Edge fan performance in air cooled condensers systems

Conradie, P. J. F. (2010-03)

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.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/4238
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