Non-steady two-phase stratified laminar flow of polymeric liquids in pipes

Summary A numerical method of solution is given for the non-steady two-phase stratified. laminar flow of various non-Newtonian fluids in pipes. In particular, the Ellis fluid model is chosen to illustrate inelastic shear thinning effects. It is shown that the method can be applied to the non-steady multi-phase stratified laminar flow of some non-Newtonian fluid models. An Oldroyd six constant model is used to illustrate the fully elastic flow. It is found that the presence of two phases of the same kind of immiscible liquids tends to suppress the typically viscoelastic response to time dependent situations that the same liquids would exhibit as a single phase. Overshoot of flow rates is reduced, if not completely eliminated in both the generation and decay of steady flows. In two-phase pulsatile flows, the flow enhancement is less marked and the time dependence of the individual flow rates can be significantly different. Theoretical results are used to interpret some of the flow instabilities encountered during the capillary flow of polymeric liquids.

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Zusammenfassung Es wird eine numerische Methode für die nichtstationäre geschichtete Zwei-Phasen-Strömung verschiedener nicht-newtonscher Flüssigkeiten durch Rohre angegeben, wobei zur Veranschaulichung unelastischer Scherentzähungseffekte speziell das Ellis-Modell ausgewählt wird. Dabei zeigt sich, daß diese Methode für die Anwendung auf nicht-stationäre Mehrphasenströmungen geschichteter laminarer Strömungen nicht-newtonscher Flüssigkeiten geeignet ist. Zur Veranschaulichung des vollständigen elastischen Fließens wird ein Oldroyd-Modell mit sechs Konstanten gewählt. Es wird gezeigt, daß die Anwesenheit von zwei Phasen nicht-mischbarer Flüssigkeiten die Unterdrückung des typisch viskoelastischen Verhaltens unter zeitabhängigen Bedingungen, wie es beim Vorhandensein einer einzigen Phase beobachtet wird, zur Folge hat. Das Überschwingen der Fließgeschwindigkeit wird sowohl beim Anfahren als auch beim Anhalten einer stationären Strömung verringert, wenn nicht gar völlig verhindert. In pulsierenden Zwei-Phasen-Strömungen ist die Geschwindigkeitserhöhung weniger ausgeprägt, und die Zeitabhängigkeit der beiden Fließgeschwindigkeiten kann wesentlich verschieden sein. Die theoretischen Ergebnisse werden dazu verwendet, einige bei der Durchströmung von Polymerflüssigkeiten durch Kapillaren beobachtete Fließinstabilitäten zu interpretieren.

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With 15 figures     

Theoretical foundations of apparent-damping phenomena and nearly irreversible energy exchange in linear conservative systems

This paper discusses a class of unexpected irreversible phenomena that can develop in linear conservative systems and provides a theoretical foundation that explains the underlying principles. Recent studies have shown that energy can be introduced to a linear system with near irreversibility, or energy within a system can migrate to a subsystem nearly irreversibly, even in the absence of dissipation, provided that the system has a particular natural frequency distribution. The present work introduces a general theory that provides a mathematical foundation and a physical explanation for the near irreversibility phenomena observed and reported in previous publications. Inspired by the properties of probability distribution functions, the general formulation developed here is based on particular properties of harmonic series, which form the common basis of linear dynamic system models. The results demonstrate the existence of a special class of linear nondissipative dynamic systems that exhibit nearly irreversible energy exchange and possess a decaying impulse response. In addition to uncovering a new class of dynamic system properties, the results have far-reaching implications in engineering applications where classical vibration damping or absorption techniques may not be effective. Furthermore, the results also support the notion of nearly irreversible energy transfer in conservative linear systems, which until now has been a concept associated exclusively with nonlinear systems.     

Effects of process parameters on supercritical CO2 extraction of total phenols from strawberry (Arbutus unedo L.) fruits: An optimization study

The aim of this work was to optimize total phenolic yield of Arbutus unedo fruits using supercritical fluid extraction. A Box–Behnken statistical design was used to evaluate the effect of various values of pressure (50–300 bar), temperature (30–80°C) and concentration of ethanol as co‐solvent (0–20%) by CO₂ flow rate of 15 g/min for 60 min. The most effective variable was co‐solvent ratio (p<0.005). Evaluative criteria for both dependent variables (total phenols and radical scavenging activity) in the model were assigned maximum. Optimum extraction conditions were elicited as 60 bar, 48°C and 19.7% yielding 25.72 mg gallic acid equivalent (GAE) total phenols/g extract and 99.9% radical scavenging capacity, which were higher than the values obtained by conventional water (24.89 mg/g; 83.8%) and ethanol (15.12 mg/g; 95.8%) extractions demonstrating challenges as a green separation process with improved product properties for industrial applications.     

Synchronous and asynchronous Pareto-based multi-objective Artificial Bee Colony algorithms

Pareto-based multi-objective optimization algorithms prefer non-dominated solutions over dominated solutions and maintain as much as possible diversity in the Pareto optimal set to represent the whole Pareto-front. This paper proposes three multi-objective Artificial Bee Colony (ABC) algorithms based on synchronous and asynchronous models using Pareto-dominance and non-dominated sorting: asynchronous multi-objective ABC using only Pareto-dominance rule (A-MOABC/PD), asynchronous multi-objective ABC using non-dominated sorting procedure (A-MOABC/NS) and synchronous multi-objective ABC using non-dominated sorting procedure (S-MOABC/NS). These algorithms were investigated in terms of the inverted generational distance, hypervolume and spread performance metrics, running time, approximation to whole Pareto-front and Pareto-solutions spaces. It was shown that S-MOABC/NS is more scalable and efficient compared to its asynchronous counterpart and more efficient and robust than A-MOABC/PD. An investigation on parameter sensitivity of S-MOABC/NS was presented to relate the behavior of the algorithm to the values of the control parameters. The results of S-MOABC/NS were compared to some state-of-the art algorithms. Results show that S-MOABC/NS can provide good approximations to well distributed and high quality non-dominated fronts and can be used as a promising alternative tool to solve multi-objective problems with the advantage of being simple and employing a few control parameters.     

Improved parallel preconditioners for multidisciplinary topology optimisations

Two commonly used preconditioners were evaluated for parallel solution of linear systems of equations with high condition numbers. The test cases were derived from topology optimisation applications in multiple disciplines, where the material distribution finite element methods were used. Because in this optimisation method, the equations rapidly become ill-conditioned due to disappearance of large number of elements from the design space as the optimisations progresses, it is shown that the choice for a suitable preconditioner becomes very crucial. In an earlier work the conjugate gradient (CG) method with a Block-Jacobi preconditioner was used, in which the number of CG iterations increased rapidly with the increasing number processors. Consequently, the parallel scalability of the method deteriorated fast due to the increasing loss of interprocessor information among the increased number of processors. By replacing the Block-Jacobi preconditioner with a sparse approximate inverse preconditioner, it is shown that the number of iterations to converge became independent of the number of processors. Therefore, the parallel scalability is improved.     

A powerful and efficient algorithm for numerical function optimization: artificial bee colony (ABC) algorithm

Swarm intelligence is a research branch that models the population of interacting agents or swarms that are able to self-organize. An ant colony, a flock of birds or an immune system is a typical example of a swarm system. Bees’ swarming around their hive is another example of swarm intelligence. Artificial Bee Colony (ABC) Algorithm is an optimization algorithm based on the intelligent behaviour of honey bee swarm. In this work, ABC algorithm is used for optimizing multivariable functions and the results produced by ABC, Genetic Algorithm (GA), Particle Swarm Algorithm (PSO) and Particle Swarm Inspired Evolutionary Algorithm (PS-EA) have been compared. The results showed that ABC outperforms the other algorithms.     

Kinetics of curing reactions for epoxy-amine/polyethersulphone resins

Differential scanning calorimetry (DSC) was used to indicate the relative extents of the different cure reactions of the 4-glycityloxyl-N, N-diglycidylaniline (MY0510), polyglycidyl ether of phenol formaldehyde novolac (DEN431) and 3,3 diamino diphenylsulphone (3,3 DDS) resin systems and how these were affected by the presence of polyethersulphone (PES). The extent of reactions at any given time decreased with increasing PES concentration and the reaction rate maximum shifted to longer times. The cured resin systems were examined using dynamic mechanical analysis (DMA). Broader β-transitions of lower intensities were observed in specimens containing PES, suggesting an increased range of relaxations within the transition.     

Transient acoustic radiation from impacted beam-like structures

Transient acoustic radiation from transverse vibrations of beams and beam-like structures is obtained by modelling the structure as a series of contiguous dipoles. A time-dependent expression is developed for sound radiation from a dipole source by Fourier synthesis. Acoustic radiation from the beam is obtained by integrating the sound pressure from the differential dipole elements over the beam length. Time-dependent integration limits are used to account for the transient effects. An analogous discrete formulation is described for beams of arbitrary geometry and density. The radiation patterns of a uniform unbaffled beam are given for frequencies below and above the critical frequency. The results are applied to model the sound radiation from an impact-excited beam.     

Three new dinuclear silver(I) complexes derived from pyrazolyl type ligands

Three NNN type ligands derived from 2,6-dichlorpyroidine, pyrazol and 3,5-dimethylpyrazole and their silver complexes were prepared in methanol media. The complex structures were characterized using IR spectroscopy, X-ray diffraction and elemental analysis. X-ray studies showed the complexes to be dimeric in structure. The two nitrogen atoms of the ligand coordinated the first Ag(I) ion whereas the second Ag(I) ion was coordinated by the third nitrogen donor. The nitrate structure was not ionic in a done of its oxygen atoms coordinated an Ag(I) ion. The Ag(I) ion was seen to be situated in a deformed tetrahedral coordination sphere. Thermogravimetric studies showed the complexes to decompose similar to explosive material. The decomposition temperature was observed to increase with increasing hydrogen atoms in the structure.     

The effect of orientation on the radiation induced degradation of polymers

A study has been made of the effect of orientation on the oxidative degradation of poly(vinylchloride) (PVC), low density polyethylene (LDPE) and high density polyethylene (HDPE) under the influence of γ- and u.v.-radiation. The effect of drawing in PVC is to increase the rate of oxidative degradation; in LDPE and HDPE, this rate decreases (especially for HDPE) both under u.v. and γ-radiation.