# AIChE Journal

Published by Wiley

Online ISSN: 1547-5905

Published by Wiley

Online ISSN: 1547-5905

Publications

Article

Antibodies that target and internalize into blood-brain barrier (BBB) endothelial cells offer promise as drug delivery agents. Previously, we identified a single-chain antibody (scFvA) capable of binding to the BBB. In an attempt to improve the binding and internalization properties of the single chain antibody (scFvA), a biotinylation tag (Avitag) was fused to scFvA and the protein secreted by yeast. The scFvA-Avitag could be biotinylated by yeast-displayed BirA enzyme and biotinylated scFvA-Avitag could be used to create scFv tetramers. Tetramerization of scFvA improved the internalization of scFvA into BBB endothelial cells, and biotinylated scFvA-Avitag could also be used to target streptavidin-coated quantum dots for BBB endothelial cell internalization. Perfusing the rat brain with scFvA-tetramer confirmed that the antigen targeted by scFvA is distributed on blood side of the BBB, suggesting the potential for downstream application of scFvA in brain-targeted drug delivery.

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Article

Mobile-phase additives, commonly used to modulate absorbate retention in gradient elution chromatography, are usually assumed to be either linearly retained or unretained. Previous theoretical work from our laboratory has shown that these modulators, such as salts in ion-exchange and hydrophobic interaction chromatography and organic modifiers in reversed-phase chromatography, can absorb nonlinearly, giving rise to gradient deformation. Consequently, adsorbate peaks that elute in the vicinity of the head of the deformed gradient may exhibit unusual shapes, form shoulders, and/or be concentrated. These effects for a reversed-phase sorbent with aqueous acetonitrile (ACN) as the modulator are verified experimentally. Gradient deformation is demonstrated experimentally and agrees with simulations based on ACN isotherm parameters that are independently determined from batch equilibrium studies using the layer model. Unusual absorbate peak shapes were found experimentally for single-component injections of phenylalanine, similar to those calculated by the simulations. A binary mixture of tryptophan and phenylalanine is used to demonstrate simultaneous concentration and separation, again in agreement with simulations. The possibility of gradient deformation in ion-exchange and hydrophobic interaction chromatography is discussed.

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Article

During the IML-2 space shuttle mission, the RAMSES instrument was operated in the Spacelab module. This continuous-flow electrophoresis device performs separation and purification of protein solutions on a preparative scale. Samples containing artificial mixtures of pure proteins were used to test the capabilities of the device, and useful separations were obtained for proteins having a mobility difference of only 3 x 10(-9) m2 V-1 s-1. Operating conditions that cannot be applied on earth were explored for two different sample concentrations, one of which is too high to allow treatment on earth. It agrees well with a previously published numerical model in that the main cause of loss in resolution in this process is the electrohydrodynamic spreading of the protein filaments.

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Article

Superparamagnetic magnetic nanoparticles were successfully functionalized with poly(methacrylic acid) via atom transfer radical polymerization, followed by conjugation to doxorubicin (Dox). Because of pH-sensitive hydrazone linkages, the rate and extent of Dox release from the particles was higher at a lower pH and/or a higher temperature than at physiological conditions. Appropriate changes to the pH and temperature can increase the drug release from the particles. Because of the released drug, the particles were found to be cytotoxic to human breast cancer cells in vitro. Such magnetic nanoparticles, with the potential to retain drug under physiological conditions and release the drug in conditions where the pH is lower or temperature is higher, may be useful in magnetic drug targeting by reducing the side effects of the drug caused to healthy tissues. In addition, they may serve as hyperthermia agents where the high temperatures used in hyperthermia can trigger further drug release.

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Article

The treatment of diseased tissues and organs is an ongoing healthcare problem that could be solved with artificial tissues.1,2 Functional tissue constructs could also decrease the time and the cost spent on the drug discovery process, which could have a direct effect on discovering cures for various diseases.1,2 Tissue engineering holds great promise for developing methods to create tissue models with the structural organization of native tissues, which could be useful for regenerative medicine and pharmaceutical research.
Native tissues contain different cell types, with each cell type having its own unique three-dimensional (3-D) extracellular matrix (ECM) environment, and mechanical properties. To recreate such complexity in engineered tissues various approaches have been used. In one such approach, cells are seeded on a degradable scaffold on which they reorganize into engineered tissues. Alternatively, cells are used to create modular tissue units with microscale polymers or without any scaffolds.3 These modular tissues can later be assembled,4 stacked,5,6 or rolled7 to form large-scale tissue constructs by mimicking the native architecture.
To generate tissue modules, photolithographic4 and soft lithographic methods8 have been used to encapsulate cells within microgels with different shapes and geometries. These cell-encapsulated microgels can be further assembled into defined geometries.3 Rigid9,10 or soft microfabricated templates11,12 can also be used to form scaffold-free tissue modules made from clusters of cells. Furthermore, tissue monolayers can be generated on 2-D substrates, which can be further stacked or rolled to fabricate macroscale tissues.5–7
Each of these techniques have their own limitations. For example, photolithography is only applicable to photocrosslinkable materials,13 whereas most soft lithographic methods rely on static microstructures, that limit the range of microgel shapes that can be fabricated.13 Also, the pattern geometries and surface properties of static microstructures cannot be changed. These static features may be limited in creating biomimetic microtissues and the retrieval of tissues from these platforms in a controlled manner. Furthermore, 2-D templates with nonswitchable surfaces require the use of enzymes or physical forces to detach monolayer of tissues, which is not desirable.14,15
Dynamic microstructures with controllable features and switchable surface properties are emerging as useful tools for creating biomimetic and retrievable modular tissues. Poly(N-isopropylacrylamide) (PNIPAAm) is a well-known stimuli-responsive polymer, which responds to temperature by changing its hydrophilicity and swelling.16–18 Properties of PNIPAAm make it favorable to fabricate dynamic platforms to overcome the static features of previous technologies. This review will highlight the current developments in PNIPAAm-based thermoresponsive platforms for tissue engineering and regenerative medicine.

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Article

A novel methodology for the de novo identification of peptides by mixed-integer optimization and tandem mass spectrometry is presented in this article. The various features of the mathematical model are presented and examples are used to illustrate the key concepts of the proposed approach. Several problems are examined to illustrate the proposed method's ability to address (1) residue-dependent fragmentation properties and (2) the variability of resolution in different mass analyzers. A preprocessing algorithm is used to identify important m/z values in the tandem mass spectrum. Missing peaks, resulting from residue-dependent fragmentation characteristics, are dealt with using a two-stage algorithmic framework. A cross-correlation approach is used to resolve missing amino acid assignments and to identify the most probable peptide by comparing the theoretical spectra of the candidate sequences that were generated from the MILP sequencing stages with the experimental tandem mass spectrum.

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Conference Paper

Experimental studies in the control of coupled distillation columns have seen performed to satisfy two objectives: 1. To provide an experimental test of previously developed operability and resiliency measures for multivariable systems. 2. To demonstrate the design of Internal Model Control (IMC) controllers for such systems and make comparisons on the basis of performance and ease of tuning with conventional algorithms like PID controllers. To attain these goals, two pilot plant distillation columns were arranged in a coupled configuration and step tests were used to identify input-output relationships. Systems with different levels of operability and resilience were selected and corresponding IMC controllers were designed and tested. The experimental results show clearly that the operability analysis is sufficient to distinguish extremes, but for fine distinctions, a knowledge of desired output changes, disturbances and model uncertainties must be included in the decision process. In addition a method to combine the sometimes contradictory resilience criteria needs to be defined. IMC is shown to be simple to implement, easy to tune, and to produce superior control performance.

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Conference Paper

Not Available

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Conference Paper

We consider a broad class of nonisothermal, spatially homogeneous
reaction systems, with fast and slow reactions. The dynamic model of
such systems exhibits stiffness (time-scale multiplicity) but is not in
a standard singularly perturbed form. For such systems, we address the
derivation of reduced order nonlinear models of the slow dynamics,
through (i) the identification of algebraic constraints that need to be
satisfied in the slow time scale (e.g. reaction equilibrium constraint
in the case of fast reversible reactions), and (ii) the derivation of
state-space realizations of the resulting differential algebraic system
that describes the slow dynamics

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Article

A study of the feasibility of using ion exchange resin systems for carbon dioxide absorption from gas streams was completed with the conclusion that such a system could compete very successfully with atmospheric control systems now in use. A detailed study of such a system based on polyethylenimine showed that this material is superior to any of the commercially available weak base resins tested. The kinetic data obtained correlated very well when a model was postulated that was based on diffusive transfer through a gas film, a water film, and the resin particle in series, with diffusion with the resin particle as the rate determining step.

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Article

An explicit, four-constant model for viscosity and normal stresses in simple shear has been developed by simplifying the integral theory of Bernstein, Kearsley, and Zapas. In essence the procedure involves curve-fitting the linear relaxation spectrum. The four constants appear also in equations for the stress distribution and for pressure drop in accelerative flow between flat plates; flow along rays is assumed. The equations reduce to second-order theory and to Newtonian theory as a Deborah number becomes small. Comparison of the predicted stress distributions with previously published stress birefringent data shows good agreement; because of the low shear rates, however, the check is not demonstrating very strong departures from the second-order asymptote. Certain other theoretical results, including pressure drop predictions, are also noted.

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Article

A mode of operation and a design technique have been developed which permit the attainment of continuous purging of impurities directly from the gas compartments of a fuel cell—either anode, cathode, or both—with the realization of minimum reactant loss, most stable voltage and current output, and operating conditions with respect to reactant gas flow and electrolyte inventory. We have found a way to eliminate the complex periodic purge valves and attendant electronics by a fuel cell system which is both simple in structure and operation and which has a high degree of reliability. The technique was suggested by the observation that in dead-ended fuel cell gas compartments, the inert impurities present in reactant gases tend to accumulate at the dead-ended portion of the cell. Hence a small amount of bleed should be placed there. This observation has been made analytically by solving numerically a system of two partial differential equations simultaneously.

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Article

Dead ended compartments concentration and current distributions calculation in space hydrogen-oxygen fuel cells, using mathematical model with convective diffusion equation

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Article

Calculations of the molar heat and entropy of adsorption for pure methane and pure ethane on silica gel at 25°C. show the heterogeneity of the adsorbent when plotted as functions of the spreading pressure. Plots are given for the activity coefficient of methane and ethane in the adsorbed phase based on experimental data for the entire range of compositions at 25°C. up to a maximum pressure of 1,400 lb./sq.in.abs. Similar results were obtained at 5, 15, and 35°C. The activity coefficients deviate from unity at intermediate compositions.

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Article

The mechanism of diffusion in an absorbent pore was studied by applying adsorption rate data to the Damköhler equation. Most of the data were taken in the multimolecular region of the nitrogen-silica gel adsorption isotherm. Vapor-phase and adsorbed-phase contributions to the total transport were separated. Vapor-phase transport increased with temperature and was most dominant at relative pressures of 0.4 to 0.6. Adsorbed-phase diffusivities were of the order of 10−2 — 10−3 sq. cm./sec. and showed some dependence on the amount adsorbed at surface coverages greater than 1.5 molecular layers.

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Article

Boiling pressure drop prediction for alkali metal bodies using correlation described by Stone and Damman

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Article

The application of integral techniques to the analysis of a high vapor velocity, two-phase, annular-mist, single-component condensing flow system is presented. A time-averaged annular liquid film thickness is defined, and appropriate interfacial and wall shear stress correlations are employed to account for the wavy nature of the interface between the entrainment-laden gaseous core and the axisymmetric annular liquid film. An empirical entrainment correlation is utilized to determine the amount of liquid flowing as entrained particles in the high velocity core region. The velocity and enthalpy distributions in the gaseous core and the annular liquid film are assumed as the power-law type. The resulting set of four nonlinear ordinary differential equations is solved numerically with the use of a digital computer. A comparison with experimental data for condensing steam is obtained. The analytical model accurately predicts the condenser length necessary for complete condensation and also predicts the dynamic quality, the heat transfer characteristics, and the static pressure distribution throughout the condensation length. The integral analysis presents some insight into the complex mechanisms and interactions which occur in high vapor velocity, two-phase, annular-mist flows and also indicates the need for improved experimental techniques to further this understanding.

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Article

This study is focused on deposition rate processes leading to inefficiency and “hot corrosion” in fossil-fuel-fired furnaces and engines. The inorganic compounds which deposit on heat exchanger surfaces and blades are formed in combustion product gases when the fuel and/or ingested air contains inorganic impurities. An improved understanding of the coupled thermodynamic, kinetic, and transport processes governing the deposition rate of inorganic oxides and salts from hot gases containing these compounds (or their precursors) can suggest more efficient test strategies and control measures. Accordingly, an optical interference method for accurately measuring the growth rate of deposits well before the onset of run-off under laboratory burner conditions has been developed.

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Article

Data are presented for wall temperatures and heat transfer coefficients for solid-vapor mixtures of parahydrogen and nitrogen flowing in an electrically heated straight tube of length 40 times its diameter. These are interpreted by the application of flat plate, constant property boundary-layer theory to models in which the solid particle geometrical distribution takes on simple limiting forms. The observed enhancement of the heat transfer coefficient over that for gas alone traveling at the same velocity is qualitatively predicted as a function of a dimensionless heat flux, the Sterman parameter qw/ρvUλ.

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Article

A flash-evaporation technique is used to obtain vapor deposition characteristics for the binary alkali sulfates K2SO4 + Na2SO4 at 1 atm above 1, 100 K. This technique gives results of immediate engineering interest, such as dewpoint temperatures, condensate composition and rates of vapor deposition as well as useful data on the system's thermodynamic characteristics. It is concluded that alkali sulfate deposition and vaporization in combustion environments are inevitably influenced by chemical reactions such as hydroxide formation. It is also concluded that solution nonideality is important even for homologous alkali-salt mixtures.
Predictions are made using convective-diffusion mass transfer theory, accounting for chemical reactions by means of effective volatilities, and assuming regular, nonideal condensate solutions. The predicted dewpoints, condensate compositions and deposition rates are quantitatively consistent with experimental observations. This approach, validated here, can be extended to more extreme conditions of engineering interest, including turbulent, high-temperature/pressure systems.

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Article

Prediction method for occurrence and type of gas- gas equilibrium in binary systems

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Article

A new generalization of boundary condition iteration (BCI) methods is developed, based on a suggestion of Denn and Aris. This simplifies to Horn's equation for up to two state equations and to previous boundary iteration methods when
is explicitly soluble for
as a function of the constants, the state and the adjoint variables. The new general method is also applicable when this latter function is unobtainable.
Distinct improvement in the convergence rates of the existing BCI methods has been obtained through the introduction of a correction specific to each state variable.
A convergence procedure for use with Horn's equation is proposed and the resultant algorithm has desirable properties.

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Article

Critical review of a recent paper in which Denison, Stevenson, and Fox (1971) discussed the sources of spectral broadening in the laser Doppler velocimeter. It is pointed out that, in their discussion, the above-mentioned authors indicated that the spread in wave vectors of the incident and detected fields and the finite length of time a scattering center stayed in the sample volume each contributed separately and independently to the observed spectral width of the scattered radiation. This statement is termed incorrect, and it is shown that the two effects are one and the same.

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Article

Isothermal profiles of the extended meniscus in a quartz cuvette were measured in the earth's gravitational field using an image-analyzing interferometer that is based on computer-enhanced video microscopy of the naturally occurring interference fringes. These profiles are a function of the stress field. Experimentally, the augmented Young-Laplace equation is an excellent model for the force field at the solid-liquid-vapor interfaces for heptane and pentane menisci on quartz and tetradecane on SFL6. The effects of refractive indices of the solid and liquid on the measurement techniques were demonstrated. Experimentally obtained values of the disjoining pressure and dispersion constants were compared to those predicted from the Dzyaloshinskii - Lifshitz - Pilaevskii theory for an ideal surface and reasonable agreements were obtained. A parameter introduced gives a quantitative measurement of the closeness of the system to equilibrium. The nonequilibrium behavior of this parameter is also presented

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Article

A new correlation method for binary gaseous diffusion coefficients from very low temperatures to 10,000 K is proposed based on an extended principle of corresponding states, and having greater range and accuracy than previous correlations. There are two correlation parameters that are related to other physical quantities and that are predictable in the absence of diffusion measurements. Quantum effects and composition dependence are included, but high-pressure effects are not. The results are directly applicable to multicomponent mixtures.

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Article

Diffusion coefficients for oxygen transport in whole blood, discussing effects of intact red cell concentration

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Article

A combined-conjugated heat-transfer and fluid-flow analysis is presented for coating fibers by CVD in a vertical cylindrical quartz reactor. The numerical model focuses on radiation and natural convection. Three case studies are performed, and the wall temperature predictions are compared to experimental measurements. In the first case, the flowing gas is hydrogen, and conduction is more important than both radiation and convection, in which case measured and predicted wall temperatures agree excellently. In the second, hydrogen is replaced by argon, thus making radiation heat transfer more important than the previous situation. Three radiation models with increasing degrees of sophistication are compared: an approximate nongray model (no wavelength dependence of emissivity), an approximate semi-gray model, and a rigorous semi-gray model with view factor calculations. Comparison with experiments suggest that a semi-gray radiative analysis is needed for correct determination of wall temperatures. The third involves argon at a lower flow rate, where natural convection effects are more pronounced. Checking the validity of the Boussinesq approximation by incorporating the explicit dependence of density on temperature in the model shows a slight difference between the velocity fields predicted using the Boussinesq approximation and those obtained using the explicit dependence of density on temperature. However, there is negligible difference between the temperature fields predicted in the two cases.

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Article

A scheme for rapidly computing the chemical equilibrium composition of hydrocarbon combustion products is derived. A set of ten governing equations is reduced to a single equation that is solved by the Newton iteration method. Computation speeds are approximately 80 times faster than the often used free-energy minimization method. The general approach also has application to many other chemical systems.

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Article

Entanglement theories for polymer solutions resemble those developed for solid rubbers. These rubberlike theories are extremely successful qualitatively; they give a good indication of the type of response observed experimentally in concentrated solutions. Quantitatively the theories are not so useful; in general they predict constant viscosities in simple shearing motions and ever-increasing tensile stress in steady elongational flow.
If it is supposed that the lifetime of the entanglements is limited partly by a maximum allowable strain magnitude, and that the network ruptures locally whenever this magnitude is exceeded, greatly improved quantitative predictions are observed. For polyisobutylene-cetane solutions, where the critical strain magnitude appears to be about 3, excellent prediction of the steady shearing viscosity curve is available starting from the measured dynamical response to small sinusoidal strains and the critical strain magnitude. Normal stress effects are also well represented; in elongational flow the tensile stress shows a slight maximum. It thus appears that the notion of network rupture is useful in guiding the selection of continuum theories for polymer fluid description.

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Article

We report an approach to fully visualize the flow of two immiscible fluids
through a model three-dimensional (3D) porous medium at pore-scale resolution.
Using confocal microscopy, we directly image the drainage of the medium by the
non-wetting oil and subsequent imbibition by the wetting fluid. During
imbibition, the wetting fluid pinches off threads of oil in the narrow crevices
of the medium, forming disconnected oil ganglia. Some of these ganglia remain
trapped within the medium. By resolving the full 3D structure of the trapped
ganglia, we show that the typical ganglion size, and the total amount of
residual oil, decreases as the capillary number Ca increases; this behavior
reflects the competition between the viscous pressure in the wetting fluid and
the capillary pressure required to force oil through the pores of the medium.
This work thus shows how pore-scale fluid dynamics influence the trapped fluid
configurations in multiphase flow through 3D porous media.

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Article

Monocrystals of calcium tartrate tetrahydrate, neodymium-doped calcium tartrate tetrahydrate, and cuprous chloride have been grown by controlled diffusion in silica gel using both metathetical and decomplexation reactions. Conditions for the optimum growth of the crystals are given and it is shown how the pH of the gel, the temperature of its formation, the concentration of the reactants which make up the gel, and the concentration of the reactants which result in the crystal are important in attaining good single crystal products. Crystals have been grown up to 11 mm. on edge in three to four weeks, and in many cases take on a form which, to all outward appearances, seem to have been cut and polished.

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Article

Commonly encountered 'passive' insulation has been improved in recent years using 'dynamic'insulation based on closed cycle cryocoolers attached to photon shields. The paper presents a novel insulation performance measure based on ideal thermodynamic limits. Each floating insulation package has a unique value. In contrast real vessels with vent tube and supports are characterized by an 'effectiveness' less than unity.

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Article

Models for unsteady water transport in fuel cell configurations of Bacon-Pratt and Whitney type are derived. Tests with a specially constructed isothermal cell producing no water and order of magnitude analysis show that diffusion through the liquid alone cannot account for the observed behavior. An analytical solution which includes diffusion in both the liquid and the gas spaces of the matrix is in better agreement with the data than models which consider diffusion in either the liquid or in the gas phase alone.

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Article

A comparison of the kinetic and diffusional models for solid-gas reactions occurring in a spherical particle is presented. The similarities and differences of the unreacted-core shrinking model and the homogeneous model are examined in light of the rate-controlling factors. In view of the similarity of the two models, it is shown that erroneous conclusions in regard to the mechanism and the activation energies may be drawn from an analysis of the experimental data. A more versatile model is presented in order to augment the two models so that wider varieties of solid-gas reaction systems may be treated. The concept of effectiveness factors in solid-gas reactions is introduced, and the influence of diffusion is ascertained.

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Article

A stochastic model of particle dispersion by turbulence, proposed by Gosman and Ioannides (1981), is evaluated. The method employs a k-epsilon model to estimate turbulence properties. Dispersion is determined by computing particle motion, with random sampling to obtain instantaneous flow properties for a statistically significant number of particle trajectories. The stochastic model yields good results particularly when eddy lifetimes are evaluated. The method allows the effects of large relative velocities between the particles and the flow, drag properties at Reynolds numbers greater than the Stokes flow regime, and the variations of local turbulence properties to be readily handled, at least for boundary layer flows.

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Article

A linearized stability analysis has been applied to a fluid flowing in a gravity field between horizontal planes in Couette flow under conditions such that the temperature of the bottom plane exceeds that of the top. It is shown that, under conditions likely to be encountered with polymer solutions, oscillatory instabilities will not be controlling. Criteria are offered for ascertaining when an analysis based upon a second-order fluid model may be expected to yield physically meaningful results. It is also shown that, for the fluid model considered, critical conditions for stability are not changed when disturbances which vary in the flow direction are substituted for those which are a function of the coordinate transverse to the flow.

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Article

Drag reduction prediction in turbulent flow with viscoelastic model, discussing solutions exhibiting elastic properties in laminar flow

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Article

The solvent extraction features mass transfer between drops and the surrounding immiscible liquid. Previous study indicated that drop formation plays an important role in extraction because 10–50% of total mass transfer occurs in this stage. It is necessary to have thorough understanding about the mechanism of mass transfer between the drop phase and continuous phase during drop formation. In this work, the level set approach was adopted to capture the interface, and unsteady mass transfer during drop formation was formulated and numerically simulated in an axisymmetric cylindrical coordinate system by solving the fluid motion coupled with mass transfer equations. Drop formation time and mass transfer parameters from the numerical simulation were compared with experimental data in the MIBK–acetic acid–water solvent extraction system. The numerical predictions were found in good agreement with the experimental measurements.

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Article

Fuel cell cavities, analyzing fluid motion purge dynamics based on anisotropic porous media model

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Article

The conductivity of highly charged membranes is nearly constant, due to
counter-ions screening pore surfaces. Weakly charged porous media, or "leaky
membranes", also contain a significant concentration of co-ions, whose
depletion at high current leads to ion concentration polarization and
conductivity shock waves. To describe these nonlinear phenomena the absence of
electro-osmotic flow, a simple Leaky Membrane Model is formulated, based on
macroscopic electroneutrality and Nernst-Planck ionic fluxes. The model is
solved in cases of unsupported binary electrolytes: steady conduction from a
reservoir to a cation-selective surface, transient response to a current step,
steady conduction to a flow-through porous electrode, and steady conduction
between cation-selective surfaces in cross flow. The last problem is motivated
by separations in leaky membranes, such as shock electrodialysis. The article
begins with a tribute to Neal Amundson, whose pioneering work on shock waves in
chromatography involved similar mathematics.

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Article

A method is presented for a relatively accurate, noniterative, computationally efficient calculation of high-pressure fluid-mixture equations of state, especially targeted to gas turbines and rocket engines. Pressures above I bar and temperatures above 100 K are addressed The method is based on curve fitting an effective reference state relative to departure functions formed using the Peng-Robinson cubic state equation Fit parameters for H2, O2, N2, propane, methane, n-heptane, and methanol are given.

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Article

Book on fuel cells electrochemistry covering direct energy conversion methods, electrode kinetics, electrocatalysis, organic substances, electrochemical combustion, research techniques, etc

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Article

The design and operation of a differential Polymer Electrolyte Membrane (PEM) fuel cell is described. The fuel cell design is based on coupled Stirred Tank Reactors (STR); the gas phase in each reactor compartment was well mixed. The characteristic times for reactant flow, gas phase diffusion and reaction were chosen so that the gas compositions at both the anode and cathode are uniform. The STR PEM fuel cell is one-dimensional; the only spatial gradients are transverse to the membrane. The STR PEM fuel cell was employed to examine fuel cell start- up, and its dynamic responses to changes in load, temperature and reactant flow rates. Multiple time scales in systems response are found to correspond to water absorption by the membrane, water transport through the membrane and stress-related mechanical changes of the membrane.

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Article

Methods for estimating the volume of the critical temperature used for the estimation of thermodynamic properties of substances are described. The possibility to estimate the critical temperature by using a combination of only eighteen atomic and structural contributions is shown. These contributions are listed and the critical temperature is given by a linear expression. By comparing the Vetere (1976) and Lydersen (1955) methods with the method discussed it is noted that while all three methods yield about the same average error (about 3%), the new method is superior in that it requires a smaller number of increments to fit data points.

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Article

Effective experimental and theoretical techniques for studying the heat transfer characteristics of a stationary evaporating meniscus formed on a flat plate immersed in a pool of liquid were developed. Integral heat transfer data were obtained for the four systems: 304 stainless steel-water, 6061 aluminum-water, 304 stainless steel-methanol, and 6061 aluminum-methanol. High rates of heat transfer were obtained in the triple interline region with a stable meniscus. Detailed descriptions of the heat flux and temperature field were obtained for the stainless steel-water and stainless steel-methanol systems. The effect of the evaporation coefficient on the heat flux distribution was evaluated. The heat transfer process in the interline region proved to be more efficient than a simple conduction process in an evaporating liquid meniscus.

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Article

Nonuniform sidewall heat flux effect on thermal stratification

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Article

The phenomenological theory previously prsented for describing the rheological properties of non-Newtonian materials was applied to two polymer solution systems. The basic shear diagram is needed over a wide range of shear rates and polymer concentrations, and such data are not readily available; however, what could be found supported the analysis. In order to confirm the theory further, ten solutions of polymethylmetacrylate in diethyphthalate with concentrations up to 55% were investigated at 40°C. The results indicated that the forward and reverse orders were 1 and 2 respectively and that the two parameters of the theory (a susceptibility to shear term and an equilibrium type of constant) were constant over the range of concentrations investigated. The flow data were reproduced to within a few percent for all solutions, although the errors were large for the very dilute concentration, where experimental difficulties precluded obtaining reliable data. The method allows correlation of polymer solution data over the range from lower to upper Newtonian viscosities and over a wide concentration range.

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Article

Complex viscosity relationship to steady state shearing in Maxwell Orthogonal Rheometer

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