Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: A novel induced draft hybrid (dry/wet) dephlegmator (HDWD) is introduced
which can enhance the performance of dry air-cooled condenser systems and a
model is developed to simulate its performance. The HDWD consists of two
stages of cooling with the steam flow in series and the air flow in parallel through
both stages. The first stage consists of downwardly inclined finned tube bundles,
similar to conventional air-cooled condenser bundles, and the second stage
comprises horizontal bare tube bundles of which the outer surface can selectively
be operated dry or wet by spraying it with deluge water. A comparison of the
HDWD with other existing and new concepts reveals the significant advantages
that this technology has over other technologies. This thesis is a continuation of
the work done by Heyns (2008), who introduced a forced draft HDWD and
investigated its performance, and Owen (2013), who conducted a parametric
investigation on the induced draft HDWD to improve the basic design proposed
by Heyns (2008). In his thermo-flow model, Heyns (2008) conducted a thermal
analysis assuming equal air flow through both stages and a constant vapor
temperature inside the bundles, while Owen (2013) solved the thermal, steam-side
pressure drop and draft equations. Both their models make use of empirical
correlations by Gaddis & Gnielinski (1985), Zukauskas (1987), Mizushina et al.
(1967) and Niitsu et al. (1967) for the performance characteristics. The current
model solves the thermal, steam-side pressure drop and draft equations of the
HDWD with better accuracy in the steam-side pressure drop calculation. The airside
heat and mass transfer and loss coefficient correlations found in literature
were found to deviate significantly from each other resulting in uncertainty
regarding their suitability. Based on the recommendations by Owen (2013), a bare
tube test bundle with 19 mm outer diameter tubes arranged with a triangular pitch
of 38 mm is therefore designed, manufactured and tested to investigate the
performance characteristics of the bundle experimentally under dry and wet
operating conditions to evaluate the correlations from literature. The experimental
data confirmed the applicability of the correlations of Gaddis & Gnielinski (1985)
and Zukauskas (1987) to predict the dry HDWD performance, since they deviated
by 7% and 5% respectively from the experimental data in die applicable range.
The heat transfer during wet operation is slightly over estimated within 5% with
the correlations of Mizushina et al. (1967) in the range of application. The air-side
pressure drop during wet operation is underestimated by 29 to 39% by Niitsu et al.
(1967) and the correlation obtained from the experimental results is therefore used
in the current model. Using the current HDWD model indicates significant performance enhancement using tubes with a smaller diameter in the delugeable
bundle compared to the larger tubes of Heyns (2008) and agrees very well with
the model of Owen (2013). / AFRIKAANSE OPSOMMING: ‘n Hibriede geïnduseerde trek deflegmator is voorgestel wat die werksverrigting
van huidige lugverkoelde kondenserstelsels kan verbeter en ‘n model is ontwikkel
wat die werksverrigting simuleer. Die deflegmator bestaan uit twee stadiums van
verkoeling met die stoomvloei in serie en die lugvloei in parallel deur beide
stadia. Die eerste stadium bestaan uit skuins, afwaartse finbuisbundels, soortgelyk
aan konvensionele lugverkoelde kondenser-finbuisbundels, en die tweede stadium
bestaan uit horisontale kaalbuisbundels waarvan die buite-oppervlak selektief
droog of nat bedryf kan word deur dit met verkoelingswater te benat. ‘n
Vergelyking tussen die deflegmator en ander huidige en nuwe konsepte toon
merkbare voordele wat die tegnologie bo die ander tegnologië het. Die tesis is ‘n
voortsetting van die werk van Heyns (2008), wie ‘n hibriede geforseerde trek
deflegmator voorgestel en die werksverrigting daarvan ondersoek het, en Owen
(2013) wat ‘n parametriese studie op die hibriede geïnduseerde trek deflegmator
gedoen het om die basiese ontwerp voorgestel deur Heyns (2008) te verbeter. In
sy termovloei-model, het Heyns (2008) die termiese analise ondersoek met die
aanname van gelyke hoeveelhede lugvloei deur beide stadia met ‘n konstante
damp-temperatuur binne die bundels, terwyl Owen (2013) die termiese,
stoomkant-drukval and trekvergelykings opgelos het. Beide hul modelle maak van
die empiriese korrelasies van Gaddis & Gnielinski (1985), Zukauskas (1987),
Mizushina et al. (1967) en Niitsu et al. (1967) gebruik vir die
werkverrigtingskarakteristieke. Die huidige model los die termiese, die
stoomkant-drukval asook die trekvergelykings van die deflegmator op met
verbeterde akkuraatheid van die stoomkant-drukval berekeninge. Die lugkant
warmte- en massaoordrag en verlieskoëffisiënt korrelasies wyk baie van mekaar
af wat lei tot onsekerhede rakende hul toepasbaarheid. Gebaseer op die voorstelle
van Owen (2013) is ‘n kaalbuisbundel met 19 mm buite-diameter buise met ‘n
driehoekige steek van 38 mm dus ontwerp, vervaardig en getoets om die
werksverrigtingskarakteristieke van die bundel eskperimenteel te ondersoek onder
droë en nat toestande om die korrelasies van die literatuur te evalueer. Die
eksperimentele data bevestig die toepaslikheid van die korrelasies van Gaddis &
Gnielinski (1985) en Zukauskas (1987) om die droë werksverrigting van die
deflegmator te voorspel, aangesien hul met 7% en 5% onderskeidelik afwyk van
die eksperimentele data in die toepaslike bestek. Die warmteoordrag tydens
natwerking is ietwat oorskat binne 5% met die korrelasies van Mizushina et al. (1967) in die bestek van toepassing. Die lugkant-drukval tydens natwerking is
onderskat met 29 tot 39% deur Niitsu et al. (1967) en die korrelasie verkry vanaf
die eksperimentele resultate is dus gebruik in die huidige model. Deur gebruik te
maak van die huidige model van die deflegmator dui merkbare werksverrigting
verbetering aan deur van buise met ‘n kleiner diameter in die benatbare bundel te
gebruik in vergelyking met die groter buise van Heyns (2008) en stem baie goed
ooreen met die model van Owen (2013).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96105 |
| Date | 12 1900 |
| Creators | Anderson, Neil Raymond |
| 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 | Unknown |
| Type | Thesis |
| Format | xvi, 83 p. : ill. |
| Rights | Stellenbosch University |
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