Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The majority of power stations in South Africa are located in coal rich, but arid
regions where wet-cooled condenser systems are not feasible from an
environmental and economic perspective. Consequently the focus on power
generation cooling has shifted towards dry-cooling systems using air-cooled
steam condensers (ACSC). The steam passing through the ACSC units is cooled
by an air-draught, mechanically induced by large diameter axial flow fans.
Consequently the effectiveness of the cooling is impacted by the performance of
these fans, which ultimately affects the overall efficiency of the power plant.
However, due to the large diameters (> 10 m) of these fans, their performance is
predicted based on small scale test results using the fan scaling laws.
The objective of this project was to develop a methodology which accurately
predicts the fan performance of more than one fan configuration using
computational fluid dynamics (CFD) software and validating the results with
experimental tests. Four fans were considered in this study of which three were
scaled fan models of large air-cooled axial fans. The performance of the scaled
fan models (L1-, L2- and N-fan) were measured in a type A, BS 848 standard fan
test facility. The geometries of the fans were scanned three-dimensionally to
obtain the models for simulation purposes. The other fan considered was an 8-
bladed axial fan designed by Bruneau (1994) and referred to as the B-fan.
Simulations were carried out for the L2-, N- and B-fan for different computational
domains while implementing the multiple reference frames (MRF) and steady
RANS approach. Three variations of the k-ε turbulence model were also
investigated.
Noticeable differences were found between the experimental and numerical
results of the B-fan. Good correlations between the numerical and experimental
fan static pressure, fan power and fan static efficiency were found for the two
scaled model fans over a large operating range. The performance of the full scale
fans, however, did not correlate well with the performance of the scaled models. It
is concluded that accurate simulations of axial fans are possible although these
domains require a large number of mesh elements. It is recommended that further
research is carried out to investigate the relationship between full scale and small
scale fan models. / AFRIKAANSE OPSOMMING: Die meerderheid steenkool kragstasies in Suid-Afrika is geleë in droë, maar
steenkool ryke streke waar natverkoelde kondensor stelsels uit ʼn omgewings en
ekonomiese perspektief nie geskik is nie. Die fokus in kragopwekking verkoeling
het dus verskuif na droë-verkoelings stelsels en spesifiek die gebruik van
lugverkoelde stoomkondensors (LVSKs). Die stoom in LVSK eenhede word
verkoel deur atmosferiese lug wat meganies geïnduseer word deur groot
aksiaalvloeiwaaiers. Die effektiwiteit van die verkoelingsproses word gevolglik
beïnvloed deur die werksverrigting van hierdie waaiers wat uiteindelik die
algehele effektiwiteit van die kragstasie beïnvloed. As gevolg van hierdie waaiers
se grootte word hulle werksverrigting egter bepaal op grond van kleinskaal
toetsresultate en deur gebruik te maak van die waaierskaleringswette.
Die hoofdoelwit van hierdie projek was om ‘n metodiek te ontwikkel wat die
werksverrigting van ʼn aksiaalwaaier akkuraat kan voorspel vir ʼn verskeidenheid
opstellings, deur gebruik te maak van berekenings vloei meganika (BVM)
sagteware en die resultate eksperimenteel te verifieer. Die projek het vier waaiers
ondersoek waarvan drie van hierdie waaiers geskaleerde modelle van groot
lugverkoelde aksiaalwaaiers was. Die werksverrigting van die geskaleerde
waaiers (L1-, L2- en N-waaier) was met ‘n tipe A, BS 848 standaard waaier
toetsfasiliteit gemeet. Die geometrie van dié waaiers was ook drie-dimensioneel
opgemeet vir simulasie doeleindes. Die B-waaier, ‘n 8 lem aksiaalwaaier, wat
ontwerp is deur Bruneau (1994) was slegs numeries ondersoek. Die L2-, N- en Bwaaier
was gesimuleer in verskillende berekeningsdomeine deur gebruik te maak
van die multi verwysingsraamwerk en gestadigde vloeiberekenings benaderings.
Drie k-ε turbulensie modelle was ook ondersoek.
Merkbare verskille tussen die eksperimentele en numeriese resultate van die Bwaaier
was waargeneem. Goeie korrelasie tussen die eksperimentele en numeriese
resultate van die geskaleerde waaiers vir ‘n wye bedryfsbestek was gevind. ‘n
Vergelyking tussen die volskaal en kleinskaal waaiers se werksverrigting het egter
beduidende afwykings aangetoon. Deur gebruik te maak van ‘n groot aantal selle
in die berekeningsdomein was dit moontlik om ʼn verskeidenheid
aksiaalvloeiwaaiers akkuraat te simuleer. Verdere navorsing wat die verhouding
tussen volskaal en kleinskaal waaiers ondersoek woord aanbeveel.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85720 |
| Date | 12 1900 |
| Creators | Augustyn, Ockert Philippus Hermanus |
| Contributors | Van der Spuy, S. J., Von Backstrom, T. W., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xix, 123 p. : ill. |
| Rights | Stellenbosch University |
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