Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Large air‐cooled heat exchangers and condensers make use of fan arrays to provide cooling. The
performance of the fan arrays are however negatively affected by distorted inlet conditions. Given
the size of these fans, quantifying exactly what the detrimental effects are is practically impossible.
This serves as motivation for developing a scaled multi‐fan testing platform that is able to mimic the
behaviour of a full‐scale array but at a more measureable and manageable scale. This investigation
was conducted in two parts. A Reynolds number investigation was conducted to determine what
effect incorporating Reynolds number effects will have on the scaled fan performance.
Computational fluid dynamics (CFD) was used to determine where turbulent transition onset occurs
on the full‐scale fan blades and trip wires were then sized and positioned appropriately to recreate
the same transition effect. From this initial investigation it was found that the trip wires have an allround
negative impact on fan performance but when compensated for by increasing the blade angle,
the tripped fan static pressure rise performance is comparable with the non‐tripped fan
performance. This suggests that the Reynolds number effects may be ignored for this scaled fan
testing investigation.
Scaled equivalents of the fans in cooling arrays were tested in a three row multi‐fan array which,
using symmetry, represents a typical bay in a full‐scale installation. Various platform heights were
simulated and the corresponding decrease in system performance was compared to a model
formulated to predict how fan volumetric effectiveness decreases with platform height. The model
deviated from the test data at very low platforms heights. A replacement fan for the scaled
equivalent fan was tested while installed as the edge fan of a multi‐fan array, the fan worst affected
by any inlet disturbance, and was found to perform similarly to the scaled equivalent fan for most
platform heights but exceeded the scaled equivalent fan’s performance for the lowest platform
height and the most adverse conditions. This proves the effectiveness of the replacement fan as an
edge fan. / AFRIKAANSE OPSOMMING: Groot lugverkoelde warmteruilers maak gebruik van waaier matrikse om verkoeling te voorsien. Die
verrigting van die waaieropstelling word egter negatief beïnvloed deur versteurde inlaattoestande.
Gegewe die grootte van hierdie waaiers is daar geen praktiese metode om die nadelige invloed van
die versteurde inlaattoestande te kwantifiseer nie. Hierdie dien as motivering vir die ontwikkeling
van ‘n multi‐waaier toetsplatform wat daartoe in staat is om die gedrag van die volskaal opstelling na
te boots maar op ‘n baie meer meetbare en hanteerbare skaal. Hierdie ondersoek was uitgevoer in
twee dele. ‘n Reynoldsgetal ondersoek was uitgevoer om te bepaal watter impak dit sal hê op die
skaalwaaier verrigting indien die Reynolds getaleffekte ingesluit word in die toetswerk. Berekende
vloeidinamka (BVD) was gebruik om te bepaal waar turbulente oorgang voorkom op die volskaal
waaierlemme en pooitjiedrade was geselekteer en geposisioneer hiervolgens om dieselfde oorgang
te herskep. Vanuit hierdie aanvanklike ondersoek was dit gevind dat die pooitjiedrade ‘n algehele
afname in verrigting tot gevolg het, maar wanneer dit oorkom word deur die lemhoek op te stel, die
gedrag en verrigting van die gepooitjiede waaier soortgelyk is aan die van die nie‐gepooitjiede
waaier. Hierdie gedrag stel voor dat die Reynoldsgetalle maar geïgnoreer kan word vir hierdie
skaalwaaier toetswerk.
Gelykwaardige skaalwaaiers van die wat in bedryf is in volskaal opstellings was getoets in ‘n drie ry
multi‐waaier opstelling wat, deur simmetrie, verteenwordigend is van ‘n tipiese straat in ‘n volskaal
opstelling. Verskeie platformhoogtes was gesimuleer en die ooreenstemmende afname in stelsel
verrigting was vergelyk met ‘n model wat geformuleer is juis om te voorspel hoe die volumetriese
effektiwiteit afneem met platformhoogte. Die model wyk af van die toetsdata by baie lae platform
hoogtes. ‘n Vervangingswaaier vir die aanvanklike geskalleerde waaier was getoets as ‘n randwaaier,
die waaier wat die ergste benadeel word deur versteurde inlaattoetstande, in die multi‐waaier
opstelling. Die vervangingswaaier het soortgelyk aan die aanvanklike waaier verrig vir meeste
platformhoogtes, maar oortref die aanvanklike waaier se werksverrigting by die laagste
platformhoogte en mees ongunstige toestande. Hierdie bewys die vermoëns van die
vervangingswaaier as ‘n randwaaier.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4238 |
| Date | 03 1900 |
| Creators | Conradie, P. J. F. |
| Contributors | Van der Spuy, S. J., Von Backstrom, T. W., 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 |
| Format | 113 p. : ill. |
| Rights | University of Stellenbosch |
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