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Articles 121 - 138 of 138

Full-Text Articles in Chemical Engineering

Measurement And Analysis Of Oxygen/Nitrogen/5a-Zeolite Adsorption Equilibria For Air Separation, Orhan Talu, Jianmin Li, Ravi Kumar, Paul M. Mathias, J. Douglas Moyer Jr, Joan M. Schork Sep 1996

Measurement And Analysis Of Oxygen/Nitrogen/5a-Zeolite Adsorption Equilibria For Air Separation, Orhan Talu, Jianmin Li, Ravi Kumar, Paul M. Mathias, J. Douglas Moyer Jr, Joan M. Schork

Chemical & Biomedical Engineering Faculty Publications

Multicomponent adsorption equilibrium data are essential for the reliable design of processes and equipment for gas separation by adsorption. We discuss techniques for the measurement and analysis of multicomponent adsorption equilibrium data, and present a comprehensive set of equilibrium data for the adsorption of oxygen and nitrogen on 5A-zeolite.

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Behavior And Performance Of Adsorptive Natural Gas Storage Cylinders During Discharge, K. J. Chang, Orhan Talu May 1996

Behavior And Performance Of Adsorptive Natural Gas Storage Cylinders During Discharge, K. J. Chang, Orhan Talu

Chemical & Biomedical Engineering Faculty Publications

Adsorbed natural gas (ANG) has the potential to replace compressed natural gas in mobile storage applications, such as in vehicles. Although a substantial research effort has been devoted to ANG, very few studies evaluate the impact of heat of adsorption on system performance. This paper concentrates on the impact of heat of adsorption on ANG performance during discharge, while the gas outflow rate is dictated by the energy demand of the application. The temperature drop and performance loss was measured with commercially available ANG cylinders under realistic conditions. Data show as high as a 37°C temperature drop at …

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Convection During Thermally Unstable Solidification Of Pb-Sn In A Magnetic Field, Hui Song, Surendra N. Tewari, H. C. Degroh Iii Apr 1996

Convection During Thermally Unstable Solidification Of Pb-Sn In A Magnetic Field, Hui Song, Surendra N. Tewari, H. C. Degroh Iii

Chemical & Biomedical Engineering Faculty Publications

Convection and macrosegregation in directionally solidified hypoeutectic Pb-38 wt pct Sn and hypereutectic Pb-64.5 wt pct Sn have been examined during upward and downward growth. Temperature fluctuations are observed along the length of the melt column during downward growth. With increasing Rayleigh number, these fluctuations change from none, to cyclic, to time periodic having multiple harmonics, and finally to random. At the higher convective driving force of 350 K temperature inversion, the transverse magnetic field decreased convective levels, strong random temperature fluctuations (flows) becoming smaller and periodic. The maximum field of 0.45 T was unable to completely eliminate convection. For …

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Time Dependence Of Tip Morphology During Cellular Dendritic Arrayed Growth, Hui Song, Surendra N. Tewari Apr 1996

Time Dependence Of Tip Morphology During Cellular Dendritic Arrayed Growth, Hui Song, Surendra N. Tewari

Chemical & Biomedical Engineering Faculty Publications

Succinonitrile-1.9 wt pct acetone has been directionally solidified in 0.7 X 0.7-cm-square cross section pyrex ampoules in order to observe the cell/dendrite tip morphologies, not influenced by the ''wall effects,'' which are present during growth in the generally used thin (about 200 mu m) crucibles. The tips do not maintain a steady-state shape, as is generally assumed. Instead, they fluctuate within a shape envelope. The extent of fluctuation increases with decreasing growth speed, as the micro structure changes from the dendritic to cellular. The influence of natural convection has been examined by comparing these morphologies with those grown, without convection, …

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Lntracrystalline Diffusion Of Benzene In Silicalite : Effect Of Structural Heterogeneity, Dhananjai B. Shah, Chang-Jie Guo, David T. Hayhurst Jan 1995

Lntracrystalline Diffusion Of Benzene In Silicalite : Effect Of Structural Heterogeneity, Dhananjai B. Shah, Chang-Jie Guo, David T. Hayhurst

Chemical & Biomedical Engineering Faculty Publications

The sorption kinetics of benzene in silicalite have been measured gravimetrically using large silicalite crystals of sizes 350 µm × 105 µm × 105 µm and 270 µm × 70 µm × 70 µm in the temperature range 283–343 K. Experiments were performed under conditions that ensured isothermal operation with intracrystalline diffusion control. An analytical expression for the Darken's correction factor (δ In P/δ In a) was derived based on the Hill–de-Boer equation and was used to determine the variation of corrected diffusivity with concentration. The transport diffusivity varied significantly with the adsorbed-phase concentration but the …

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Activity Coefficients Of Adsorbed Mixtures, Orhan Talu, Jianmin Li, Alan L. Myers Jan 1995

Activity Coefficients Of Adsorbed Mixtures, Orhan Talu, Jianmin Li, Alan L. Myers

Chemical & Biomedical Engineering Faculty Publications

Experimental and simulated data for adsorption of gas mixtures on energetically heterogeneous surfaces like activated carbon and zeolites exhibit negative deviations from ideality. The deviations are large in some cases, with activity coefficients at infinite dilution equal to 0.1 or less. Similar molecules form ideal mixtures, but molecules of different size or polarity are nonideal. Equations for bulk liquid mixtures (Wilson, Margules, etc.) do not apply to isobars for adsorbed mixtures. A two-constant equation for activity coefficients as a function of composition and spreading pressure is in good agreement with theory, simulation, and experiment.

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Adsorption Equilibrium Of Benzene-P-Xylene Vapor Mixture On Silicalite, Jianmin Li, Orhan Talu Dec 1993

Adsorption Equilibrium Of Benzene-P-Xylene Vapor Mixture On Silicalite, Jianmin Li, Orhan Talu

Chemical & Biomedical Engineering Faculty Publications

Adsorption equilibrium of benzene-p-xylene vapor mixture on silicalite is measured at 70^oC with a specially designed cyclic volumetric apparatus at pressure levels of 2.53 and 1.20 kPa. The isobaric isotherms are S-shaped, and selectivity curves at different pressures cross over; the p-xylene selectivity at 2.53 kPa is higher than that at 1.20 kPa over a certain composition range. The heterogeneous ideal adsorption solution (HIAS) model implemented on two patches qualitatively predicts these highly unusual behavior. The observed extraodinary phenomena are attributed to structural heterogeneity, a result of the tight-fit of sorbate molecules in silicalite …

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Optimal Selection Of Metabolic Fluxes For In Vivo Measurement. Ii. Application To Escherichia Coli And Hybridoma Cell Metabolism, Joanne M. (Savinell) Belovich, Berhard O. Palsson Mar 1992

Optimal Selection Of Metabolic Fluxes For In Vivo Measurement. Ii. Application To Escherichia Coli And Hybridoma Cell Metabolism, Joanne M. (Savinell) Belovich, Berhard O. Palsson

Chemical & Biomedical Engineering Faculty Publications

A method of analysis was presented in part I of this series for determining the fluxes in a biochemical network that are the optimal choices for experimental measurement. This algorithm is applied to two important biological models: Escherichia coli and a hybridoma cell line (167.4G5.3). Our results show that potentially poor choices for in vivo measurement of metabolic fluxes exist for both model systems. For the subset of reactions in E. coli that was studied, the condition number of the augmented stoichiometric matrix reveals that a 60-fold amplification of experimental error during computations is possible. The biochemical network of the …

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Optimal Selection Of Metabolic Fluxes For In Vivo Measurement. I. Development Of Mathematical Methods, Joanne M. (Savinell) Belovich, Bernhard O. Palsson Mar 1992

Optimal Selection Of Metabolic Fluxes For In Vivo Measurement. I. Development Of Mathematical Methods, Joanne M. (Savinell) Belovich, Bernhard O. Palsson

Chemical & Biomedical Engineering Faculty Publications

The measurement of uptake and secretion rates is often not sufficient to allow the calculation of all internal metabolic fluxes. Measurements of internal fluxes are needed and these additional measurements are used in conjunction with mass-balance equations to calculate the complete metabolic flux map. A method is presented that identifies the fluxes that should be selected for experimental measurement, and the fluxes that can be computed using the mass-balance equations. The criterion for selecting internal metabolic fluxes for measurement is that the values of the computed fluxes should have low sensitivity to experimental error in the measured fluxes. A condition …

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Network Analysis Of Intermediary Metabolism Using Linear Optimization. I. Development Of Mathematical Formalism, Joanne M. (Savinell) Belovich, Bernhard O. Palsson Feb 1992

Network Analysis Of Intermediary Metabolism Using Linear Optimization. I. Development Of Mathematical Formalism, Joanne M. (Savinell) Belovich, Bernhard O. Palsson

Chemical & Biomedical Engineering Faculty Publications

Analysis of metabolic networks using linear optimization theory allows one to quantify and understand the limitations imposed on the cell by its metabolic stoichiometry, and to understand how the flux through each pathway influences the overall behavior of metabolism. A stoichiometric matrix accounting for the major pathways involved in energy and mass transformations in the cell was used in our analysis. The auxiliary parameters of linear optimization, the so-called shadow prices, identify the intermediates and cofactors that cause the growth to be limited on each nutrient. This formalism was used to examine how well the cell balances its needs for …

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Solutal Partition Coefficients In Nickel-Based Superalloy Pwa-1480, Surendra N. Tewari, M. Vijayakumar, James E. Lee, P. A. Curreri Jul 1991

Solutal Partition Coefficients In Nickel-Based Superalloy Pwa-1480, Surendra N. Tewari, M. Vijayakumar, James E. Lee, P. A. Curreri

Chemical & Biomedical Engineering Faculty Publications

Solutal profiles in dendritic single-crystal specimens of PWA-1480 nickel-base superalloy, which were directionally solidified and quenched, were examined on several transverse cross-sections to obtain the partition coefficients. Similar to their nickel-base binaries, the partition coefficients of tantalum, titanium, and aluminum were found to be less than unity; those of tungsten and cobalt were greater than unity. The partition coefficients were temperature independent in the range 1584-1608 K. The contribution of solid-state diffusion to microsegregation was observed to be negligible.

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Dendrite Spacings In Directionally Solidified Superalloy Pwa-1480, M. Vijayakumar, Surendra N. Tewari, James E. Lee, P. A. Curreri Feb 1991

Dendrite Spacings In Directionally Solidified Superalloy Pwa-1480, M. Vijayakumar, Surendra N. Tewari, James E. Lee, P. A. Curreri

Chemical & Biomedical Engineering Faculty Publications

Primary dendrite spacings and side-branch coarsening kinetics were examined in specimens of the single-crystal multicomponent commercial superalloy PWA-1480, which were directionally solidified in a positive thermal gradient. The experimentally observed dependence of primary dendrite spacings and side-branch coarsening kinetics on growth rate and thermal gradient were in agreement with the behavior predicted by analytical models developed for binary alloys.

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Dendrite Tip Radii In Directionally Solidified Pb-8.4-Atmospheric-Percent-Au, Surendra N. Tewari Dec 1990

Dendrite Tip Radii In Directionally Solidified Pb-8.4-Atmospheric-Percent-Au, Surendra N. Tewari

Chemical & Biomedical Engineering Faculty Publications

The cell/dendrite tip radii in directionally solidified Pb-8.4at.%Au have been investigated as a function of the growth speed and thermal gradient in the liquid at the tip. Dendrite growth models are not able to predict quantitatively the tip radii and tip compositions separately because of the occurrence of thermosolutal convection during growth. However, the relationship between the destabilizing solutal gradient, the stabilizing thermal gradient and the capillarity at the tip assumed using the ''marginal stability'' criterion is supported by the experimental data.

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Heat And Momentum Transfer Analogies For The Transitional And Turbulent Flow Of A Non-Newtonian Power-Law Fluid In A Heated Pipe, Prapat Wangskarn, Bahman Ghorashi Mar 1990

Heat And Momentum Transfer Analogies For The Transitional And Turbulent Flow Of A Non-Newtonian Power-Law Fluid In A Heated Pipe, Prapat Wangskarn, Bahman Ghorashi

Chemical & Biomedical Engineering Faculty Publications

A model is proposed for the transfer of heat to non-Newtonian power-law fluids flowing in heated horizontal pipes. Comparisons with the existing models, based on the absolute-percent-arithmetic-average-deviation and the percent-standard-deviation, show that under the transitional and turbulent flow regimes the proposed correlation fits the experimental data more accurately over a wide range of flow behavior index and there are no restrictions for its use when applied to pseudoplastic fluids.

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A Numerical Solution For The Turbulent Flow Of Non-Newtonian Fluids In The Entrance Region Of A Heated Circular Tube, Prapat Wangskarn, Bahman Ghorashi, Rama Subba Reddy Gorla Mar 1990

A Numerical Solution For The Turbulent Flow Of Non-Newtonian Fluids In The Entrance Region Of A Heated Circular Tube, Prapat Wangskarn, Bahman Ghorashi, Rama Subba Reddy Gorla

Chemical & Biomedical Engineering Faculty Publications

Numerical solutions of conservation equations are obtained for turbulent flow of non-Newtonian fluids in a circular tube. The forward marching procedure of Patankar and Spalding^1 was implemented in order to obtain the simultaneous development of the velocity and temperature fields by using the apparent viscosity of fluids. Prandtl's mixing length concept is used to determine the apparent turbulent shearing stress. Furthermore, local and average Nusselt numbers are obtained in the entrance region, as well as in the fully developed region. For the case of the fully developed region, values of the Nusselt numbers …

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Asymptotic Boundary-Layer Solutions For Mixed Convection From A Vertical Surface In A Micropolar Fluid, Rama Subba Reddy Gorla, Paul P. Lin, An-Jen J. Yang Jan 1990

Asymptotic Boundary-Layer Solutions For Mixed Convection From A Vertical Surface In A Micropolar Fluid, Rama Subba Reddy Gorla, Paul P. Lin, An-Jen J. Yang

Mechanical Engineering Faculty Publications

Using the theory of micropolar fluids due to Eringen, asymptotic boundary layer solutions are presented to study the combined convection from a vertical semi-infinite plate to a micropolar fluid. Consideration is given to the region close to the leading edge as well as the region far away from the leading edge. Numerical results are obtained for the velocity, angular velocity and temperature distribution. The missing wall values of the velocity, angular velocity and thermal functions are tabulated. Micropolar fluids display drag reduction and reduced surface heat transfer rate when compared to Newtonian fluids.

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Mixed Convection In Vertical Internal Flow Of A Micropolar Fluid, Rama Subba Reddy Gorla, Bahman Ghorashi, Prapat Wangskarn Jan 1989

Mixed Convection In Vertical Internal Flow Of A Micropolar Fluid, Rama Subba Reddy Gorla, Bahman Ghorashi, Prapat Wangskarn

Chemical & Biomedical Engineering Faculty Publications

The theory of micropolar fluids due to Eringen is used to formulate a set of equations for the flow and heat transfer characteristics of the combined convection micropolar flow in vertical channels. It is found that the microstructure and substructure parameters have significant effects on the flow and thermal fields. By making the Newtonian solvent more and more micropolar, it is possible to obtain drag reduction as well as reduced heat transfer characteristics.

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Analogy Among Heat And Momentum-Transfer For Non-Newtonian Fluids In Laminar-Flow Through Pipes, Bahman Ghorashi, Bela Hirsch Jan 1982

Analogy Among Heat And Momentum-Transfer For Non-Newtonian Fluids In Laminar-Flow Through Pipes, Bahman Ghorashi, Bela Hirsch

Chemical & Biomedical Engineering Faculty Publications

No abstract provided.

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