bluuebunny/crossref_metadata_2025 huggingface dataset:
Mass transfer to a drop stream from a field liquid
Authors: Huang Yi‐You , Lu S. M.
Published: March 2009

Mass transfer from a stream of drops falling freely in a stagnant liquid was investigated. Drop streams were produced by a dripping method and by a jet breakup method. Water and isobutanol, mutually saturated, were used as the dispersed and the continuous phases. Sodium hydroxide was transferred from isobutanol to water drops which were initially free of solute. The mass transfer resistance is on the continuous phase side. The mass transfer coefficient and terminal velocity of drop streams were measured experimentally. The experimental results show that the mass transfer coefficient in the drop stream is affected by the shielding effect of the previous drops. The experimental data have been correlated as Kt/Ut0.5 versus interdrop distance l, a relationship describing the effect of the interdrop distance on the mass transfer coefficient in the continuous phase.
Experimental test of a model for laminar slurry flow with sedimentation
Authors: Clarke Patrick F. , Charles Michael E.
Published: March 2009

The ability of a flow‐sedimentation model to simulate the flow of a slowly‐settling suspension being transported in the laminar regime through a pipeline with a constant overall pressure drop imposed on it was assessed using experimental scaled‐down pipeline data. Comparison of predicted volumetric flow rate versus time profiles to those observed suggested that the blockage process took place in two steps. Initially, a sediment grew on the lower pipe wall and the flow gradually lessened, as was modelled. As the flow slowed down, ultimately a plug, which enclosed the full cross‐section of the pipe, formed and lead to the rapid blockage of the pipe. It was envisioned that the granular properties of the concentrated suspension became dominant during the final blockage process. A deposit velocity criterion was also developed from the flow‐sedimentation model and was used to generate a deposit velocity versus pipe diameter plot. Results from the plot indicate that the laminar pipeline flow of a slowly‐settling suspension is possible in small diameter pipes.
Enzyme mass transfer coefficient in aqueous two‐phase systems: Modified spray extraction columns
Authors: Pawar P. A. , Veera U. Parasu , Sawant S. B. , Joshi J. B.
Published: March 2009

The fractional dispersed phase hold‐up and mass transfer coefficients were measured in modified spray columns of 50 mm i.d. using an aqueous two phase system of polyethylene glycol (PEG 4000)‐sodium sulphate‐buffer. The mass transfer coefficients were measured for amyloglucosidase and β‐galactosidase. Both co‐current and countercurrent modes of operation were investigated.

The dispersed phase hold‐up (ϵD) and the dispersed phase and the continuous phase mass transfer coefficients (kDa, kCa) increased with increasing dispersed phase velocity. An increase in the phase concentration of sodium sulphate and PEG was found to reduce ϵD, kDa, and kCa. The performance of the modified spray column is compared with the conventional spray column. The modifications resulted into about a ten‐fold enhancement in the throughput and about a five‐fold reduction in the value of the height of a transfer unit (HTU ). It has been shown that the value of HTU of the order of 1 m can be obtained. Empirical correlations for ϵD and kDa, kCa have been proposed.
System identification and PID controller tuning using band‐pass filters
Authors: Natarajan K. , Gilbert A. F.
Published: March 2009

An online recursive system identification technique using band‐pass filters has been developed to estimate the continuous‐time frequency response of any process control system at a number of discrete frequencies. Tuning of PID controllers employs a gradient optimization technique, based on the estimated discrete frequency response of the process rather than a transfer function model of the process. The performances of the identification technique and controller tuning algorithm are demonstrated by a simulation and by experimental results on a distillation column composition control.
Bubble drag in contaminated non‐newtonian solutions
Authors: Rodrigue Denis , De Kee Daniel , Fong C. F. Chan Man
Published: March 2009

The motion of a bubble in an infinite fluid is examined in the case where the surrounding fluid is non‐Newtonian and contains impurities. An expression is developed for the drag force as a function of the shear‐thinning character as well as of the concentration of surfactant of the fluid. The obtained expression for the drag force correlates quite nicely with experimental data for small bubbles.
Flow of viscoelastic polymer solutions in mixed beds of particles
Authors: Tiu Carlos , Zhou James Z. Q. , Nicolae Gilda , Fang Tunann. , Chhabra Raj P.
Published: March 2009

New extensive pressure drop‐flow rate data are reported for the creeping flow of well characterised viscoelastic polymer solutions through packed beds of mixed size spheres and of spheres and cylinders. It is established that the effective mean surface diameter is adequate in correlating the pressure loss data in flow through packed beds of mixed size and shape. A distinct correlation exists between the excess pressure loss observed with viscoelastic fluids and the Weissenberg number.
Liquid transport on a nylon surface moving between liquids through an air‐filled chamber
Authors: Dickey Leland C. , Dallmer Michael F. , Boswell Thomas
Published: March 2009

The flow rate of liquid carried on a nylon strand moving from a liquid filled space, through an air filled space, to another liquid filled space was determined from measurements of electrical conductance of the separated liquids. The measurements are consistent with the transmission of a liquid layer on the nylon surface of constant thickness, independent of surface velocity. The layer thickness is low enough that an adsorptive strand can carry adsorbate from a solution at a practical rate. The effective concentration of solution taken from an adsorption chamber by a saturated adsorbent strand is estimated to be at least 5.8 (λ/S) times the chamber concentration, where λ is the chamber length and S the line speed.
Flow field in the freeboard of vortexing fluidized bed
Authors: Chyang Chien‐Song , Wan Hou‐Peng , Chen Chih‐Chuan
Published: March 2009

A systematic investigation on the flow field in a vortexing fluidized bed cold model was reported. The gas velocity profiles within the freeboard with diameters of 0.19 m and 0.29 m were measured by using a five‐hole pitot tube. A new parameter, called vortex number, Vor defined as the ratio of tangential velocity to axial velocity of the swirling gas stream, was proposed for representing the swirl intensity. Vor is found to be increased with secondary air velocity, and decreased with primary air velocity and diameter of secondary air nozzles. It is also found that the profile of swirl flow is significantly affected by the arrangement of the secondary air nozzles. The effects of inserted length of secondary air nozzles and geometric structure of expansion section on the swirl flow are also studied. Based on the experimental data, a correlation is presented to estimate the vortex number. Vortex number is found to be a function of the geometric structure of exhaust tube, diameter of secondary air nozzle and tangential air flow rate.
Assessment of hazards posed to fluid‐borne cells in airlift reactors
Authors: Yang Junzheng , Glasgow Larry
Published: March 2009

In sparged reactors, interfacial phenomena can produce very energetic liquid‐phase motions; the important interfacial events may include bubble formation, bubble breakage and coalescence, and bubble disengagement. The latter has generally been singled out as a leading cause of cellular damage and death in the large‐scale culture of mammalian cells. In the present work, the danger to cells posed by disengagement phenomena in airlift reactors is quantified through the combination of three separate factors: 1) the number of exposures per hour of operation; 2) the mean residence time (per exposure) in the region of the disengagement disturbances; and 3) the disturbance energy contained in the appropriate range of frequencies. A system for estimating hazard levels in aerated reactors (based upon these three factors) is proposed. The methodology described in this paper makes quantitative comparison of both reactors and reactor operations possible.
Stirring as foam disruption (SAFD) technique in fermentation processes
Authors: Hoeks Frans W. J. M. M. , Van Wees‐Tangerman Carla , Luyben Karel Ch. A. M. , Gasser Kurt , Schmid Sergio , Mommers Henricus M.
Published: March 2009

Foam reduction through stimng was studied in 20 L bioreactors with artificial media and with an actual biotransforma‐tion process. For a given stirrer configuration and within a certain range of the broth mass, the foam height was correlated with the broth mass, i.e. the distance between upper stirrer and dispersion surface, and with the superficial gas velocity. Increasing the stirrer speed often resulted in reducing the foam height. A mechanistic model was developed for the Stirring As Foam Disruption (SAFD) technique, relating the foam height to the horizontal liquid velocity near the dispersion surface. The model illustrates the general applicability of the SAFD technique and points to foam entrainment as the major mechanism for the foam disruption.
Measuring the amount of crystallinity in solutions using DSC
Authors: Coutinho João A. P. , Calange Sandra , Ruffier‐Meray Veronique
Published: March 2009

The amount of solid that forms in a solution at temperatures below the cloud point, is an important quantity in the design of crystallisation processes. A new method using differential scanning calorimetry (DSC) to measure the fraction of crystallised solution, α' is proposed. A very good agreement is obtained between the data measured by the new calorimetric method and using alternative techniques. A simple graphic version of the calculation procedure is also presented. It is shown to produce quick and fair estimates for the solid fraction by a simple analysis of a plot of enthalpy variation with temperature.
Numerical analysis on optimal zone lengths for each pass in multipass zone‐refining processes
Authors: Ho Chii‐Dong , Yeh Ho‐Ming , Yeh Tzuoo‐Lun
Published: March 2009

The effect of zone length on the separation efficiency in multipass zone‐refining processes has been investigated theoretically. The optimal zone length for maximum separation efficiency in each zone pass has been determined. As a well known fact (Davies, 1959), the best performance in the first pass is achieved by normal‐freezing operation. In multipass operations, the optimal zone lengths in each pass and their corresponding maximum fraction of solute removal were obtained with distribution coefficients k and number of passes n as parameters. The results showed the optimal zone lengths for all passes increase with distribution coefficient, but decrease with pass number.
Viscoplastic flows in ducts
Authors: Van Pham Thong , Mitsoulis Evan
Published: March 2009

Axial flows in generalized ducts are analyzed for viscoplastic materials behaving as Bingham plastics with a yield stress. A constitutive equation proposed by Papanastasiou is used, which applies everywhere in the flow field in both yielded and practically unyielded regions. Numerical simulations are presented in several two‐dimensional cross‐sectional geometries, such as square and rectangular ducts (straight and concave), and eccentric annular conduits, for different flow rate and pressure drop ranges. The extent and shape of yielded/unyielded regions are shown as the dimensionless yield stress or Bingham number increases. Master curves are given for the dimensionless flow rate vs dimensionless pressure drop or vs Bingham number for quick engineering calculations useful in practical applications of materials processing.
A new method for predicting viscosity of pure organic liquids
Authors: Gürbüz Yücel Hìlal , Özdoǧan Sìbel
Published: March 2009

A new semi‐theoretical method based on Enskog's hard sphere theory for dense fluids and the principle of corresponding states is presented for predicting viscosity of pure organic liquids. The viscosities of 75 organic liquids—37 acyclic and 38 cyclic hydrocarbons—were calculated using this method which requires critical properties and normal boiling point as input data. The predictions were compared with empirical data and other prediction methods. Highly satisfactory results were obtained over a wide range of temperatures (0.45 < Tr< 0.80).
Etude numérique de l'influence de l'inclinaison sur l'évaporation d'un film liquide s'écoulant sur une paroi plane isotherme ou à flux de chaleur imposé
Authors: Mezaache El Hacene , Daguenet Et Michel
Published: March 2009

Les auteurs étudient numériquement, à l'aide d'une méthode implicite aux différences finies centrées et à maillage variable, l'influence de l'inclinaison sur l'évaporation d'un film liquide s'écoulant sur une paroi plane, isotherme ou à flux de chaleur imposé, horizontale ou inclinée, en supposant l'existence de couches limites laminaires bidimension‐nelles à propriétés physiques variables. Dans le cas d'un système eau‐air humide, ils comparent leurs résultats à ceux d'autres auteurs et étudient les influences de la vitesse d'entrée de l'écoulement d'air et de l'inclinaison de la plaque. Ils montrent que, pour le cas d'une paroi isotherme, l'inclinaison de la plaque influe sur les phénomènes de transfert de masse et de chaleur, principalement aux faibles vitesses de l'écoulement d'air et pour des angles inférieurs à 10°. Dans ce domaine, la température de l'interface est d'autant plus élevée que l'inclinaison est grande de sorte que les densités des flux de vapeur et de chaleur de changement de phase augmentent et que la longueur d'assèchement diminue. Lorsque la paroi est traversée par un flux de chaleur de densité imposée, c'est toujours pour les angles d'inclinaison inférieurs à 10° que les influences de ce paramètre et de la vitesse de l'air sur l'épaisseur du film liquide et sur sa vitesse d'interface sont les plus importantes. Contrairement au cas d'une paroi isotherme, l'accroissement de la vitesse d'entrée de l'air réduit la température d'interface; l'inclinaison influe peu sur la température et la densité du flux massique évaporé ainsi que sur le transfert de masse et de chaleur à l'interface. D'une façon générale, que la paroi soit isotherme ou à flux de chaleur imposé, le transfert de chaleur est dominé par celui lié à la transition liquide‐vapeur.
Dynamics of the fischer‐tropsch synthesis over a supported cobalt catalyst
Authors: Khodadadi Abbas A. , Hudgins Robert R. , Silveston Peter L.
Published: March 2009

Step‐change experiments between H2, CO, and syngas mixtures with time resolution of ca. 0.3 s were undertaken to critically test mechanisms proposed in the literature for the Fischer‐Tropsch synthesis. A silica‐supported cobalt catalyst was used. Results suggest C2+ olefins and branched paraffins form from a carbon deposit on the catalyst surface. Two pathways appear to exist for methane formation. The first of these is from the carbon deposit through direct hydrogenation and through hydrogenolysis of the long‐chain materials formed. The second pathway is hydrogenation of strongly adsorbed CO.
Local bubble behavior in three‐phase fluidized beds
Authors: Chen Z. , Zheng C. , Feng Y. , Hofmann H.
Published: March 2009

Bubble behavior, including bubble Sauter diameter, bubble rise velocity, bubble frequency and local gas holdup in different radial and axial positions, was measured using a dual electro‐conductivity probe in air‐water‐glass beads fluidization systems. It has been found that the bubble characteristics differ significantly in various flow regimes, depending on the operating conditions; the radial distribution of bubble parameters also changes from one flow regime to another. Thus, it is necessary to employ local bubble behavior in the modeling of three‐phase fluidized beds.
A generalised back‐flow model to predict the tracer response in liquid—liquid stagewise contactors
Authors: Das Parichay K.
Published: March 2009

A generalized transient back‐flow model to predict the transient tracer concentration in a multistage extraction column has been developed. The model does not assume any extra stage at the end of the contactor and is based on unified formulation. The solution can be obtained in a straight forward way by using the linear operator theoretic approach as opposed to Laplace transform.
Interstage backmixing of an aerated multistage, mechanically‐agitated, compartmented column
Authors: Takriff Mohd Sobri , Penney W. Roy , Fasano Julian B.
Published: March 2009

The interstage backmixing in a multistage, mechanically‐agitated, compartmented (MSAC) column was determined experimentally, using air‐water. The effects of impeller speed, impeller diameter and both superficial liquid velocity and superficial gas velocity through the interstage opening were investigated. Both the counter‐current and co‐current flow of air and water in the column were investigated. As air superficial velocity through the opening increased from zero, the interstage backmixing significantly decreased initially, reached a minimum, then increased slowly to a maximum after which it decreased continually with further increase in superficial gas velocity. The effect of the gas flow on interstage backmixing was correlated in dimensionless form.
Turbulence in stirred tanks: Anisotropic, approximate, and applied
Authors: Kresta Suzanne
Published: March 2009

Over the last ten years, many ways of characterizing the turbulence in stirred tanks have been proposed, and the importance of the local rate of dissipation of turbulent kinetic energy (ϵ) to various processes has been clarified. In this paper, our understanding of the role of ϵ is examined for the blend time of miscible fluids, for drop break‐up, for reactor design, for cell damage in bioreactors, for gas dispersion, for crystallization, and for flocculation and coagulation. The conceptual difficulties inherent in approximate measurements of ϵ are discussed with examples and background theory. Particular attention is paid to the various length and time scales present in the tank, the anisotropic nature of the flow field, and the effect of organized structures on turbulence measurements. Progress in the area over the last ten years is reviewed in the context of these limitations.
Theoretical investigation into instability of a refrigeration system with an evaporator controlled by a thermostatic expansion valve
Authors: Ibrahim Ghaleb A.
Published: March 2009

A theoretical model is developed and solved to investigate the instability of a refrigeration system with an evaporator controlled by a thermostatic expansion valve. An evaporator time constant is used to account for the delay of the liquid refrigerant distribution along the two phase region. Results show that there is an evaporator critical time constant, below which the system operates in a stable manner. This critical time constant is found to decrease with decreasing the partial load and to increase with increasing the contact thermal resistance and the two‐phase region heat transfer coefficient. The bulb size is also found to have a great effect on the stability.
Kinetics of fructose‐glucose isomerization with sweetzyme type A
Authors: Bravo V. , Jurado E. , Luzón G. , Cruz N.
Published: March 2009

A study has been made of the kinetics of fructose‐glucose enzymatic isomerization with an immobilized glucose isomerase, Sweetzyme A, at 60°C and with initial fructose concentrations of between 0.1 and 2.0 M. In the kinetic study, the effects of internal and external transport were considered, and it was found that when the data were fitted to a kinetic of a pseudo‐first‐order type, the non‐enzymatic reaction could not be disregarded at low enzyme and high substrate concentrations. When non‐enzymatic isomerization is taken into account, the true enzymatic‐reaction constant can be calculated, giving values for maximum rate of 1.39 · 10−6 mol (kg·s)−1 and for Michaelis‐Menten constant of 1.24 M. Establishing the influence of the transport in the interior of the catalyzing particles has enabled the determination of a value for effective diffusivity of 0.59 · 10−10 m2·s−1.
Viscous and yield stress properties of athabasca topped heavy oil
Authors: De Kee Daniel , Chornet Esteban , Zhang Wenqi
Published: March 2009

This contribution reports on a study of the rheological behavior of Athabasca topped heavy oil as a prototype oil derived from western Canadian bitumen. Mixtures of crudes with additives such as pentane and toluene are studied. Data obtained using three different rheometers superpose rather well. Observed non‐Newtonian behavior was successfully modeled by a simplified equation, derived from a model proposed by De Kee and Chan Man Fong (1994). Yield stress data were determined using a technique which does not involve extrapolation. Both yield stress as well as viscosity data obey Arrhenius type relations over the temperature range studied.
Liquid—liquid equilibria of ternary ETBE‐ETOH‐H2O and quaternary ETBE‐ETOH‐H2O‐TBA mixtures
Authors: Quitain A. T. , Goto S.
Published: March 2009

Liquid‐liquid equilibria of ETBE‐EtOH‐H2O mixtures are measured at 15,25 and 35°C. UNIQUAC and NRTL equations are fitted to the experimental data using ASPEN PLUS. Both the experimental and correlated values of the equilibrium compositions are compared with the values predicted by UNIFAC method. The same procedure is extended to quaternary ETBE‐EtOH‐H2O‐TBA system at low TBA concentration.
Predictions on bubble and solids movement in laboratory polyethylene fluid beds as visualized by X‐ray computer assisted tomography (CAT) scanning
Authors: Zarabi Taghi , Kantzas Apostolos
Published: March 2009

Solid and gas distributions are tomographically quantified as a function of position with high resolution in a series of laboratory fluid beds containing air and polyethylene particles. The resolution used is 0.4 mm by 0.4 mm by 3 mm. The laboratory models are Plexiglas columns of 10 cm in diameter and the settling bed L/D ratios vary between one and three. Large particles (up to 1.5 mm in diameter) of high density polyethylene and linear low density polyethylene are used. The superficial gas velocities vary from the minimum fluidization velocity to 50 cm/s. In this paper, the analysis of fluid bed CAT scanner images is extended to show bubble, emulsion and dense phase distribution. The analysis is also used to determine the bubble diameter and to predict the flow direction of solid particles as well as the velocity of descending solids. The voidage frequency distributions of a bed at different gas flow rates are compared to each other and the voidage threshold values corresponding to gas, emulsion and dense phases are determined. These threshold values are used to prepare ternary images that clearly show the parts of the bed cross‐section corresponding to bubble, emulsion and dense phases.
Enhancement of mass transfer in flow channels under thermal gradients
Authors: Bendrich Guido , Shemilt Leslie W.
Published: March 2009

Overall mass transfer coefficients, at the solid liquid interface in a rectangular cross‐section flow reactor, were obtained using the limiting current technique. Empirical correlations were developed for single‐phase flow for a full range of surface configurations, for laminar and turbulent flow regimes, and for isothermal and non‐isothermal conditions. Isothermal mass transfer was almost doubled by the selection of the reactor slope and surface configuration. Imposition of up to a 30°C difference at the interface, enhanced mass transfer approximately four times, over the isothermal case. Mathematical simulation for mass transfer in flow reactors, is shown to agree within 15% of experimental values found in the literature and for the experiments reported here.
Mass transfer from spherical particles and reservoirs into quiescent liquids
Authors: Doan Huu D. , Trass Olev , Fayed Muhammad E.
Published: March 2009

A continuous weighing technique was developed for measuring urea transfer (carbamide, a fertilizer) from a single opening on a coated sphere in a stagnant liquid. Urea release was determined from the changes of the particle weight with time. Mass transfer coefficients for Rayleigh numbers from 1.8 × 107 to 6.8 × 1010 were measured and compared with those for uncoated urea spheres and literature data. For the opening oriented vertically upward in water, natural convection enhanced the transfer rate by 1.8 times compared to that for urea diffusion only. In other opening orientations (45°, 90°, 135° and 180° to the vertical), natural convection provided the major mechanism for the release. A model for urea diffusion was also developed. It agrees well with experimental data.
L'électrolyseur dans l'optique de la dynamique des procédés
Authors: Fahidy Thomas Z.
Published: March 2009

This article written for the non‐specialists reviews the various methods for modeling electrolyzer behavior. Deterministic and stochastic models are discussed and the adaptation of process dynamic to electrolysers is emphasized.
A numerical study of the accelerating motion of a dense rigid sphere in non‐newtonian power law fluids
Authors: Chhabra Rajendra P. , Soares Armando A. , Ferreira Jose M.
Published: March 2009

The equations of motion of an accelerating sphere falling through non‐Newtonian fluids with power law index n in the range 0.2 ≤ n ≤ 1.8 were integrated numerically using the assumption that the drag on the sphere was a function of both power law index and terminal Reynolds number, Ret For 10−2 ≤ Ret ≤ 103 both dimensionless time and distance travelled by the sphere under transient conditions showed a much stronger dependence on the flow behaviour index, n, for shear‐thinning than for shear‐thickening fluids. The form of this dependence is investigated here. Furthermore, results in four typical shear‐thinning fluids suggested a strong correlation between the distance and time travelled by the sphere under transient conditions and the value of the fluid consistency index. The analysis reported herein is, however, restricted to dense spheres falling in less dense fluids, when additional effects arising from the Basset forces can be neelected.
Dynamic modelling of consecutive reactions: Application to the acrylonitrile amination
Authors: Kadri Brahim , Fabre Bernard , Accary Armand , Kessler Mathieu
Published: March 2009

When dealing with optimal control problems to maximize the selectivity of reactions for fine chemical synthesis, representative kinetic and thermodynamic models should be available. While literature appears to be very extensive on theoretical approaches to solve the problem, examples presenting complete models of chemical transformations are scarce. This paper presents the identification of consecutive reactions carried out in a batch reactor. Material and energy balances, satisfying dynamical state evolutions in the temperature range 20‐60°C are deduced, for concentrations of acrylonitrile ranging up to 1.6 kmol·m−3. The stoichiometric network is simplified into two reactions, one reversible and one irreversible. Reaction enthalpies are measured from isothermal runs conducted in the RC1 heat‐flow calorimeter from Mettler Toledo.
Effect of pulp fibres on gas holdup in a flotation column
Authors: Janse Peter , Gomez Cesar O. , Finch James A.
Published: March 2009

Column flotation is an emerging technology in the deinking of recycled paper. Deinking efficiency depends primarily on the effect of four physical variables: gas and accepts flowrates, bubble size distribution, and pulp consistency. Experiments to establish operating ranges for these variables by determining their effect on gas holdup were conducted in a laboratory column installed at Bowater's Gatineau (Quebec) mill which processes a pulp (70% ONP/30% OMG) with about 1% consistency. The results showed the general trends expected from a review of previous studies: gas holdup increases with gas and accepts flowrates and with smaller bubble size, and decreases for higher pulp consistencies. However, the review also demonstrated that the published information is of limited application as the bubble size was much larger than that encountered in industrial flotation practice, primarily because of the use of pure water. Industrial pulps contain in most cases surface active agents which have a substantial effect on forming and preserving a small size bubble population.
An investigation of heat transfer from a vertical tube in a spouted bed
Authors: Macchi Arturo , Bi Hsiaotao T. , Legros Robert , Chaouki Jamal
Published: March 2009

An experimental investigation on heat transfer from a vertical tube in a gas—solid spouted bed has been conducted. Values of heat transfer coefficients (hs) have been found to vary between 95 and 230 W/m2°C. Maximum values of hs are always at the spout axis and decrease monotonically towards the column wall. The drop is most important at the spout‐annulus boundary. Most of the effects from different parameters can be explained by the flow patterns of the gas, although particle convection still contributes to some extent to the heat transfer rate. Equations correlating hs in the spout and the annulus have been developed.
The futility of raffinate reflux revisited
Authors: Rao D. P.
Published: March 2009

The role of reflux in equilibrium separation processes has been examined from a mechanistic viewpoint. The raffinate reflux — presaturation of solvent with raffinate in a separate unit (presaturator) — has been demonstrated to be futile in the past, considering the stages to be ideal. We have examined the utility of raffinate‐like reflux in all the equilibrium separation processes. The nature of mass transfer in these processes with and without presaturator and its implications in the design and analysis have been presented.
Treatment of industrial wastewater using zeolitite and sepiolite, natural microporous materials
Authors: Brigatti Maria Franca , Frigieri Paola , Gardinali Christian , Medici Luca , Poppi Luciano , Franchini Giancarlo
Published: March 2009

This work investigates the ability of natural microporous materials, such as a zeolite‐rich tuff (zeolitite) and a modulated phyllosilicate (sepiolite), to remove heavy‐metal ions from simulated inorganic polluted industrial wastewater. Fixed beds of sepiolite and zeolitite were percolated by a solution of Co2+, Cu2+, Zn2+, Cd2+, and Pb2+ (concentration of each cation, 2 ⊗ 10−3 N; total concentration, 10−2 N) and were regenerated with a 2 ⊗ 10−3 N Na+ solution. The order of decreasing affinity was, for sepiolite: Cu2+ > Zn2+ > Cd2+ > Pb2+ ≅ Co2+, and, for zeolitite: Pb2+ “Cd2+ > Cu2+ > Zn2+ > Co2+. After regeneration with Na+ solution, a fraction of the retained heavy metals was quickly released by the beds as follows: sepiolite, Co2+ ≅ Pb2+ > Cd2+ > Zn2+ > Cu2+; zeolitite, Cd2+ > Cu2+ ≅ Zn2+ > Co2+ > Pb2+. XRD and DTA‐TGA analyses examined structural changes in the natural and final materials.
Resination and decarboxylation reactions in fusion synthesis of ca‐resinates
Authors: Sundqvist Satu , Paatero Erkki , Tenhola Harri
Published: March 2009

The reaction steps in fusion synthesis of Ca‐resinates include a fast, irreversible resination reaction and a slow decarboxylation of rosin acids. The kinetics of the reactions was studied separately in a laboratory scale batch reactor. The kinetic data were obtained by acid number titrations and FTIR measurements. Resination was observed to be a fast irreversible reaction in the temperature range 190 to 235°C. Rate equations for the decarboxylation reaction were derived based on plausible mechanistic reaction steps of free and solvating rosin acids. The parameters of the rate equations were estimated for syntheses at different reaction temperatures (265 to 285°C) and the kinetic model was successfully applied to predict the experimental kinetics of rosin acid decarboxylation.
Pressure and voidage fluctuations in slugging fluidized beds
Authors: Bi Hsiaotao
Published: March 2009

In fully developed slugging fluidized beds, the maximum amplitude of absolute pressure fluctuations is reached with increasing superficial gas velocity when the slug length reaches a maximum, and the separation distance between successive slugs starts to decrease. Uc, the superficial gas velocity at which absolute pressure fluctuations reach a maximum, thus indicates the early stage of transition from slugging to core‐annular flow. Uc, identified based on standard deviations of differential pressure fluctuations or local voidage fluctuations, can be predicted by slug flow models and does not signify a transition to turbulent fluidization.
CFD modeling of flow, macro‐mixing and axial dispersion in a bubble column
Authors: Thakre Shirish S. , Phanikumar Docca V. , Khare Ashok S. , Joshi Jyeshtharaj B.
Published: March 2009

The flow pattern in a bubble column depends upon the column diameter, height, sparger design, superficial gas velocity and the nature of gas–liquid system. In this paper, the effect of some of these parameters have been simulated using Computational Fluid Dynamics (CFD). The relationship of these parameters with the interphase force terms has been discussed. A complete energy balance has been established. Using this methodology, the flow patterns reported by Hills (1974), Menzel et al. (1990), Yao et al. (1991) and Yu and Kim (1991) have been simulated. Excellent agreement has been shown between the CFD predictions and the experimental observations. The above model has been extended to homogenization of an inert tracer. In order to confirm this model, mixing experiments were carried out in a 200 mm i.d. bubble column. A radioactive tracer technique was used for the measurement of mixing time. Tc‐99m (99m Tc), in the form of sodium pertechnate salt, was used as the liquid phase tracer. Good agreement has been shown between the predicted and the experimental values of mixing time. The model was further extended for the estimation of axial dispersion coefficient (DL). Excellent agreement between the simulated and the experimental values of the axial dispersion coefficient confirms the predictive capability of the CFD simulations for the mixing process.
Détermination électrochimique du nombre de sherwood minimum pour un milieu macro‐poreux (fritté — lit fixe de grains)
Authors: Vilar Eudésio Oliveira , Coeuret FrançOis
Published: March 2009

Le travail applique la méthode électrochimique de mesure des coefficients de transfert de matiére solide/liquide à la recherche expérimentale de la valeur du nombre de Sherwood pour le transfert stationnaire de matière par diffusion moléculaire entre un matériau poreux et un liquide contenu dans ses pores. Ce nombre de Sherwood minimum est déterminé pour le cas des frittés et pour celui des lits fixes de grains sphériques. Les aspects théoriques s'appuient sur l'analogie du problème considéré avec celui de la compétition entre diffusion moléculaire et réaction chimique hétérogene dans les catalyseurs poreux.
Growth of Rhizobium leguminosarum on peat in rotating bioreactors
Authors: Jauhari Ritika , Gray Murray , Holloway Greg
Published: March 2009

The legume inoculant Rhizobium leguminosarum was grown on peat in roller bottles and a rotating drum bioreactor. Growth conditions were first determined using experiments in roller bottles. The best growth rate and cell count were obtained with peat containing 40% moisture (wet basis) and a volume fraction of moist peat of 0.3 in the roller bottle bioreactors. A cell count of 1.3 to 1.9 × 109 CFU/g was achieved in 4 d or less, from an initial inoculum of 106 CFU/g. In a rotating drum bioreactor, the growth of R.leguminosarum on peat with sucrose as the main carbon source was completed after 4 d. The majority of growth was in the first 2 d, based on carbon dioxide evolution. These results showed that growth of R. leguminosarum was more rapid in the rotating drum than in bags of peat, due to enhanced oxygen transfer.
Amino acids profiles in a ph‐auxostat
Authors: Lin Yen‐Han , Ji Wei
Published: March 2009

The proportions of amino acids changed dramatically in a pH‐auxostat as the dilution rate was increased by feeding a medium with a low buffering capacity. A brief period of auxostatic culturing converts an elective mixed culture to a nearly pure culture, and this selection is accelerated by lowering the buffering capacity. As the specific growth rate was increased, the organisms utilized some of amino acids partially and/or completely, while others were essentially unchanged or even enriched. Such an enrichment effect was greatest at the highest specific growth rate.
Biodegradation and detoxification of wood leachate from pentachlorophenol‐treated poles
Authors: Mollah A. Hamid , Allen D. Grant
Published: March 2009

The pentachlorophenol (PCP) in leachate, generated from size‐reduced PCP‐treated poles, was degraded using a mixed culture containing Arthrobacter sp. in cyclic batch bioreactors in non‐sterile conditions. Complete degradation of PCP was achieved for a five‐month period for a concentration of 50 mg PCP/L and 12 h cycle time. The adsorbable organic halogen (AOX) concentration of the reactor effluent was reduced by two orders of magnitude compared to the feed, and the chemical oxygen demand (COD) was reduced by 50%. The increase in chloride ion concentration also suggests that PCP was mineralized to end products. In tests to increase the process throughput, complete degradation of PCP was also achieved in the cases for 120 mg PCP/L and a 12 h cycle time or 50 mg PCP/L and a 6 h cycle time. Daphnia magna toxicity tests showed that the presence of PCP in leachate caused toxicity, and the biodegradation of PCP resulted in significantly reducing the effluent toxicity to a value similar to that of PCP‐free nutrient solution.
Sequencing batch reactor technology for the purification of concentrated dyehouse liquors
Authors: Hemmi Martin , Krull Rainer , Hempel Dietmar C.
Published: March 2009

A sequencing batch reactor (SBR) technology for the purification of concentrated reactive azo‐dye containing residual dyehouse liquors from a padding process was developed and investigated. Within the treatment cycle, the anoxic dye cleavage, the aerobic mineralization of organic compounds, in combination with the biodegradability‐achieving partial oxidation with ozone, are carried out sequentially. Anoxic decolourization of the residual liquor without addition of an auxiliary substrate was observed, and a 90% biological degradation of the dyehouse liquor's recalcitrant organic compounds was achieved. COD decreased by 95% and AOX (adsorbable organohalogenic compounds) by 90%. Within the whole process, the colour of the concentrated wastewater decreased by 98%.
Continuous separation of suspensions containing light and heavy particle species
Authors: Nasr‐El‐Din Hisham A. , Masliyah Jacob H. , Nandakumar Krishnaswamy
Published: March 2009

Continuous separation of bidisperse suspensions containing particles of significantly different size and density in a vertical settler was examined. The effects of the feed total solids volume fraction, composition, and flow rate on the performance of the settler were investigated. For feed total solids volume fractions less than 0.1, a kinematic model based on the Patwardhan and Tien (1985) expression for relative velocity was found to predict the experimental measurements fairly well over a wide range of parameters. For feed total solids volume fractions greater than 0.2, a strong local instability was observed in the settler. This local instability significantly improved the performance of the settler in some cases.
Experimental study and mathematical modeling of gaseous toluene biofiltration by thermophilic active compost
Authors: Karamanev Dimitre G. , Matteau Yanick , Ramsay Bruce A.
Published: March 2009

The main goal of this work was to develop a mathematical model of the process of toluene biofiltration by thermophilic active compost. The model parameters were determined in laboratory‐scale experiments with a biofilter, as well as in microcosm experiments. Our experiments have shown that there are two distinctive shapes of compost particles: flat and round ones. The retention time distribution was also determined experimentally. The experimental results of the kinetics, retention time distribution and particle shape were used to develop a mathematical model of the process. Toluene and oxygen concentration profiles were calculated as a function of the particle depth. It has been shown that the oxygen concentration is always is excess and therefore, no anaerobic zones can be expected. A significant intraparticle mass‐transfer resistance was predicted for the case of round particles while the effect of internal mass‐transfer was not that important in the flat particles. The toluene concentration profile as a function of the bioreactor axial coordinate was calculated and compared to the experimental data.
Vapour—liquid equilibrium of H2S‐Hydrocarbon mixtures using a generalized cubic equation of state
Authors: Valderrama José O. , Arce Pedro F. , Ibrahim Ahmed A.
Published: March 2009

A generalized cubic equation of state proposed by one of the authors has been applied to the calculation of vapour‐liquid equilibrium (VLE) of hydrogen sulfide‐containing systems. Experimental VLE data for hydrogen sulfide + hydrocarbons, taken from the literature, have been systematically studied using the generalized equation and conventional van der Waals's mixing rules. The interaction parameter required in the mixing rules was obtained for thirteen systems at different temperatures, and a correlation for the interaction parameter as a function of the reduced temperature of the hydrocarbon solvent is proposed. The correlation for the interaction parameter is recommended for predicting VLE in processes in which hydrogen sulfide mixtures are involved.
Experimental influence of kinetic inhibitors on methane hydrate particle size distribution during batch crystallization in water
Authors: Pic Jean‐Stéphane , Herri Jean‐Michel , Cournil Michel
Published: March 2009

This paper reports an experimental study of methane hydrate crystallization, crystallization and dissociation cycles are performed in an isothermal and isobaric pressurised stirred reactor. Both methane gas consumption and methane hydrate particles population size distribution (PSD) (calculated from turbidimetric measurements) are recorded. The influence of pressure, stirring and two kinetic inhibitors (PVP and FXAP) is quantified. The crucial moment of the additive introduction (dissolved before or injected during crystallization) is particularly focused on. Finally, the bases of a kinetic inhibition model are raised, introducing a dead zone for crystal nucleation and growth.'
Structure‐H gas hydrates in petroleum reservoir fluids
Authors: Tohidi B. , Østergaard K. K. , Danesh A. , Todd A. C. , Burgass R. W.
Published: March 2009

An integrated experimental/modelling investigation was conducted on the potential of newly discovered strueture‐H (sH) hydrates formation in petroleum reservoir fluids. A thermodynamic model was validated against a series of experimental data on a natural gas with various quantities of methylcyclohexane (MCH). Three mixtures were tested where structure‐II (sII), sII/sH and sH were the stable structures. The validated thermodynamic model was employed to predict the stable hydrate structure for a large number of real reservoir fluids, (i.e., black oils, volatile oils and gas condensates). The results showed that sII is the stable hydrate structure for all systems investigated in this work. However, sH might co‐exist with sII in some reservoir fluids where transportation of hydrates as slurry is being considered.
Den Zucker im Brei suchen
Authors: Hummel Sandra , Pflüger Maren , Ziegler Anette‐G.
Published: March 2009

Wenn Babys an Diabetes Typ 1 erkranken, kann das auch an ihrer Ernährung liegen. Eine groß angelegte Studie untersucht die Rolle des Glutens als Auslöser
Ein Forum für das Wissensmanagement
Authors: Dzwonnek Dorothee
Published: March 2009

Von Planung bis Personalführung, von Steuerung bis Selbstevaluation: Warum die DFG mit einem Curriculum auf die zunehmende Komplexität der Forschungsarbeit reagiert – und wie sie dabei eigene Akzente setzt
Wahlverwandtschaften in Westafrika
Authors: Unterstell Rembert
Published: March 2009

Die Sozialanthropologin Erdmute Alber untersucht den Wandel familiärer Beziehungen auf dem „Schwarzen Kontinent”︁ – und hat dabei auch Europa im Blick
„Ein Raunen im Saal”︁
Authors: Finetti Marco
Published: March 2009

Wie bekannt ist die Exzellenzinitiative im Ausland? Und wie wird sie dort gesehen? Nach einer Informations‐ und Werbetour durch die USA sprach Marco Finetti mit Annette Schmidtmann von der DFG und Hans‐Georg Kräusslich vom Exzellenzcluster „Cellular Networks”︁
Im virtuellen Reich der Myrmekologen
Authors: Pfeiffer Martin
Published: March 2009

Die staunenswerte Vielfalt der Ameisenfauna Südostasiens zeigt ein neues wissenschaftliches Internetportal. Auf den hochaufgelösten Automontagefotos sind selbst winzigste Körperdetails zu erkennen – eine wertvolle Hilfe für Artenforscher in aller Welt
Anxiety does not predict response to antidepressant treatment in late life depression: results of a meta‐analysis
Authors: Nelson J. Craig , Delucchi Kevin , Schneider Lon S.
Published: March 2009

Objective

Previous studies of mixed aged and older adult samples with major depressive disorder (MDD) reported reduced depression response in anxious patients, but a systematic review and analysis has not been performed. Our aim was to determine if anxiety predicts antidepressant response in previously identified placebo‐controlled trials of second generation antidepressants for late‐life depression.

Method

From a previous systematic review that identified ten randomized, placebo‐controlled trials of community dwelling patients aged 60 or older with major depression, anxious patients were identified by a score ≥7 on the anxiety/somatization factor of the Hamilton Depression Rating Scale (HDRS). Response was defined as 50% or greater improvement on the HDRS or the Montgomery Asberg Depression Rating Scale. A meta‐analysis was performed using a random effects model to calculate Odds Ratios (OR).

Results

Data were available from eight trials having ten drug‐placebo contrasts that included 2322 anxious and 1387 non‐anxious patients. The odds ratio for response to drug compared to placebo in anxious patients was 1.57 (95% CI 1.15, 2.14; z = 2.86, n = 10, p < 0.001), in non‐anxious patients was 1.44 (95% CI 1.15, 1.80, z = 3.21, n = 10, p < 0.001), and did not differ between groups. Pooled response rates to drug and placebo respectively were 49.4% vs 37.4% in anxious patients and 44.2 vs 35.5% in non‐anxious patients.

Conclusions

In randomized, placebo‐controlled trials, anxiety in late‐life depression was not associated with decreased response to second generation antidepressants. Copyright © 2009 John Wiley & Sons, Ltd.