Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Water collection systems are used in wet-cooling towers (WCTs) with fill over
which water to be cooled flows and in evaporative air-cooled heat exchangers
(EACHEs) having deluged tube bundles over which water flows to transfer heat
from the tubes. They collect and remove water falling from the bottom of the fill
or heat exchanger tube bundle while allowing air to pass with limited flow
resistance. There are basically two types of collection systems, categorized as
trough and basin systems. Trough systems comprise of multiple, evenly spaced
parallel troughs extended in one direction with inclined capture plates to direct
water into the troughs. The water collects in the troughs and drains under gravity
to a collecting tank or manifold from where it is pumped to the sprayers. In basin
systems water falls directly into an open basin under gravity where it is collected
and can be pumped to the sprayers. The hybrid (dry/wet) dephlegmator (HDWD)
for air-cooled steam condensers, which is being developed at Stellenbosch
University as discussed by Heyns (2008), Owen (2013) and Anderson (2014),
requires a more effective water collection system with a lower pressure drop than
what current designs have to offer.
In this thesis, an existing trough system is systematically evaluated by means of
various high speed camera and flow experiments to determine its performance
characteristics and to find ways to improve its catchment effectiveness. A
modification is proposed which increases the effectiveness from approximately
92% to 100 % with a relatively small increase in pressure drop, by adding a small
deflector plate and reducing the spacing between adjacent troughs. Experimental
data and CFD models are used to determine the performance characteristics of the
modified trough system for design purposes.
For comparison, various basin system designs are proposed and investigated using
CFD, where the baseline model is validated by means of experimental data of
rectangular cooling tower inlets by Kröger (2004). Rectangular cooling tower
inlets are relevant as they have a similar re-circulating flow pattern to what is seen
with the water basin inlets at the vicinity of the inlet wall. The numerical data is
correlated to determine empirical relations for the flow performance
characteristics.
The comparison between the modified trough and the different basin systems
yields that the trough system requires significantly less fan and pumping power
than basin systems and the costs are also expected to be less. / AFRIKAANSE OPSOMMING: Wateropvangstelsels word gebruik in nat koeltorings en verdamping verkoelers,
waar waterdruppels in teen-vloei is met n lugstroom. Die stelsel vang die water
wat val op en verwyder dit uit die lugstroom met 'n minimale lugweerstand. Daar
is twee wateropvangstelsels wat as volg gekategoriseer word: trog stelsel en
wateropvangbak stelsel. 'n Trog stelsel bestaan uit eweredige gespasieerde trôe
parallel aan mekaar met 'n skuinsvlak om water in die kanaal op te vang. Water
dreineer as gevolg van swaartekrag na 'n opvangs tenk waarvan dit terug gepomp
word na die sproeiers. In 'n wateropvangbak stelsel val water direk in die bak en
word terug gepomp na die sproeiers. 'n Lugverkoelde kondenserstelsels met 'n
hibriede (droog/nat) deflegmator wat huidiglik by die Stellenbosch Universiteit
ontwikkel word benodig 'n meer effektiewe wateropvangstelsel met 'n lae drukval.
In hierdie tesis word bestaande trog stelsels sistematies geëvalueer deur middel
van verskeie toetse met 'n hoë spoed kamera en lugvloei eksperimente om die
werkverrigtingskarakteristieke te bepaal en om die opvangsvermoë te verbeter. 'n
Verbetering word voorgestel wat die opvangsvermoë verbeter van ongeveer 92 %
na 100 % met 'n relatiewe klein verhoging in die drukval deur 'n klein leilem by te
voeg en die spasiëring tussen trôe te verminder. Eksperimentele data en BVD
(berekeningsvloeidinamika) modelle word gebruik om die werkverrigtingskarakteristieke
te bepaal van die nuwe trog stelsel vir ontwerps doeleindes.
Die modelle is bekragtig deur gebruik te maak van literatuur van inlaatverlies
korrelasies vir reghoekige koeltorings, soos gedoen deur Kröger (2004). Die inlaat
van reghoekige koeltorings het soortgelyke vloeipatrone en vloeiwegbreking soos
wat by die inlaat van die wateropvangbak stelsel gesien word. Die numeriese data
word gebruik om 'n vergelyking vir die vloei karakteristieke te bepaal.
'n Vergelykende studie tussen die nuwe trog stelsel en die wateropvangbak stelsel
het bewys dat die trog stelsel noemenswaardig minder waaier drywing en pomp
drywing benodig.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95920 |
| Date | 12 1900 |
| Creators | Du Plessis, Jacques J. P. |
| Contributors | Reuter, Hanno Carl Rudolf, Stellenbosch University. Faculty of Engineering. Department of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xvi, 80 p. : ill. |
| Rights | Stellenbosch University |
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