bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of convective velocity on longitudinal diffusivities in a fluidized cascade separator
Authors: Muzyka D. , Beeckmans J. M.
Published: March 2009

Experimental results are presented on the separation of trace quantities of charcoal particles from salt crystals in a counter‐current fluidized cascade, for a range of paddle velocities extending over two decades. Interpretation of these data suggests that longitudinal diffusivity D is a function of horizontal convective velocity vH. The dependence of D on vH is attributed to mechanisms similar to those occurring when a pulse of soluble dye is suddenly injected into a solvent flowing in a pipe or a capillary, a situation first analyzed by Taylor(1,2).

Experimental measurements were also made on the dispersion of a thin vertical layer of tracer material, following fluidized channel flow, using the same materials and conditions as were used in the fluidized cascade experiments. These data confirmed the general form of the dependence of D on vH found with the cascade, but yielded much lower values. The reasons for the discrepancy are not known, and further work is required to clear up this discrepancy.
Reliability and limitations of pulse chromatography in evaluating properties of flow systems: 1. modelling and experimental considerations
Authors: Gangwal S. K. , Hudgins R. R. , Silveston P. L.
Published: March 2009

Reproducibility of response characteristics and parameters derived therefrom, and adequacy of the Kubin‐Kucera model for pulse chromatography were investigated experimentally using the physisorption of methane and ethane on silica gel. Reproducibility was found to be excellent, while the agreement of predicted and observed effects of velocity, particle size, temperature and bed length on model parameters confirmed the adequacy of the model. Agreement of the pore diffusivity and the adsorption equilibrium constant with values measured by other techniques provide further support for the model. Rearrangement of model terms shows that the rate coefficient for physisorption and the mass transfer coefficient cannot be measured using chromatography.
Quasi‐Newton methods for convergence acceleration of cyclic systems
Authors: Soliman M. A.
Published: March 2009

This paper describes a version of Quasi‐Newton methods for solving a set of non‐linear algebraic equations. This method is simple, efficient, and requires little computer storage. This makes it suitable for the calculations of recycle streams in the simulation of chemical processes. Two examples are worked out to illustrate the good convergence of the present method as compared to commonly used methods.
Effect of drag‐reducing additives on free oscillatory flow
Authors: Mccomb W. D. , Ayyash S.
Published: March 2009

The damping rates of free oscillations in U‐tube manometers were measured in water and aqueous solutions of Polyox WSR 301, Separan AP273 and a wetting agent (Aerosol OT). The manometers were made from flexible plastic (PVC) or glass tube. Small reductions of the linear damping constant by low concentrations of Polyox and Aerosol additives in the PVC tubes were attributed to a reduction in surface tension effects. All the additives increased the linear damping constants in both types of manometer, when used at larger concentrations. This was found to be due solely to increased solution viscosity.

Large fractional reductions in damping due to Polyox in the PVC‐tube systemwere associated with the nonlinear oscillations in the final period of the decay. This effect has not yet been explained.
Economics of fermentation processes for SCP production from agricultural wastes
Authors: Mooyoung M. , Moreira A. R. , Daugulis A. J.
Published: March 2009

Twelve scenarios are considered as potential energy‐conserving processes for the simultaneous production of feed SCP and fuel gas from agricultural wastes. These scenarios are alternative schemes within three basic processing strategies that include either free‐standing anaerobic digestion systems or integrated anaerobic/aerobic fermentation systems. Material and energy balances were performed and used for preliminary process economic evaluations for farm‐based operations.

The free‐standing anaerobic fermentation systems, and some of the systems based on semi‐solid or liquid aerobic fermentations appear to be the most attractive ones with the present technical know‐how. Raw materials and energy are the major components of the final product cost, which can be dramatically reduced by technological breakthroughs now being developed. Sensitivity analyses reveal that scale of operation has a significant effect on the protein production cost. Projections made for a period of 5 and 10 years from the present indicate that the economic viability of the scenarios is better in future markets where protein costs are expected to increase rapidly.
Reliability and limitations of pulse chromatography in evaluating properties of flow systems II. end effects
Authors: Gangwal S. K. , Hudgins R. R. , Silveston P. L.
Published: March 2009

Dead volume cannot be avoided in measurements of kinetic and transport parameters using pulse gas chromatography. A criterion is derived for the bed volume necessary to make these dead volume effects negligible. Application of the criterion and assumptions made in its development are discussed.
Le rendement de deux réservoirs agités en série avec alimentation séparée, basé sur la cinétique de monod
Authors: Lo S. N. , Marchildon L. , Valade J. L.
Published: March 2009

The performance of a bioreactor composed of two chemostats in series can be affected significantly by the split of feed into two, one for each chemostat, for reactions following Monod kinetics. Under certain operating conditions, split of feed can be greatly beneficial to the reactor performance.

Optimization of performance is discussed; a general criterion is presented, applicable to either the maximization of overall conversion for a given total residence time or the minimization of total residence time for a given overall conversion. The maximization of overall conversion has also been studied with respect to the feed‐split ratio. The dimensionless Michaelis‐Menten constant is a very important parameter in the selection of optimal operating conditions.
Continuous emulsion polymerization of vinyl acetate. Part I: Experimental studies
Authors: Kiparissides C. , Macgregor J. F. , Hamielec A. E.
Published: March 2009

An interesting feature of commercial continuous emulsion polymerization reactors is the important phenomenon of sustained oscillations. Laboratory investigations of emulsion polymerization in a continuous stirred tank reactor (CSTR) have shown that the conversion, number of polymer particles and other related properties often oscillate widely with time. These oscillations can lead to emulsifier levels too small to adequately cover polymer particles resulting in excessive agglomeration and reactor fouling. Herein is reported an extensive experimental study of vinyl acetate emulsion polymerization in a CSTR. The effects of initiator and emulsifier concentrations, mean residence time and rate of agitation on the production rate and size distribution of polyvinyl acetate latices were investigated. Domains of reactor operation which give rise to sustained oscillations and massive agglomeration of the latex are mapped which give rise to sustained oscillations and massive agglomeration of the latex are mapped out. The effect of different start‐up policies on reactor transients were also investigated.
Continuous emulsion polymerization of vinyl acetate. Part III: Detection of reactor performance by turbidity‐spectra and liquid exclusion chromatography
Authors: Kiparissides C. , Macgregor J. F. , Singh S. , Hamielec A. E.
Published: March 2009

Herein is reported an experimental evaluation of turbidity‐spectra and of liquid exclusion chromatography (LEC) for the online and offline monitoring of polymer particle size during the continuous emulsion polymerization of vinyl acetate. It is shown that these analytical techniques satisfactorily follow the change of particle size for reactor operation under conditions of sustained oscillations.
Energetic aspects of turbulence promotion applied to electrolysis processes
Authors: Storck A. , Hutin D.
Published: March 2009

This paper presents a simple and rational method for determining how much hydrodynamic factors influence the rate of production in electrochemical systems using turbulence promoters in various alternative flow conditions.

Empirical and theoretical data correlations of limiting current densities (or mass transfer coefficients) and pressure drops are presented in unobstructed channels as well as for eddying flow induced by different types of eddy promoters.

Based on the dimensional analysis and on the experimental results, it is shown that, within a given range of variations, all the promoters have an equivalent energetic effectiveness.

However, when the conversion factor of the reacting species through the electrochemical reactor is near unity (complete transformation), this conclusion is no longer valid and the general methodology presented in this work shows that the rates of production present large differences depending on the system considered, the less sophisticated system (unobstructed channel) being the most effective.
Wave profiles on inclined falling film
Authors: Esmail M. N.
Published: March 2009

The profiles of waves travelling over the free surface of a liquid film, falling along an inclined flat wall, have been calculated, using a non‐linear technique of dynamic analysis. The wave profiles range from a simple nearly sinusoidal shape with small amplitudes, to a complicated profile close to solitary waves with high amplitudes. The results agree with earlier experimental observations, and are consistent with the results of the hydrodynamical theory of stability. Some of the solution trends have been observed to a lesser extent in previous non‐linear theories. It is clear that the phenomena associated with wave formation on a falling film, observed under the experimental conditions, arise because the problem is essentially non‐linear.
Interfacial tension from height and diameter of a single sessile drop or captive bubble
Authors: Malcolm J. D. , Elliott C. D.
Published: March 2009

The silhouette of a sessile drop submerged in a transparent bulk phase appears to possess a contact angle of 180° with a plane solid support, when the drop is separated from the solid surface by a thin film of surrounding fluid. A computer‐aided analysis of the generalized sessile drop form leads to an explicit equation for interfacial tension dependent only on drop height (from apex to solid support) and the magnitude of the drop equatorial diameter. The equation is valid for a wide range of physically realizable drops. Measurements of drop profile coordinates or the location of the drop equator are not required for the use of the method, leading to improvements in accuracy relative to current practice.
Exclusion of gas sparger influence on mass transfer in bubble columns
Authors: Deckwer W.‐D. , Hallensleben J. , Popovic M.
Published: March 2009

Gas phase CO2 concentration profiles were measured in two sizes of bubble columns with different gas spargers and with the liquid phase (tap water) entrance or exit (cocurrent or countercurrent flow) at a certain height above the gas distributor. The region of high turbulence intensity near the sparger was locally separated from the region of high mass transfer rates in such columns. A modified back flow cell model was applied to describe the experimental data. The kL‐values obtained from fitting the profiles agreed for both columns and, in addition, did not differ for cocurrent and countercurrent flow. This is in remarkable contrast to previous findings(10,11). The large influence of the gas sparger on the kL‐values even in tall bubble columns was thus demonstrated. It is thought that this may probably be one of the reasons why correlations for prediction of kL differ so significantly.
Extraction of whole fermentation broth with karr reciprocating plate extraction column
Authors: Karr A. E. , Gebert W. , Wang M.
Published: March 2009

The conventional equipment employed in the pharmaceutical industry for extracting fermentation broths is the centrifugal extractor. However, a recent case history indicates that the Karr Reciprocating Plate Extraction Column should be considered for such applications.

A pharmaceutical company had been using a Podbielniak centrifugal extractor to extract a whole fermentation broth. However, they could not feed the broth to the extractor unless they pretreated the broth by a “hand wash” or a preliminary batch extraction. Subsequently, it required three passes through the centrifugal machine to achieve the desired degree of extraction. On the other hand, with one pass through the Karr Column, essentially complete extraction was achieved. The advantages evident included a 55% reduction in solvent requirements, and substantially less capital cost, utilities cost, maintenance cost, and solvent losses.
The application of the characteristic method to shock tube data that simulate a gas pipeline rupture
Authors: Cronje J. S. , Bishnoi P. R. , Svrcek W. Y.
Published: March 2009

A numerical procedure is described to solve the equations for single phase, one dimensional, unsteady, compressible, frictional flow with heat transfer. The procedure is based on Hartree's ‘hybrid’ method for solving the governing hyperbolic partial differential equations. Computations for flows in a shock tube are presented which show good agreement with experimental data available for methane and argon.
Spray atomizer droplet spectrum measurement
Authors: Picot J. J. C. , Tomey T. D. , Smedley J. B. , Kristmanson D. D.
Published: March 2009

The gamma function distribution is used to discuss droplet size variation for flat fan and round orifice atomizers. A technique of using multiple‐probe devices to measure droplet size, distribution and flux when the form of the distribution is known is described. Experimental results with a four‐unit conductance probe device are given for a Spraying Systems Tee‐jet operating with a slightly conducting liquid at 4.2 dm3/s and at an air velocity of 75.6 m/s. Probe results give a mass mean diameter of 68 μm while the standard photographie method gives 78 μm. A material balance using probe results gives a liquid flow of 6.0 dm3/s. The accuracy of this method is easily improved by adding more units, but the restrictions of conducting liquid and the mechanical problems of probe construction and calibration indicate that optical probes should be investigated.
Surface area prediction for two phase drops in an immiscible liquid
Authors: Pinder K. L.
Published: March 2009

The three interfacial areas of a liquid drop evaporating in an immiscible continuous liquid have been measured from three‐dimensional still photographs. Five dispersed phases in water have been used.

From empirical correlations for the vapour bubble open angle and eccentricity with the physical parameters of the system, the initial drop diameter and the vapour ratio, the three interfacial areas may be predicted. The maximum error in the predictions were found to be ±5.2% for the liquid‐liquid area, ± 17.1% for the vapour cap area and ±15% for the internal vapour‐liquid area for drops of initial diameters less than 0.4 cm.
Aerodynamics of a vibrated fluid bed
Authors: Gupta Rahul , Mujumdar A. S.
Published: March 2009

Results of an experimental study on the aerodynamics of a vertically vibrated fluidized bed of cross‐section 0.2 × 0.2 m are presented and discussed. Variables studied included frequency (0‐105 s−1), amplitude (0‐5xl0−3 m), bed height (12.5‐100×10−3 m), particle size (900‐3900 μm), particle density (570‐890 kgm−3), particle shape factor (0.55‐1.00) and the particle surface characteristics, i.e. presence of surface moisture.

The effect of vibrational parameters on the fluidized bed pressure drop, the newly defined minimum mixing velocity, Umm and overall aerodynamic behaviour of the bed is discussed on the basis of quantitative as well as visual observations. Empirical correlations are proposed for δPmf and Umm, which were both found to decrease significantly with increase in the vibrational acceleration.
Effect of swirl and confinement on the flow and temperature fields in an inductively coupled r.f. plasma
Authors: Boulos Maher I. , Gagne Ronald , Barnes Ramon M.
Published: March 2009

A mathematical model was used for the calculation of the flow and temperature fields in the fire‐ball of an inductively coupled plasma (ICP) under confined and free discharge conditions taking into account gravity and swirl in the sheath gas. Computations were made for an argon plasma at atmospheric pressure operating at a power level of 3kW and a frequnecy of 3 MHz. Natural convection has a negligible effect on the flow and temperature fields under confined discharge conditions, but a significant effect, for the free plasma discharge. The back flow in the discharge was substantially reduced in the presence of swirl for swirl velocities over the range 0‐70 m/s. With a moderate increase in swirl, the conduction heat flux to the wall decreased but increased with the further increase in swirl.
Second‐law efficiency analysis of a coal gasification process
Authors: Rodriguez S. J. Luis , Gaggioli Richard A.
Published: March 2009

The present paper summarizes a comprehensive Second‐Law analysis of the SYNTHANE process of coal gasification(1), based on the available‐energy concept as applied to design conditions and data.

The analysis yields an overall process efficiency of 46%. For every 100 MJ of useful energy supplied with coal, 51 MJ are consumed during the various unit operations while effluents carry 3 MJ. Unit 30, Steam and Power Production, consumes nearly 20 MJ; Unit 15, Gasification, used up nearly 16 MJ; Units 12 and 14, Coal Preparation and Feeding, about 5 MJ; Units 16 and 17, Raw Gas Quenching and Shift Conversion, 4 MJ; Unit 32, Oxygen Plant, approximately 2 MJ; other miscellaneous units contribute a combined available‐energy destruction of 4 MJ.

The Second‐Law analysis unveils the inefficiencies present in the process and their sources, thus pinpointing the opportunities for improvement in the SYNTHANE process.
Model reduction of high‐order multistage systems by the method of orthogonal collocation
Authors: Wong Kin Tuck , Luus Rein
Published: March 2009

A straightforward model reduction procedure is developed for high‐order multistage systems. It is proposed to generate a partial differential equation from the original system and then to use the orthogonal collocation procedure to establish a low‐order reduced model. This low‐order model can then be used for time‐optimal control with the assurance that the optimal control, as determined for the reduced system, can be applied to the original system. The procedure is illustrated with a 20‐plate gas absorber which is eventually reduced to 5 state equations.
Evaporation under an impinging jet: A numerical model
Authors: Mujumdar A. S. , Li Y.‐K. , Douglas W. J. M.
Published: March 2009

A numerical model is presented to predict the flow and coupled heat and mass transfer characteristics under a round laminar jet impinging normally on a plane wall maintained at a constant wet‐bulb temperature. The full Navier‐Stokes energy and conservation of species equations in their primitive form are solved using a finite difference technique for the case of a jet of hot humid air impinging on an isothermal wet surface. It is found that a modified Sherwood number defined in terms of a log‐mean, mole fraction driving potential renders the former insensitive to the evaporation rate.
Bulk and interfacial physical properties of aqueous solutions of sodium lauryl sulphate: Part IV: Dilute aqueous solution behavior by electron spin resonance studies and by pH and surface tension measurements
Authors: Vijayan S. , Ramachandran C. , Woods D. R.
Published: March 2009

The electron spin resonance spectrum of the nitroxide label 2,2,6,6 – TetraMethyl – 4 – Piperidone – Oxide (TEMPO) has been investigated in aqueous solutions of a purified and commercially available impure samples of sodium lauryl sulphate (NaLS) for a wide range of concentrations. The spectra were recorded at 24°C as a function of surfactant concentration. The reorientational correlation times Tθ of the TEMPO label in aqueous solutions were calculated using the Kivelson's theory. Using the Tθ data qualitative analysis has been carried out in an attempt to understand the microscopic effects produced by the hydrophobic part of the surfactant on the water structure and the hydrophobic‐hydrophobic interactions in water.

Four major discontinuities in the τθ results have been identified with the purified NaLS system. They are found to occur at NaLS concentrations of 0.008 wt.%, 0.015 wt.%, 0.23 and 1.73 wt.%. The latter two concentrations represent the first and the second critical micelle concentration (CMC) of the surfactant while the first two concentrations reveal the existence of premicellar association and dissociation processes, respectively. These discontinuities have been also confirmed by the pH data and by surface tension results from the du Noüy ring method.

The effect of addition of lauryl alcohol and sodium chloride on τθ values was also studied. The additive action has been found to produce an additional discontinuity, corresponding to the mixture CMC, in the τθ versus concentration plot. Analysis of other effects such as solution aging and hydrolysis of NaLS are also included.

The applicability of the spin labelling technique for the study of aqueous solution behavior of NaLS is discussed by comparing data reported in the literature.
Kinetic investigation of complex pseudo mass action systems by use of the pulse method
Authors: Christoffel Erhard G. , Surjo Indarto T. , Robschlager Karl‐H.
Published: March 2009

With simultaneous isomerization and cracking of the five hexane isomers on a bifunctional Pt/Al2 O3‐catalyst as a model reaction, which has been shown to follow pseudo mass action kinetics, it is demonstrated how the microcatalytic pulse technique can be applied for the kinetic analysis of complex linear reaction networks. From the experimental data relative rate constants for the individual reaction steps have been obtained by use of the Wei‐Prater‐method. The results are compared with results from continuous operation.
Kinetic investigation of the isomerization of C8‐aromatics
Authors: Röbschäger Karl‐H. , Christoffel Erhard G.
Published: March 2009

The kinetics of isomerization of C8‐aromatics on a bifunctional Pt/zeolite catalyst has been studied at 422°C, total pressures of 7.102 KPa to 18.102 KPa and H2/hydrocarbon ratios of 3 to 18 in a fixed bed reactor. The rate of ethyl‐benzene isomerization can be described on the basis of a bifunctional reaction mechanism. For modeling the rates of interconversion of the C8‐aromatics linear rate laws are suitable as long as hydrogen and hydrocarbon partial pressures are kept constant.
Process heat transfer: Some practical problems
Authors: Watkinson A. Paul
Published: March 2009

Some practical methods of reducing tube side thermal resistance in process heat exchangers are discussed, both for clean surfaces and in the presence of water side fouling. Factors of importance in hard water scaling are outlined. Gains to be made by changes in velocity, tube geometry and surface area augmentation are explored.
Bitumen separation for experimental use
Authors: Vorndran L. D. L. , Serres A. J. , Donnelly J.K. , Moore R. G. , Bennion D. W.
Published: March 2009

A solvent extraction procedure is presented for separating large quantities of bitumen to be used in laboratory experiments. The effectiveness of various solvents is discussed. Data are presented on the properties of extracted bitumen, the unextracted residue and the light ends lost during solvent removal. The effect of bitumen contact with oxygen is also discussed.
Kinetics of oxidation of cuprous chloride by oxygen in aqueous hydrochloric acid solutions
Authors: Hikita H. , Ishikawa H. , Matsuda M.
Published: March 2009

The rates of absorption of oxygen into aqueous cuprous chloride solutions containing hydrochloric acid were measured at 15, 25 and 35°C using a baffled agitated vessel operated batchwise and the experimental results were analyzed with the chemical absorption theory.

The reaction between oxygen and cuprous chloride was found to be second order, i.e. first order with respect to oxygen and CuCl2− ion which is the actual reactive species in aqueous cuprous chloride solutions containing hydrochloric acid. The reaction rate constants were calculated and correlated as a function of temperature.
Enthalpy of solution of carbon dioxide in diethanolamine solutions
Authors: Kahrim A. , Mather A. E.
Published: March 2009

Calorimetric measurements of the enthalpy change upon solution of CO2 in diethanolamine solutions ranging from 2.0 to 5.0 mol/L have been made over the temperature range 25° to 75°C.
A fluidized bed retort for oil sands
Authors: Donnelly J. K. , Moore R. G. , Bennion D. W. , Trenkwalder A. E.
Published: March 2009

Fluid bed retorting of oil sands is a viable method of extracting oil from mined oil sands. The process is based on a direct heating concept in which one vessel is utilized for the pyrolysis and vaporization of the bitumen contained in the oil sand and for the burning of the residuals which remain with the sand.

Experimental results show that a significantly upgraded liquid hydrocarbon product can be obtained. Oil yields can exceed eighty per cent of the bitumen present in the feed material. The sulfur content of the produced oil is reduced. Gas produced can have a significant heating value and contains sulfur mainly in the form of hydrogen sulfide. Refluxing of the overhead product increases liquid yields and reduces the sulfur content of the oil. Water injection and the use of enriched air has a beneficial effect on the process. Thermal efficiencies in excess of eighty per cent can be achieved without recovering the heat from the expended sand.
Vapor‐liquid equilibria for the ternary system n‐Heptane/n‐Propanol/l, chlorobutane and its constituent binaries at 318.15 and 338.15 K
Authors: Ashraf F. A. , Vera J. H.
Published: March 2009

Isothermal liquid‐phase composition — total pressure, x‐P, data were measured for the ternary system n‐heptane/n‐propanol/l, chlorobutane and its constituent binaries at 318.1 S and 338.15 K. A total pressure static equilibrium apparatus was used. The binary x‐F data were correlated using four semi‐empirical local‐composition expressions for the activity coefficients, i.e. the Wilson, the LSG, the LCG and the UNIQUAC equations. The performance of these equations to predict the ternary data has been compared. In general, all four equations were found to give good predictions. The best results were obtained with the Wilson and the LCG equations.
Finite difference simulation of die swell for a newtonian fluid
Authors: Hill G. A. , Shook C. A. , Esmail M. N.
Published: March 2009

The phenomenon of die swell for Newtonian fluids has been successfully simulated using a finite difference numerical method. The calculations predict the surface shape of Newtonian jets over a range of Reynolds numbers from 4.2 to 92.3 for both rectangular slits and cylindrical tubes. The calculated die swells for tubes compare favourably to experimental data. Velocity profiles and pressure distributions in jets exiting from slits or tubes are also predicted. The numerical data were incorporated into a momentum balance expression to demonstrate factors influencing this phenomenon. Other solutions were calculated to predict the effect of gravity and a sudden perturbation in flow on the resulting jet shape.
The application of robust and non‐interacting control schemes to a heat‐exchanger stirred tank process
Authors: Taylor P. A. , Wright J. D. , Tu T.
Published: March 2009

An experimental study involving the digital computer implementation of four multivariable control schemes to a heat‐exchanger stirred process has been performed. The control schemes varied in their complexity and in the amount of process information required for their design. The analysis of the experimental data shows how each controller handled the asymmetric non‐linearity and dead times inherent in the process. The development of the theory shows why the best control was not always achieved with the most sophisticated controller. The controllers are suitable for industrial applications.
Electrochemical simulation of heat and mass transfer in agrometeorology
Authors: Schuepp P. H.
Published: March 2009

Diffusion and convection controlled electrode reactions have been used to study a wide variety of agricultural heat and mass transfer problems. The paper reviews applications to the heat and mass transfer of plants in free and forced convection, the role of electrochemical simulation on the development of predictive models for soil‐atmosphere and soilcrop transfer and investigations of transfer in intermittent flow.

Where field data are available they tend to confirm the validity of the technique. The biggest deficiency, noticeable particularly in intermittent flow around turbulence‐producing obstacles (vegetation, barriers), appears to be the fact that presently‐used models cannot deal adequately with two – and three – dimensional flow and sporadic boundary‐layer penetrations by irregular ‘events’. Electrochemiluminescent flow visualization may help in developing better qualitative and quantitative descriptions of such flows.
The flow of rarefied gases through long tubes of circular cross‐section
Authors: Datta Ravindra , Rinker Robert G.
Published: March 2009

A brief review is presented of various models of rarefied gas flow in long tubes. The complex treatments based on the Boltzmann equation provide only numerical solutions for the transition region unless some arbitrary assumptions are made, while those based on the traditional approach of simple kinetic theory have usually involved empiricism to a greater or lesser extent. An analytic expression is derived here based on a physically realistic model, making use of simple kinetic theory and containing no arbitrary assumptions. The model is completely predictive and adequately describes the flow in long tubes over the entire pressure range, from free‐molecule to continuum laminar flow, and also predicts the “Knudsen minimum” in the transition region. The concept of a “geometric mean free path” is introduced and appears to be useful in analyzing rarefied gas dynamics in a confined space. A relation is also obtained for the viscosity coefficient in the transition region.
Entrainment of particles from a pilot scale fluidized bed
Authors: George S. E. , Grace J. R.
Published: March 2009

Particles entrained from a pilot scale fluidized bed of sand having a mean size of 102 μm have been captured and analysed at superficial air velocities up to 1.3 m/s. Variation of bed temperature over the range 300 to 445 K and insertion of a tube bundle in the splash zone had little effect on the measured entrainment fluxes. Existing correlations for predicting entrainment from fluidized beds gave widely divergent results, and generally differed markedly from the experimental data. Of the correlations tested, the graphical saturation carrying‐capacity correlation of Zenz and Weil gave the best agreement with the experimental data. The size distribution of particles carried over differed widely from the size distribution in the bed at low gas velocities but approached the in‐bed distribution at higher velocities.
Concentration distributions in laminar pipe flow with distorted velocity profiles
Authors: Jain S. C. , Chen B. H.
Published: March 2009

A laminar flow field in which the velocity profile may be distorted in a predictable manner was achieved in a 7‐cm porous pipe with uniform wall injection over the ranges of variables: 0≤ λ ≤ 2, 200 ≤ NRe ≤ 800 and 0.05 ≤ X ≤ 0.2.

A mathematical model was then developed to describe the concentration distribution of a gaseous tracer discharged continuously from a finite source in this particular flow field. Experimental measurements taken over the same ranges of variables verified the validity of this model. The result from this study may be useful in the water desalination process using reverse osmosis.
Gas absorption at a liquid surface agitated by vortex rings
Authors: Rohatgi A. , Baird M.H.I.
Published: March 2009

Underwater vortex rings have been formed at orifices of between 25.4 and 63.5 mm diameter and projected upwards at the surface of the water. The conditions of ring formation at which significant surface deformation occurs have been correlated. The absorption of pure carbon dioxide by the water surface with impinging vortex rings has been measured and related to the following variables: time of fluid impulse through the orifice, orifice diameter, volume of displaced liquid, and depth of submergence. A simplified mass transfer model based on the penetration theory approximately correlates the data.
The effect of saline concentration on the viscous properties of lignite water suspensions
Authors: Darby Ron , Mallett Mark W.
Published: March 2009

The influence of saline in small concentrations on the rheological behavior of concentrated suspensions of lignite in water was determined. It was found that for solids volume fractions below about 40%, the suspension viscosity exhibited a slight minimum at a saline concentration of about 1 mmol/L whereas the viscosity exhibited a maximum at this same saline concentration for solids volume fractions above about 40%. An explanation is offered in terms of the electrostatic effects of adsorbed ions and crowding effects.
Dynamic simulation of multicomponent distillation
Authors: Morris C. G. , Svrcek W. Y.
Published: March 2009

A program has been developed for the dynamic simulation of large scale chemical processes. The simulator has a highly modular structure and an explicit integration routine which is capable of handling large systems of stiff ordinary differential equations. The use of an explicit method reduces computer storage requirements and greatly simplifies the writing of new modules.

Unit subroutines have been written which are capable of describing multicomponent distillation columns without resorting to conventional thermodynamic equilibrium calculations. The absence of these iterative routines reduces computation time and allows tray efficiencies to be handled in a more natural manner than is possible with Murphee efficiencies. The program also includes an advanced thermodynamic property package based on the Peng Robinson equation of state.

An industrial process consisting of two distillation columns with a combined total of seventy‐five mass transfer stages, has been successfully simulated and the computed results have been compared with dynamic data collected from plant tests.
Analysis of coal‐oil mixture sedimentation by modified continuity wave theory
Authors: Ekmann James M. , Klinzing George E.
Published: March 2009

Coal‐oil mixtures which have the potential to stretch oil usages have been analyzed as to their sedimentation behavior by applying a modification of the continuity wave theory as developed by Kynch. Three coal‐oil systems have been studied and have been shown to follow the pseudo continuity wave theory by assigning a degree of agglomeration to the coal particles. With the presence of surfactants, the sedimentation of the mixtures could be similarly analyzed. The general effects of particle size of the coal and temperature of the system have been considered and presented as guidelines for design.
Flow characteristics of a laminar swirling impinging jet: A numerical study
Authors: Huang B. , Mujumdar A. S. , Douglas W. J. M.
Published: March 2009

The primitive Navier‐Stokes equations were solved to predict the flow field induced by a partially confined swirling laminar jet impinging normally on a flat surface. A study is made of the influence of the jet Reynolds number, nozzle‐to‐plate spacing, axial and swirl velocity profiles at nozzle exit plane, size of the confining and impingement plate and uniform suction applied at the plate. An interesting feature of the flow configuration is the predicted development of a recirculation bubble in the stagnation region which influences the heat and mass transfer characteristics. Axial and swirl velocity profiles at entry have dominant influence on the development of the flow field.
Intraparticle mass tranfer in weak acid ion‐exchanger
Authors: Kataoka Takeshi , Yoshida Hiroyuki
Published: March 2009

Resin phase mass transfer in a weak acid ion‐exchanger was analyzed based on a shrinking core model. It was assumed that H‐form core and metallic ion‐form shell appear in sorption of metallic ion, while metallic ion‐form core and H‐form shell appear in regeneration of metallic ion‐type resin. At the moving boundary, instantaneous irreversible reaction occurs, namely, neutralization reaction in the sorption and the protonation reaction in the regeneration. The Nernst‐Planck equation was applied to the fluxes of ions diffusing through the shell and the analytical solutions of sorption and regeneration rates were derived by assuming a pseudo‐steady state diffusion. Those solutions agreed fairly well with the experimental results in R‐H‐NaOH system (sorption) and in R‐Na‐HCl, R‐Cu‐HCl and R‐Cu‐H2SO4 systems (regeneration).
Gas‐liquid reactions in packed beds: The effectiveness of static hold‐up in presence of gas side resistance
Authors: Patwardhan V. S.
Published: March 2009

The interfacial area in a packed bed may be divided into two parts, i.e. the interfacial area corresponding to the dynamic hold‐up and that corresponding to the static hold‐up. The effectiveness of the latter for gas absorption with a chemical reaction can become quite low due to the depletion of the liquid phase reactant in the static hold‐up. As a result, the effective interfacial area may become substantially smaller. This aspect has been investigated earlier for liquid phase controlled absorption with a chemical reaction. In this paper, a procedure is developed for calculating the effectiveness of the interfacial area of the static hold‐up for the case of significant gas‐side mass transfer resistance for a second‐order chemical reaction. It is shown that the gas‐side mass transfer resistance increases the effectiveness of the static hold‐up. The results are presented in a convenient graphical form. It is shown that under certain conditions this effectiveness is quite sensitive to the magnitude of the gas‐side mass transfer resistance. The analysis presented here is based on the film theory.
Estimation of critical data by equation of state
Authors: Schmidt G. , Wenzel H.
Published: March 2009

A recently proposed cubic equation of state was used to predict critical temperature Tc and pressure pc from liquid density at room temperature and from boiling temperatures generally at 13 kPa and 100 kPa. Calculated and experimental critical data are compared for some 270 substances. For non‐associating substances the values were generally found to be in close agreement. The method was then used to produce values of Tc, pc as well as acentric factors ω for nearly 1700 compounds. Comparative calculations were performed with Soave's as well as Peng and Robinson's equations and showed that application of these equations is restricted. Examples are given to show that the method may be extended to cover associating substances.
Analysis of fluidized bed catalytic cracking regenerator models in an industrial scale unit
Authors: De Lasa H. I. , Errazu A. , Barreiro E. , Solioz S.
Published: March 2009

Fluidized bed regenerator models, under steady state conditions, have been reconsidered because of recent significant changes in the technology of fluidized bed regenerators. Zeolitic catalysts, temperatures of the dense bed at about 700°C and lower CO/CO2 relationships are the new characteristics of the units.

Following these innovations the operating conditions of the industrial catalytic cracking regenerator of Destileria La Plata, Yacimientos Petroliferos Fiscales, Argentina, were significantly modified. As a result, an important improvement in the coke conversion was observed. Five different conventional fluidized bed models using experimental data from the industrial regenerator have been tested. The analysis considers bubbles and grid jet regions, and for each model, the prediction of the regenerator performance is shown. The CSTR model is the most successful in this regard.
Computation of optimal control policy with singular subarc
Authors: Reddy K. V. , Husain Asghar
Published: March 2009

Singular subarcs appear in the solution of an optimal control problem when one or more of the control variables appear linearly in both the performance index and differential constraint equations or just in the constraint equations. In such cases, the Pontryagin's(1) Maximum Principle yields no information regarding the possible candidates for such subarcs to be optimal trajectories, since the associated Hamiltonian is also linear in the control variables. In the chemical engineering literature such problems have been reported, for instance, in the optimal control of a continuous stirred reactor(2,3,4) in the optimally distributed feed reactors(5), in the optimal catalyst distribution along a tubular reactor(6,7) and in the optimal design of a plug flow tubular reactor(8).
Effect of the physical properties of gas on the volume of bubble formed from a submerged single orifice
Authors: Tsuge Hideki , Tanaka Yasumitsu , Hibino Shin‐Ici
Published: March 2009

The effects of the gas properties on the volume of a bubble formed from a submerged single orifice in the presence of pressure fluctuations in the gas chamber are investigated experimentally. The bubble volumes are affected by the specific heat ratio of gas and/or the gas density depending on the dimensionless capacitance number Nc.

An extended two stage bubble formation model is proposed by considering the physical properties of gas. The bubble volumes calculated by the present model compare reasonably well with the experimental results.
Hydrodynamicst axial mixing and mass transfer in rotating disk contactors
Authors: Zhang S. H. , Ni X. D. , Su Y. F.
Published: March 2009

Correlations for predicting characteristic velocity both above and below the critical rotor speed have been obtained under conditions with and without solute transfer.

It has been found that (1) above the critical rotor speed, the characteristic velocity U0 is proportional to g/DrN2, whereas below this value a transition region exists where Uo is proportional to (g/DrN2)0.26; (2) multiple regression analysis of the experimental data of continuous phase axial mixing shows that the axial dispersion coefficient varies not only with the rotor speed and modified velocity of continuous phase but also with the velocity of dispersed phase.

With varying RDC operations, the true value of Kod corrected for axial mixing changes continually between the limiting values predicted from stagnant and fully turbulent drop models. However, the highest experimental values were only 30 to 40% of those predicted by the Handlos‐Baron model at the same drop Peclet number.
Dispersion and hold‐up in bubble columns — comparison of rigid and flexible spargers
Authors: Rice Richard G. , Tupperainen Jorma M. I. , Hedge Robyn M.
Published: March 2009

The performance of a new type of bubble generating device, the rubber sheet sparger, is contrasted and compared with rigid spargers. Impulse response tests were analyzed using the weighted‐moments method to determine voidage and dispersion coefficients in counter‐current bubble columns of nominal diameters two, four, six and twelve inches. The flexible rubber sheet sparger produced more uniform emulsions, smaller bubbles and larger voidages than perforated plates, while dispersion coefficients were reduced for a range of superficial gas velocities. The dispersion data seem to fit the isotropic turbulence model, with slight modifications. It is demonstrated that the rubber sheet sparger is self‐regulating, with hole size increasing in direct proportion to pressure drop across the sparger.
A simplified driving force model for activated carbon adsorption
Authors: Peel R. G. , Benedek A.
Published: March 2009

The use of two simplified driving force expressions are investigated for describing the intraparticle rate behaviour during adsorption onto activated carbon. A previously developed numerical solution to the surface diffusion model is used to compare the linear and quadratic driving force approximation when non‐linear isotherms and time variant boundary conditions are present. The results show that while the linear driving force equation is a poor approximation of the exact solution, the quadratic driving force is a good approximation, and its use in a kinetic model of activated carbon adsorption gives as good a description of adsorption behaviour as is given by the more detailed surface diffusion model. The driving force model has the advantage of being easier to solve, and the numerical solution requires significantly less computational effort.
A novel approach to spray drying using plasmas of water vapour
Authors: Gauvin W. H.
Published: March 2009

The technical feasibility of drying an aqueous solution in the form of a fine spray of droplets in contact with the water vapor generated by the evaporation of the solution has been amply demonstrated in the course of the extensive experimental work which accompanied the development of the Atomized Suspension Technique (AST). In the present paper, it is proposed to replace the external heating formerly used in an AST system by a stream of plasma‐generated superheated steam as the sole source of heat. The ratio of plasma steam required to total evaporation (circa 1 to 24) is extremely low. Based on a computer program developed in this laboratory, a simulation of the proposed operation is presented for an industrial installation. The calculations indicate that a considerable reduction in equipment size should result. No gas compression is required and operation under pressure is now possible. Most important is the considerable saving in energy resulting from the recovery of the heat in the exhaust steam from the process. An approximate estimate of capital and operating costs is presented.
Conversions and temperature rises in a tubular flow reactor with uncontrolled wall heat transfer
Authors: Golding J‐A. , Vena F. , Gorowski D.
Published: March 2009

A study has been made of the acetic anhydride‐water reaction in a flow reactor where there was heat loss from the reactor wall. Runs were carried out at varying inlet acetic anhydride concentrations and Reynolds numbers. The laminar flow model with heat loss at the wall was found to give good agreement with experimentally observed conversions and overall temperature rises. In addition, predicted radial profiles for this model gave a better representation of measured temperature profiles than had been obtained when assuming reaction conditions were adiabatic.
Studies of molybdena‐alumina catalysts. X. temperature programmed desorption of H2S and thiophene
Authors: Ramachandran R. , Massothm F. E.
Published: March 2009

Temperature programmed desorption (TPD) and reduction (TPR) studies were carried out on H2S and thiophene adsorbed on Mo/Al2O3 and CoMo/Al2O3 catalysts. Freshly sulfided and pyridine poisoned catalysts were run. For sulfided catalysts, the major products of desorption of thiophene were thiophene and butene, leaving a carbonaceous residue. Subsequent TPR in H2 effected complete removal of the residue with formation of H2S, thiophene and butene. The residue appeared to consist of an easily reactive thiophene polymer and a less‐reactive, sulfur‐containing coke. Runs on poisoned catalysts showed less adsorption but product profiles were similar, showing that the adsorption characteristics of the remaining sites were not significantly altered.