bluuebunny/crossref_metadata_2025_split huggingface dataset:
Binary mixture of monostearin‐distearin monolayers at the air–water interface
Authors: De la Fuente Feria Julia , Patino Juan M. Rodríguez 
Published: June 2004

AbstractThe study of mixed films has become of considerable interest both from theoretical and practical points of view. The π‐A isotherms of monostearin‐distearin (about 50% 1,3‐ and 50% 1,2‐isomers) mixed films spread on water as a function of emulsifier ratio and temperature were studied in an automated Langmuir‐type film balance. When molecules of both emulsifiers are spread on the air–water interface they are packed more closely together than when either emulsifier is present alone, and they enter into some form of association. This association can be demonstrated by surface pressure‐area isotherms and by thermodynamic studies. The characteristics of the mixed films, their elasticity and miscibility, which are of interest in emulsion or foam stability are discussed. A molecular model established can explain the interactions between film and subphase molecules and their relationships with variables of the process (pressure and temperature). This model fits the calculated thermodynamic parameters.
Cross‐flow ultrafiltration of micellar surfactant solutions
Authors: Markels John H. , Lynn Scott , Radke Clayton J. 
Published: June 2004

AbstractA Steady‐state fouling‐resistance and osmotic‐pressure model is used to predict flux in the laminar, Cross‐flow ultrafiltration of micellar cetyl ( =hexadecyl)pyridinium chloride (CPC) solutions at 0.01‐M NaCl background electrolyte. The model assumes a constant overall hydraulic resistance including the effect of surfactant fouling and native membrane resistance. Measurements of osmotic pressures of CPC solutions at 0.01‐M NaCl as a function of surfactant concentration describe the effect of concentration polarization on permeate flux. Two types of asymmetric polythersulfone membranes are used : 5,000 molecular weight cutoff (MWCO) membranes that allow partial monomer permeation, but quantitatively reject all micelles; 50,000 MWCO membranes that allow some micelle permeation. For the former, the intrinsic refection coefifient for monomer, measured separately, is sufficient to describe surfactant rejection, without adjustable parameters. Predictions of the volumetric flux of the permeate, including the value of the limiting flux, agree well with the experimental results over the entire range of pressure drop, axial velocity, and bulk surfactant concentration. For the 50,000 MWCO membrances, the data are described using a best‐fit value of the overall surfactant rejection coefficient. For the first time, unusual behavior is observed experimentally in which the flux levels off with increasing pressure drop. Both effects are in accord with the proposed model. No gel layer need be postrulated to explain the flux behavior of either membrane type.
Multiple roll systems: Residence times and dynamic response
Authors: Benjamin D. F. , Anderson T. J. , Scriven L. E. 
Published: June 2004

AbstractIn roll coating as in other coating processes the coating liquid often suffers changes in properties on the time of the coating flow, that is, from fractions of a second upward depending on the amount of recirculation and recycling. The agents of change may be chemical reaction, colloidal aggregation, or evaporation. Hence the mean residence time and the residence time distribution of the liquid are important to designers and operators of coating processes. Here, building on the examination of roll‐coating systems by Benjamin et al. (1995), the residence times of liquid coated by representative arrays of multiple rolls in the “forward roll” mode and relatively starved feed condition (neglecting the possibly significant effects of “rolling banks” and other internal recirculations when they are present) are analyzed. The dynamic response of these transfer coaters to step changes in the feed gap and to periodic gap changes, as from roll and bearing run‐out, are also analyzed. No reports of operating or laboratory experiments are available for comparison. Nevertheless the results make plain how these quality‐limiting features may depend don the number of rolls used; their sizes, speed, and arrangement, and the properties of the coating liquid.
Analysis of multidimensional models of monolith catalysts for hybrid combustors
Authors: Groppi G. , Belloli A. , Tronconi E. , Forzatti P. 
Published: June 2004

AbstractDistributed parameter models of the single channel of a monolith combustor have been derived from progressively simplified assumptions. Simulation results are compared to assess the importance of the different physicochemical phenomena occurring in the combustor and to identify the simplest adequate model. For typical operating conditions of the hybrid combustor (gas and wall temperature not exceeding 1,073 and 1,273 K, respectively, high flow rate and pressure, natural gas as fuel), the results show that variations of gas properties have to be considered while homogeneous combustion can be neglected. Assumption of the approximate radial profile of axial velocity with invariant parabolic shape, rather than the rigorous solution of momentum balance and the continuity equation, provides accurate results. Moreover, for simulation of ceramic monoliths, backward heat transmission by wall conduction can be neglected with a substantial saving of computational labor.
Adaptive multirate state and parameter estimation strategies with application to a bioreactor
Authors: Gudi Ravindra D. , Shah Sirish L. , Gray Murray R. 
Published: June 2004

AbstractThe design and development of a mu8ltirate software sensor for use in the chemical process industry are presented. The measurements of process outputs that arrive at different sampling rates are formally accommodated into the estimation strategy by using rhwe multirate formulation of the iterated extended kalman filter. Measurement delays associated with some of the process outputs are included in the system description by addition of delayed states. Observability issues associated with state and parameter estimation in a multirate framework are discussed and modified measurement equations are proposed for systems with delayed measurements to ensure relatively “strong” system observability. The evaluation of the proposed multirate state and parameter estimator through simulations and an experimental application on afed batch fermentation system gave satisfactory performance.
Mechanistic description and experimental studies of electrochromatography of proteins
Authors: Basak Subir K. , Ladisch Michael R. 
Published: June 2004

AbstractElectrochromatography is a form of gradient liquid chromatography in which an axial electric potential is applied to columns packed with gel‐filtration media. Experimental methodology and a mechanistic model are further developed for a system that minimizes Joule heating at electric field strengths of 100 V/cm by dissipating heat through a cooling jacket and use of a cooled, low ionic strength eluting buffer. Focusing of proteins can be achieved in a 15‐mm‐dia. Column by the interplay of eluent velocity, electrophoretic migration rate, and electrically induced concentration polarization when the stationary phase is more conductive than the mobile phase. Voltage gradients of up to 125 V/cm for eluent velocities at 18–25 cm/h separate binary protein mixtures of Bhb‐α‐lactalbumin, BSA‐myoglobin, and α‐lactalbumin‐myoglobin over Sephadex G‐100 and G‐50. Retention times are consistent with values obtained from a mechanistic nonlinear model.
Robust output regulation for nonlinear chemical processes with unmeasurable disturbances
Authors: Wu Wei , Chou Yi‐Shyong 
Published: June 2004

AbstractIt becomes a problem when the input‐output feedback linearization of nonlinear processes presents unmeasurable disturbances that appear linear in the model and are not in the span of control input space. The prcsented hybrid nonlinear controller, which consists of a nonlinear static state fredback with a series of a adjustable parameters and an internal model, can achieve disturbance attenuation and offset‐free performance. The major advantage of the proposed control system design is to reject disturbance without producing a vigorous control action. A simple estimation method of computing a single parameter that replaces a series of adjustable parameters of the controller is developed. The proposed estimation strategy of computing a single parameter is based on the Lyapunov stability theory. These control schemes are illustrated by an example of a chemical reactor to obtain satisfactory control.
Separation devices for gas mixing
Authors: Agrawal Rakesh , Xu Jianguo 
Published: June 2004

AbstractWhen two fluid streams with different compositions mix, a significant amount of exergy is lost Utilizing the mixing exergy of gaseous streams of different compositions can reduce equipment cost and energy consumption as well as generate electric power. Suitable modification of known separation processes such as distillation, membranes, adsorption, and absorption to convert them into efficient mixing processes is discussed in detail Mixing may also be combined with a separation process such that the same device is used for both purposes which results in the use of the mixing exergy. This combined separation/mixing process is a single and relatively simple device with efficiencies not typically attainable in the generally used two‐step method of separation followed by mixing. For such applications, some is∼ teresting results are presented for the processes using membrane, adsorption and absoqrion devices.
Bubble dissolution viscous liquids in simple shear flow
Authors: Favelukis Moshe , Tadmor Zehev , Talmon Yeshayahu 
Published: June 2004

AbstractThe dissolution of a gas bubble in a viscous Newtonian liquid in simple shear and creeping flow was studied experimentally A simple theoretical model for bubble growth or dissolution at high Peclet numbers is also presented. The main result of the model shows that for high capillary numbers (slender bubbles) the dissolution or growth rate is proportional to the shear rate to the 3/8 power The experimental work was carried out in a Couette apparatus. Air and carbon dioxide bubbles were injected into polymer liquids (low‐molecular‐weight polyisobutylenes) and photographed under shear. No “tip‐streaming” was observed, and experimental results compared favorably with predictions of the simple model, based on a mechanism that combines diffusion and convection.
Predicting drying in coatings that react and gel: Drying regime maps
Authors: Cairncross Richard A. , Francis Lorraine F. , Scriven L. E. 
Published: June 2004

AbstractThe competition between drying and reactions in a liquid coating containing precursors to a random network polymer can give rise to a variety of drying phenomena. Solidification, or gelation, of the polymer may occur before, after, or during the removal of solvents from the coating. Rates of drying and reaction are probed by solving the equations of mass transfer by diffusion along with chemical reaction in one dimension. Solutions to this system of equations are obtained by Galerkin's method with finite‐element basis functions and entail large‐scale computation. Skinning, or solidification at the surface of the coating while the bulk is still liquid, occurs in thick coatings when the diffusional resistance to drying is significant, that is, at high mass‐transfer coefficients. Homogeneous solidification occurs in thin coatings at low mass‐transfer coefficients. Drying regime maps represent these solidification phenomena as regions in parameter space.
Fluidization characteristics of biobone particles used for biocatalysts
Authors: Ellis N. , Margaritis A. , Briens C. L. , Bergougnou M. A. 
Published: June 2004

AbstractLiquid–solid fluidization characteristics of irregularly shaped Biobone particles were studied in a fluidized bioreactor column 2.35 m high and 0.1 m dia. The wet biobone particles had a density of 1,890 kg/m3. Two size ranges were studied: 1.70–2.36 mm and 1.25–2.36 mm. The Biobone is a natural cheap material composed of collagen, which is a strong protein structure, embedded with microcrystals of hydroxyapatite and calcium phosphate, and it is an excellent matrix of commercial importance used for the immobilization of enzymes, whole cells and other biocatalysts. Fluidization characteristics of Biobone particles, which include measurements of pressure drops, holdups, minimum fluidization velocities, particle entrainment, and residence time distributions at different water superficial velocities, are reported. Because of the highly irregular shape of Biobone particles, new fluidization behavior was observed, which was much different from the fluidization behavior of spherical particles reported in the literature. A new channeling index, Ic, is proposed to quantify the channeling characteristics of fluidized Biobone particles, and a new parameter, α, was developed to distinguish the transition between fixed and fluidized states of the Biobone particles.
Dean vortices with wall flux in a curved channel membrane system: 2. The velocity field
Authors: Chung Kun Yong , Brewster Mary E. , Belfort Georges 
Published: June 2004

AbstractThe velocity and pressure fields and the effect of wall flux on these fields in a spiral channel are presented. As fluid flows inward through a spiral channel with constant gap and permeable walls, the streamwise flux decreases while the curvature increases. Thus, by balancing the stabilizing effect of wall suction with the destabilizing effect of increasing curvature, established vortices can be maintained along the spiral channel. This approach is used to prescribe spiral geometries with different wall fluxes. Using a weakly nonlinear stability analysis, the influence of wall flux on the characteristics of Dean vortices is obtained. The critical Dean number is reduced when suction is through the inner wall only, is slightly reduced when suction is equal through both walls, and is increased when suction is through the outer wall only. The magnitude of change is proportional to a ratio of small numbers that measures the importance of the effect of curvature. In membrane filtration applications the wall flux is typically 2 to 5 orders of magnitude less than the streamwise flow. If the radius of curvature of the channel is of the order of 100 times the channel gap, the effect on the critical Dean number is within 2% of the no‐wall flux case. If the radius of curvature is sufficiently large, however, it is possible to observe effects on the critical Dean number that approach O(1) in magnitude for certain parameter ranges.
Solving linear diffusion‐reaction networks in porous catalyst particles using BEM
Authors: Karur Sriganesh R. , Ramachandran P. A. 
Published: June 2004

AbstractMultiple diffusion reactions are frequently encountered in the modeling of heterogeneous catalytic reactors. Obtaining an accurate estimate of the yield and selectivity in such reactions is crucial for an optimal design of reactors. Due to the inadequacy of analytical techniques in handling nonuniform catalyst shapes and mixed boundary conditions, numerical techniques are often employed to compute these design parameters. Among other numerical techniques, the boundary element method (BEM) is a superior method to solve linear diffusion reaction problems. The integral nature of the BEM formulation allows for boundary‐only discretization of the particle, thus reducing the computer execution time and the data preparation effort. A boundary element algorithm is developed to solve a network of linear diffusion reactions in porous catalyst particles in two dimensions. For this purpose, a matrix of fundamental solutions is defined and derived. The developed algorithm is applied to complex reaction networks to obtain the yield of intermediates for nonregular catalyst shapes and nonuniform boundary conditions. The method can be used as a design tool to study particle scale modeling in detail and can be incorporated into an overall reactor model.
Prediction of electrodeposition rates from an impinging jet
Authors: Li Quan , Walker J. D. A. 
Published: June 2004

AbstractA mathematical model and numerical algorithm are developed to predict electrodeposition rates from a 2‐D jet of electrolyte that impinges on a flat surface. The principal situations of interest are for applied voltages that produce current densities below the limiting current. The motion is assumed to be at high speed with the jet inducing a thin laminar boundary layer on the surface; a progressively thinner concentration layer and an electrochemical double layer near the surface are accounted for. Two cases, corresponding to a submerged and unsubmerged jet, are considered. A boundary integral method is used to compute the current density along the plate in a general iterative numerical procedure coupled to the solution of the hydrodynamic, concentration and electrochemical boundary layers. The results show that relatively high deposition rates occur near the point of impingement and that altering the jet angle relative to the surface influences local electrodeposition rates significantly.
Hollow‐fiber membrane‐based rapid pressure swing absorption
Authors: Bhaumik S. , Majumdar S. , Sirkar K. K. 
Published: June 2004

AbstractA novel gas purification technique called rapid pressure swing absorption (RAPSAB) was developed by integrating the best features of membrane contacting, gas‐liquid absorption, and pressure swing adsorption (PSA). In this cyclic separation process, a well‐packed microporous hydrophobic hollow‐fiber module was used to achieve nondispersive gas absorption from a high‐pressure feed gas into a stationary absorbent liquid on the module shell side during a certain part of the cycle followed by desorption of absorbed gases from the liquid in the rest of the cycle. The total cycle time varies between 20 s and upwards. Separation of mixtures of N2 and CO2 (around 10%) where CO2 is the impurity to be removed was studied using absorbent liquids such as pure water and a 19.5% aqueous solution of diethanolamine (DEA). Three RAPSAB cycles studied differ in the absorption part. Virtually pure N2 streams were obtained with DEA as absorbent demonstrating the capability of bulk separation to very high levels of purification. Numerical models developed predict the extent of purification for pure water and the DEA solution for one of the simpler cycles. Model simulations describe the observed behavior well.
Crystallization of phenanthrene from toluene with carbon dioxide by the GAS process
Authors: Berends Edwin M. , Bruinsma Odolf S. L. , De Graauw Jan , van Rosmalen Gerda M. 
Published: June 2004

AbstractThe crystallization of phenanthrene from toluene with carbon dioxide as the antisolvent gas is described. In the GAS process, a pressurized gas is dissolved into a liquid solvent, where it causes a volumetric expansion and lowers the solubility of the solute. Theoretical models are presented for the liquid‐phase expansion and the solubility as a function of pressure and temperature. The Nývlt theory for batch crystallization is adapted to predict the pressure profile in the crystallizer needed to maintain a constant supersaturation and growth rate. Generation of seeds is accomplished via a pressure pulse at the saturation pressure. The average particle size of the phenanthrene could be varied from 160 to 540 μm. Creation of seeds doubles the particle size and reduces the coefficient of variation significantly. The residual amount of toluene in the crystals without treatment is approximately 70 ppm. The particles are agglomerates of phenanthrene crystals.
On‐line parameter estimation in a high‐pressure low‐density polyethylene tubular reactor
Authors: Kiparissides C. , Verros G. , Pertsinidis A. , Goossens I. 
Published: June 2004

AbstractThe high throughput and operating cost of the reactor provide the economic incentive in considering the on‐line optimization of the LDPE tubular reactor. For an on‐line optimization procedure it is crucial to develop a flexible and adaptive on‐line parameter estimator, which based on the appropriate measurements from the reactor will adjust certain key model parameters so that the model can capture the actual reactor operation and reliably be used for the real‐time optimization of the reactor performance. Various issues involved in developing the on‐line estimator for such applications as the mathematical modeling of the reactor, the selection of the adjustable model parameters and reactor measurements, the decomposition of the problem according to the characteristic time constants of various disturbances, and the efficient and robust solution of the mathematical problem are discussed. The tools developed were successfully used on an EXXON high‐pressure LDPE tubular reactor. Results from the numerical experiments that are compared with scaled data from a real reactor show that the estimated temperature profiles agree remarkably with those observed at various phases of the reactor operation.
One‐sided single‐pellet technique for adsorption and intraparticle diffusion
Authors: Dog̈u Timur , Yasyerli Nail , Dog̈u Gülsen , McCoy Ben J. , Smith J. M. 
Published: June 2004

AbstractThe one‐sided single‐pellet dynamic technique introduced in this article is shown to be a very effective and simple method for the analysis of adsorption and diffusion in porous solids. Moment expressions are presented for reversible and irreversible adsorption processes. Since the adsorption equilibrium constant is the only unknown parameter in the first moment expression, this parameter can be evaluated from a single set of pulse‐response experiments. This technique to evaluate the adsorption equilibrium constant is illustrated using ethylbromide as tracer. It is also shown that for a very strongly adsorbing tracer, such as 1,2‐dichloroethane in soil, modified moment expressions derived with a semiinfinite boundary condition are necessary unless a criterion developed in this work is satisfied.
Coke effect in mass transport and morphology of Pt‐Al2O3 and Ni‐Mo‐Al2O3 catalysts
Authors: García‐Ochoa F. , Santos A. 
Published: June 2004

AbstractThe effect of high levels of coke deposit on catalyst properties and mass transport through the pores space was studied using commercial catalysts, Pt‐Al2O3 and Ni‐Mo‐Al2O3. Changes in porosity, pore‐size distribution and internal surface area of several aged catalysts were compared to those of fresh catalyst. Effective diffusivity was also measured by pulse chromatography. For Pt‐Al2O3, which shows a high initial porosity (0.93) and a relative high mean pore radius (300 Å), catalyst properties remain unchanged while coke content increased. For the Ni‐Mo‐Al2O3 catalyst (with initial porosity of 0.53 and mean pore radius of 50 Å), however, with an increase of 15% in coke content, isolated void regions appear, and porosity, internal surface area and effective diffusivity decrease sharply. Pore and stochastic models were used to interpret the effective diffusivity experimentally measured. A structural parameter in each case, tortuosity factor in pore models, and coordination number in the percolation model were calculated. When coke produces significant changes in catalyst morphology, the tortuosity factor almost doubles its initial value for a coke content of 20%. On the contrary, the percolation model seems to predict changes accurately in porosity, mass trasport coefficient, and an isolated prosity growing from the coordination number matched for a fresh catalyst.