bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prediction of the first normal stress difference in polymer solutions
Authors: Meister Bernard J. , Biggs R. Dale 
Published: June 2004

AbstractShear stress and first normal stress difference data are presented for several polymer solutions undergoing steady shear rates from 1.0 to 100,000 sec.−1. The steady shear response is divided into three regions as a function of increasing shear rate. These are the diffusion controlled linear region, a moderate shear rate region where shear controls the entanglement‐disentanglement process, and a high shear rate region where aggregation of polymer molecules occurs. The transitions between the three regions are clearly illustrated by using a group designated as the rotation rate function.A molecular model is derived for the shear controlled region that allows prediction of the first normal stress difference from the viscosity function and one additional constant that depends only on the molecular species. The White‐Metzner equation is found to adequately describe the aggregation region at high shear rates.
An experimental study of steady state multiplicity in a loop reactor
Authors: Root R. B. , Schmitz R. A. 
Published: June 2004

AbstractSteady state multiplicity in an adiabatic loop reactor was studied in experiments employing the reaction between sodium thiosulfate and hydrogen peroxide in aqueous solution. The steady state characteristics of the loop reactor were predicted by a method which utilized batch reactor data of temperature vs. time directly. The method was based on the assumption of plug flow with negligible axial dispersion and on a single‐step chemical kinetic model. Experimental results verify the existence of multiple steady states on ranges of feed flow rates and recycle ratios and demonstrate the capability of the simple model for predicting the qualitative and quantitative features of the reactor steady state.Some observations were made of the effect of large disturbances on the stability of the reactor while operating in a multiple state region. Results for such cases illustrate reactor instability in the sense that a transition to a new steady state takes place provided the disturbance is sufficiently large.
On the structure of dissolving thin liquid films
Authors: Suciu D. G. , Smigelschi Octavian , Ruckenstein Eli 
Published: June 2004

AbstractThe structure of thin circular films, formed over a flat water surface during the dissolving (influenced by surface forces) of isobutanol, is examined by performing film thickness and surface velocity measurements. The thicknesses were obtained by light absorption determinations, and the velocities by a stroboscopic method. The film profiles and the dynamic wetting angles obtained differ markedly from those corresponding to a static lens. This is explained by considering the equilibrium between dynamic surface tensions instead of that between static surface tensions.
Physical effects in red blood cell trauma
Authors: Nevaril C. G. , Hellums J. D. , Alfrey C. P. , Lynch E. C. 
Published: June 2004

AbstractRed blood cell damage and destruction are important problems in the use of artificial valves, heart‐lung machines, and other devices which pump or process blood. An experimental study has been made on the mechanism of cell damage. Damage was defined by three types of observations on blood which had been subjected to trauma: (a) release of hemoglobin from cells (hemolysis), (b) morphological changes observed microscopically, and (c) red cell life span studies in rabbits using a Cr51 tagging technique.Three types of physical forces which might be injurious to red cells were studied; shearing stress (of known, constant magnitudes from a concentric cylinder viscometer), pressure variations (from studies in a static pressure cell), and direct impact of solid surfaces (from studies in a device which simulates the seating action of artificial heart valves).The study shows that high shearing stress may be primarily responsible for mechanical cell damage under certain important circumstances. There is a critical shearing stress above which cell damage increases markedly. Much of the cell damage does not appear as an immediate release of hemoglobin. Many cells undergo morphological changes and exhibit shortened average life span in vivo. The morphological changes due to shearing stress are very similar to the changes observed in patients who have hemolytic anemia associated with artificial valves.
Base film over which roll waves propagate
Authors: Woodmansee Donald E. , Hanratty Thomas J. 
Published: June 2004

AbstractThe liquid that moves along the duct walls in the annular regime observed in gas‐liquid flows often consists of a series of flow surges (roll waves) moving over a thin liquid film (base film). At a given gas velocity there is a critical flow rate of the liquid below which roll waves are not present. Measurements of the height and wall stress are presented to support the notion that the conditions in the base film are close to those which exist at the critical liquid flow rate.
Temperature—separation factor relationships in gaseous diffusion
Authors: Tock R. W. , Kammermeyer Karl 
Published: June 2004

AbstractA theoretical equation was developed to predict the enrichment produced by a single stage porous Vycor diffusion cell as a function of temperature. The separations of five binary gas mixtures were measured experimentally over a temperature range of 80 to 600°K. The agreement between theoretical predictions and experimental results was good over most of the temperature range. The largest deviations occurred when the operating temperature approached the critical temperatures of the gases. Mixtures of oxygen‐carbon dioxide and helium‐nitrogen were observed to become nonseparative at predicted temperatures. Overall, both separation and separative capacity were observed to increase with a decrease in temperature.
Mass transfer at the solid‐liquid interface for climbing film flow in an annular duct
Authors: Sutey A. M. , Knudsen J. G. 
Published: June 2004

AbstractA method utilizing a diffusion controlled electrochemical reaction was used to measure average and instantaneous mass transfer coefficients at the solid‐liquid interface in upward gasliquid climbing film flow in a vertical annular duct. These measurements give some indication of the mechanics of flow of the film, the extent of turbulence at the inner wall, and the effect of film thickness and wave motion on the mass transfer process at the inner wall. Predictions of incipient downflow of the film, shear stress at the inner wall, and interfacial shear stress were obtained from these measurements. Fluctuations in the velocity gradient at the inner wall were also studied. Results of this study are in good agreement with previous work and with theoretical predictions based on simplified momentum balance concepts.
A method for measuring particle diffusivity in two‐phase flow in the core of a duct
Authors: Briller Richard , Robinson Myron 
Published: June 2004

AbstractA relatively simple, reliable means is described for measuring particle diffusivity in a particlefluid system in the core of a duct. Particles are injected into the midstream of the duct from a line source positioned normal to the direction of fluid flow. Particle diffusivity is calculated from measurements of the standard deviations of the particle concentration profiles at various downstream distances from the injector. At an air velocity of 10 ft./sec. under room conditions, 1μ oil droplets are found to exhibit a diffusivity of about half that of air alone under the same conditions.
Effects of surfactants on mass transfer inside drops
Authors: Huang W. S. , Kintner R. C. 
Published: June 2004

AbstractA model is presented to account for reduced mass transfer to drops falling through a continuous phase which contains a surface active agent. The fluid flow patterns are essentially laminar. The reduction in mass transfer is said to be due to a reduction in available interfacial transfer area and to changes in both velocity and pattern of internal circulation. These are shown to be functions of contact time and can be characterized. Experimental values agreed with the theoretically predicted ones with a deviation of less than 10%.
Diffusion in pulsating flow in a distensible conduit
Authors: Fagela‐Alabastro Estrella B. , Hellums J. D. 
Published: June 2004

AbstractAn earlier study on interphase mass transfer in pulsating laminar flow has been extended to the case of a distensible tube. The physical situation studied corresponds to developed flow in a long tube with a traveling pressure wave of small amplitude impressed on the steady flow. The tube wall is free to expand radially. Asymptotic solutions are developed for large and small values of the frequency parameter. The interphase flux is much greater in distensible conduits than in the corresponding case in rigid conduits.
Heat transfer to solid‐vapor mixtures of cryogens below their triple points flowing through heated tubes
Authors: Jones M. C. , Giarratano Patricia J. , Simpson A. U. 
Published: June 2004

AbstractData 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.
The use of positive feedback control systems to improve reactor performance
Authors: Gaitonde N. Y. , Douglas J. M. 
Published: June 2004

AbstractPositive feedback control systems sometimes can be used to make stable chemical reactors generate periodic outputs. For one set of system parameters the time average conversion obtained from the oscillating reactor was approximately 20% higher than the economic optimum steady state value; for another case the time average operating cost was approximately 5% lower than that corresponding to the optimum steady state design. A general method for predicting when an improvement can be obtained is presented.
A digital simulation of transient oxygen transport in capillary‐tissue systems (cerebral grey matter). Development of a numerical method for solution of transport equations describing coupled convection‐diffusion systems
Authors: Reneau Daniel D. , Bruley Duane F. , Knisely Melvin H. 
Published: June 2004

AbstractThe mechanism by which oxygen is transported from capillaries into tissue for cell respiration has been a subject of interest since the work of August Krogh in 1919. Mathematical analyses of the diffusion process have been obtained by several investigators (11, 12, 18), but are limited in scope by the complicated nature of the problem. However, the solutions that exist give enough insight to inspire a more rigorous treatment. With the advant of electronic computers more complete analyses are now within reach (16).The human brain accounts for less than 4% of the total body weight, yet it uses 15 to 20% of the total body oxygen consumption. This high metabolic rate makes the brain particularly vulnerable to any change in the normal oxygen supply. The fact that following a cessation of cerebral blood flow, unconsciousness develops within 10 sec., and irreversible damage within 10 min., demonstrates the importance of understanding the dynamics of oxygen supply to the brain.
Viscoelasticity in shearing and accelerative flows: A simplified integral theory
Authors: Adams E. B. , Bogue D. C. 
Published: June 2004

AbstractAn 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.
Evaporation rates of volatile liquids in a laminar flow system: Part II. Liquid mixtures
Authors: Clark Michael W. , King C. Judson 
Published: June 2004

AbstractAn approach has been developed for predicting rates of interphase mass transfer under conditions of high flux and high concentration level. A rectangular channel device has been used to measure rates of evaporation of four solutes, carbon disulfide, n‐pentane, cyclopentane, and ethyl ether, from n‐tridecane into flowing nitrogen. The evaporation rate of carbon disulfide agreed with the prediction of the interphase theory up to a carbon disulfide mole fraction of 0.30 in the bulk liquid. For the other three systems, a concentration gradient induced, surface tension driven cellular convection served to increase liquid‐phase coefficients substantially. A correlation was obtained for the effect of this cellular motion on the liquid‐phase mass transfer coefficient.
Mass transfer in a nonuniform impinging jet: Part I. Stagnation flow‐velocity and pressure distribution
Authors: Scholtz M. T. , Trass Olev 
Published: June 2004

AbstractA theoretical solution for the impingement flow of a jet with a parabolic velocity distribution is given. Viscous generation and diffusion of vorticity in the jet were neglected. Experimental velocity and pressure distributions measured in an impinging jet of air originating with Poiseuille flow compare well with theory, thus justifying the assumption of inviscid flow. Pressure distributions on the deflecting surface were independent of nozzle height in the range 1 to 12 nozzle radii. For lower nozzle heights the effect of the constriction of flow between the nozzle and the surface followed the predicted behavior.
On the temperature field of a square column embedding a heating cylinder
Authors: Shih F. S. 
Published: June 2004

AbstractAn analysis of the two‐dimensional temperature field of a square column embedding a heating cylinder is presented. The analysis leads to a solution in finite series which gives rise to rapidly converging numerical results. The series coefficients computed for the extreme case of the cylinder being a line find a way of parametrization, which then furnishes the solutions for finite cylinders up to the case of the cylinder diameter being half of the column thickness. Results in five‐digit accuracy are presented. The method is simple and direct. In addition, it retains the same concise formal solution for a variety of boundary conditions.
Transitional flow in concentric annuli
Authors: Rothfus R. R. , Newby R. A. 
Published: June 2004

AbstractA general means is proposed for predicting transitional velocity patterns in concentric annuli and between parallel plates from behavior in tubes. As in laminar and turbulent flow, transformations of space coordinates yield identical profiles under specific conditions of comparison. Predictions are confirmed by published data and can be related to recent theoretical proposals.
Stability analysis of a continuous flow stirred tank reactor with consecutive reactions
Authors: Sabo David S. , Dranoff Joshua S. 
Published: June 2004

AbstractThe stability of a continuous flow stirred tank reactor with consecutive chemical reactions A→B→C was investigated here for the first time. The system equations were integrated numerically, and parts of the three‐dimensional phase space were generated for systems having one and three steady states, respectively.The surface separatrix was determined by trajectory plotting after extensive computation. The system was also analyzed by Liapunov's second method. Krasovskii's form was used to generate Liapunov functions which proved to be satisfactory but extremely conservative in the estimation of the largest possible regions of asymptotic stability.
A probabilistic time delay description of flow in packed beds
Authors: Buffham B. A. , Gibilaro L. G. , Rathor M. N. 
Published: June 2004

AbstractA simple model for describing residence time distributions (RTD) in packed beds is derived and applied to a trickle flow system. It is based on the concept of fluid elements being randomly delayed in time on their passage through the bed and leads to a simple and flexible mathematical description.
Wiener‐Hopf methods for unstable, nonminimum phase processes
Authors: Lim H. C. , Bankoff S. G. 
Published: June 2004

AbstractIt is shown that existing methods for design of optimal regulators by the Wiener‐Hopf procedure must be modified in order to be applicable to unstable and/or nonminimum phase plant or disturbance transfer functions, such as are frequently encountered in the chemical industry. Solutions are developed for three cases: I. stable, but possibly nonminimum phase, plant and disturbance transfer functions; II. minimum phase, but possibly unstable, plant with no restrictions on the disturbance transfer functions; and III. prestabilized, with a proper modification to retain the original control effort inequality constraints, but possibly nonminimum phase plant and disturbance transfer functions. Case III gives the general solution for regulation of linear, time‐invariant, lumped‐parameter systems. When prestabilization is not necessary, it reduces to case I. Where applicable, solutions by the method of case II frequently involve less algebra than in case III.
Wiener‐Hopf methods for unstable, nonminimum phase processes. Part II. Application to a Stirred Tank Reactor
Authors: Lim H. C. , Bankoff S. G. 
Published: June 2004

AbstractThe Wiener‐Hopf procedure for synthesis of optimum constrained linear feedback regulators has been extended in part I to all linear time‐invariant lumped parameter systems. The solution is here applied to the control of the output concentration of an exothermic, stirred tank reactor operating close to an unstable steady state, by constrained manipulation of a cooling water flow rate, in the presence of a randomly fluctuating inlet concentration.When the spectral density of disturbance is given (for example, white noise through a first‐order time delay, or a series of randomly alternating steps), the optimum controller has three modes: proportional, derivative, and integral with minor feedback. The responses of the nonlinear reactor and the linearized reactor control systems to a series of alternating deterministic step inputs and Gaussian distributed inputs are simulated, and a sensitivity study of the linearized system with respect to variations in process, controller, and disturbance parameters is made in order to demonstrate the feasibility of the method.
Simultaneous heat and mass transfer in free convection boundary layers
Authors: Saville D. A. , Churchill S. W. 
Published: June 2004

AbstractExpressions are derived for the heat and mass transfer coefficients for laminar free convection driven by simultaneous differences in temperature and composition for the asymptotic cases of equal Schmidt and Prandtl numbers approaching zero, equal Schmidt and Prandtl numbers approaching infinity, Schmidt number approaching infinity and Prandtl number approaching zero, and Schmidt number larger than Prandtl number and Prandtl number approaching infinity.The results are applicable for horizontal cylinders or vertical axisymmetric bodies with arbitrary body contours insofar as the approximations of boundary‐layer theory are valid. The results compare favorably with existing solutions and experimental results for particular conditions.
An experimental study of unstable states in a loop reactor
Authors: Root R. B. , Schmitz R. A. 
Published: June 2004

AbstractAn adiabatic loop reactor was operated at naturally unstable steady states in experiments employing the reaction between sodium thiosulfate and hydrogen peroxide in aqueous solution. The unstable states, the intermediate states in a multiple state regime, were stabilized by manual manipulation of the recycle ratio. Resulting temperature data agreed well with those predicted from a plug‐flow model. Observations of the transient response to small disturbances from the intermediate states verified that they were indeed unstable as had previously been predicted theoretically. Cursory attempts to stabilize the system by means of automatic feedback control employing a three‐mode controller were unsuccessful.
Characteristics of inclusions in the dispersed phase of liquid‐liquid suspensions
Authors: Kessler D. P. , York J. L. 
Published: June 2004

AbstractThe classical emulsion is made up of drops of one liquid dispersed in a containing liquid. Under certain circumstances, however, some of the containing phase may form drops within the drops of the dispersed liquid, giving rise to a structure known as a double‐multiple emulsion. This study was an investigation of the hydrodynamic formation of these structures.Double‐multiple emulsions were produced by using both transient and steady state liquid injection, with a cylindrical jet configuration. Analysis of the spray was by means of high‐speed photography.The distribution of the large drops and that of the included drops were both found to be represented satisfactorily by a log‐normal probability function. A simplified model based on the use of nozzle parameters satisfactorily correlated percent included area and volume as a function of Reynolds number and Weber number. Large dispersed phase drops contained proportionally many more inclusions than did the smaller sizes.The mechanism of inclusion formation was found to involve the drawing out of a ligament or sheet from the flowing jet, followed by the recoalescence of the free end of this ligament or sheet with the main jet body, entraining in the process a portion of the containing phase. Thus, the inclusions predate the formation of the drops of the dispersed phase from the jet disruption.
Liquid‐phase dispersion in packed beds with two‐phase flow
Authors: Furzer I. A. , Michell R. W. 
Published: June 2004

AbstractLiquid‐phase Peclet numbers have been measured for 1/4 in. Raschig rings with countercurrent air flow in a 2 in I.D. column. The response curve has been analyzed by a computer program, since the output data was collected directly on paper tape. The Peclet number calculated from a moments analysis is considered unreliable, and the diffusion model can be rejected for the liquid phase. If the Peclet number is calculated by a least‐squares fit, and if the result is forced through the peak in the response curve, then a correlation for over one hundred runs with gas flows from 0 to 99% of flooding is given by Equations (7) and (8).
Venturi and other atomizing scrubbers efficiency and pressure drop
Authors: Calvert Seymour 
Published: June 2004

AbstractParticle collection efficiency and gas pressure drop for venturi and other atomizing scrubbers can be predicted by means of equations developed in this paper. The significance of the details of the liquid atomization process, the collection of particles on single drops, and the uncertainty regarding them are discussed. The role of drop holdup in the scrubber throat is also important.