bluuebunny/crossref_metadata_2025_split huggingface dataset:
Beyond log‐normal distributions: Hermite spectra for solving population balances
Authors: Hamilton Robert A. , Curtis Jennifer S. , Ramkrishna Doraiswami 
Published: April 2004

AbstractThe oft‐used log‐normal distribution for solving many population‐balance problems is in fact a degenerate case of a Hermite function expansion of the solution in log particle‐size coordinate. Corrective capabilities of such an expansion constitute vast improvements not only over those using the log‐normal distribution, but also over discretization methods in that moments other than those designed for in the latter are predicted with much higher accuracy, although at greater computational cost. The Hermite spectral method is compared with known analytical results and other computational techniques for particle dynamic processes involving agglomeration, breakage, and growth. This method is extremely accurate and flexible, as evidenced by the wide range of problems it can solve, both transient and steady state, along with perfectly mixed or convection dominant problems. Particle distributions are allowed to evolve according to the physics of the process, not constrained by restrictive assumptions inherent in the prespecified form of the distribution.
Distillation in hollow fibers
Authors: Zhang Guoliang , Cussler E. L. 
Published: April 2004

AbstractDistillation in hollow fibers can give better, more productive separations than distillation in random or structured packing. Since the hollow fibers used have little resistance to mass transfer, the selectivity of the separation depends on the relative volatility, just as in conventional distillation. Because the fibers are nonporous, the distillation can operate at high flows which normally cause flooding, and at low flows which normally compromise loading. As a result, the turndown ratio is nearly infinite and the height of a transfer unit can be as small as desired. Experiments do give values consistent with correlations developed for other membrane modules, although the practical value of hollow fiber distillation is uncertain because of the materials limitations.
Liquid‐phase mass transfer in spray contactors
Authors: Yeh Norman K. , Rochelle Gary T. 
Published: April 2004

AbstractThe liquid‐phase mass transfer in sprays has been measured with carbon dioxide desorption by collecting and analyzing samples of the spray. Experiments were conducted with laboratory‐ (0.009 to 0.13 L/s) and pilot‐scale (6.4 to 12.8 L/s) centrifugal hollow‐cone spray nozzles at pressure drops from 34 kPa to 138 kPa. Significant mass transfer occurred during sample collection, and a quench sampling method was developed to minimize this effect. The number of liquid‐phase transfer units (NL) due to spray impact onto walls and liquid pools was often as much as the spray NL. Approximately 60% of the spray NL occurs in the liquid sheet before droplet formation, and the droplet region can account for less than half of the total NL of the spray.
Effect of the size and amount of ZrO2 addition on properties of SrCo0.4Fe0.6O3−δ
Authors: Yang Li , Tan Liang , Gu Xuehong , Qi Hong , Jin Wanqin , Zhang Lixiong , Xu Nanping 
Published: April 2004

AbstractThe effects of ZrO2 addition with various particle sizes (1, 3, and 56 μm) and various amounts (0, 1, 3, 5, 7, 9 wt. %) on structure, oxygen permeation, and stability of SrCo0.4Fe0.6O3−δ (SCF) were investigated. XRD and EDX analysis revealed that the dissolution of Zr cation into the B site of SCF phase occurred with the addition of ZrO2, resulting in a lattice expansion of SCF at elevated temperatures. The dissolution amount of Zr in the SCF phase increased with a decrease of ZrO2 particle size and an increase in the amount of ZrO2 added, and, therefore, resulted in a decrease of oxygen permeation flux of the membranes and an increase in their structural stability in a helium atmosphere. This study indicated that adding a certain amount of Zr cation in SCF oxide was an effective route to sustain the structural stability of SCF in low oxygen partial pressure, and the optimum ZrO2 addition was 3 wt.% with a particle size of 1 μm, which greatly improved the structural stability without significantly changing the oxygen permeability of SCF.
Hierarchical multiobjective strategy for particle‐size distribution control
Authors: Immanuel Charles David , Doyle Francis Joseph 
Published: April 2004

AbstractA multiobjective optimization formulation is presented to track a desired particle‐size distribution (PSD) trajectory in semi‐batch emulsion polymerization. This is done in a hierarchical framework, controlling the individual processes of nucleation, growth, and coagulation that determine the PSD. An evolutionary technique, the Nondominated Sorting Genetic Algorithm, is employed as the optimization tool. Experimental implementation of these open‐loop optimal recipes yield promising results, but simultaneously highlight the importance of feedback corrective action. Preliminary state/parameter estimation studies are performed, which show an ability to estimate the full distribution and related states from the available measurements (relative distribution, latex density, and feed rates), and also elucidate the requirements in the strategy to be employed for estimation. The potential for on‐line feedback is examined using experimental data, in view of the irreversibilities and process limitations.
Screening for profitable retrofit options of chemical processes: A new method
Authors: Uerdingen Eric , Fischer Ulrich , Hungerbühler Konrad , Gani Rafiqul 
Published: April 2004

AbstractA new systematic methodology for screening retrofit options to improve the economics of a continuous chemical process is organized in three stages: 1. base case analysis; 2. generation of retrofit options; and 3. rough economic evaluation of the retrofit options. In stage 1, the flowsheet of a process, based on the steady‐state mass and energy balances of a representative process operating state (base case), is decomposed into open and cycle component path flows with their corresponding flow rates. In the path flow assessment, variable process costs are then allocated to these component flows through two economic indicators representing raw material consumption, and energy and waste cost. Additional physico‐chemical path flow indicators characterizing the degree of nonideality of the process are also calculated. In stage 2, the results of the path flow assessment are used to identify possible retrofit options with the help of recommended retrofit actions. In stage 3, the impact of retrofit options on variable costs of the base case is estimated and discussed in terms of its technical feasibility. This method has been applied to the hydro‐dealkylation process for the toluene production. Several promising retrofit options were identified through this method. The results demonstrate how the new method supports the systematic identification of economically beneficial retrofit options for chemical processes.
Simple and safe method for determining explosion limits at elevated pressures
Authors: Chen Jenq‐Renn , Liu Kensin 
Published: April 2004

AbstractA simple and safe method for determining the explosion limits at elevated pressures and temperatures is developed by using a small explosion test cell with a pressure balancing and containment design. Tests at elevated pressure are achieved by balancing the test‐cell pressure and the containment‐vessel pressure. If the vapor in the test cell is flammable and ignites, the overpressure will rupture the test cell but remain confined safely by the containment vessel. The method successfully achieved explosion‐limit measurement at pressures up to 5.5 MPa with all the equipment components rated at a pressure of only 13.9 MPa. Results are presented for hydrogen and methane at ambient condition and elevated pressures, and shown to be in good agreement with the data in the literature. Preliminary results on the upper explosion limits of cyclohexane at cyclohexane oxidation conditions are also reported. The method will greatly benefit the study of explosion limits at elevated pressures and the safety of hydrocarbon/air oxidation processes.
High shear skim milk ultrafiltration using rotating disk filtration systems
Authors: Ding Lu‐Hui , Akoum Omar , Abraham Antoine , Jaffrin Michel Y. 
Published: April 2004

AbstractThe ultrafiltration (UF) of UHT (sterilized at ultrahigh temperature) skim milk with two prototypes rotating disk systems of 15.5 and 26 cm i.d. using the same 50 kDa PES membrane is investigated. The larger stainless steel unit had a maximum rotation speed of 1,500 rpm. The smaller nylon unit had a maximum speed of 3,000 rpm. Disks equipped with radial vanes of various heights were used in the tests. The large module yielded a stabilized permeate flux of 276 L h−1m−2 at 45°C and a transmembrane pressure (TMP) of 1,000 kPa when fitted with a 2‐mm vanes disk rotating at 1,500 rpm, confirming the reduction of concentration polarization by high shear rate. The mean shear rate on membrane γm was shown to be proportional to (kω)1.8, where ω was the disk angular velocity and k was a coefficient depending upon vanes height. Permeate fluxes observed with the two modules at various speeds and with different disks were well correlated by a single function of mean shear rate, given in Lh−1m−2 by J = 0.301 γm0.552. In concentration tests with a 6‐mm vanes disk, the permeate flux remained constant until a volume reduction ratio (VRR) of 3, then decayed to a theoretical VRR maximum of 9.2 at zero flux. It can thus be concluded that rotating disk filtration devices are very efficient in UF as high shear reduces concentration polarization. The specific power consumed per m3 of permeate was found to be less for the smooth disk than for a disk with vanes.
Single drop impaction on a solid surface
Authors: Park Heungsup , Carr Wallace W. , Zhu Junyong , Morris Jeffrey F. 
Published: April 2004

AbstractAn experimental and theoretical study is presented on spreading and retracting of a single drop impacting on a smooth surface at room temperature. The experimental study showed the influence of kinetic energy, liquid‐solid interaction, and energy dissipation on the impact process. The results are reported for Reynolds number from 180 to 5,513, Weber number from 0.2 to 176, four different liquids (distilled water, n‐Octane, n‐Tetradecane, and n‐Hexadecane), and four different surfaces (slide glass, uncoated silicon wafer, HMDS coated silicon wafer, and Teflon film). A theoretical model based on an energy balance was developed to predict the maximum spreading ratio at low impact velocity. The key novel feature of this model is that the shape of the drop is assumed to be a spherical cap during the spreading process. When compared to models in the literature, the present model not only gives better predictions for low drop impact velocities, but also in most cases gives predictions that are within 10% of the experimental data at high impact velocities.
Nonequilibrium capillary pressure and relative permeability curves of porous media
Authors: Tsakiroglou C. D. , Theodoropoulou M. A. , Karoutsos V. 
Published: April 2004

AbstractHistory matching of unsteady immiscible displacement experiments performed on model porous media reveals that nonequilibrium capillary pressure and relative permeability functions are sensitive to the dominating flow pattern. As the capillary number increases, the network displacement pattern changes gradually from invasion percolation cluster to stable displacement. For primary drainage, the capillary pressure and relative permeability curves are increasing functions of the capillary number. The dependence of the relevant macroscopic parameters on the capillary number is consistent with power laws derived from scaling arguments of gradient percolation theory, which describes the growth of the displacement front. The material coefficient of the thermodynamic theory of capillary pressure changes mildly with fluid saturation and is a decreasing function of the capillary number.
Modeling adsorption of cane‐sugar solution colorant in packed‐bed ion exchangers
Authors: Broadhurst Hugh A. , Rein Peter W. 
Published: April 2004

AbstractThe removal of cane‐sugar solution colorant by packed‐bed ion exchangers was modeled using a linear driving‐force adsorption model. Adsorption of colorant is a complex subject, since color is an indiscrete mixture of many components, making it difficult to measure and even more challenging to model. Three resins were investigated: a strong‐acid cation (SAC), a weak‐base anion (WBA), and a standard sugar industry strong‐base anion decolorizing resin. Batch testing of the resins produced linear isotherms, indicating that the colorant is dilute. Results from column testing showed that a plug‐flow model with a constant linear isotherm was sufficient in all cases except the SAC resin. The SAC adsorption parameter decreased sharply as the pH increased, causing the colorant to be desorbed from the resin. This situation must be avoided if optimal decolorization is to be achieved.
Multivariable terrain methods
Authors: Lucia Angelo , Feng Yang 
Published: April 2004

AbstractA novel geometric terrain methodology was recently presented for finding all physically relevant solutions and singular points to chemical process simulation problems based on intelligently moving along special integral curves of the gradient vector field to guide both uphill and downhill movement. The terrain methodology is extended here to include multivariable problems and integral curve bifurcations. The integral curves of interest are those associated with valleys and ridges and characterized as a collection of extrema in the norm of the gradient over a set of level curves. It is shown that integral curves can undergo tangent, pitchfork, and other types of bifurcations and that terrain methods are clearly superior to differential arc homotopy‐continuation methods on problems that exhibit parametric disconnectedness. Several examples, including a pair of CSTR problems, a retrograde flash calculation, and the task of finding all azeotropes for a heterogeneous ternary mixture, are used to show that terrain methods represent a reliable, efficient, and global way of solving multivariable process engineering simulation and optimization problems. Geometric illustrations are used whenever possible to clarify underlying ideas.
New maximum‐likelihood method for reduction of distribution‐coefficient data
Authors: Marshall Simon L. 
Published: April 2004

AbstractThe sampling distributions for the activity coefficient γ and distribution ratio (or K‐value) in binary fluid mixtures are derived from the assumptions that the pressure errors are negligible, and that the vapor and liquid composition measurements from which they are derived are normally distributed with known mean and variance. The distribution of K is shown to be not normal, with deviations from normality becoming particularly pronounced at the extremes of the composition range. The dispersion of this distribution is considerably greater than that predicted by the classic error‐propagation formula. Deviation from normality invalidates the most important assumption implicit in the use of the least‐squares criterion as the basis for parameter estimation from activity‐coefficient data. This has important implications for the estimation of Henry's law constants for solutes in very dilute solutions, as well as for Raoult's law‐based infinite‐dilution activity coefficients. The use of the exact distributions of γ and K as the basis for a more rigorous maximum‐likelihood method for parameter estimation in excess Gibbs energy models based on either Henry's law or Raoult's law standard states is demonstrated.
Correlating polymer resin and end‐use properties to molecular‐weight distribution
Authors: Hinchliffe Mark , Montague Gary , Willis Mark , Burke Annette 
Published: April 2004

AbstractThe prediction of polymer resin and end‐use properties for a dual‐reactor solution polyethylene process is investigated. Polymer molecular‐weight distribution (MWD) is highly influential in achieving the desired properties, but the extent of the importance and key areas of distribution to achieve specific properties are less well understood. The best empirical approach for resin and end‐use property prediction using the entire MWD along with other influential variables as inputs is investigated. Two modeling methods are considered: partial least squares (PLS) and a novel strategy that uses the weight fraction of polymer in a given molecular‐weight range (referred to as a binning technique). Both linear and nonlinear variants of the two algorithms are used. The intention is to develop a model that facilitates the analysis of the simultaneous influences of process operating conditions and resin characteristics such as MWD on a specified set of end‐use properties. Results demonstrate that the nonlinear variant of the binning technique provides the highest accuracy as well as indicating regions of MWD that are of greatest influence. Such information is particularly useful for the control of the polymerization reactors.
Identification of an ideal reactor model in a secondary combustion chamber
Authors: Bass Charles A. , Barat Robert B. , Lemieux Paul M. 
Published: April 2004

AbstractTracer analysis was applied to a secondary combustion chamber of a rotary kiln incinerator simulator to develop a computationally inexpensive networked ideal reactor model and allow for the later incorporation of detailed reaction mechanisms. Tracer data from sulfur dioxide tracer experiments were reconstructed using a least‐squares approximation that eliminated the intrinsic response of the measurement device and produced a residence time distribution between various points of the combustor. A model was chosen based on the best fit to tracer data, and consistency with physical geometry and temperature measurements. The resulting model showed that the active path was 1 s shorter than the mean residence time calculated from the total volumetric flow. The analysis found that complete mixing between the kiln gas and burner stream occurs farther downstream than originally expected. Results underscore the importance of turbulent mixing in reactor design and suggest that different design criteria are needed to ensure complete combustion.
Solubility of CO2 in (H2O+piperazine) and in (H2O+MDEA+piperazine)
Authors: Kamps Álvaro Pérez‐Salado , Xia Jianzhong , Maurer Gerd 
Published: April 2004

AbstractA thermodynamic model for describing the phase equilibrium for the system CO2+methyldiethanolamine+water has been extended, allowing for the presence of piperazine. Model parameters are estimated from new experimental results for the solubility of carbon dioxide in aqueous solutions of piperazine (for piperazine molalities up to 4 mol per kilogram of water, temperatures between 313 and 393 K, and pressures up to about 9.6 MPa). The model is tested by comparing predicted and experimental carbon dioxide solubilities in aqueous mixtures of both amines (2 molal MDEA+2 molal piperazine, at 353 K, and pressures up to about 6.4 MPa).
Relationship between volume expansion, solvent‐power, and precipitation in GAS processes
Authors: Striolo Alberto , Elvassore Nicola , Parton Tiziana , Bertucco Alberto 
Published: April 2004

AbstractDilute solutions of ethyl cellulose (ETC) in acetone and of poly(ethylene oxide) (PEO) in ethyl acetate, acetonitrile, ethyl acetate‐acetonitrile, and acetonitrile–water mixtures were expanded isothermally by compressed CO2. Onset precipitation pressures were visually measured through a windowed cell.Toward a rational understanding of the molecular mechanisms involved in gas antisolvent (GAS) processes, saturated‐liquid‐phase volume expansion and solvent power were monitored by UV‐vis spectroscopy for the solvent mixtures considered in the precipitation experiments. Ferrocene absorbance and phenol blue absorption‐peak‐wavelength shifts were used as probes to assess saturated‐liquid‐phase volume expansion and solvent power, respectively.For the first time, a correlation between a microscopic bulk property, solvent power, and the onset precipitation pressure of a solute is reported. Because of preferential interactions with the dye (hydrogen bonds), the correlation breaks down when even small amounts of water are present in the solvent mixture.The results presented here suggest that UV‐vis spectroscopy constitutes a valuable tool for understanding some phenomena related to supercritical‐fluid technology.
Mixing of pseudoplastic fluids using helical ribbon impellers
Authors: Shekhar S. Murthy , Jayanti S. 
Published: April 2004

AbstractHelical ribbon impellers are widely used in chemical and process industries for the mixing of pseudoplastic fluids of high viscosity. The design of such impellers is based on an assumed linear relation between shear rate and the rotation speed of the impeller. A number of computational fluid dynamics (CFD) simulations of the flow field have been carried to verify this hypothesis. It is shown that while the shear rate varies greatly within the mixing vessel, there does exist a linear relationship between the impeller speed and the local shear rate near the tip of the impeller. The proportionality constant Ks associated with this linear relation is found to be dependent on the geometric parameters of the system, but is largely independent of the flow behavior index. Based on these results, a new correlation, applicable to both Newtonian and power‐law fluids for power consumption, is proposed.
Microstreaming effects on particle concentration in an ultrasonic standing wave
Authors: Spengler J. F. , Coakley W. T. , Christensen K. T. 
Published: April 2004

AbstractIt is shown that the magnitude of Rayleigh microstreaming convective drag on microparticles in water in a 3.2‐MHz ultrasonic standing wave can be comparable to the lateral direct radiation force in the nodal plane (DRF1) and can significantly influence the microparticle aggregation. The transducer of a single half‐wavelength chamber was excited to give a single particle aggregate. The estimated sound pressure amplitude was 0.5 MPa. Particle image velocimetry (PIV) measurements gave the average microstreaming velocity in the nodal plane as 450 μm·s−1, which is comparable to the 340‐μm·s−1 value calculated from Rayleigh's theory. Movement of 25‐μm latex particles was primarily determined by DRF1, while that of smaller 1.0 μm, particles was determined by Rayleigh microstreaming. A 15‐μm latex particle velocity map, simulated from microstreaming data, the measured velocity map of 25‐μm particles, and the cube‐dependent relationship between DRF1's on particles of different sizes, was in reasonable agreement with a measured velocity map. Further evidence for the importance of microstreaming came from the result that velocities for 1‐ and 25‐μm particles were of similar magnitude, but were opposite in direction.