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Modelling of conventional and microchannel delugeable tube bundle for a direct air-cooled steam condenser
No full textA dissertation report submitted in fulfilment of the requirements for the degree of doctor of philosophy in mechanical engineeringThis study presents the thermal performance modelling of conventional and microchannel
delugeable tube bundle which incorporated into a second stage of the induced Hybrid
(Dry/Wet)) Dephlegmator (HDWD). Hybrid dry/wet dephlegmator was proposed to
replace a Conventional Dephlegmator (CD) of a direct Air-Cooled Condenser (ACC)
system, coupled to 30 MW steam turbine of a generating unit. The Conventional
Delugeable Tube Bundle (CDTB) thermal performance was modelled and configured
using one- and two - dimensional models by employing heat and mass transfer approach.
The geometric parameters for both first and second stages tube bundles of HDWD were
derived from that of CD of ACC system of the considered generation unit. Therefore, the
thermal performance of CDTB was optimised to ensure highest performance, and
appropriate geometric parameters that are corresponding to that of CD and available space
for installation. The best CDTB configuration’s performance was compared to similar
existing Delugeable Round Tube Bundle (DRTB) in literatures. When the tube pitch
varied from 25 mm to 38 mm, the DRTB’s heat transfer rate and air-side pressure drop
were found to be in the range of 1.4 to 2 times and 1.3 to 2.2 times that of CDTB,
respectively. The Microchannel Delugeable Tube Bundle (MDTB) thermal performance
was analysed using semi-empirical model, which comprises of microchannel heat transfer
and flow correlations. The size and geometric parameters of MDTB was equivalent to that
of CDTB, and the only difference was that, the MDTB has microchannel/ ports on the
steam-side. The MDTB thermal performance was found to increase as the hydraulic
diameter of the channels decreased. The thermal performance comparison of the CDTB
and MDTB at bundle, component and system levels was carried out. At all the levels, the
MDTB performance was higher than that of CDTB. However, this higher performance
came at expense of higher steam-side pressure drop. As the ambient air temperature
increased from 32 ℃ to 44 ℃, the MDTB’s heat transfer rate for 140 hydraulic
diameter was found to be 9 to 6 % higher than that of CDTB. The air-side pressure drop
variations between the two bundles were insignificant. Furthermore, the thermal
performance of HDWD incorporated with either CDTB or MDTB was compared to that
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of CD at component and system levels. At system level, and as the ambient air temperature
increased from 32 ℃ to 44 ℃, the heat transfer rate of the CD was found to be 27 % to 31
% less than that of HDWD incorporated with either CDTB or MDTB. The Air-side
pressure drop for HDWD was found to be about 41 % higher than that of CD.
Additionally, the steam turbine output and net powers were found to be higher when the
ACC was incorporated with HDWD than when CD was incorporated into AC
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
Numerical performance evaluation of a delugeable flat bare tube air-cooled steam condenser bundle
Get PDFThesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: In this study, one and two-dimensional models are developed for the evaluation of
the thermal performance of a delugeable flat tube bundle to be incorporated in the
second stage of an induced draft hybrid (dry/wet) dephlegmator (HDWD) of a
direct air-cooled steam condenser (ACSC). Both models are presented by a set of
differential equations. The one-dimensional model is analysed analytically by
using three methods of analysis which are: Poppe, Merkel, and heat and mass
transfer analogy. The two-dimensional model is analysed numerically by means
of heat and mass transfer analogy method of analysis whereby, the governing
differential equations are discretised into algebraic equations using linear upwind
differencing scheme. The two-dimensional model’s accuracy is verified through a
comparison of the two dimensional solutions to one dimensional solutions.
Satisfactory correlation between the one and two-dimensional results is reached.
However, there is a slight discrepancy in the solutions, which is mainly due to the
assumptions made in one-dimensional model. The effect of tube height, tube
pitch, tube width, deluge water mass flow rate, frontal air velocity, steam, and air
operating conditions on the heat transfer rate and air-side pressure drop for both
wet and dry operating modes are investigated. The long tube height, large tube
width, small tube pitch, and high frontal air velocity are found to increase the tube
bundle’s performance. However, this performance is associated with a high airside
pressure drop. The performance of the deluged flat tube bundle is found to be
less sensitive to the changes in the deluge water mass flow rate and air operating
conditions. Furthermore, the best configuration of a delugeable flat tube bundle is
identified through a comparison to round tube bundle presented by Anderson
(2014). The performance of the round tube bundle is found to be around 2 times,
and 1.5 times of that of flat tube bundle, when both bundles operate as an
evaporative and dry air-cooled condenser respectively.AFRIKAANSE OPSOMMING: In hierdie studie is een en twee-dimensionele modelle ontwikkel vir die
evaluering van die termiese prestasie van 'n benatbare plat buis bundel in die
tweede stadium van 'n geïnduseerde ontwerp hibriede (droë / nat ) deflegmator
van 'n direkte lugverkoelde stoom kondensator. Beide modelle is aangebied deur
'n stel van differensiaalvergelykings. Die een-dimensionele model is analities
ontleed deur die gebruik van drie metodes van analise wat: Poppe, Merkel, en die
hitte en massa-oordrag analogie. Die twee-dimensionele model is numeries
ontleed deur middel van hitte en massa-oordrag analogie metode van analise
waardeur , die regerende differensiaalvergelykings gediskretiseer in algebraïese
vergelykings met behulp van lineêre windop differensievorming skema. Die tweedimensionele
model se akkuraatheid is geverifieer deur 'n vergelyking van die
twee dimensionele oplossings te een dimensionele oplossings. Bevredigende
korrelasie tussen die een en twee-dimensionele resultate bereik word. Maar daar is
'n effense verskil in die oplossings, wat is hoofsaaklik te wyte aan die aannames
wat gemaak in een-dimensional model. Die effek van buis hoogte, buis
toonhoogte, buis breedte, vloed water massa-vloeitempo, frontale lug snelheid,
stoom, en in die lug werktoestande op die hitte oordrag snelheid en lug - kant
drukval vir beide nat en droë maatskappy modi word ondersoek. Die lang buis
hoogte, groot buis breedte, klein buisie toonhoogte, en 'n hoë frontale lug snelheid
gevind die buis bundel se prestasie te verhoog. Tog is hierdie prestasie wat
verband hou met 'n hoë lug - kant drukval. Die prestasie van die oorstroom plat
buis bundel gevind word minder sensitief vir die veranderinge in die vloed water
massa-vloeitempo en lug werktoestande. Verder is die beste opset van 'n
benatbare plat buis bundel geïdentifiseer deur 'n vergelyking met ronde buis
bundel aangebied deur Anderson (2014). Die prestasie van die ronde buis bundel
gevind word om 2 keer, en 1.5 keer van daardie plat buis bundel , wanneer beide
bundels funksioneer as 'n damp en droë lugverkoelde kondensor onderskeidelik
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
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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