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Elektronik kutular için bir eksenel akış fanının performans karakterizasyonu ve optimizasyonu
No full textThermal management of high power electronic components have become a challenging and critical issue for thermal engineers. Forced convection electronic enclosures comprises of fans to provide fluid flow through the system to remove heat efficiently. In this study, performance characterization of an axial fan for electronic enclosures has been performed computationally and experimentally. For this purpose, by using the three-dimensional CAD model of a fan with Computational Fluid Dynamics (CFD) are evaluated in comparision with the experimental data. An experimental system was designed and built for the validation of numerical models. All the measurements were carrried out in a wind tunnel which was designed and manufactured according to the Air Movement Control Assosciation (AMCA) standard 210-99, 1999. In order to make relevant comparisions, a detailed computational model of the wind tunnel setup along with the fan were modeled. Moving Reference Frame (MRF) technique is used for the modelling of an axial fan and the simulations were performed by utilizing realizable k–ε turbulence model with enhanced wall function to determine flow and pressure fields over a range of flow rates. Experimental investigation in the wind tunnel by measuring the pressure rise and flow rate through the fan by using multiple nozzles which was also designed and manufactured according to the Air Movement Control Assosciation (AMCA) standard 210-99, 1999. Understanding of the overall fan efficiency as a function of the volumetric flow rate and th improvement concerning with the losses occur across the fan are described. In the second phase of the study, power losses of an axial fan are investigated to determine the effect different components on the overall efficiency. Moreover, it deals with the modeling of mechanical, electrical, thermal and electromagnetic losses which focus especially on an outer rotor brushless DC motor. Efficiency of a fan depends on its electrical and mechanical designs as well as the environmental conditions that the fan is exposed to. Typically, the overall efficiency of an axial fan varies between 15 to 40 percent. Power losses may be due to electrical, aerodynamic or mechanical design components. Losses occurring in an axial fan motor have become a critical issue in which high inertial effects, low power, low cost and high efficiency are desired. In order to design an efficient motor, it is important to accurately predict the power losses which are usually dissipated in the form of heat. Reduction of these losses leads to a decrease in the motor temperature and, therefore, has a positive effect on the fan reliability. Expressions for calculating the inverter losses, motor losses and mechanical losses are derived. The power losses obtained are then used as heat sources when evaluating the thermal performance of the motor. By using a two-dimensional model, computational fluid dynamics (CFD) simulations are performed to analyze the core loss distribution across the motor. The results are utilized to determine evaluate the overall efficiency of the system.Yüksek güçlü elektronik komponentlerin ısıl yönetimi, termal mühendisler için zorlayıcı ve kritik bir problem haline gelmiştir. Zorlanmış taşınımlı elektronik mahfazalar, sistemdeki ısıyı verimli bir şekilde ortadan kaldırmak için akış yaratan fanlardan oluşmaktadır. Bu çalışma kapsamında, elektronik mahfazalarda kullanılan eksenel bir fanın performans karakterizasyonu üzerine sayısal ve deneysel çalışmalar gerçekleştirilmiştir. Bu amaç ile bir fanın üç boyutlu CAD modeli kullanılarak hesaplamalı akışkanlar dinamiği ile deneysel veriler ile karşılaştırılması yapılmıştır. Sayısal modellerin doğrulamasını yapmak amacıyla bir deneysel düzenek tasarlanmış ve kurulmuştur. Tüm ölçümler, Air Movement and Control Association (AMCA- Hava Hareket ve Kontrol Kurumu) 210-99,1999 standardına uygun olarak tasarlanmış ve üretilmiş bir rüzgar tüneli içerisinde gerçekleştirilmiştir. Tutarlı karşılaştırmalar yapmak adına, fan ile birlikte rüzgar tüneli düzeneğinin sayısal modeli hazırlanmıştır. Eksenel bir fanın modellemesi sırasında Hareketli Referans Çerçevesi (Moving Reference Frame) tekniği kullanılır. Akış hızları aralığı üzerine, akış ve basınç alanlarına karar vermek için geliştirilmiş duvar fonksiyonu ile gerçekleştirilebilir k–ε türbülans modeli kullanılarak simülasyonlar yapılmıştır. Rüzgar tünelinde yapılan deneysel araştırmalar, fandan kaynaklanan basınç artışı ve akış hızı ölçülerek tamamlanmıştır. Bu ölçümler sırasında AMCA 210-99, 1999 standardına uygun olarak tasarlanmış ve üretilmiş birden fazla çıkış ağzı (nozzle) kullanılmıştır. Fanın toplam verimlilik kavramı, hacimsel debiye ve fan boyunca oluşan kayıplar ile ilgili gelişmelere bağlı bir fonksiyon olarak tanımlanmaktadır. Çalışmanın ikinci fazında, farklı komponentlerin genel verim üzerindeki etkisini görmek amacıyla eksenel fanın güç kayıpları araştırılmaktadır. Dahası, güç kayıpları özellikle fırçasız doğru akım motorunun dış rotoruna odaklı mekanik, elektriksel, termal ve elektromanyetik kayıpların modellemesi ile bağlantılıdır. Bir fanın verimliliği, elektriksel ve mekanik tasarımına bağlı olmakla birlikte fanın maruz kaldığı çevre koşullarına da bağlıdır. Genellikle, bir eksenel fanın toplam verimliliği %15 ila %40 arasında çeşitlilik göstermektedir. Güç kayıpları; elektriksel, aerodinamik veya mekanik tasarım parçalarından kaynaklanabilir. Yüksek atalet etkisi, düşük güç, düşük maliyet ve yüksek verim beklendiğinde, eksenel fanlar üzerinde oluşan kayıplar kritik bir problem haline gelir. Verimli bir motor tasarlamak için genellikle ısı formunda oluşan güç kayıplarını doğru olarak öngörmek önemlidir. Bu kayıpların giderilmesi motor sıcaklığının düşmesine yol açar ve bu sayede, fanın güvenilirliğini arttırır. Evirici kayıpları, motor kayıpları ve mekanik kayıpları hesaplamak için formüller türetilmiştir. Güç kayıpları belirlenmiş ve sonra motorun termal performansını değerlendirmek için güç kaynağı olarak kullanılmıştır. İki boyutlu bir model kullanılarak, motor üzerindeki çekirdek kaybı dağılımını analiz edebilmek amacı ile hesaplamalı akışkanlar dinamiği (HAD) simülasyonları üzerine çalışılmıştır. Sonuçlar, sistemin genel verimliliğine karar verebilmek için kullanılmıştır
An investigation into performance characteristics of an axial flow Fan using CFD for electronic devices
No full textDue to copyright restrictions, the access to the full text of this article is only available via subscription.Rotating fans are widely utilized in thermal management applications and their accurate characterization has recently become even a more critical issue for thermofluids engineers. The present study investigates the characterization of an axial fan computationally and experimentally. Using the three-dimensional CAD models of the fan, a series of computational fluid dynamics (CFD) simulations were performed to determine the flow and pressure fields produced by the axial mover over a range of flow rates. In order to validate the computational model findings, experiments were conducted to obtain the pressure drop values at different flow rates in an AMCA (Air Movement and Control Association) standard 210-99, 1999 wind tunnel. These data sets were also compared with the fan vendor’s published testing data. A reasonably good agreement was obtained among the data from these three separate sources. Furthermore, an attempt was made to understand the overall fan efficiency as a function of the volumetric flow rate. It was determined that the maximum overall fan efficiency was less than 27% correlating well with the computational results
Investigation of power distribution on an axial fan
No full textDue to copyright restrictions, the access to the full text of this article is only available via subscription.Forced convection cooling systems utilize fans which can be axial or radial, small or large in many different configurations. Efficiency of a fan depends on its electrical and mechanical designs as well as the environmental conditions that the fan is exposed to. Typically, the overall efficiency of an axial fan varies between 15 to 40 percent. Power losses may be due to electrical, aerodynamic or mechanical design components. Losses occurring in an axial fan motor have become a critical issue in which high inertial effects, low power, low cost and high efficiency are desired. In order to design an efficient motor, it is important to accurately predict the power losses which are normally dissipated in the form of heat. The present study starts with an investigation of the power losses of an axial fan experimentally and computationally. Moreover, it deals with modeling of mechanical, electrical, thermal and electromagnetic losses which focus especially on an outer rotor brushless DC motor. Reduction of these losses leads to a decrease in the motor temperature and, therefore, has a positive effect on the fan reliability. Expressions for calculating the inverter losses, motor losses and mechanical losses are derived. The power losses obtained are then used as heat sources when evaluating the thermal performance of the motor. By using a two-dimensional model, computational fluid dynamics (CFD) simulations are performed to determine the iron losses across the motor. These results are utilized to determine evaluate the overall efficiency of the system.Aselsan ; SSM (undersecretary of Turkish ministry of defense
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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