Elena B. Martin, Francisco Sastre, Angel Velazquez and Abderrahmane Baïri
This paper aims to study the influence that the second invariant of the rate-of-strain tensor of a power law polymeric fluid (aqueous solution of hydroxyethyl cellulose [HEC]) has…
Abstract
Purpose
This paper aims to study the influence that the second invariant of the rate-of-strain tensor of a power law polymeric fluid (aqueous solution of hydroxyethyl cellulose [HEC]) has on convective mixing performance downstream of a 3D confined oscillating prism. Newtonian and non-Newtonian Reynolds numbers, the mass concentration of HEC and prism oscillation frequency were varied.
Design/methodology/approach
A conceptual problem was designed. Its objective was to analyze the convective mixing of two adjacent flow streams when they pass around a moving confined prism. The rectangular prism had a square section, and its sinusoidal motion was prescribed inside a channel with a square section too. OpenFOAM libraries were used to simulate the flow field. Regarding prism motion, the icoDyMFoam solver was used. The problem was analyzed both at the global level (mixing parameter) and local level (detailed flow topology).
Findings
For constant Reynolds number, increasing mass concentrations of HEC (in the range from 0.2% to 0.5%) led to better mixing parameters. The improvement was linked to the effect that the second invariant of the rate-of-strain tensor had on flow topology. It was found that mixing is maximum when the prism motion and its wake (the frequency of the first instability) are synchronized. In practical terms, this means that the optimum stirring frequency does not need to be very high; it suffices that it ensures that synchronization occurs. The dominant vorticity shedding pattern found was the so-called 2P mode. However, a significant difference was found when compared to the free-stream situation. While in the former, the two vorticity regions that make up the 2P pair come from the prism, in the present confined case, one came from the prism, and the other came from the wall. Another difference was that in the present case, the 2P pairs were much more elongated than in the free stream case, and this had a significant influence on the stretching and bending of streak lines and, therefore, on mixing.
Practical implications
The study that has been presented has a practical industrial implication for the processes industry because it provides guidelines to design active mixers that deal with aqueous power law polymeric solutions. In parallel, it opens up some new research lines in the direction of studying whether the mixing concept might be modified so as to develop a fully passive system that could be far simpler and, possibly, more attractive to industry.
Originality/value
The originality and value of the study are associated to the systematic approach that has been followed. It has allowed to establish a clear pattern regarding the active mixing behavior of HEC solutions in confined flows. To the best of authors’ knowledge, this could be the first study of this type in the literature. Also, the study has contributed to understand the vorticity shedding patterns that appear in these types of problems and how they shape wake topology and, consequently, mixing performance. The finding that optimum mixing requires synchronization of stirring motion frequency and wake first natural frequency of instability may help to improve the design and operation of industrial mixers dealing with polymeric aqueous solutions.
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Francisco Sastre, Elena B. Martin, Angel Velazquez and Abderrahmane Baïri
This paper aims to compare the performance of flow pulsation versus flow stirring in the context of mixing of a passive scalar at moderate Reynolds numbers in confined flows. This…
Abstract
Purpose
This paper aims to compare the performance of flow pulsation versus flow stirring in the context of mixing of a passive scalar at moderate Reynolds numbers in confined flows. This comparison has been undertaken in two limits: diffusion can be neglected as compared to convection (very large Peclet) and diffusion and convection effects are comparable. The comparison was performed both in terms of global parameters: pumping power and mixing efficiency and local flow topology.
Design/methodology/approach
The study has been addressed by setting up a common conceptual three-dimensional problem that consisted of the mixing of two parallel streams in a square section channel past a square section prism. Stirring and pulsation frequencies and amplitudes were changed and combined at an inlet Reynolds number of 200. The numerical model was solved using a finite volume formulation by adapting a series of open-source OpenFOAM computational fluid dynamic (CFD) libraries. For cases with flow pulsation, the icoFoam solver for laminar incompressible transient flows was used. For cases with stirring, the icoDyMFoam solver, which uses the arbitrary Lagrangian–Eulerian method for the description of the moving dynamical mesh, was used to model the prism motion. At the local flow topology level, a new method was proposed to analyze mixing. Time evolution of folding and wrinkling of sheets made up of virtual particles that travel along streak lines was quantified by generating lower rank projections of the sheets onto the spaces spanned by the main eigenvectors of an appropriate space-temporal data decomposition.
Findings
In the limit when convection is dominant, the results showed the superior performance of stirring versus flow pulsation both in terms of mixing and required pumping power. In the cases with finite Peclet, the mixing parameters by stirring and flow pulsation were comparable, but pulsation required larger pumping power than stirring. For some precise synchronization of stirring and pulsation, the mixing parameter reached its maximum, although at the expense of higher pumping power. At the local flow topology level, the new method proposed to quantify mixing has been found to correlate well with the global mixing parameter.
Originality/value
A new systematic comparative study of two methods, stirring and pulsation, to achieve mixing of passive scalars in the mini scale for confined flows has been presented. The main value, apart from the conclusions, is that both methods have been tested against the same flow configuration, which allows for a self-consistent comparison. Of particular interest is the fact that it has been found that accurate synchronization of both methods yields mixing parameters higher than those associated to both methods taken separately. This suggests that it is possible to synchronize mixing methods of a different nature to achieve optimum designs. The new theoretical method that has been proposed to understand the mixing performance at the local level has shown promising results, and it is the intention of the authors to test its validity in a broader range of flow parameters. All these findings could be taken as potential guidelines for the design of mixing processes in the mini scale in the process industry.
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Eric Alfredo Rincón-García, Miguel Ángel Gutiérrez-Andrade, Sergio Gerardo de-los-Cobos-Silva, Roman Anselmo Mora-Gutiérrez, Antonin Ponsich and Pedro Lara-Velázquez
This paper aims to propose comparing the performance of three algorithms based on different population-based heuristics, particle swarm optimization (PSO), artificial bee colony…
Abstract
Purpose
This paper aims to propose comparing the performance of three algorithms based on different population-based heuristics, particle swarm optimization (PSO), artificial bee colony (ABC) and method of musical composition (DMMC), for the districting problem.
Design/methodology/approach
In order to compare the performance of the proposed algorithms, they were tested on eight instances drawn from the Mexican electoral institute database, and their respective performance levels were compared. In addition, a simulated annealing-based (simulated annealing – SA) algorithm was used as reference to evaluate the proposed algorithms. This technique was included in this work because it has been used for Federal districting in Mexico since 1994. The performance of the algorithms was evaluated in terms of the quality of the approximated Pareto front and efficiency. Regarding solution quality, convergence and dispersion of the resulting non-dominated solutions were evaluated.
Findings
The results show that the quality and diversification of non-dominated solutions generated by population-based algorithms are better than those produced by Federal Electoral Institute’s (IFE’s) SA-based technique. More accurately, among population-based techniques, discrete adaptation of ABC and MMC outperform PSO.
Originality/value
The performance of three population-based techniques was evaluated for the districting problem. In this paper, the authors used the objective function proposed by the Mexican IFE, a weight aggregation function that seeks for a districting plan that represents the best balance between population equality and compactness. However, the weighting factors can be modified by political agreements; thus, the authors decided to produce a set of efficient solutions, using different weighting factors for the computational experiments. This way, the best algorithm will produce high quality solutions no matter the weighting factors used for a real districting process. The computational experiments proved that the proposed artificial bee colony and method of musical composition-based algorithms produce better quality efficient solutions than its counterparts. These results show that population-based algorithms can outperform traditional local search strategies. Besides, as far as we know, this is the first time that the method of musical composition is used for this kind of problems.
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Uncertainty is one of the principal features of public administration in Colombia. Therefore, presenting a clear and consistent analysis is difficult. This uncertainty exists…
Abstract
Uncertainty is one of the principal features of public administration in Colombia. Therefore, presenting a clear and consistent analysis is difficult. This uncertainty exists alongside interesting efforts to modernize institutions. Among the challenges faced by public administration in Colombia, we find corruption, illegal bands of drug traffickers, and the lack of trust between critical actors involved in governance. The aim of this chapter is to share an analysis that illustrates the difficulties and contradictions faced by those working in the public sector.
“Colombia is a legal social state organized in the form of a unitary republic, decentralized, with the autonomy of its territorial units, democratic, participatory, and pluralistic, based on respect of human dignity, on the work and solidarity of the individuals who belong to it, and the predominance of the general interest” (National Constitution, 1st Article).
“Colombia is a legal social state organized in the form of a unitary republic, decentralized, with the autonomy of its territorial units, democratic, participatory, and pluralistic, based on respect of human dignity, on the work and solidarity of the individuals who belong to it, and the predominance of the general interest” (National Constitution, 1st Article).
The dictionaries reviewed in this article are the Appleton's New Cuyas…, revised in 1972; Cassell's…, revised in 1978; Collins…, 1st edition in 1971; Diccionario moderno…Larousse…
Abstract
The dictionaries reviewed in this article are the Appleton's New Cuyas…, revised in 1972; Cassell's…, revised in 1978; Collins…, 1st edition in 1971; Diccionario moderno…Larousse, revised in 1976, and the Simon and Schuster's International…, 1st edition in 1973. These dictionaries, all presently in print in the United States, are one volume, table‐top or hand‐size dictionaries, each containing more than 1,000 pages.
In a country where judicial institutions are known to be inefficient and where activists have traditionally not engaged in legal mobilization, what explains the emergence of NGO…
Abstract
In a country where judicial institutions are known to be inefficient and where activists have traditionally not engaged in legal mobilization, what explains the emergence of NGO strategic litigation? The author argues that a change in the legal opportunity structure impacts how activists interact with the legal system. Comparing two states in Mexico, the author demonstrates that the introduction of private prosecution rights opened the door for activists to litigate femicide cases. The emergence of strategic litigation has helped improve compliance with international human rights law and has had a demonstration effect on how to use the law to press for accountability.
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Purpose: This chapter analyzes the policies of immigration control implemented in Mexico in 2014 to deter the migration of Central Americans to the United States, and their impact…
Abstract
Purpose: This chapter analyzes the policies of immigration control implemented in Mexico in 2014 to deter the migration of Central Americans to the United States, and their impact on Central American youth migrants.
Methods: This chapter draws from three pools of data: (1) participant observation and interviews conducted with minor migrants in Mexico from 2015 to 2019; (2) Mexican and US government data on detentions and deportations of Central American minor migrants; and (3) publicly available information on Mexican and Guatemalan government programs and media campaigns targeted at addressing the migration of Central American minor migrants.
Findings: This chapter posits that the policies of migrant detention and deportation implemented in Mexico in 2014 turned the entire country into a borderland for Central Americans. These policies expanded the areas of migrant surveillance, detention, and deportation beyond Mexico’s traditional border regions, which, in turn, made youth migrants’ journeys through Mexico more precarious and prone to violence.
Research implications: This chapter examines the impact of immigration and border control policies implemented in Mexico and anti-immigration propaganda on Central American youth, and it demonstrates how Mexico has been converted into an expanded US border territory in an attempt to prevent migrants from reaching the United States’ physical borderland.
Value: This chapter analyzes the impact of US-led detention and deportation policies aimed at Central American migrants throughout Mexico, rather than just in the traditional border regions. These relatively novel policies are at the forefront of immigration control and warrant special attention.
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Carlos César de Oliveira Lacerda, Ana Sílvia Rocha Ipiranga and Ulf Thoene
The city of Fortaleza, capital of the state of Ceará in the north-east of Brazil, presents a paradox as a present-day tourist destination, while also marked by features and…
Abstract
Purpose
The city of Fortaleza, capital of the state of Ceará in the north-east of Brazil, presents a paradox as a present-day tourist destination, while also marked by features and processes characteristic of cities in the Global South, such as high levels of social inequality with fragmented urban margins and vulnerabilities. This research problematizes the idea of “historical ruins” proposed by Walter Benjamin as a viable way to understand how the organization process of today's city margins can be “denaturalized” by the past. The objective of this research is to assess how the urban margins of the city were organized as a history of resistance.
Design/methodology/approach
In theoretical terms, this research links critical urban studies with critical approaches to organizational history (COH) based on Walter Benjamin's philosophical concepts of “ruins” and “progress”. The historical and archival methodology, consisting of 193 documents, suggests the existence of a philosophical–historical nexus that helps explain the spatial fragmentation of the city, and especially the urban margins in the western region of Fortaleza.
Findings
The Benjaminian notion of “historical ruins” has been exemplified by the Brazilian government practices confining migrants fleeing drought in internment camps on the margins of the city of Fortaleza in three waves beginning in 1877, 1915 and 1932 respectively. The effects of such confinement policies put into practice in the name of “progress” influenced the organization of large urban spaces on the city's margins, whereas on the other hand, the analyses advanced in this research reflect on alternatives to re-frame the history of the organization of the margins of Fortaleza through a set of practices of resistance.
Originality/value
Based on the concept of “denaturalization”, and through re-activation of the memory of a circumstantial past, the gaze of the “ruins”, as represented by the belief in “progress” addressed in official reports of government confinement policies, spaces of resistance have emerged where new possibilities for the future of the city can be imagined.
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Graciela Bensusán and Maria Lorena Cook
The July 2, 2000, electoral victory of Vicente Fox of the opposition National Action Party (PAN) as president of Mexico marked an historic turning point in that country’s…
Abstract
The July 2, 2000, electoral victory of Vicente Fox of the opposition National Action Party (PAN) as president of Mexico marked an historic turning point in that country’s political development. The ouster from power of Mexico’s Institutional Revolutionary Party (PRI) after seventy-one years promised to rupture the long-time alliance between organized labor, the state, and the PRI. A transition to a democratic political regime would create new opportunities for the struggling independent labor movement in Mexico. More importantly, a political transition would make possible for the first time a shift away from an authoritarian-corporatist system of industrial relations toward a democratic model of labor governance.
Sartaj Chaudhary and Ajoy Kumar Dey
The past decade has seen a proliferation of research on service quality in education. However, little attempt has been made to understand the impact of student perceived service…
Abstract
Purpose
The past decade has seen a proliferation of research on service quality in education. However, little attempt has been made to understand the impact of student perceived service quality on sustainability practices of the university or the effect of such practices on student satisfaction. To bridge this gap, this paper aims to propose a conceptual framework to examine the relationships between service quality, sustainable practices and student satisfaction from the perspective of students.
Design/methodology/approach
A quantitative methodology was employed, and data were collected through an online structured questionnaire. Responses were gathered from undergraduate students (n = 419) studying in four colleges affiliated to a university in Delhi, India. Exploratory and confirmatory factor analyses were used to validate the instruments. Structural equation modelling was used to examine the associations between the constructs.
Findings
The research revealed that student perceived service quality in education has a significant effect on their perception of sustainable practices of the university and student satisfaction. Further, sustainable practices predict student satisfaction.
Research limitations/implications
The findings may guide the key decision-makers in the education industry to incorporate service quality and sustainable practices in their strategy and thereby enhance student satisfaction.
Originality/value
This research is the first of its kind to examine the impact of service quality as perceived by students on the perception of sustainability practices of the university. Further, it empirically tests the effect of perceived sustainability practices on student satisfaction.