Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Air-cooled steam condensers (ACSCs) are used in the power generation industry to directly
condense turbine exhaust steam in areas where cooling water is expensive or unavailable.
Large axial flow fans force ambient air through A-frame heat exchanger bundles made up of a
number of rows of finned tubes through which the steam is ducted and consequently
condensed during the heat transfer process to the air. The heat rejection rate or performance
of an ACSC is proportional to the air mass flow rate, determined by fan volumetric
performance, and the temperature difference between the finned tubes and the air.
The air flow through a 30 fan ACSC (termed the generic ACSC) operating under windy
conditions is solved using the commercial computational fluid dynamics (CFD) code FLUENT
and the required data is extracted from the solution to calculate performance trends. It is
found that fan performance is reduced due to a combination of factors. The first is additional
upstream flow losses caused by separated flow occurring primarily at the leading edge of the
ACSC and secondarily at the fan bellmouth inlets. The second factor leading to reduced fan
performance is the presence of distorted flow conditions at the fan inlets. Hot plume air
recirculation is responsible for decreased ACSC thermal performance due to increased fan inlet
air temperatures. It is found that reduced fan performance is the greater contributor to
reduced ACSC performance.
The performance effects of varying two geometrical parameters of the generic ACSC, namely
the fan platform height and the windwall height, are investigated under windy conditions. It is
found that each parameter is linked to a specific mechanism of performance reduction with
the fan platform height affecting fan performance and the windwall height affecting
recirculation. The respective platform and windwall heights specified for the generic ACSC are
found to provide acceptable performance results.
To mitigate wind induced performance reductions a number of modification and additions to
the ACSC are investigated. These primarily aim at improving fan performance and included the
addition of walkways or skirts, the addition of wind screens beneath the fan platform,
removing the bellmouth fan inlets, using different types of fans and increasing fan power. The
addition of a periphery walkway and windscreens is considered to be the most practical
methods of improving ACSC performance under windy conditions. The generic ACSC is
modified to include both modifications and under high wind conditions the performance is
found to increase measurably. The modifications also resulted in the ACSC performance being
less sensitive to wind direction effects. / AFRIKAANSE OPSOMMING: Lugverkoelde kondensators word in die kragopwekkings industrie gebruik om turbine
uitlaatstoom te kondenseer, veral in gebiede waar verkoelingwater duur of onbeskikbaar is.
Aksiaalvloei-waaiers forseer omgewingslug deur A-raam warmteuitruiler bondels wat bestaan
uit verskeie rye vinbuise. Die uitlaatstoom vloei in die vinbuise en kondenseer as gevolg van
die warmteoordrag na die lug. Die warmteoordragkapasiteit van die lugverkoelde stoom
kondensator is eweredig aan die massavloei-tempo van die lug, wat bepaal word deur die
waaierwerkverigting, en die temperatuur verskil tussen die vinbuise en die lug.
Die lugvloei deur 'n 30 waaier lugverkoelde stoom kondensator (genoem die generiese
lugverkoelde stoom kondensator) onderworpe aan winderige toestande word opgelos deur die
gebruik van die kommersiële vloeidinamika-pakket, FLUENT. Die nodige data is onttrek uit die
oplossing en werkverrigting neigings is bereken. Dit is gevind dat waaierwerkverigting
verminder as gevolg van 'n kombinasie van faktore. Die eerste is bykomende vloeiverliese wat
veroorsaak word deur vloeiwegbreking wat plaasvind primêr by die voorste rand van die
lugverkoelde stoom kondensator asook by die klokvormige waaier-inlate. 'n Tweede faktor wat
lei tot vermindere waaierwerkverigting is die teenwoordigheid van lugvloeiversteurings by die
waaier-inlate. Hersirkulering van warm pluim lug is ook verantwoordelik vir verminderde
lugverkoelde stoom kondensator werkverrigting. Daar word bevind dat die vermindering in
waaierwerkverrigting die grootste bydraende faktor tot vermindere lugverkoelde stoom
kondensator werkverrigting is.
Die effek van verandering van twee geometriese lugverkoelde stoom kondensator parameters,
naamlik die waaierplatformhoogte en die windwandhoogte is ondersoek onder winderige
toestande. Daar word bevind dat elk van die parameters gekoppel is aan 'n spesifieke
meganisme van vermindere lugverkoelde stoom kondensator verrigting: Die
waaierplatformhoogte beïnvloed waaierverrigting terwyl die windwandhoogte hersirkulering
beinvloed. Daar word ook bevind dat die onderskeie waaierplatform- and windwandhoogtes
van die generiese lugverkoelde stoom kondensator, van so 'n aard is dat dit aanvaarbare
werkverrigting tot gevolg het.
Om verlaging in werksverrigting in winderige toestande te verminder is verskeie modifikasies
en byvoegings tot die lugverkoelde stoom kondensator ondersoek wat primêr gemik is op
verbetering in waaierwerkverigting. Die ondersoek dek die byvoeging van 'n loopvlak, die
byvoeging van windskerms onder die waaierplatform, verwydering van die klokvormige
waaier-inlate, die gebruik van verskillende waaiers en die verhoging van waaierdrywing. Daar
was besluit dat die byvoeging van 'n loopvlak rondom die rand van die lugverkoelde stoom
kondensator en die byvoeging van windskerms die mees praktiese manier was om die
lugverkoelde stoom kondensator verigting te verbeter. Die generiese lugverkoelde stoom
kondensator was aangepas om beide veranderings in te sluit en meetbare verbetering in
werkrigting was verkry. Die veranderings het ook meegebring dat die lugverkoelde stoom
kondensator minder sensitief is vir windrigting effekte.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4153 |
| Date | 03 1900 |
| Creators | Joubert, Retief |
| Contributors | Kroger, D. G., University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 67 p. : ill. |
| Rights | University of Stellenbosch |
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