bluuebunny/crossref_metadata_2025 huggingface dataset:
Self‐Tuning control of fischer‐tropsch synthesis in a tube‐wall reactor
Authors: Rohani Sohrab , Quail D. W. , Bakhshi N. N.
Published: March 2009

This paper describes the implementation of a self‐tuning controller (STC) on a bench‐scale tube‐wall reactor for the Fischer‐Tropsch synthesis using a plasma‐sprayed iron catalyst. The concentration of the hydrocarbons in the C10 range in the reactor effluent was controlled by manipulating the H2/CO ratio of the inlet synthesis gas. The output of the self‐tuner was cascaded to two PI‐controllers which maintained a constant total inlet gas flow rate as well as ensuring the desired H2/CO ratio. The concentration measurement was performed by an on‐line gas chromatograph with an analysis time of approximately 30 s. The performance of the STC in set‐point tracking, rejection of randomly occurring deterministic disturbances, and estimation and adaptation to the unknown process dead time was investigated. The STC was able to reduce the variance of the process output and of the manipulated variable when compared to the variances obtained with a PI‐controller.
Prandtl number effect on combined free and forced laminar convection in the thermal entrance region of a horizontal tube
Authors: Chou F. C. , Hwang G. J.
Published: March 2009

This note presents the Prandtl number effect on combined free and forced laminar convection in the thermal entrance region of a horizontal tube by a numerical vorticity‐velocity method. The tube wall is heated with a uniform wall heat flux. Vorticity‐velocity governing equations in cylindrical coordinates and an evaluation of boundary vorticity on the tube wall are presented along with a numerical method of solution. Local Nusselt number variations are shown for Pr = 100 and 10 and compared with the existing data for Pr → ∞. It is observed that the large Prandtl number assumption is valid for Pr = 10 within a difference of 4% at Ra = 1 × 105. The numerical results are compared against the available experimental data with good agreement.
Flow and heat transfer characteristics of structural viscosity fluids
Authors: Gaidos R. E. , Darby R. , Wickern G.
Published: March 2009

Laminar friction loss and heat transfer characteristics for a non‐Newtonian fluid described by a general viscosity function of the structural type have been computed for tube and slit geometries. The model includes most other models for fluids without a yield stress as special cases. The Graetz problem for constant wall temperature and temperature independent properties has been solved, including viscous dissipation, for the transverse and axial temperature distribution. Both momentum and energy transport characteristics are shown to be strongly dependent upon a dimensionless fluid time constant, which characterizes the transition from Newtonian to non‐Newtonian shear thinning behavior. A direct and exact analogy between the momentum and energy transport mechanisms is demonstrated for hydrodynamically and thermally fully developed flow, provided the heat transfer rate is represented by a suitably defined Nusselt number.
Solids circulation in a spout‐fluid bed with draft tibe
Authors: Berruti Franco , Muir James R. , Behie Leo A.
Published: March 2009

A 20 cm diameter semi‐cylindrical spout‐fluid bed with a draft tube has been used to study the effects of operating and geometric parameters on the solids circulation rates at ambient temperature. A new technique has been developed for measuring the solids fluxes with great accuracy. Solids circulation rate data have been found to be strongly influenced by both geometry and relative magnitude of spouting and auxiliary gas flowrates, as they in turn affect the flow of the gas‐solid mixture inside the draft tube. The solids circulation rate was greatly enhanced when an auxiliary flow aerated the annular region and such enhancement has been found to be linearly dependent on the auxiliary flow contribution to the total gas flow and on the distance between the base of the draft tube and the inlet nozzle.
Enhancement of SO2 sorption on lime by structure modifiers
Authors: Shadman F. , Dombek P. E.
Published: March 2009

The presence of certain inert compounds in lime can improve the rate and the final limiting conversion significantly during the lime SO2 reaction. This physical effect is primarily due to modification of porosity. In particular, the enhancement appears to he due to increase in macro‐porosity and macro‐pore diffusivity; this in turn increases the sulfation rate and decreases pore plugging. In certain lime application processes, these compounds (structure modifiers) can be added to lime as beneficial additives to promote the reaction. Experimental data on the effect of kaolin, silica and bauxite as structure modifiers are presented. A theoretical model is developed which explains the observed effects both qualitatively and quantitatively.
Gas holdup in a bubble column with immikible liquid mixtures
Authors: Bandyopadhyay N. , Ray P. , Dutta B. K.
Published: March 2009

Experimental measurement of gas holdup was carried out in a medium‐size gas‐liquid‐liquid bubble column with a multiple nozzle sparger plate using air, water and organic liquids. It was found that the fractional holdup depends on gas velocity, liquid properties, phase inversion in the liquid mixture as well as spreading coefficient of the organic liquid. In the presence of a liquid with a negative spreading coefficient the holdup is a minimum at the phase inversion point. but the reverse is true for a liquid with a positive coefficient of spreading. Observed bubble characteristics have been discussed. Correlations for gas holdup have been developed for different ranges of liquid composition.
Comparison of indices for the scaling and corrosion tendency of water
Authors: Müller‐Steinhagen H. M. , Branch C. A.
Published: March 2009

Three commonly used fouling indices to characterize the scaling and corrosion tendencies of water, namely the Saturation Index, the Langelier Saturation Index and the Ryznar Stability Index, have been compared and checked for consistency. While the first two indices give similar results, major deviations between the predictions of saturation and stability indices were found.
An agitated bubble column for use in potash flotation
Authors: Karolat W. H. , Hill G. A.
Published: March 2009

A novel, agitated bubble column was designed, constructed and operated for the purpose of potash flotation. This report describes the apparatus and presents some typical results regarding bubble size distribution, gas hold‐up and flotation efficiency.

It was found that the column produced mean bubble diameters and overall gas hold‐ups that could be predicted by empirical correlations presented earlier in the literature for aerated, agitated tanks. The column also achieved both a high percentage recovery ( > 90%) and a high product purity (97%).
Gas absorption rates in a stirred cell with plane interface in the presence of fine particles
Authors: Quicker G. , Alper E. , Deckwer W.‐D.
Published: March 2009

The rates of absorption of carbon dioxide into water and into 0.5 mol/L equimolar carbonate buffer solutions (containing varying amounts of arsenite) were measured in a stirred cell with plane interface in the presence of fine solids (activated carbon, kieselguhr and alumina). Experiments show that the absorption rate increases significantly when the activated carbon loading increases up to about 0.2 g/L and thereafter remains constant. No significant effects were observed for other solids. The results could be explained in terms of a “shuttle” mechanism where particles adsorb gas near the interface which is then followed by desorption (or reactions) in the bulk.

At very high loadings (above 10 vol.%), the absorption rate decreased for all particles and this could be explained by the blockage of the interface and/or by the sharp increase in the suspension viscosity.
Toxicity of organic solvents to fatty acid forming bacteria
Authors: Hayward Gordon , Lau Isaac
Published: March 2009

The inhibition of fatty acid formation in the anaerobic digestion of synthetic swine manure by several solvents has been studied. The solvents tested were commonly used for the recovery of acetic acid from dilute aqueous solutions. Negligible inhibition was observed with kerosene and tri‐octyl phosphine oxide. The latter compound was added as a carrier to increase the solubility of fatty acids in the organic phase. The most toxic solvent tested was di‐isopropyl ether with Aliquat 336 added as a carrier. The use of published oralLD50values for rats was found to provide a qualitative estimate of the bacterial inhibition by a solvent when divided by the water solubility of the solvent.
Hydrodynamics of erosion of heat exchanger tubes in fluidized bed combustors
Authors: Bouillard J. X. , Lyczkowski R. W. , Folga S. , Gidaspow D. , Berry G. F.
Published: March 2009

The hydrodynamics of fluidization for two thin “two‐dimensional” fluidized beds, one containing a centrally located rectangular obstacle and the other containing three square tubes roughly approximating a portion of a fluidized bed combustor (FBC), was solved using the FLUFIX/MOD2 computer program. The monolayer energy dissipation erosion model extended to include solids viscous stress was compared with the Finnie erosion model. The material properties of the eroding surface are introduced through the hardness for both erosion models. Hydrodynamic and erosion convergence studies were performed for the first bed. Computed erosion rates from the monolayer energy dissipation erosion model compare more favorably for both beds with available erosion data than those from the Finnie erosion model.
Vertical pneumatic conveying of particle plugs
Authors: Konrad K. , Totah T. S.
Published: March 2009

Dense‐phase pneumatic conveying of solids offers many advantages over dilute‐phase conveying. The lower air velocities, and, consequently, lower particle velocities, result in lower pipe wear and lower particle attrition. This paper describes an experimental program that has been undertaken to study the flow pattern of cohesionless solids in vertical transport and to measure the parameters influencing the pressure drop required to move a single plug of solids. Highspeed photographic techniques have been used to observe the flow pattern of polyethylene particles (diameter ≏ 3 mm) in the vertical riser section of a circulating unit constructed from pipes with an internal diameter of 50.8 mm. The flow pattern resembles that of square‐nosed slugging in a fluidized bed. The solids move up as “plugs” of bulk solids that occupy the entire cross‐section of the pipe. Particles are seen to “rain” down from the back of one plug and then to be collected by the front of the next plug. Collecting these particles causes a stress on the plug front which is transmitted by powder mechanics forces axially through the plug and radially to the wall. The pressure drop required to move a single plug of cohesionless solids through the transport pipeline was measured as a function of the plug length, particle properties, pipe diameter, and the frontal stress. The results of these experiments are compared with a theoretical model.
Heat transfer in a liquid‐liquid spray column
Authors: Lin F. , Ford J. D.
Published: March 2009

A theoretical and experimental study of direct contact heat transfer in a kerosene‐water spray column has been carried out. A mathematical model for the process with a drop size distribution is proposed, and the associated computer program for the numerical solution developed. Correlations for the overall area heat transfer and axial dispersion coefficients for the column were obtained.

Applying the mathematical model with experimentally obtained parameters, temperature profiles of both phases could be predicted. Comparisons with previous work in the literature support the present study. From the results, operation with uniform drop size in a short column is recommended.
Experimental studies of heat transfer to horizontal tubes in a pilot‐scale fluidized‐bed combustor
Authors: Bardakci Tevfik , Molayem Benjamin
Published: March 2009

Experimental data are obtained for the overall heat transfer coefficient between immersed horizontal tube bundles and an atmospheric fluidized bed combuster burning high‐sulfur coal. Limestone (1000 μm size) is used as the bed material. Tests are conducted with coal and limestone addition at overall average bed temperatures ranging from 1028 to 1116 K, and fluidizing velocities ranging from 2.08 to 3.14 m/s. The overall heat transfer coefficients of the horizontal tube sections increase as the height from the distributor plate increases, except for the top tubes located in the splash zone. The average overall heat transfer coefficients of all horizontal tube sections increases as the fluidization velocity and overall bed temperature increase.
Hydrodynamically induced gel breakdown in pipes
Authors: Viswanathan T. , Khilar Kartic C.
Published: March 2009

A new model is reported to describe the dynamics of hydrodynamically induced breakdown of oil gel in pipes. Hitherto, the reported models (Davenport and Somper, 1971; Govier and Fogarasi, 1972; Rao et al. 1985a) cannot predict some observed inherent features of the breakdown process relating to its rates. The present model can predict these desiderata as well as delineate the effects of microscopic parameters such as size and shape of wax crystallites on the dynamics of breakdown. The model is based on a concept that energy imparted to the gelled structures is consumed in the breakdown process. Predictions of this model on breakdown time agree reasonably well with measurements. Important considerations relating to the amount of pressure head required for different diameters of pipe as well as for different dimensions of crystallites are analysed using this model.
A study of ionic transfer in electrodialysis process with laminar flow
Authors: Huang Ting‐Chia , Wang Jun‐Hsien
Published: March 2009

The concentration profile in a laminar flow of the diluent of a parallel‐plate electrodialysis stack is derived by assuming operation at the limiting current density. The Nusselt mass transfer number is found to depend on the Reynolds number, the Schmidt number and the dimensionless hydraulic equivalent diameter according to (Nu)theo. = 3.7 · (Re · Sc · de/L)1/3. An empirical correlation of the Reynolds number, the Schmidt number, and the shape factor of the electrodialysis cell, with the ionic mass transfer rate in ion exchange membrane electrodialysis is obtained by measuring the limiting current densities at various conditions. The resulting empirical mass‐transfer correlation, (Nu)exp. = 3.91 · Re0.333 · Sc0.328 · (de/L)0.352, holds for sodium acetate as dialysate at concentrations ranging from 0.0106 to 0.0508 kmol/m3, viscosities ranging from 0.608 to 0.926 mPa · s, temperatures ranging from 15 to 55°C, axial velocities ranging from 0.341 to 4.55 cm/s, and for cell thicknesses of 0.32 and 0.94 cm, and is found to be in agreement with the equation obtained from theory. The effects of concentration, flow rate and temperature on the limiting current density are also studied. The relationship between the thicknesses of the diffusion layer and the Reynolds number has been analyzed.
Modelling of catalytic naphtha reformers
Authors: Bommannan D. , Srivastava R. D. , Saraf D. N.
Published: March 2009

A simple kinetic model has been used to simulate catalytic naphtha reformers. The model idealises naphtha to three constituents, namely, paraffins, naphthenes and aromatics, with average properties assigned to each class. Out of the many reactions the mixture can undergo, four major reactions have been considered for which the kinetic parameters have been estimated using plant production data. The reactor model is validated against two different sets of plant data. The agreement between predicted results and observations is generally good. A sensitivity analysis of operating parameters on reactor performance revealed that, while temperature affects the aromatics production significantly, the effect of pressure is negligible.
Olefin conversion over zeolite H‐ZSM‐5
Authors: Norval G. W. , Phillips M. J. , Virk K. S. , Simons R. V.
Published: March 2009

The conversion of propene, 1‐butene and 2‐methylpropene over zeolite H‐ZSM‐5 has been studied in the temperature range 663–773 K. While propene and 1‐butene yield similar products, that from 2‐methylpropene contains less aromatics, but a greater fraction of xylenes. The time on stream behaviour of the aromatics from this latter olefin demonstrates that the difference in product yield and selectivity is due to pore mouth blockage resulting from the formation of iso‐butyl cations on the external zeolite surface.
Liquid solidification in low peclet number pipe flows
Authors: Lee S. L. , Hwang G. J.
Published: March 2009

The combined effects of axial conduction and solidification on heat transfer and pressure drop in pipe flows are investigated by the use of a modified Galerkin finite element method. To allow for the upstream heat conduction, the domain of study is extended from X = ‐∞ to X = ‐∞ as has been done in previous analyses. As a preliminary study on the effect of axial conduction, the present investigation assumes a superheat ratio that is sufficiently large (To > Tf or Tw ≈ Tf) such that solidification begins at a location near X = 0. For numerical convenience, the infinite domain ‐∞ ≤ X ≤ ∞ is transformed onto a finite domain ‐1 ≤ z ≤ 1. The energy equation for the liquid‐phase is then solved by a modified Galerkin finite element method. For better numerical stability, a procedure is proposed for controlling the numerical error that might propagate from the singular point (X, R) = (O, Ro). The profile of the solid‐liquid interface, the heat transfer rate and the pressure drop are presented for various values of Peclet number, Pe = 1, 3, 5, 10 and 30, and for the modified superheat ratio, c = 0.1, 0.5, 5.0, and ∞.
Novel pilot plant technique for sizing gas absorbers with chemical reactions
Authors: Tontiwachwuthikul Paitoon , Meisen Axel , Lim C. J.
Published: March 2009

A new procedure, called the Novel Pilot Plant Technique (NPPT), for designing gas absorbers with chemical reactions is proposed. The technique is based on the premise that full‐scale absorption columns can be sized by making a minimum number of tests using small‐scale pilot plants. Two special features of the technique are that (i) detailed design parameters (such as mass transfer coefficients, reaction kinetics, physical properties) need not be known and (ii) complex calculations are avoided. The validity of the technique is demonstrated for the CO2‐NaOH system, for which the absorber height can be calculated accurately from first principles.
Studies of the fischer‐tropsch synthesis on a colbalt catalyst. III. mechanistic formulation of the kinetics of selectivity for higher hydrocarbon formation
Authors: Sarup B. , Wojciechowski B. W.
Published: March 2009

Mechanistic models are derived to quantify selectivity in the Fischer‐Tropsch synthesis. The models are fitted to experimental selectivity data obtained on a cobalt catalyst and are found to give a satisfactory fit. Results show that branching reactions can be explained by assuming a rate limiting 1‐2 hydrogen shift. For small molecules the 1‐2 shift takes place on one site, whereas larger molecules need an adjacent sit for the shift to take place. The “break” arises from the sum of two Anderson‐Schulz‐Flory distributions arising on two different locations.
On chemical equilibrium of pseudo‐one‐element systems: Application to oligomerization
Authors: Norval G. W. , Phillips M. J. , Missen R. W. , Smith W. R.
Published: March 2009

For a chemical system involving reacting species (such as oligomers) whose molecular formulae are of the form [(E1)a1 (E2)a2 … (EM)aM]n, where E is an element, both the equilibrium distribution and sensitivity analysis can be computed as for a one‐element system. The resulting simplification means that the former requires the solution of a single polynomial equation, and the latter allows explicit calculation of the relevant sensitivity coefficients. The treatment is illustrated for the catalytic oligomerization of olefins.
Blood, guts and chemical engineering
Authors: Sefton Michael V.
Published: March 2009

Basic chemical engineering sciences have been used to address selected medical problems. The natural anticoagulant, heparin, has been immobilized to a polyvinyl alcohol (PVA) coating on polyethylene or polyurethane, to prepare a blood compatible material. Modelling of the relationship between the rate of heparin leakage from the coating and the blood heparin concentration at the blood material interface supported the conclusion that the observed inhibition of clot formation induced by the material was due to the activity of the covalently immobilized heparin. The relationship between flow resistance and tube diameter was used to devise an ex vivo system for demonstrating this activity: 1 mm ID heparin‐PVA coated tubing was tested in a parallel flow circuit with a 3 mm ID silicone tubing so as to control the blood flow through the 1 mm test tubing. In another area of chemical engineering activity in biomedical sciences, live mammalian cells have been microencapsulated in a polymer membrane to prevent the host's antibodies, that are outside the capsule, from causing the immune destruction of the to‐be‐transplanted cells (e.g., pancreatic islets for the treatment of diabetes). These works illustrate the use of chemical engineering in nontraditional ways, consistent with what some consider the new “paradigm” for our profession.
Heat transfer in turbulent forced convection between parallel‐plates
Authors: özisik M. N. , Cotta R. M. , Kim W. S.
Published: March 2009

The thermal entry region heat transfer due to turbulent forced convection of a Newtonian fluid inside a parallel‐plate duct maintained at constant uniform temperature is solved analytically and the local Nusselt numbers are determined with a high degree of accuracy up to the region very close to the inlet. The calculated local Nusselt numbers are compared with those obtained from a recently proposed empirical correlation.
Solubility of H2S, CO2 and their mixtures in an AMP solution
Authors: Teng T. T. , Mather A. E.
Published: March 2009

The solubility of H2S, CO2 and their mixtures in a 3.43 molar solution of 2‐amino‐2‐methyl‐1‐propanol (AMP) has been determined at 50°C at partial pressures between 4 and 5650 kPa. A mathematical model has been used to correlate the data for the individual gases in the solvent. The parameters obtained have been used to predict the partial pressures in the four‐component system. In general the predicted values are in good agreement with the experimental data.
Flow regimes and mass transfer in counter‐current bubble columns
Authors: Uchida S. , Tsuyutani S. , Seno T.
Published: March 2009

Counter current bubble columns have the feature that specific gas‐liquid interfacial area and gas holdup are larger than those for standard and cocurrent bubble columns. In this study, three different flow regimes, churn‐turbulent flow, bubble flow and bubble down‐flow, have been observed in a counter‐current bubble column and correlations of gas holdup and volumetric liquid‐phase mass transfer coefficient have been proposed as functions of operating variables such as the superficial velocities of gas and liquid, the gas‐liquid slip velocity and the liquid properties.
Mass transfer in electrochemical reactors employing gas evolving mercury pool cathodes
Authors: Sedahmed G. H. , Ahmed A. M.
Published: March 2009

The effect of H2 evolution on the mass transfer coefficient of the cathodic reduction of potassium ferricyanide at a mercury cathode was studied with the aim of (i) comparing the mass transfer behaviour of a Hg cathode with that of solid electrodes under gas evolving conditions, and (ii) testing the effect of surface active agents on the mass transfer behaviour of a H2‐evolving Hg cathode. For a given H2 discharge rate the mass transfer coefficient at a mercury cathode was much higher than the value at a solid cathode. The mass transfer coefficient at the H2‐evolving Hg cathode was found to decrease in the presence of Triton X‐100 surfactant by an amount ranging from 62.6% to 86.2% depending on H2 discharge rate and surfactant concentration. A simple mathematical model was formulated to explain the results. The presence of surfactant was found to increase the cell voltage.
Experimental investigation of some hydrodynamic factors affecting slurry pipeline wall erosion
Authors: Shook C. A. , McKibben M. , Small M.
Published: March 2009

Using a non‐intrusive technique, particle velocities and concentrations have been measured as functions of position on the pipe wall for water slurries of two different sands. The experimental conditions correspond to both low (fine particles) and high contact load flows.

Although the velocity and concentration distributions for the two sands were quite different, flux distributions computed from the product of velocity and concentration were similar. The flux distributions are used to interpret wall erosion distributions for sands of these sizes. In the case of the coarser sand, there is evidence that the contact load mechanism contributes significantly to abrasive wear. In this case, scaleup of erosion test results may be possible, using concepts provided by mechanistic flow models. For the finer sand, wall erosion rates appear to be reduced by a lubrication force.
The phase behaviour of the propane‐water system: A review
Authors: Harmens A. , Sloan E. Dendy
Published: March 2009

The paper gives an integral description of the phase behaviour of the propane‐water system from very high to very low pressures in the form of a series of consecutive isobaric T, x‐diagrams. A new p, T — projection is presented. Didactic aspects are emphasised and the heuristics of the relationships between the diagrams outlined. Special attention is given to the equilibria involving hydrates. Other aqueous binary systems of similar behaviour are briefly summarised.
Écoulements et transferts de chaleur dans les Échangeurs à plaques traitant des produits visqueux newtoniens et pseudoplastiques 1. Modélisation des variations du diamètre hydraulique
Authors: Leuliet Jean‐Claude , Maingonnat Jean‐François , Lalande Marc
Published: March 2009

Les performances d'un échangeur de chaleur à plaques sont souvent traduites par des corrélations qui contiennent le diamètre hydraulique, généralement calculé comme valant deux fois la distance entre‐plaques. Nous avons observé expérimentalement que cette valeur de la distance entre‐plaques n'était pas constante, mais dépendait des paramètres tels que le serrage des plaques entre elles et/ou la pression des fluides au sein des canaux. Les variations de cette distance entre‐plaques avec les conditions opératoires ont été étudiées à travers des mesures de chute de pression pour l'écoulement isotherme de fluides Newtoniens. Deux types de plaques ont été testés: des plaques à cannelures droites et des plaques de type chevrons.

Pour les plaques à cannelures droites expérimentées, la valeur de la distance entre‐plaques est indépendante de la pression des fluides dans les canaux. En revanche, elle peut ětre multipliée par 1.18 quand on passe d'un serrage où toutes les plaques sont bien en contact à un serrage proche de la fuite. Pour les plaques de type chevrons, la valeur de la distance entre‐plaques dépend à la fois du serrage de l'appareil et de la pression des fluides, et a varié au maximum dans un rapport 1.52. Les variations de cette distance entre‐plaques ont été modélisées à l'aide de relations simples qui ont permis d'obtenir, pour les deux échangeurs et pour l'ensemble des régimes d'écoulement, une courbe de frottement indépendante du serrage des plaques et de la pression des fluides.
Extended fourier series solutions for diffusion problems with irregularly shaped boundaries and mixed boundary conditions
Authors: Ruth Douglas
Published: March 2009

A general method is developed for the solution of any two‐dimensional, linear diffusion problem which possesses at least one straight line of symmetry. This method is based on extending the classic Fourier series solution to emcompass problems with irregular boundaries and mixed boundary conditions. In order to validate the technique, it is applied to problems with known answers, or to problems which may be solved in more than one coordinate system. The method is demonstrated to be accurate and easily implemented on a desk‐top type computer. The procedure is suitable for solving complex problems for their own sake, or for validating numerical computer codes. Extensions of the method to three dimensions and problems with convective boundary conditions are discussed.
Linearization of diffusion equations with chemical reaction: Generalization of Hikita‐Asai approximation
Authors: Asai S.
Published: March 2009

A technique is presented for the linearization of the reaction term of the differential equations describing mass transfer accompanied by chemical reaction, which is nonlinear with respect to the concentration of a solute transferring across the interface between two phases. The proposed approximation is demonstrated to yield remarkable accuracy by the analysis of a few diffusion problems under steady and unsteady state conditions.
The role of hydrogen in coal particle disintegration at elevated temperatures
Authors: Pozzobon Robert A. , Shaw J. M. , Yushun Sun
Published: March 2009

Coal particle size is considered to be a variable of secondary importance in coal/oil co‐processing and coal liquefaction. This finding is inconsistent with the proposed mechanism for coal particle disintegration, and product yields realized in previous large scale dissolution experiments. Coal particles are shown to break up as a consequence of hydrogen‐coal interactions occurring during preheating. The proposed mechano‐chemical mechanism for coal particle disintegration was identified through direct observation of disintegrating coal particles at elevated temperatures and pressures. Implications for the design of preheaters for coal/oil co‐processing and coal liquefaction are discussed.
Natural convection heat transfer enhancement through latent heat transport in vertical parallel plate channel flows
Authors: Yan W. M. , Lin T. F.
Published: March 2009

A numerical analysis is carried out to investigate the effects of latent heat transfer, in connection with the vaporization of a liquid film, on natural convection heat transfer in a vertical parallel plate channel. Major nondimensional groups identified are GrT, GrM, Pr and Sc. Results for Nusselt and Sherwood numbers are specifically presented for the air‐water and air‐ethanol systems under various heating conditions to illustrate the heat transfer enhancement through latent heat transfer during the evaporation processes. Considerable enhancement in heat transfer due to the exchange of latent heat was clearly demonstrated.
Testing of a spherical dual‐tipped optical fiber probe for local measurements of void fraction and gas velocity in two‐phase flows
Authors: Moujaes S. F.
Published: March 2009

An alternate and easy method of constructing an optical liber probe tip is presented for the study of different two‐phase flow variables such as local time‐averaged void fraction, gas velocity and interfacial bubble passage frequency. The proposed probe tip has similar response characteristics to the “U‐bend” single fiber probe and is easier to construct than the 90° wedge tipped probe. The signal from the spherical tip seems to be insensitive to changes in bubble velocity as opposed to the 90° wedge and is more advantageous at higher velocities. The signal from the spherical tip has the same time duration as the signal changes from liquid to gas and vice versa for the same bubble velocity. A simplified model is presented to describe the balance of forces around the spherical tip when a bubble is penetrated. The model offers a qualitative explanation of why the non‐dimensional response intensity decreases as the bubble velocity increases.
Study of a downward gas jet in a two–dimensional fluidized bed
Authors: Shen Z. , Briens C. L. , Kwauk M. , Bergougnou M. A.
Published: March 2009

The study of a downward gas jet was performed in a two–dimensional (2–D) fluidized bed of sand particles under conditions of minimum fluidization and at atmospheric pressure and room temperature. The jet shifted through a cyclic sequence of left–central–right–central–left positions. The probability of the left and right jets was 40% each, while the less stable central jet occurred only 20% of the time. Discrete probability distributions of jet presence for each of the three jet configurations and an overall distribution are presented. They show that jets are dominant along the external walls of the nozzle. The depth of the downward jet increased with air flowrate in agreement with the correlation from Massimilla and Russo (1973).
Dilute acid hydrolysis of lignocellulosics: An application to medium consistency suspensions of hardwoods using a plug flow reactor
Authors: Abatzoglou N. , Koeberle P. G. , Chornet E. , Overend R. P. , Koukios E. G.
Published: March 2009

A one‐stage process for the high temperature rapid dilute acid hydrolysis of hardwoods, to produce simultaneously furfural and fermentable sugars, is described. A continuous plug flow reactor unit designed to hydrolyse medium consistency wood suspensions (up to 13% w/w in solids) has been operated at capacities up to 90 kg/h, with temperatures ranging from 190°C to 240°C and 20‐120 s as residence times. The final products, mainly furfural and sugars, have been analyzed using high performance liquid chromatography. Yields of 15 kg of hexoses (30% of the theoretical potential) and 10 kg of furfural (65% of the theoretical potential) for 100 kg of sawdust (dry basis) have been obtained. Two pseudokinetic modeis were used to simulate the pentosan and hexosan acid hydrolysis reactions. A Flowtran Simulation has been conducted resulting in mass and energy balances for an eventual industrial unit.
Calculation of infinite dilution activity coefficients by the NRTL and UNIQUAC models
Authors: Demirel Y.
Published: March 2009

Infinite dilution activity coefficients have been calculated for 42 binary systems using the NRTL and UNIQUAC models. Temperature dependent parameters of the models are used in the calculations. These parameters have been estimated by using excess Gibbs free energy and enthalpy of mixing data simultaneously. The calculated values are compared with experimental infinite dilution activity coefficients obtained by extrapolation of vapor‐liquid equilibrium (VLE) data published in the literature. The agreement between the calculated and experimental values is poor for highly nonideal system. The selection of the best model is difficult and may be system dependent.
The yield stress of fibre suspensions
Authors: Bennington C. P. J. , Kerekes R. J. , Grace J. R.
Published: March 2009

Yield stresses were determined for commercial wood pulp suspensions and synthetic fibre suspensions of low and medium mass concentration. The yield stresses measured represent interfibre failure of the network rather than failure between the suspension and a solid surface. The measurements were carried out in a rotary viscometer at low yield stresses and in a concentric rotary shear tester at yield stresses in excess of 2500 Pa. The experimental results were correlated with the volumetric concentration Cv in equations of the form τy = aCbv where a and b are constant for a given fibre type. It was found that b ≃ 3, in agreement with the predictions of a theoretical model of fibre network strength based upon the interlocking of elastically bent fibres. The dependence of the yield stress on the fibre properties of aspect ratio and modulus of elasticity was not adequately predicted by the model, suggesting that fibre bending alone did not account for the network strength over the concentration range studied.
Experimental study of sawdust and coal particle mixing in sand or catalyst fluidized beds
Authors: Hemati M. , Spieker K. , Laguérie C. , Alvarez R. , Riera F. A.
Published: March 2009

This paper presents an experimental study in order to establish mixing and segregation conditions of wood sawdust and coal particles in a fluidized bed of sand or alumina particles. Experiments were performed at room temperature under atmospheric pressure. Simple equipment was used to divide the bed into layers and useful results could be obtained in a short period of time. The influence of fluidization velocity, time of an experiment, size and concentration of sawdust or coal particles was investigated.

Uniformity of mixing was found to increase with an increase in the fluidization velocity. For u/umf less than 2.5, strong segregation occurred between sawdust and sand particles.

Determination of good mixing conditions will be useful in gasification studies of sawdust and coal.
Development of mixing rules for predicting the viscosity of bitumen and its fractions blended with toluene
Authors: Mehrotra Anil K.
Published: March 2009

A comprehensive model is presented for predicting the liquid‐mixture viscosity of bitumen and its fractions diluted with toluene. The proposed model is based on the Walther two‐parameter viscosity‐temperature correlation and a simple viscosity mixing rule. New viscosity data at 22‐100°C are presented for 14 blends of Cold Lake bitumen and its fractions with toluene. All of these data are well correlated by the Walther correlation with AAD < 2%. The predictions from a recently proposed simple mixing formula for toluene‐bitumen blends viscosity are well within an order of magnitude of the data. The blend viscosity predictions are improved substantially by use of a temperature‐dependent viscous interaction parameter. For predicting the viscosity of toluene‐diluted whole bitumen, the bitumen is characterized both as a “black‐oil” and as a mixture of five fractions or pseudocomponents. The calculation procedure for the viscosity of toluene‐diluted bitumen is outlined and the two characterization approaches are evaluated.
Factors affecting the decay of batch liquid‐liquid dispersions
Authors: Jeelani S. A. K. , Pandit A. , Hartland S.
Published: March 2009

A model which predicts the shape of the time dependent sedimentation and coalescence profiles during batch decay, allowing for binary coalescence and increasing hold‐up in the sedimentation zone, and the effect of the height of the dense‐packed zone on the interfacial coalescence rate, is presented. The model is verified using the experimentally observed increase in drop size with time.

Analysis of twenty five liquid‐liquid systems covering a wide range of physical properties, operating conditions and settler geometry indicates that sigmoidal or exponential sedimentation profiles are obtained depending on whether the initial Reynolds number is less or greater than unity, respectively.
Segregation in a stirred fluidized bed
Authors: Zhang Z. , Beeckmans J. M.
Published: March 2009

A bed of particulate solids supported by an upward current of gas can be stirred at moderate power input per unit volume using thin horizontal rods mounted on a vertical shaft. The bed is fluidized, but bubbles are suppressed below a critical value of the fluidizing velocity. Stirring increases bed bulk density and reduces the minimum fluidizing velocity. Segregation in a stirred fluidized bed is enhanced with both flotsam and jetsam tracer particles, but the rate of segregation is reduced with flotsam tracers. The stirred fluidized bed may be useful as a device for dry separation of solids.
Devolatilization and combustion of large coal particles in a fluidized bed
Authors: Zhang J. Q. , Becker H. A. , Code R. K.
Published: March 2009

Devolatilization and combustion of large particles of Eastern Canadian coals (Evans and Minto), 5‐50 mm dia., were studied in a bench‐scale atmospheric fluidized bed reactor at 1023‐1173 K with 0.5 mm sand particles as the bed material. The devolatilization time, mass loss history, changes in proximate volatiles content and C/H mass ratio, and temperature history at the centre of the particle during devolatilization were determined. The mass loss during devolatilization is correlated with the proximate volatiles content of the parent coal. The devolatilization time is correlated with the initial particle diameter by a power‐law relation with an exponent of 1.54‐1.64. The results show insignificant effect of superficial velocity on devolatilization.
Liquid circulation characteristics in jet loop reactors
Authors: Jain D. K. , Patwari A. N. , Khan A. A. , M. Bhagawantha RAO
Published: March 2009

Liquid‐velocity profile measurements in the annular region of a jet‐loop reactor for a gas liquid system are reported, which facilitate evaluation of local phenomena. The range of variables studied included superficial gas velocities of 0‐16 cm · s−1 and superficial liquid velocities of 0‐0.6 cm · s−1. The main observations made with respect to the radial profile of axial liquid velocity are:

a) a trend reversal in the changeover from a liquid phase system to a gas‐liquid system;

b) at low gas loading rates of 1‐3 cm · s−1 it is insensitive to liquid injection rates;

c) at high liquid injection rates it shows a minimum.

A correlation has been proposed to predict the circulation Reynolds number for the two‐phase system.
Backmixing of liquid in horizontal multiple‐impeller vessels
Authors: Fukuda T. , Idogawa K. , Akiyoshi M. , Ando K.
Published: March 2009

The batch mixing model for liquid as the continuous phase of a gas‐liquid system in a horizontal multiple‐impeller vessel was applied to continuous flow operation. The back flow ratio was determined by measuring the residence time distribution. The relation between back flow ratio and operating variables was found to be similar to that for a vertical multiple‐impeller vessel. A method for estimating the back flow ratio in a horizontal multiple‐impeller vessel, from the mixing time in a single‐impeller vessel, was presented.
Heat transfer coefficients in finned‐coil stirred‐tank systems
Authors: Kizilçeç Fatma , Ilsenönsan Z. , Borak Fahir
Published: March 2009

Steady‐state and transient heat transfer coefficients were determined for a finned‐coil, stirred‐tank system using flat‐blade turbine impellers in water. Fin spacing, flowrate, hot water temperature and agitator speed were varied for Re between 20 000 ‐ 110 000 for the agitated side.

Individual transfer coefficients were calculated from the experimental overall coefficients. The correlation developed for predicting external transfer coefficients in agitated systems with finned‐tube coils was tested against transient data.
Le raisonnement qualitatif‐quantitatif de QQSIM
Authors: Tetreault Mario , Lapointe Jean , Marcos Bernard
Published: March 2009

Cette publication montre que les algorithrnes de raisonnement qualitatif manipulent les qualitiés par une caractérisation des valeurs réelles. Un exemple simple fait ressortir la signification qualitative du raisonnement de QSIM (Qualitative SIMulation), son calcul par intervalles et ses limitations. Par la suite, on propose une extension de QSIM pour intégrer differentes connaissances (règles de production, raisonnernent qualitatif, ordre de grandeur, calcul quantitatit) dans un algorithme de simulation qualitative‐quantitative (QQSIM) en qualifiant les données sous forme d'intervalles. Cette extension permet l'utilisation du raisonnement qualitatif sur un système de traitement d'eaux usèes. Pour terminer, on montre que cette approche s'applique dans un contexte de systèmes‐experts.
Analysis and tuning of adaptive generalized predictive control
Authors: Mcintosh Andrew R. , Shah Sirish L. , Fisher D. Grant
Published: March 2009

The adaptive Generalized Predictive Controller (Clarke et al., 1987a, b) is capable of controlling plants with variable dead‐time, unknown model orders and unstable poles and zeros. This paper shows how the GPC control law can be written in an equivalent general linear transfer function form which simplifies closed‐loop (eg. root locus) analysis. Three recommended strategies for selecting the design parameters during the commissioning stage allow the user to adjust the closed‐loop speed of response on‐line using only a single active tuning parameter. Experimental runs confirm the ability of adaptive GPC to provide a consistent closed‐loop response in spite of large process changes.
Predictive Control of a Circulating Fluidized Bed Combustor
Authors: Venugopal S. , Gupta Y. P. , Basu P.
Published: March 2009

The acceptance of CFB combustion in process and utility industries for generating steam has been increasing because of its ability to burn a wide variety of fuels efficiently and in an environmentally acceptable manner. Work on control of this emerging technology is beginning to appear. This paper evaluates the performance of two predictive control algorithms (the Dynamic Matrix Control and a simplified version) for control of temperature and pressure drop in a pilot scale CFB combustor. The robustness of the algorithms is studied on a model of the CFB combustor. The experimental and simulation results show the suitability of the two control algorithms for control of the CFB combustor.
Control policies for an industrial acetylene hydrogenation reactor
Authors: Brown Michael W. , Penlidis Alexander , Sullivan Gerald R.
Published: March 2009

This paper addresses the problem of finding optimal operational policies for an acetylene reactor for day to day operation. A lumped parameter model based on four main reactions is developed and used to examine the effects of the reactor manipulated variables on key reaction parameters. An optimal and a sub‐optimal operational policy which minimize the ethylene loss over time are formulated and the solution techniques are presented. The results indicate that the reactor model is in good agreement with industrial plant data. The performance of the optimal control policy is very similar to the performance of the sub‐optimal control policy. However, the sub‐optimal formulation, while retaining the dominant features of the optimal response, reduces the computational requirements. Finally, some issues concerning the real‐time implementation of an advanced acetylene reactor control scheme are presented. These include the estimation of the optimum regeneration cycle, a recursive model update algorithm, the process optimizer and their overall coordination. A preliminary analysis of the benefits associated with the advanced control scheme suggests a considerable reduction in the yearly ethylene loss.
Effects of wettability and pore geometry on mobilization of oil and gas in physical models and application to water‐alternating‐gas (WAG) injections
Authors: Kong V. W. Tang , Wardlaw N. C.
Published: March 2009

Experiments in capillary tubes show that the mobilization of discontinuous oil and/or gas in a hydrophobic (oil‐wet) system requires a pressure gradient of about 6 to 7 times larger than for a comparable water‐wet system. The mobilization pressure is directly proportional to the contact angle hysteresis and interfacial tension and inversely proportional to tube radius.

For experiments in glass micromodels, where pores were ∼ 3 times as large as connecting throats, mobilization pressures for oil‐wet systems were only ∼ 1.7 times as large as for equivalent water‐wet systems and pore geometry had more effect on mobilization pressure than did differences in wettability. These pore‐level events are thought to affect mobility within WAG banks used to stabilize gas drives.
Temperature field within a devolatilizing coal particle
Authors: Tomeczek Jerzy , Kowol Jan
Published: March 2009

The aim of the present research was to test a mathematical model of coal devolatilization. Verification of the thermal conductivity, specific heat capacity and endothermic heat of pyrolysis was carried out by measurement of the coal particle temperature at the outer surface and in the center of the particle. The model, with recommended thermal and transport data, was then tested on the basis of gaseous products generation rates and total mass loss during experiments with coal granules of size 4‐20 mm and coal grains 0.08‐5 mm dropped into a hot fluidized bed.