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LF Gladden

Publications and source records attributed to LF Gladden.

5 recordsLinked to original sources
PubMed2000

Probing Ganglia Dissolution and Mobilization in a Water-Saturated Porous Medium using MRI.

Magnetic resonance imaging (MRI) is used to probe the evolution of geometric characteristics such as the volume, shape, surface area, and cluster size of octanol ganglia trapped in a model porous medium, in this case a packing of spheres, as they dissolve into a mobile aqueous phase. The resulting pore-scale information is used to assess various assumptions used in existing models of the dissolution process. Dissolution of the ganglia was characterized by a reduction in the overall number of ganglia with little effect on the shape and mean of the volume distribution of the ganglia. This apparently anomalous result is explained by dissolution of the ganglia until they reach a critical size, which is dependent on the structure of the pore space, at which point they are mobilized and subsequently removed from the porous medium. The shape of the entrapped ganglia is characterized by a fractal dimension in the range 2.2-2.3, suggesting that models which assume a Euclidean geometry for the entrapped ganglia are appropriate. No significant change in the shape of entrapped ganglia is observed during dissolution. In agreement with the results of earlier workers, most hydrocarbon ganglia exist as singlets within the pore structure. Copyright 2000 Academic Press.

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PubMed2000

Heterogeneous catalyst design using stochastic optimization algorithms

We describe the application of two stochastic optimization algorithms to heterogeneous catalyst design. In particular, we discuss the optimal design of a two-component catalyst for the diffusion limited A + B --> 0 and A + B2 --> 0 reactions in which each of the reactants are adsorbed specifically on one of the two distinct catalytic sites. The geometric arrangement of the catalytic sites that maximizes the catalyst activity is determined by the use of a genetic algorithm and a simulated annealing algorithm. In the case of the A + B --> 0 reaction, it is found that the catalyst surface with the optimal active site distribution, that of a checkerboard, is approximately 25% more active than a random site distribution. A similar increase in catalytic activity is obtained for the A + B2 --> 0 reaction. While both the genetic and simulated annealing algorithms obtain identical optimal solutions for a given reaction, the simulated annealing algorithm is shown to be more efficient.

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PubMed1999

Magnetic Resonance Imaging Study of the Dissolution Kinetics of Octanol in Porous Media.

Magnetic resonance imaging (MRI) is used to visualize the dissolution of entrapped ganglia or "blobs" of octanol within the pore space of a randomly packed bed of glass ballotini, by a mobile aqueous phase. MRI provides three dimensional images, able to distinguish the solid, hydrocarbon, and aqueous phases, as well as velocity maps of the mobile aqueous phase. Dissolution of the hydrocarbon phase has been modeled using a one dimensional advection-dispersion description incorporating a mass transfer term between the hydrocarbon and aqueous phases. Essential to this mass transfer term is a description of the interfacial area between the hydrocarbon and aqueous phases which is actively involved in dissolution and which can be determined directly from the images. The experimental data are best modeled by evaluating an effective interfacial area term characterizing the hydrocarbon/water boundary which excludes the narrowest constrictions within the interparticle space. MRI visualizations of the structure of the pore space and the flow processes occurring within it, demonstrate that heterogeneities in the flow at the length-scale of individual pores within the interparticle space cause significant heterogeneity in the dissolution process which becomes significant at low hydrocarbon saturations. Copyright 1999 Academic Press.

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PubMed1999

Echo-planar imaging of porous media with spatial resolution below 100 &mgr;m

A modified version of the echo-planar imaging technique incorporating a Carr-Purcell train of 180 degrees rf pulses (PEPI) has been implemented on a standard spectrometer. It is demonstrated that artifacts in the image due to cumulative errors in the rf field can be reduced by replacing each 180 degrees pulse by a composite sequence of three rf pulses. Artifact-free 3D images at 94 &mgr;m voxel resolution are obtained within 15 min. This technique has been applied to study the drying process in an initially water-saturated model porous medium with characteristic T*2 of order 700 &mgr;s. Copyright 1999 Academic Press.

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