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Analiza sredice eksperimentalne naprave MOTEL z računalniško dinamiko tekočin (RDT)
No full textThe aim of this thesis is to perform Computational Fluid Dynamics (CFD) analysis of the core of the Modular Test Loop (MOTEL) facility designed and built in Lappeenranta–Lahti University of Technology LUT using the simulation software ANSYS Fluent. Even though the power distribution in the core of the MOTEL facility is five-stepped cosine, for this study flat and cosine power distributions are also simulated to compare different parameters e.g., temperature, density, velocity with the existing five-stepped cosine power distribution. Two meshes were created for demonstrating the effect of mesh density. Two vertical planes are created in the middle of the modelled geometry to take temperature and velocity contours and analyse the way they change while flowing from inlet to outlet. Four lines are created adjacent to the four instrumentation rod walls and velocity, temperature and turbulence kinetic energy profiles are analysed along those lines. Better heat transfer is observed for cosine power distribution as the difference between the average and highest temperature is the least. The line adjacent to the instrumentation rod 1, which is near the centre of the core, shows least fluctuation in temperature, velocity, and turbulence kinetic energy profiles. When simulating the case for 990kW power and five-stepped cosine power distribution with both Shear Stress Transport (SST) and standard k-ϵ model, there were some differences between the result. This is due to the limitation of standard k-ϵ model in simulating near-wall boundary and capturing the transitions in natural circulations flows.Cilj magistskega dela je izvedba študije enofaznega toka tekočine skozi sredico modularne testne zanke MOTEL (ang. »Modular Test Loop«), ki je bila zasnovana in razvita na Tehnični univerzi Lappenranta-Lahti (LUT) na finskem. Študija je bila izvedena z uporabo metod računalniške dinamike tekočin v programskem okolju ANSYS Fluent. Obravnavali smo tri različne porazdelitve toplotnega toka znotraj sredice: petstopenjsko kosinusno porazdelitev, ki ustreza realnemu stanju, ter homogeno in kosinusno porazdelitev. Pri tem smo primerjali vpliv porazdelitve moči na različne parametre toka, kot so temperatura, gostota in hitrostno polje. Ustreznost uporabljene prostorske diskretizacije smo utemeljili s primerjavo rezultatov simulacij istega primera na dveh različno gostih računskih mrežah. Temperaturno in hitrostno polje toka skozi sredico zanke MOTEL smo opazovali na dveh navpičnih ravninah v sredini obravnavane geometrije. Podrobneje smo analizirali temperaturno in hitrostno porazdelitev ter porazdelitev turbulentne kinetične energije na stenah štirih instrumentacijskih palic. V primeru s kosinusno porazdelitvijo toplotne moči je bil prenos toplote najboljši, saj je bila razlika med povprečno in najvišjo temperaturo najmanjša. Najnižje fluktuacije temperature, hitrosti in turbulentne kinetične energije so bile ob steni instrumentacijske palice 1, ki je najbližje osi sredice. Pri simulacijah primera s toplotno močjo 990 kW in petstopenjsko kosinusno porazdelivijo moči, smo opazili pomembnejše razlike v rezultatih med simulacijami izvedenimi s tubulentnim modelom prenosa strižnih napetosti k-ω (ang. »Shear-Stress Transport (SST) k-ω model«) in modelom k-ϵ. To je posledica omejitev modela k-ϵ povezanih s popisom toka blizu stene in modeliranjem naravne konvekcije
Computational fluid dynamics analysis of steam condensation in nuclear power plant applications
Get PDFDetailed experimental and numerical investigations of safety systems and various key
components of nuclear power plant are important from both view points of safety and
economical aspects. This thesis presents the computational fluid dynamics (CFD) analysis
of steam condensation phenomena appearing in a pressure suppression pool (PSP) of a
boiling water reactor (BWR) and in a low-pressure (LP) steam turbine.
The PSP is one of the key systems which provide a large pressure and heat sink by condensing
steam into a denser volume of water. In this thesis, two direct contact condensation
(DCC) modes appearing during steam blowdown in BWR PSP are investigated. 2D
and 3D simulations of a PSP test facility were conducted by using the Eulerian-Eulerian
two-fluid approach. For this purpose, two CFD codes, OpenFOAM and NEPTUNE CFD
were used. The interfacial heat transfer between steam and water was modelled by using
different DCC models. The open pool test facility (POOLEX) and the pressurizing
drywell-wetwell suppression pool facility (PPOOLEX) tests of Lappeenranta University
of Technology (LUT) were used as references. Various issues namely performance of
DCC models, significance of reference bubble diameter, and sensitivity of subcooling
rate on DCC phenomena were studied. The results confirmed that the surface divergence
model by Lakehal et al. (2008) predicts the mildly sheared interfacial DCC case
well. The incompressible solver was not able to predict rapid pressure variation in chugging
simulations. The compressible two-phase solver of OpenFOAM was stable enough
and able to invoke the chugging phenomenon of POOLEX steam blowdown tests. The
surface renewal model of by Hughes and Duffey (1991) and the DCC model of Coste
(2004) achieved good predictions of the chugging simulations of the POOLEX test. The
influence of grid refinement on the DCC phenomena was assessed employing a grid convergence
index for POOLEX simulations. Results indicate that an adequate grid density
is essential to resolve the flow details and to acquire the correct rates of DCC. In the
PPOOLEX chugging simulations, different issues namely the performance of different
DCC models, the influence of turbulence modeling, interfacial momentum transfer, geometry
and interface initialization were briefly analyzed. The significance of interfacial
area modelling on the chugging DCC was examined by employing the Rayleigh-Taylor
Interfacial area model by Pellegrini et al. (2015). The results showed that interfacial area modeling and turbulence modelling were the dominant factors for the chugging DCC
modelling in the PPOOLEX simulations.
Steam turbines are vital for power generation, and therefore, the studies aiming to the
efficiency improvement of steam turbines are crucial for efficient power plants. As the
exhaust pressure of steam turbines is designed to be low to achieve the maximum energy
output, the steam temperature drops due to rapid expansion in the last stages of the LP
steam turbine. Steam condenses and, as a result, additional losses appear. The presence
of moisture in the LP turbine decreases the overall efficiency. This thesis was partially
aimed to study the non-equilibrium condensing steam flow in LP turbine by using the
ANSYS CFD codes. In all simulations, the mixture of vapour and liquid phases was
solved by employing Reynolds-averaged Navier-Stokes equations based on the Eulerian-
Eulerian approach. The classical nucleation theory was adopted to model nucleation process.
Droplet growth models were used to calculate the droplet growth rate. Throughout
this work, condensing steam flows were modelled with various computational domains
including convergent-divergent nozzles, a stationary cascade of turbine and 3D statorrotor
stage. The influence of local geometrical details of steam turbine blades including
blade trailing edge shapes, dimple inclusion and blade surface tapering on the flow expansion,
condensation phenomena and corresponding loss generation was studied. The
study demonstrated that the shape and size of the blades have a significant impact on the
entire condensing flow field and the loss generation in the LP turbine. The results revealed
that the elliptic trailing edge shape resulted in minimum losses. After including dimple
profiles, the Wilson point was altered and the location of condensation disturbance was
changed. Overall 8% reduction was noted in total loss with 100 μm dimple profile compared
to the base profile without dimple. The influence of turbulence modelling studies
revealed that the accurate turbulence modelling is required for precise condensing steam
flow prediction. The modified two-equation turbulence models are able to predict accurate
wet-steam flows.ei tietoa saavutettavuudest
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
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
CFD Simulation of Two-phase and Three-phase Flows in Internal-loop Airlift
Get PDFAirlift reactors are pneumatically agitated reactors that have been widely used in chemical, petrochemical, and bioprocess industries, such as fermentation and wastewater treatment. Computational Fluid Dynamics (CFD) has become more popular approach for design, scale-up and performance evaluation of such reactors. In the present work numerical simulations for internal-loop airlift reactors were performed using the transient Eulerian model with CFD package, ANSYS Fluent 12.1. The turbulence in the liquid phase is described using κ- ε the model. Global hydrodynamic parameters like gas holdup, gas velocity and liquid velocity have been investigated for a range of superficial gas velocities, both with 2D and 3D simulations. Moreover, the study of geometry and scale influence on the reactor have been considered. The results suggest that both, geometry and scale have significant effects on the hydrodynamic parameters, which may have substantial effects on the reactor performance. Grid refinement and time-step size effect have been discussed.
Numerical calculations with gas-liquid-solid three-phase flow system have been carried out to investigate the effect of solid loading, solid particle size and solid density on the hydrodynamic characteristics of internal loop airlift reactor with different superficial gas velocities. It was observed that averaged gas holdup is significantly decreased with increasing slurry concentration. Simulations show that the riser gas holdup decreases with increase in solid particle diameter. In addition, it was found that the averaged solid holdup increases in the riser section with the increase of solid density. These produced results reveal that CFD have excellent potential to simulate two-phase and three-phase flow system
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