bluuebunny/crossref_metadata_2025_split huggingface dataset:
Form factors for deformed spheroids in stokes flow
Authors: O'Brien Vivian 
Published: June 2004

AbstractClosed analytic Stokes flow solutions for general shapes are quite improbable, but semianalytic numerical procedures allow flow calculations for a variety of shapes. The change in drag with change in shape from a sphere, here expressed in terms of a form factor, is discussed and compared to empirical shape factors developed from sedimentation experiments.
Iterative techniques in optimization I. Dynamic programming and quasilinearization
Authors: Lee E. Stanley 
Published: June 2004

AbstractThe quasilinearization technique is used to overcome the dimensionality difficulties of dynamic programming. The approach is based on the fact that if the difference or differential equations are linear, their closed forms ofsolution can be obtained. This solution permits us to separate the effects due to the initial state from the effectsdue to the control variables. By using this separation combined with quasilinearization, the dimensionality of the functional equation of dynamic programming can be reduced to one in most cases. First, the optimization problem in cross‐current extraction with discontinuous objectionfunction is used to illustrate the technique. Then the technique is generalized to systems of difference and differential equations with fairly general objective functions.
An approximate solution for countercurrent heat exchangers
Authors: Tien Chi , Srinivasan Seshadri 
Published: June 2004

AbstractAn approximate solution is presented for the countercurrent parallel plate exchanger with laminar flow. With the use of the integral method, the problem is reduced to one of solving a pair of first‐order differential equations in a straightforward manner. Comparisons between the results of this work and those obtained from a more elaborate orthogonal expansion technique are found to be excellent.
Liquid film flow‐rates in two‐phase flow of steam and water at 1000 lb./sq. in. abs
Authors: Singh Kuldip , Pierre C. C. St. , Crago W. A. , Moeck E. O. 
Published: June 2004

AbstractA knowledge of liquid‐film flow rates is important for design purposes when accurate predictions are required of the conditions under which dryout heat flux occurs in nuclear reactors and boilers. Liquid‐film flow rates were measured for a steam‐water mixture in cocurrent, upward annular flow in a tube at a pressure of 1,000 lb./sq.in.abs. Sinters located at the test section exit were used to extract the liquid film after the method of the Harwell group. Sinter lengths of 2, 1, and 1/2 in. were employed to investigate the effect of length on the extracted liquid flow rates. The test section was a stainless steel pipe of inside diameter 0.493 in., approximately 200 diam. in length. The total mass flux ranged from 0.2 to 0.7 × 106 lb.m/hr.sq.ft. and the quality varied from 0.3 to 0.92.The experimental film flow rates were found to increase with decreasing quality. In the range of parameters investigated, the curves of film flow rate at constant quality vs. mass flux showed a maximum at a fixed value of steam velocity. At the same total mass flux and quality the film flow from the 1/2 in. sinter was lowest, suggesting that the crests of high amplitude roll waves overshot the sinter. Film flow rates were consistently higher than the theoretical predictions using Levy/s model. About one‐third of the measured flow rates were twice as high as predicted.
The estimation of parameters for a commonly used stochastic model
Authors: Sweet A. L. , Bogdanoff J. L. 
Published: June 2004

AbstractA region into which particles arrive in a random manner, remain a random amount of time, and then leave is considered. This model is used in penetration theories of heat and mass transfer. From observations of the number of particles present at any time, it is desired to estimate arrival and exit statistics, residence time statistics, and average rates of transfer across the region. Assuming arrival is a Poisson process, equations governing the above statistics are derived. Some problems in spectral analysis arising from the use of nondifferentiable stochastic processes are solved. Estimators for important parameters are discussed, and it is shown that generally they are biased. A derivation linking the rate of transfer across the region with the rates of transfer of particles is obtained and compared with other such results.
The direct determination of the effect of pressure on enthalpy of a mixture of methane and propane
Authors: Mather A. E. , Powers J. E. , Katz D. L. 
Published: June 2004

AbstractA new throttling flow calorimeter has been incorporated into the recycle facility of the Thermal Properties Laboratory. Energy is added to the expanding gas while it flows through a stainless steel capillary tubing from an insulated resistance wire located inside the entire length of the capillary. The calorimeter is designed to operate at pressures up to 2,000 lb./sq.in.abs. in the temperature range from −240 to +250°F.Data on the isothermal effect of pressure on enthalpy for a mixture containing 5 mole % propane in methane are presented and compared with data from the literature.
Transport of toluene through fully swollen polyethylene
Authors: Coughlin Robert W. , Pollak Frank A. 
Published: June 2004

AbstractExperiments have been carried out to measure the permeation of tritium‐labeled toluene through polyethylene films fully swollen with chlorobenzene, mesitylene, cumene, toluene, ethylbenzene, cyclohexane, tetrahydronaphthalene, and decahydronaphthalene. The results show characteristic Arrhenius temperature dependence over the range 25 to 40°C. The permeation of toluene through the films appears to be enhanced by increased solubility of the swelling agent (estimated from the work of others) in the film and there also appears to be a rough correlation between permeability of toluene and the boiling points and vapor pressures of the swelling agents. The range of permeabilities measured at 25°C. is 2.09 × 10−7 to 0.51 × 10−7 sq.cm./sec., the extremes of measured permeation activation energy, Ep, are 11.41 to 16.68 kcal./mole, and the pre‐exponential factor, Po, falls within the interval 36.59 to 1.29 × 105 sq.cm./sec. A very definite linear relationship or compensation effect is evident between Po and Ep. Except as mentioned above, none of these quantities appears to correlate uniformly with the following properties of swelling solvent: molecular weight, dipole moment, specific gravity, vapor pressure, boiling point, heat of vaporization, critical temperature, viscosity, surface tension, molar volume, molecular area or other molecular dimensions.
Effects of ultrasonic vibrations on heat transfer to liquids by natural convection and by boiling
Authors: Wong S. W. , Chon W. Y. 
Published: June 2004

AbstractThe effects of ultrasonic vibrations on heat transfer to water and methanol by natural convection and by boiling were measured at three ultrasonic energy levels with frequency ranging from 20.6 to 306 kcycles/sec., using electrically heated platinum wires of diameters 0.007 and 0.010 in. Up to an eight‐fold increase in heat transfer coefficient was obtained in natural convection, but the effects diminished with increased temperature difference and became negligible in the well‐developed nucleate boiling region. High‐speed photographs showed that the increase was due to the motion of cavitation bubbles on the wire surface. The heat transfer results were correlated by local cavitation activity values measured by a technique developed for this work.
Stable explicit difference approximations to parabolic partial differential equations
Authors: Liu Shean‐Lin 
Published: June 2004

AbstractA finite‐difference method is developed for numerical solution of parabolic partial differential equations. This technique is explicit and stable. It is shown that the present method is more accurate and faster, in terms of computer time, than the Crank‐Nicholson method. A method of handling nonlinear problems is also presented. Two examples are given to illustrate the present technique. The first problem is a linear diffusion equation. The second problem deals with two simultaneous nonlinear parabolic partial differential equations with Neumann boundary conditions describing the steady state of a packed‐bed catalytic reactor with radial mixing.
Optimization of complex chemical plants by a gradient technique
Authors: Lee E. Stanley 
Published: June 2004

AbstractThe gradient technique and Lagrange multiplier are used to obtain the optimum of complex chemical plants. The advantage of this approach is its ability to handle nearly all types of complex stages in a natural way. This approach is used to solve a heterogeneous complex chemical process with recycle. It is shown that although there are many different iteration loops, the convergence rate is fast even with rough starting values and only 0.3 minute is needed to obtain the optimum operating conditions.
Mass transport in porous materials under combined gradients of composition and pressure
Authors: Gunn Robert D. , King C. Judson 
Published: June 2004

AbstractAn expression is derived for the analysis of gas‐phase mass transport in porous media in the presence of gradients in pressure and mole fraction. The behavior of porous media is contrasted with that of capillary tubes. A continuous‐flow diffusion and permeation apparatus was employed for studies of mass transport in a fritted glass diaphragm. Measurements were obtained at varying levels of pressure and cover both isobaric binary diffusion and the permeation of pure gases and gas mixtures. These experimental results and previous data obtained by Hewitt and Sharratt and by Mason, et al. bear out the form of the equation and successfully provide independent checks of the three constants necessary to characterize a given porous medium.
Drying polymers during screw extrusion
Authors: Coughlin R. W. , Canevari G. P. 
Published: June 2004

AbstractPartial removal of dissolved or absorbed solvent from polymers can be accomplished during the process of screw extrusion. This paper shows how two simple transport models based either on an effective diffusivity or on an empirical mass transfer coefficient can be combined with the fluid mechanical equations which describe polymer flow during screw extrusion. In this way, the drying of solvent from a polymer during extrusion can be correlated in terms of the design and operating parameters of the extruder screw and a mass‐transfer coefficient or an effective diffusivity. This approach is illustrated employing data obtained by using two extruders of different size and two different solvent‐polymer systems. Furthermore, it is pointed out how the results can be used to predict the extent of drying during screw extrusion as well as how modifications in extruder‐screw design can permit more extensive drying of polymers during the extrusion process.
Drop formation from cylindrical jets in immiscible liquid systems
Authors: Meister Bernard J. , Scheele George F. 
Published: June 2004

AbstractA theoretical analysis is presented for predicting the size of drops formed from a laminar cylindrical jet when one Newtonian liquid is injected through a nozzle into a second immiscible Newtonian liquid. The analysis couples stability theory with the requirement that the disturbances travel at the same velocity as the jet interface. Comparison of the theory with experimental data for thirteen mutually saturated liquid‐liquid systems covering a wide range of physical properties shows a mean error of 11.7% in prediction of the specific surface.
A comparison between rheological data for polymer melts and the Spriggs four‐constant viscoelastic model
Authors: Denson C. D. , Prest W. M. , O'Reilly J. M. 
Published: June 2004

AbstractAn experimental and analytical study was made to determine how well the material functions, derived from the Spriggs four‐constant viscoelastic model, could describe the rheological properties of polymer melts. Viscosity and elasticity of selected polymer melts were experimentally determined in the rotational and oscillatory modes using a Weissenberg Rheogoniometer. The Spriggs model was chosen for study because of its success in describing experimental data for polymer solutions and because of its uniqueness in combining results from molecular theory with results from the theories associated with continuum mechanics. It was found that the model provides a good description of the rheological data for polymer melts and that some of the model parameters depend upon the molecular characteristics of the polymer. Since this model contains a small number of well defined constants, it should be useful in developing dimensionless engineering correlations for the complex flows encountered in processes of industrial importance. Deviations between the theoretical and experimental results are discussed and deficiencies of the model noted.
The dynamic modeling, stability, and control of a continuous stirred tank chemical reactor
Authors: Ramirez W. Fred , Turner Brian A. 
Published: June 2004

AbstractA realistic CSTR model was developed and verified experimentally. The reaction studied was the exothermic, base sodium hydroxide catalyzed decomposition of hydrogen peroxide. The model was used to evaluate the usefulness of the following stability analyses: steady state analysis, local linearization and Liapunov's direct method through Krasovskii's theorem. The effect of control valve hysteresis on the system was also investigated.
Saturated‐liquid and vapor densities for polar fluids
Authors: Halm Roland L. , Stiel Leonard I. 
Published: June 2004

AbstractRelationships have been developed for the saturated‐liquid density and the compressibility factor of saturated vapors by an extension of Pitzer's acentric factor approach. The fourth parameter for polar fluids defined previously by the authors in terms of the vapor pressure was utilized. For the saturated‐liquid density and the critical compressibility factor quadratic terms were necessary to accurately represent the data for a wide range of normal and polar fluids including large polar molecules. Comparisons for substances not used in the development of the relationships indicate that good results can be obtained for polar fluids by the method of this study.
Gaseous diffusion in the transition pressure range
Authors: Mistler T. E. , Correll G. R. , Mingle J. O. 
Published: June 2004

AbstractMeasurements of the effective self‐diffusion coefficients for carbon dioxide and methane were performed in the transition pressure range. The experiments utilized carbon‐14 tagged gases and semiconductor radiation detectors in a transient type of experiment. A detailed analysis of the errors associated with the experiments indicated that the accuracy of the measurements was near 5%. The results verify that the additive resistance law is valid for the representation in the transition range. The unknown effects of surface diffusion make the values to be employed in this law subject to review. As an example one surface diffusion model is considered.
Temperature gradients in turbulent gas streams: Investigation of the limiting value of total prandtl number
Authors: Chia Wu‐Sun , Sage B. H. 
Published: June 2004

AbstractMeasurements of the total viscosity and total conductivity were made as a function of position and Reynolds number for the flow of air between two parallel plates with a separation of approximately 0.7 in. The temperature of the upper plate was 130.0°F. and that of the lower plate 70.0°F. The investigations were carried out at Reynolds numbers from 40,000 to 100,000 and were in good agreement with earlier data obtained at Reynolds numbers up to 40,000. The results obtained indicate little change in the total Prandtl number with increasing Reynolds number from the value of the molecular Prandtl number.
Performance of tray columns operated in the cycling mode
Authors: Gerster J. A. , Scull H. M. 
Published: June 2004

AbstractTray efficiencies were measured for desorbing ammonia from water by air in a small sieve‐tray column operated in the cycling mode, that is, with alternate flow of vapor and liquid. The actual efficiency improvement obtained was compared with that theoretically possible assuming the liquid flows without mixing when dropped. A mixing model was proposed and the mixing parameter evaluated from the experimental data.
Two‐phase flow through porous media
Authors: Slattery John C. 
Published: June 2004

AbstractIn the context of a previously proposed new description for multiphase flow through porous media, we examine constitutive equations for gi, the force per unit volume which phase i exerts upon the pore walls and other adjacent fluids. The principle of material difference is used to determine the most general dependence of gi upon saturation gradient for a nonoriented (no porosity gradient) permeable structure.Three problems are solved and the results compared with analyses based upon our interpretation of Muskat's equations. The first concerns a semi‐infinite porous column in air, the bottom of which is saturated with a liquid. The same saturation distribution is found with our approach as with Muskat's equations.The analysis of the second problem indicates the relation between our relative permeability and that of Muskat.The jump balances for mass and for momentum at a surface of discontinuity (or shock wave) with respect to volume averaged variables are derived. The significance of solutions in which such surfaces of discontinuity appear is discussed.In the third problem, a plane surface of discontinuity with respect to local saturation moves through an infinite permeable structure. This is similar to the displacement of oil by an aqueous solution in a secondary recovery process. The results are comparable to those with Muskat's equations only in the limit where capillary pressure is neglected (the Buckley‐Leverett case). When capillary pressure differs from zero, Muskat's equations do not admit a shock wave solution.
Stabilizing effects of surface‐active agents on a film flow
Authors: Lin S. P. 
Published: June 2004

AbstractThe effects of surface‐active agents on the stability of a liquid film is reinvestigated. The present analysis differs from the previous works in the treatment of the surface boundary conditions. The well‐known damping and stabilizing effects of surface‐active agents are shown to be due to the redistribution of surface material caused by wave motions and diffusion. The equations of neutral stability for both cases of soluble and insoluble surface‐active agents are obtained.
Perturbation chromatography in chemically reactive systems
Authors: Deans H. A. , Horn F. J. M. , Klauser Gernot 
Published: June 2004

AbstractA one‐dimensional column is considered in which a number of chemical reactions with arbitrary kinetics may take place among an arbitrary number of components. Initially, the column is in complete chemical and physical equilibrium. A localized small perturbation is introduced in the column at time t = 0. It is shown that, in general, this initial perturbation separates into a definite number of peaks which move with different velocities. Each peak broadens according to an asymptotic relation, depending on a characteristic dispersion coefficient. If n is the number of components, m the number of independent reactions, and σ the number of equations of state to be considered, there are n‐m‐σ peaks. These peaks do not correspond to single substances as in classical chromatography, but each peak has an eigencomposition. The velocities of the peaks are derived as functions of stoichiometry and equilibrium data. The dispersion coefficients depend, in addition, on the kinetics of the chemical reactions and on the rate of mass transfer. Thus, perturbation chromatography offers a means of determining both equilibrium and rate data. The theory is illustrated by means of two examples.
Momentum, heat, and mass transfer to a continuous cylindrical surface in axial motion
Authors: Vasudevan Ganapathy , Middleman Stanley 
Published: June 2004

AbstractThe transport equations for the region exterior to a cylindrical jet issuing continuously from an orifice are solved through the introduction of a similarity transform. The possibility of mass transfer normal to the jet is allowed. Of particular interest are the local transport coefficients (Cf, NNu, NSh) and their dependence on the rate of transfer from the jet.
The effect of Lewis number on the stability of a catalytic reaction
Authors: Lee James C. M. , Luss Dan 
Published: June 2004

AbstractAn extensive numerical study was carried out to determine the effect of Lewis number on the stability of a chemical reaction occurring inside a porous catalyst pellet. It is found that when the Lewis number is different from 1, the coupling between the concentration and temperature causes several pathological effects during the transient periods. One of the most interesting phenomenon is the occurrence of a unique unstable steady state with a periodic appearance of a very hot spot.
Predictive feedback control of a continuous flow stirred tank reactor
Authors: Huber C. I. , Kermode R. I. 
Published: June 2004

AbstractA novel feedback control system, called apredictive feedback control system, is developed for the regulation of the exit composition of a continuous flow stirred tank reactor (CFSTR). The control system utilized two basic feedback signals. One is the effluent concentration of the composition to be controlled. This is measured by a batch type of composition analyzer such as a chromatograph. The other is a predictive feedback signal which continuously predicts the difference between the actual value of the controlled variable and the measurement supplied by the analyzer. The predictive signal is generated from a plant model which approximately relates the controlled variable and the continuously measured reactor temperature.Unlike direct feedback control systems, the stability of the predictive system is unaffected by the periodic sampling and time delays introduced by the batch analyzer. Moreover, at steady state the predictive feedback signal disappears, and, like direct feedback systems, predictive feedback systems yield very accurate steady state control.A computer simulation of the predictive feedback control of a particular CFSTR has shown that predictive control is considerably more effective in composition control than conventional direct feedback control, is more effective than conventional temperature control, and retains the advantages of direct feedback control while partially eliminating the undesirable effects caused by the batch analyzer.
The Mechanism of heat transfer in a spray column heat exchanger: II. Dense packing of drops
Authors: Letan Ruth , Kehat Ephraim 
Published: June 2004

AbstractTemperature profiles of water in a spray column heat exchanger, 15 cm. in diameter and 150 cm. long, operating with a dense packing of kerosene drops, were measured. The range of superficial velocities was 0 to 0.8 cm./sec. of water and 0.5 to 1.7 cm./sec. of kerosene. The bottom of the dense packing was either slightly above or 15 cm. below the bottom of the column proper.The physical picture of heat transfer is similar to that for dispersed packings of drops and emphasizes the dominant role of wakes in the heat transfer mechanism. The mathematical equations for dispersed packings of drops were modified to take into account the reduction of wake size at the interface of the two packings and the difference in the mixing patterns at the top of the column. An empirical allowance for the effect of bypassing is suggested. The volume of the wakes and the rate of wake shedding were estimated from the temperature profiles. General agreement was found between the theory and the experimental data of this and three other studies.