422 research outputs found

    Anomalous low temperature specific heat of He-3 inside nanotube bundles

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    Helium atoms and hydrogen molecules can be strongly bound inside interstitial channels within bundles of carbon nanotubes. An exploration of the low energy and low temperature properties of He-3 atoms is presented here. Recent study of the analogous He-4 system has shown that the effect of heterogeneity is to yield a density of states N(E) that is qualitatively different from the one-dimensional (1D) form of N(E) that would occur for an ideal set of identical channels. In particular, the functional form of N(E) is that of a 4D gas near the very lowest energies and a 2D gas at somewhat higher energies. Similar behavior is found here for He-3. The resulting thermodynamic behavior of this fermi system is computed, yielding an anomalous form of the heat capacity and its dependence on coverage.Comment: 11 pages, 6 figure

    Quasi-one and two-dimensional transitions of gases adsorbed on nanotube bundles

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    Grand canonical Monte Carlo simulations have been performed to determine the adsorption behavior of Ar and Kr atoms on the exterior surface of a rope (bundle) consisting of many carbon nanotubes. The computed adsorption isotherms reveal phase transitions associated with the successive creation of quasi-one dimensional lines of atoms near and parallel to the intersection of two adjacent nanotubes.Comment: 12 pages, 6 figures, submitted to J. Chem. Phy

    Simple Model of Capillary Condensation in porous media

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    We employ a simple model to describe the phase behavior of 4He and Ar in a hypothetical porous material consisting of a regular array of infinitely long, solid, parallel cylinders. We find that high porosity geometries exhibit two transitions: from vapor to film and from film to capillary condensed liquid. At low porosity, the film is replaced by a ``necking'' configuration, and for a range of intermediate porosity there are three transitions: from vapor to film, from film to necking and from necking to a capillary condensed phase.Comment: 14 pages, 7 figure

    Bose-Einstein Condensation of Helium and Hydrogen inside Bundles of Carbon Nanotubes

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    Helium atoms or hydrogen molecules are believed to be strongly bound within the interstitial channels (between three carbon nanotubes) within a bundle of many nanotubes. The effects on adsorption of a nonuniform distribution of tubes are evaluated. The energy of a single particle state is the sum of a discrete transverse energy Et (that depends on the radii of neighboring tubes) and a quasicontinuous energy Ez of relatively free motion parallel to the axis of the tubes. At low temperature, the particles occupy the lowest energy states, the focus of this study. The transverse energy attains a global minimum value (Et=Emin) for radii near Rmin=9.95 Ang. for H2 and 8.48 Ang.for He-4. The density of states N(E) near the lowest energy is found to vary linearly above this threshold value, i.e. N(E) is proportional to (E-Emin). As a result, there occurs a Bose-Einstein condensation of the molecules into the channel with the lowest transverse energy. The transition is characterized approximately as that of a four dimensional gas, neglecting the interactions between the adsorbed particles. The phenomenon is observable, in principle, from a singular heat capacity. The existence of this transition depends on the sample having a relatively broad distribution of radii values that include some near Rmin.Comment: 21 pages, 9 figure

    Reaction Engineering Routes to Waste Gasification for Sustainable Living Environments

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    There is an increasing pressure to reduce waste generation and dependence upon fossil fuels in our society. The approach investigated in this project aims to address both concerns by formulating a low-temperature gasification process to process long-chain polymers typically found in municipal waste. Gasification routes which convert plastic and bio-waste into useful fuel syngas products has been extensively investigated. The novelty of the approach examined here consists on the use of a variety of catalysts, which can promote high conversion in gasification reactions at much lower temperature and pressure conditions. This route overcomes some of the financial and environmental shortcomings of typical gasification routes, such as incineration, currently in use as waste-management strategies. Utilizing a small batch reactor, the kinetics of several, predominantly polyethylene, waste simulants have been examined in the presence of both platinum and ruthenium-based catalysts. Using gas chromatography, the conversion of the carbon source was quantified and compared for the two different catalysts and different reaction conditions. Promising results were obtained, these results compare favorably with results found in the literature. A phenomenological model has been formulated to characterize the liquid phase gasification reactions and their interrelation with transport phenomena occurring in an heterogeneous reaction environment. Through the use of computational fluid dynamics (CFD), the effect of mixer speed on vortex shape has been modeled. These results are currently being incorporated into the model in the form of a detailed characterization of transport phenomena occurring during the gasification dynamics. Moreover, the refined model is anticipated to enable optimization of the reactor operation, and reducing or de-convoluting any transport limitation that may be affecting kinetic determinations.https://engagedscholarship.csuohio.edu/u_poster_2014/1030/thumbnail.jp

    Permeability of Microporous Carbon Preforms

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    The permeability of microporous amorphous carbon preforms with varying pore size and pore distributions has been experimentally examined. The porous structures have been characterized by mercury porosimetry and by quantitative metallography of pressure-infiltration-cast metal matrix composites based on the carbon preforms. The permeability shows a linear correlation with the fraction porosity and the square of the pore diameter
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