bluuebunny/crossref_metadata_2025_split huggingface dataset:
A neural‐network based model of bioreaction kinetics
Authors: Saxén Björn , Saxén Henrik 
Published: March 2009

AbstractA neural‐network based model of the kinetics in a fermentation process is presented. In the development and application of the model, the state of the process was estimated by an independent model based on elemental balances and an electroneutrality condition. The aim of the work was a model that describes the overall kinetic relations well enough to be used for on‐line simulation and prediction. Both feed‐forward and partially recurrent networks were investigated. The networks were trained off‐line, but in the on‐line application they are adapted to the process conditions by adjusting a set of correction factors. The approach is illustrated on a number of batch runs of Saccharomyces cerevisiae, where the networks are demonstrated to be able to accurately describe the biphasic growth.
Regression analysis of a chemical reaction fouling model
Authors: Vašák F. , Epstein N. 
Published: March 2009

AbstractA previously reported mathematical model for the initial chemical reaction fouling of a heated tube is critically examined in the light of the experimental data for which it was developed. A regression analysis of the model with respect to that data shows that the reference point upon which the two adjustable parameters of the model were originally based was well chosen, albeit fortuitously.
Modeling of surface intermediates under forced periodic conditions applied to CO2 methanation
Authors: Marwood Michel , Doepper Ralf , Renken Albert 
Published: March 2009

AbstractForced oscillations of the carbon dioxide concentration in a hydrogen feed were applied to the carbon dioxide methanation reaction with simultaneous gas phase and surface analysis. The response of the gas phase and surface species to these repeated dynamic conditions show a time shift following the sequence CO2 → formate → CO → methane, but can be modeled by a simple model involving one single adsorbed surface intermediate and a reservoir in equilibrium with this intermediate. The dynamic behavior of this intermediate is very close to the variation of the IR absorption band associated with formate and carbonate species.
Understanding of resonance phenomena on a catalyst under forced concentration and temperature oscillations
Authors: Van Neer F. J. R. , Kodde A. J. , Den Uil H. , Bliek A. 
Published: March 2009

AbstractResonance is an interesting phenomenon that may be observed for reactions on catalytic surfaces during periodic forcing of operating variables. Forcing of the variables for non‐linear systems may result in substantially changed time averaged behaviour. These resonance phenomena have been observed experimentally by coincidence rather than by systematic analysis. It is not clear for what type of reaction kinetics such behaviour may be expected and predictions are therefore impossible. Clearly, this forms a serious obstacle for any practical application.In this work we set out to analyse the nature of resonance behaviour in heterogeneously catalysed reactions. A Langmuir Hinshelwood microkinetic model is analysed. It is demonstrated that for weakly non‐linear forcing variables — as inlet concentrations — forcing leads to resonance phenomena in terms of the reaction rate only in case high total surface occupancies exist in the steady state. In contrast, forcing of strongly non‐linear variables — like temperature — may give rise to resonance phenomena for both low and high surface occupancies. Necessary conditions for resonance to occur are derived. The analysis of resonance phenomena is greatly simplified by the availability of explicit analytical expressions as can be derived from Carleman linearization. We will demonstrate the merits of Carleman linearization as compared to numerical integration.
A periodic flow reversal reactor: An infinitely fast switching model and a practical proposal for its implementation
Authors: Sun Q. , Young B. , Williams D. F. , Glasser D. , Hildebrandt D. 
Published: March 2009

AbstractIn a catalytic reactor the solid heat capacity is relatively high compared to that of the gas so that even relatively slow periodic flow reversal approximates infinite switching. An internally consistent model is developed which assumes plug‐flow of the gas, neglects conduction in the direction of flow and, by having different gas and solid temperatures, allows heat transfer between the gas and solid. It is shown that this reactor can in certain situations achieve higher conversions in a given volume of catalyst than an adiabatic plug‐flow reactor for exothermic reversible reactions. It is further shown that these equations also model the limit of a more industrially desirable counter‐current steady‐state reactor.
Coking kinetics of a Cr2O3/Al2O3 catalyst during 1‐butene dehydrogenation: Effect of H2 partial pressure
Authors: Romero E. , Rodríguez J. C. , Peña J. A. , Monzón A. 
Published: March 2009

AbstractThe influence has been studied of the partial pressure of hydrogen (0–30 kPa) upon the coking rate of a Cr2O3/Al2O3 commercial catalyst during 1‐butene dehydrogenation. Coke deposition has been analysed using a monolayer‐multilayer reversible coke growth model (MMRC model). This model provides good fits to the experimental data, within the range of partial pressure of H2 studied, and allows us to estimate the main kinetic parameters involved in the coking‐deactivation process. The results obtained reveal a dual effect of hydrogen: competition against 1‐butene for the active sites and the removal of coke precursors from the catalyst surface. Bom effects diminish the coking rate as the H2 partial pressure is increased.
On bitumen liberation from oil sands
Authors: Basu S. , Nandakumar K. , Masliyah Jacob H. 
Published: March 2009

AbstractLaboratory experiments were performed to investigate the effect of pH on (a) bitumen film thinning and film rupture process (b) bitumen/water contact line displacement and (c) the static contact angle of bitumen on a glass surface in the presence of an aqueous medium. A coated bitumen film on a glass surface was found to thin down and rupture spontaneously when a few drops of water having a pH of 11 was placed on it. In another experiment, a bitumen coated glass plate was submerged in water. The contact line of an initially circular bitumen film on the glass surface displaced in the inward direction to take the shape of a droplet. Measurement of the dynamic contact angle of bitumen with time showed that the bitumen/water contact line displacement was faster at a pH of 3 than at a pH of 11. However, the static contact angle of bitumen on the glass surface was found to be large at the high pH of 11, a condition conducive to easy detachment of bitumen droplet from the glass surface. The above observations suggest that a pH cycle might be desirable in bitumen liberation from oil sands.
An automatic pid controller tuning method by frequency response techniques
Authors: Huang Chi‐Tsung , Chou Chin‐Jui , Chen Li‐Zen 
Published: March 2009

AbstractAn alternative Ziegler‐Nichols (1942) controller tuning technique was proposed in this study. Under the proportional control of a single‐loop control system, an arbitrary pulse testing in the set point was introduced to the system. The ultimate frequency and gain could both be directly calculated from the transients by frequency response techniques without any trial and error procedures. PID controller settings were thus obtained according to the Ziegler and Nichols' rules. Furthermore, this technique was extended to the tuning of a cascade control system. A procedure for simultaneously tuning the primary and secondary controllers with both loops in proportional control from a single pulse testing also is presented.
Mass transfer to a drop stream from a field liquid
Authors: Huang Yi‐You , Lu S. M. 
Published: March 2009

AbstractMass 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

AbstractThe 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

AbstractThe 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

AbstractAn 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

AbstractThe 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

AbstractNew 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

AbstractThe 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

AbstractA 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

AbstractIn 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

AbstractFoam 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

AbstractThe 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

AbstractThe 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

AbstractAxial 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

AbstractA 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

AbstractLes 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

AbstractStep‐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

AbstractBubble 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.