m and 206 ± 26 s/m from the experiment.
Date: December 2008
Creator: Mohiti Asli, Ali
Partner: UNT Libraries

Numerical Methods for a Porous Medium Equation

Description: The degenerate parabolic equation has been used to model the flow of gas through a porous medium. Error estimates for continuous and discrete time finite element procedures to approximate the solution of this equation are proved and a new regularity result is described.
Date: August 1978
Creator: Rose, M. E.
Partner: UNT Libraries Government Documents Department

Variational particle scheme for the porous medium equation and for the system of isentropic Euler equations

Description: We introduce variational particle schemes for the porous medium equation and the system of isentropic Euler equations in one space dimension. The methods are motivated by the interpretation of each of these partial differential equations as a 'steepest descent' on a suitable abstract manifold. We show that our methods capture very well the nonlinear features of the flows.
Date: December 10, 2008
Creator: Westdickenberg, Michael & Wilkening, Jon
Partner: UNT Libraries Government Documents Department