bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling of Self‐Induced Oscillations in the Mixing Head of a RIM Machine
Authors: Li Xiaojin , Santos Ricardo J. , Lopes José Carlos B. 
Published: July 2010

AbstractIn this paper, the self‐induced oscillations in the mixing head of a RIM machine were modelled. An analytical and simple correlation was derived between the Strouhal number and the averaged pressure drop along the amplitude of the oscillation in the mixing chamber. This correlation theoretically identified that the frequency of the oscillations could be well correlated by the jet Reynolds number, Red, and the dimensionless distance between the two jets as proposed by Denshchikov et al., Fluid Dyn. 3, 460‐462 (1983). The flow field dynamics in the mixing head was simulated successfully by Fluent and the computed pressure fluctuations were used to calculate the frequencies of the oscillations in the mixing head. The calculated Strouhal numbers are in good agreement with the dominant frequency from the power spectra of the measured velocity component ux (Santos, 2003). Finally, the effect of Red and Froude number, Fr, on the Strouhal number was investigated in the impingement region. The average Strouhal number showed a decrease with the Reynolds numbers, due to the increasing randomness of flow field in the impingement region. It was also found that the operations at lower values of Fr presented an increasing stability up to the point where the system is unable to present dynamic evolution. The model in this paper provides a theoretical starting point towards understanding of the quantities of the oscillatory flow in the mixing head, as well as a numerical approach to evaluate the dominant frequency in the mixing chamber.
On the Effect of Non‐Linearity on Linear Quadratic Regulator Stability and Performance
Authors: Guay Martin , Forbes J. Fraser 
Published: July 2010

AbstractIn this paper, two new local measures of non‐linearity are introduced to quantify the sensitivity of controller stability and performance for linear controllers operating on a non‐linear plant. The measure quantifies the departures from optimality of locally linear quadratic regulators. The main difference between this technique and all other techniques presented in the literature is that the analysis can be used directly in the control design step. If a linear controller can be shown to operate as intended, despite the non‐linearity, then a practitioner can apply a linear controller to the non‐linear systems with the guarantee that a certain degree of performance can be assured, at the design step.
A Novel Data‐Driven Bilinear Subspace Identification Approach
Authors: Yang Hua , Li Shaoyuan 
Published: July 2010

AbstractSubspace identification methods for bilinear systems perform computation with data matrix exploding. Huge computational burdens have been the biggest problem that prohibits real applications of bilinear subspace identification. In this paper, we propose a novel approach with the identification of bilinear predictor model from input‐output data with enhanced computational efficiency. Based on the displacement structure theory, the QR factorization is replaced with a fast Cholesky factorization, which deals with the curse of huge dimensionality and therefore reduces the computation cost. These improvements make the bilinear subspace approach more computationally efficient with good prediction ability. Finally, the proposed control approach is illustrated with a simulation of the non‐linear continuously stirred tank reactor (CSTR) system.
Experimental Tests and Modelling of an Electrodeionization Cell for the Treatment of Dilute Copper Solutions
Authors: Mahmoud Akrama , Muhr Laurence , Grévillot Georges , Lapicque François 
Published: July 2010

AbstractThe paper presents the results of experimental and theoretical investigations of an electrodeionization process for the removal of metal cations from dilute solutions. The ability of this technique to treat 100 ppm copper solutions using cationic membranes and ion‐exchange resins between the membranes was studied. Fair abatement yields were obtained in the 100 mm high resin bed in long‐term runs, and solutions of an appreciable copper ion concentration could be produced in the cathode chamber. The process capacity was limited by significant deposition of copper at the cathode, non‐even distribution of current density, and side‐diffusion to the anode chamber. Additional tests were then carried out using a 15 mm resin bed. The more even current distributions allowed the effect of the resin stiffness and the current density on the removal yield to be thoroughly observed. Steady‐state operation of the resin bed was modelled using generalized expressions of the various transport rates. Results of the model clearly showed the significance of solid‐liquid interactions on the transport processes.
Removal of SO2 by Activated Carbon Fibre Impregnated with Transition Metals
Authors: Gaur Vivekanand , Sharma Ashutosh , Verma Nishith 
Published: July 2010

AbstractPhenolic resin based activated carbon fibres (ACF) impregnated with oxides of various transition metals were investigated for the catalytic oxidation of SO2 into H2SO4. Oxidation was carried out in the packed bed tubular reactor in the presence of O2 and H2O. The activity of the various metals impregnated on ACF was observed to be in the order, Cu>Ni>Co>Cr. It was found that the metal oxides were dispersed as monolayer on ACF up to ∼5% (w/w) loading, beyond which crystallites formation occurred. A kinetic mechanism for the catalytic oxidation of SO2 into H2SO4 was proposed and incorporated in a transport model developed to explain the experimental breakthrough data.
A Modified Simplex Method for Solving 1‐Norm Minimization Problem in Model Predictive Control
Authors: Gupta Yash P. 
Published: July 2010

AbstractSince the simplex method requires the polyhedron to be in the positive domain, the 1‐norm minimization problems are formulated by substantially increasing the size of the LP problems. This paper presents a simple modification that enables the simplex method to be directly applicable to a polyhedron, which extends into the negative domain. That is, instead of requiring the problem to change, the method is changed to fit the problem. The modification eliminates the need to increase the size of the problem and thus eliminates the associated computational effort. The proposed method skips iterations and Phase 1 of the simplex method. Its computational advantage is verified in two examples.
Hydrodynamic Modelling of Internal Loop Airlift Reactor Applying Drift‐Flux Model in Bubbly Flow Regime
Authors: Chriastel L. , Kawase Y. , Znad H. 
Published: July 2010

AbstractA new model for the liquid circulation rates in airlift reactor (ALR) is presented. The model is based on the energy balance for the flow loop (riser, turn riser‐downcomer, downcomer, and turn downcomer‐riser) coupled with a drift flux theory of two‐phase flow gas‐liquid system, considering a bubbly flow regime. The predicted values of the liquid circulation rates by the developed model are compared with experimental results performed in a 22 dm3 internal loop airlift reactor and with the results obtained in the literatures. The proposed model predicted the experimental results very well. Slip velocity relationship based on the drift flux model was proposed; including the gas holdup, bubble size and the liquid physical properties. The predicted slip velocity was similar to that obtained from the literature. The study revealed that appropriate arrangements of internal bioreactor parts can positively influence the liquid circulation velocity at the same energy consumption. The proposed models are useful in the design; scale up and characterization of the internal loop airlift reactors, and provides a direct method of predicting hydrodynamic behaviour in gas‐liquid airlift reactors.
Experimental Investigations of Regimes of Bubble Formation on Submerged Orifices Under Constant Flow Condition
Authors: Badam V. K. , Buwa V. , Durst F. 
Published: July 2010

AbstractRegimes of bubble formation on a submerged orifice under constant flow conditions were investigated experimentally. The effects of orifice diameter, surface characteristics (contact angle and roughness) and surface tension on the regimes of bubble formation were studied for a wide range of gas flow rates. In particular, the transitions of period‐1 to period‐2 bubbling regime, with pairing or with coalescence at the orifice, and period‐2 to chaotic bubbling were investigated in detail. An attempt is made to provide a generalized bubble formation regime map constructed using appropriate dimensionless numbers. The physical understanding of various bubbling regimes and the experimental data on the effects of various system parameters are expected to contribute to the development and validation of analytical and CFD models
Bifurcation Analysis on Pt and Ir for the Reduction of NO by CO
Authors: Mantri Dinesh , Mehta Viral , Aghalayam Preeti 
Published: July 2010

AbstractDue to the importance of the NO‐CO reaction in current catalytic converters, reduction of NO by CO on Pt group catalysts is important to study. Various reaction mechanisms have been proposed for the NO‐CO reaction on Pt(100), which shows bifurcations, kinetic oscillations and multiple steady states under ultra high vacuum (UHV) conditions due to complex surface dynamics. Some experiments on supported Pt group catalysts reported in literature show oscillations and bistability under atmospheric conditions as well. Industrially relevant conditions require the modelling and detailed analysis of the system at atmospheric pressure. We have proposed a reaction mechanism for the NO‐CO system on Pt group catalysts and coupled it with an isothermal PSR model to obtain solutions at atmospheric conditions with the continuation software CONTENT 1.5, at different operating conditions. Simulation results suggest that Pt(111) shows bifurcations at certain operating conditions while Ir(111) shows stable solutions at all the operating conditions studied here.
Relationship on Stabilizability of LTI Systems by P and PI Controllers
Authors: Zhang Zhiping , Wang Qing‐Guo , Zhang Yong 
Published: July 2010

AbstractThis paper investigates the relationship on stabilizability of linear time‐invariant (LTI) systems by P and PI controllers. Elementary tools such as the Routh stability criterion and Root‐Locus method are employed in the analysis. It is found that PI can stabilize all the systems that P stabilizes but in general the converse is not true. The cases with the equivalence of stabilizability by P and PI are established and they are in general low‐order systems with few zeros. The cases with non‐equivalence are also identified.
Transition from Batch to Continuous Operation in Bio‐Reactors: A Model Predictive Control Approach and Application
Authors: Mhaskar Prashant , Aumi Siam 
Published: July 2010

AbstractThis work considers the problem of determining the transition of ethanol‐producing bio‐reactors from batch to continuous operation and subsequent control subject to constraints and performance considerations. To this end, a Lyapunov‐based non‐linear model predictive controller is utilized that stabilizes the bio‐reactor under continuous mode of operation. The key idea in the predictive controller is the formulation of appropriate stability constraints that allow an explicit characterization of the set of initial conditions from where feasibility of the optimization problem and hence closed‐loop stability is guaranteed. Additional constraints are incorporated in the predictive control design to expand on the set of initial conditions that can be stabilized by control designs that only require the value of the Lyapunov function to decay. Then, the explicit characterization of the set of stabilizable initial conditions is used in determining the appropriate time for which the reactor must be run in batch mode. Specifically, the predictive control approach is utilized in determining the appropriate batch length that achieves stabilizable values of the state variables at the end of the batch. Application of the proposed method to the ethanol production process using Zymomonas mobilis as the ethanol producing micro‐organism demonstrates the effectiveness of the proposed model predictive control strategy in stabilizing the bio‐reactor.
Characteristics‐Based Model Predictive Control of a Catalytic Flow Reversal Reactor
Authors: Fuxman A. M. , Forbes J. F. , Hayes R. E. 
Published: July 2010

AbstractThis paper describes the formulation and tuning of a model‐based controller for a catalytic flow reversal reactor (CFRR). A plug flow non‐linear pseudo‐homogeneous mathematical representation of the process is used to model the mass and energy transport phenomena for the model‐based controller. A combination of the method of characteristics and model predictive control (MPC) technology is used to formulate the controller (Shang et al., Ind. Eng. Chem. Res. 43(9) 2140–2149 (2004)). Mass extraction from the midsection of the reactor is used as the manipulated variable. Numerical simulations are used to show the performance of the formulated controller. The performance of the controller is evaluated on a simulated catalytic flow reversal reactor unit for combustion of lean methane streams for reduction of greenhouse gases emissions.
Dependence of the Error in the Optimal Solution of Perturbation‐Based Extremum Seeking Methods on the Excitation Frequency
Authors: Chioua Moncef , Srinivasan Bala , Guay Martin , Perrier Michel 
Published: July 2010

AbstractIn perturbation‐based extremum‐seeking methods, an excitation signal is added to the input, and the gradient, computed from the correlation between the input and output variations, is forced to zero. The main drawback of the method is that the speed of convergence, which is linked to the dither frequency, is slow due to the low value of dither frequency typically chosen. Increasing the excitation frequency may cause instability, but that could be corrected by phase compensation. In this paper, it is shown that an additional problem exists, i.e., the distance between the optimum and solution reached by the perturbation method is proportional to the square of the frequency of excitation and does not go to zero even when the amplitude of the excitation goes to zero. However, for Wiener/Hammerstein approximations, the error will indeed go to zero with the excitation amplitude. Simulation results on a distributed reaction system are used to illustrate the concepts presented in this work.
Detection, Diagnosis and Root Cause Analysis of Sheet‐Break in a Pulp and Paper Mill with Economic Impact Analysis
Authors: Imtiaz S. A. , Shah S. L. , Patwardhan R. , Palizban H. A. , Ruppenstein J. 
Published: July 2010

AbstractSheet‐break is a long standing problem in the pulp and paper industry. This study is concerned with the analysis of process data to diagnose causes of sheet‐breaks and therefore significant down times. PCA was used to model the process and a combined index based on the Hotelling's T2 and Squared Prediction Error (SPE) was developed as a sheet‐break detection indicator. As the process is subject to external disturbances, changes and frequent interruptions, pre‐processing of the data played an important role in getting consistent results. We used several novel techniques for data selection, scaling and modelling. The models were validated using a large validation data set with known fault conditions. The developed model, data visualization tool and engineering judgement was used for off‐line diagnosis of root causes of sheet‐breaks. Several operational changes were recommended and implemented on the process resulting in significantly reduced sheet‐breaks. Key Performance Indicators calculated before and after the changes shows the significant economic gain as a result of this 'data‐mining' project.
Enhanced Performance Assessment of Subspace Model‐Based Predictive Controller with Parameters Tuning
Authors: Zhang Qiang , Li Shaoyuan 
Published: July 2010

AbstractThis study focuses on performance assessment of model predictive control. An MPC‐achievable benchmark for the unconstrained case is proposed based on closed‐loop subspace identification. Two performance measures can be constructed to evaluate the potential benefit to update the new identified model. Potential benefit by tuning the parameter can be found from trade‐off curves. Effect of constraints imposed on process variables can be evaluated by the installed controller benchmark. The MPC‐achievable benchmark for the constrained case can be estimated via closed‐loop simulation provided that constraints are known. Simulation of an industrial example was done using the proposed method.
Synthesis of Gold Nanoplates in Lecithin Lamellar Liquid Crystals
Authors: Wang Luyan , Chen Xiao , Sun Zhenwen , Chai Yongcun 
Published: July 2010

AbstractGold nanoplates mixed with spherical nanoparticles were prepared in lecithin lamellar liquid crystals containing non‐ionic surfactants as reductant. The effects of the concentrations of surfactants, reactants and salt on the formation of the nano‐products are discussed. The selective adsorption of lecithin headgroups on metal surfaces plays an important role in nanoplate formation. However, this effect is weakened by the large volume of the headgroups and only a few plates can be observed. Using biological liquid crystals as a template to synthesize the anisotropic noble metal nanoparticles will be helpful for better understanding the formation of nanostructures with controllable morphologies in biomimetic systems.
Surface Characteristics of Kaolinite and Other Selected Two Layer Silicate Minerals
Authors: Miller Jan D. , Nalaskowski Jakub , Abdul Baseer , Du Hao 
Published: July 2010

AbstractThe electrokinetic features and interfacial water structure, as revealed from molecular dynamics simulations (MDS) are considered with respect to the anisotropic features of selected two layer silicate minerals. Planar structures of kaolinite and antigorite are compared to the, compositionally equivalent, tubular structures of halloysite and chrysotile with respect to the pH dependency of zeta potential as determined from the electrophoretic mobility measurements. The importance of the atomic mismatch between the tetrahedral and octahedral sheets in a particular bilayer is discussed in order to explain the electrokinetic behaviour of these two layer silicate minerals. Interfacial water structure from MDS suggests that the silica tetrahedral surface is not wetted by water. In the case of planar silicates structural imperfections are considered to explain wetting characteristics. The possibility of polarity reversal (domain inversion) within a tetrahedral/octahedral layer and an out‐of‐order layer (inserted layer) within the tetrahedral/octahedral stack are considered in order to explain electrokinetic behaviour and wetting characteristics.
Liquid Transport in a Coalescing Froth
Authors: Ireland Peter M. , Jameson Graeme J. 
Published: July 2010

AbstractA previous study (Ireland and Jameson, J. Colloid Interface Sci., 314 207‐213 (2007)) demonstrated that a “drift‐flux” model could describe liquid transport in a stable rising froth with added “wash water.” In the present study, a drift‐flux model was used to describe a rising coalescing froth. This model incorporated the effect of liquid released into the froth by coalescence. Vertical profiles of liquid fraction and bubble size were obtained in a laboratory cell; a novel technique was used for measuring bubbles deep within the cell. These data were consistent with the predictions of the drift‐flux model.
Early Events in the Precipitation Fouling of Calcium Sulphate Dihydrate under Sensible Heating Conditions
Authors: Fahiminia Feridoun , Watkinson A. Paul , Epstein Norman 
Published: July 2010

AbstractSupersaturated aqueous solutions of calcium sulphate, an inverse solubility salt, were circulated through a 9 mm i.d. stainless steel tube in which they were subjected to a constant and uniform heat flux at Reynolds numbers ranging from 2100 to 36 000. Precipitation fouling of the tube surface, which was monitored and measured thermally, resulted in calcium sulphate dihydrate (gypsum) scales. Measured delay times decreased with increasing bulk solute concentration, Cb, in accord with classical nucleation kinetics, decreased with increasing surface temperature Ts, its reciprocal correlating with Ts in the Arrhenius manner, and decreased with increasing fluid velocity V up to V &&num;8776; 0.5 m/s before flattening out. Initial linear fouling rates,Rfo, at Cb = 3400 ppm, also yielded Arrhenius plots, with fouling activation energies increasing almost eight‐fold over the 0.1–1.6 m/s velocity range. This result implies a shift in the mechanism of fouling rate control with increasing velocity from mass transfer, which is weakly temperature dependent, to surface integration, which is strongly temperature dependent. The “Initial Fouling Rate Model,” which simulates this mechanistic shift with a unique dependence of the surface‐integration step on the residence time of the fluid at the tube wall, was used to represent, by least‐squares fitting, 84 fouling rate data points at different values of V and Ts, with three adjustable parameters. Observed trends of Rfo with V and clean wall Ts were qualitatively captured by the model, but quantitative agreement was imperfect. Substantial quantitative improvement was effected by introducing into the model an additional temperature dependence of the surface‐integration term—resulting in one additional adjustable parameter—rationalized as a method of accounting for the previously neglected temperature‐dependent nucleation that accompanies crystal growth. The fouling investigation was supplemented by an experimental study of crystal growth kinetics.
Interpretation of Bitumen Recovery Data from Batch Extraction Tests
Authors: Omotoso O. , Friesen W. I. , Mikula R. J. 
Published: July 2010

AbstractSmall‐scale batch tests are often used to compare oil sand samples and to understand processing trends for process variables such as temperature, water chemistry, and ore properties. The uncertainty associated with the value of bitumen recovery determined from a carefully performed batch test is approximately 4%, a level that can have significant economic implications when commercial production rates are considered. This paper discusses several methods for determining bitumen recovery and shows the preferred, although seldom used, method for calculating this value.