1,720,969 research outputs found
Energy and exergy analysis of cooling systems in office building
No full textConsulta en la Biblioteca ETSI Industriales (7985)[EN] The purpose of this study is to gain insight into the process of cooling of buildings with a standard installation.
The relation between work and changes in entropy generation arise from the simultaneous treatment of the first and
second laws referred as exergy (or available energy) analysis. In this study , it is discuss a thermodynamic analysis of
the whole facility. A parametric study of each sub-system, in which the whole system is divided to, is carried out to
determine the variation of the second law efficiency as a function of mass flow rate, relative humidity and temperature.
An energetic analysis is also studied in addition to the irreversible losses, which are calculated by a further application
of the second law, and it is double checked , by applying an exergy balance on each sub-system.
The great importance of this exergy analysis is that it allows a direct comparison between different energy
types (e.g. heat, electricity, fuel) on a common basis, and the concept of exergy consumption is useful for expressing
how and where energy is dispersed in the course of the energy conversion and heat transfer steps. And this is one of the
main goals of this study, to calculate the exergy flows of the system, and finally be able to draw the energy and exergy
flow diagrams.
The results show that most of the exergy losses take place in the refrigerant cycle and in the heat transfer
through the heat exchangers. In addition the energetic parameters, the COP and the energetic efficiency is not as high as
it could be. The common solution suggested to improve these two last parameters and decrease the exergy losses is to
reduce the inner temperature lift in the refrigerant cycle.Lluch Peris, ME. (2009). Energy and exergy analysis of cooling systems in office building. https://riunet.upv.es/handle/10251/34337.Archivo delegad
Retrofit für Prozesse mit mehreren Betriebsfällen für praktisches Wärmeübertragernetzwerk-Design
Get PDFProcess integration addresses the challenge of reduction in energy consumption by heat recovery in the processing industry. Its main focus lies on the grassroot design for new plants. However, a large portion of existing plants were built during times with low energy prices and thus, little focus on energy efficiency. Hence, retrofitting existing plants has a high potential to improve the overall energy efficiency in the process industry. Due to the industry’s orientation towards small volume, high value-added production demanding multi-product and multi-purpose plants, the focus of the process industry shifts to multi-period operation. Hence, process integration for such processes is more challenging as heat exchanger networks need to be flexible to handle multi-period operation. To overcome these challenges, research is also shifting more towards retrofitting existing plants and multi-period production. Further, for industry, it is more important to consider practical challenges within the optimization and be able to guide the optimization towards more practical plant designs rather than finding the best possible solution requiring complex and expensive controlling systems. The research in this thesis focuses on developing a method addressing the challenge of retrofitting multi-period processes for practical heat exchanger network design. To ensure practical designs, additional constraints are considered in the optimization. These constraints increase the complexity of the already NP-hard in the strong sense optimization problem. Hence, the developed method resorts to metaheuristic optimization algorithms. A possible hybrid trajectory-based as well as a hybrid evolutionary-based algorithm are investigated whereby the latter has prevailed. The implemented algorithm is split into two stages. A Genetic Algorithm optimizes the heat exchanger network topology and a Differential Evolution optimizes the heat loads for every operating period. To ensure feasible heat transfer in every operating period, bypass and admixer configurations, which ensure flexible operation of the heat exchangers, are analyzed to ensure feasible mixer temperatures by solving the logarithmic mean temperature analytically using the Lambert W-function. In recent years, reduction in greenhouse gas emissions has become more important for industry. Hence, greenhouse gas emissions are considered as a second objective in addition to the total annual cost. Therefore, the algorithm is using an NSGA-II sorting algorithm and hypervolume indicators to perform a Pareto optimization. The developed algorithm is applied successfully to a case study from the literature and one from the industry. The results for the multi-objective optimization showed that the weighting between capital costs for retrofit and utility demand, causing operating costs and greenhouse gas emissions, has a large impact on the final design. This also implies that a change in energy costs or an improvement in the efficiency of the utility system has a significant impact on the final design.Prozessintegration befasst sich mit der Reduzierung des Energiebedarfs durch Wärmerückgewinnung in der Prozessindustrie. Der Hauptfokus liegt auf der Planung neuer Anlagen. Allerdings wurde ein Grossteil der bestehenden Anlagen in Zeiten niedriger Energiepreise gebaut als Energieeffizienz in der Planung keine grosse Rolle gespielt hat. Daher besteht ein grosses Potenzial in der Nachrüstung bestehender Anlagen zur Verbesserung der Energieeffizienz in der Prozessindustrie. Aufgrund des Trends zur Herstellung von kleinen Produktmengen mit hoher Wertschöpfung werden Mehrproduktanlagen und Mehrzweck-Anlagen benötigt welche flexibel in verschiedenen Betriebsfällen betrieben werden können. Um den Betrieb für jedes Produkt gewährleisten zu können nimmt die Komplexität des Designs sowohl als auch der Optimierung mit der Anzahl der Betriebsfälle zu. Um diese Herausforderungen zu meistern setzt sich auch die Forschung mehr mit der Nachrüstung von bestehenden Anlagen und der Produktion mit mehreren Betriebsfällen auseinander. Weiter ist es für die Industrie wichtig, dass Herausforderungen aus der Praxis in die Optimierung mit einbezogen werden und dass die Optimierung in Richtung praxistauglichen Analgendesigns gelenkt werden, ohne dass auf komplexe Kontrollsysteme zurückgegriffen werden muss. Der Fokus dieser Thesis liegt in der Entwicklung einer Optimierungsmethode für die Nachrüstung von Prozessen mit mehreren Betriebsfällen. Um praxisnahe Designs zu gewährleisten, werden zusätzliche Randbedingungen in der Optimierung mitberücksichtigt welche Herausforderungen aus der Praxis mit einbeziehen. Diese zusätzlichen Randbedingungen erhöhen die Komplexität des ohnehin schon NP-schweren Optimierungsproblem. Daher verwendet der entwickelte Optimierungsansatz metaheuristische Algorithmen. Für den Algorithmus wurde ein hybrider, auf Trajektorien basierter, Algorithmus wie auch ein hybrider evolutionärer Algorithmus untersucht, wobei sich letzterer durchgesetzt hat. Dieser Algorithmus ist zweistufig wobei ein Genetischer Algorithmus für die Optimierung der Topologie des Wärmeübertragernetzwerkes und eine Differential Evolution für die Optimierung der Wärmeleistungen der Wärmeübertrager in jedem Betriebsfall eingesetzt wird. Mit der Integration von Beipass- und Beimischschaltungen kann die Flexibiltät des Wärmeübertragernetzwerkes gewährleistet werden. Dabei werden die Mischtemperaturen mithilfe der Lambert W-Funktion analytisch berechnet. Die Reduzierung von Treibhausgasemissionen hat in den letzten Jahren für die Industrie an Bedeutung gewonnen. Daher werden Treibhausgasemissionen, zusätzlich zu den jährlichen Gesamtkosten, als zweite Zielfunktion mitbetrachtet. Für die Pareto-Optimierung werden dafür ein NSGA-II-Sortieralgorithmus und Hypervolumenindikatoren verwendet.Der entwickelte Algorithmus wurde erfolgreich auf ein Fallbeispiel aus der Literatur und ein Fallbeispiel aus der Industrie angewendet. Die Ergebnisse der multikriteriellen Optimierung zeigen, dass die Gewichtung zwischen den Nachrüstungkosten und dem Energiebedarf, der die Betriebskosten und Treibhausgasemissionen verursacht, einen grossen Einfluss auf das Design haben. Dies bedeutet auch, dass eine Änderung der Energiekosten oder eine Verbesserung der Effizienz des Versorgungssystems einen signifikanten Einfluss auf das Design haben
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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