Experimental investigation of the effects of windscreens on air-cooled condenser fan performance and dynamic blade loading

Marincowitz, Fredrik Simon (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Air-cooled condensers (ACCs) are the preferred cooling method for power plants that make use of the Rankine cycle in regions that have limited water resources. However, using air as the cooling fluid has its limitations as environmental conditions such as wind affects ACCs thermal performance. Wind specifically influences the ACCs perimeter fans, as the strong cross-flow caused by winds results in distorted inflow conditions which lead to a reduction in fan performance and excessive dynamic blade loading. One method used to mitigate these effects is the use of windscreens along the perimeter of the fan platform, but studies done on this topic are however inconclusive as computational fluid dynamics (CFD) studies indicate windscreens help increase perimeter fan performance while site specific full-scale experimental studies indicate windscreens are mostly beneficial in reducing the dynamic blade loading. As the exact influence of windscreens on the perimeter fans appears to be not well understood, a controllable and repeatable experimental investigation was deemed a good method to aid in this understanding. This experimental investigation was then done on a scaled ACC fan row at a fixed platform height, consisting of 3 fans, and subjected to a controllable cross-flow to simulate wind. Using this test setup, the fan performance and dynamic blade loading under strong cross-flow could be investigated and used as a baseline to compare with the results once a windscreen was installed. The results indicated that with increasing cross-flow the performance of the perimeter fan suffered increasingly due to the formation of a separation region on the upstream edge of the bellmouth. This then resulted in a significant difference between the up-and downstream velocity profiles into the perimeter fan (perpendicular to the blade) which led to an increase in the dynamic loading on the fan blade. With the installation of a windscreen the perimeter fan’s performance was mostly negatively affected as the majority of the incoming flow was deflected away from the intake of the perimeter fan, and the flow permeating through the windscreen was insufficient to help improve the performance. In most cases the windscreen did however help to reduce the difference in up-and downstream velocity profiles into the perimeter fan, reducing the dynamic blade loading on the perimeter fan. Where the fan performance results with and without a windscreen, for the scaled ACC fan row, had very similar trends to that recorded at a full-scale facility of a similar dimensionless platform height which instilled confidence in the experimental methods used.

AFRIKAANSE OPSOMMING: Lugverkoelde kondensors (LVKs) is die verkose afkoel metode vir kragsentrales wat gebruik maak van die “Rankine” siklus in gebiede met beperkte waterbronne. Die gebruik van lug as verkoelings medium het egter sy beperkings as gevolg van verskeie omgewings veranderlikes, insluitend wind effekte. Sterk atmosferiese wind veroorsaak ʼn daling in die LVK se termiese vermoë. Die wind beïnvloed spesifiek die LVKs se randwaaiers, as gevolg van kruisvloei wat deur die wind veroorsaak word, dié lei tot versteurings in die invloeipatrone van die waaiers en lei tot 'n afname in die waaier se volumetriese vermoë asook ʼn toename in die dinamiese belasting van die waaierlemme. Een metode wat gebruik word om hierdie effekte te verminder, is die gebruik van windskerms wat geïnstalleer word om die rand van die waaierplatform. Die studies wat oor hierdie onderwerp gedoen is, is egter onbeslis omdat die numeriese vloei dinamika studies (NVD) aandui dat windskerms help om die randwaaiers se volumetriese vermoë te verbeter onder winderige toestande, terwyl volskaalse eksperimentele studies dui dat windskerms meestal net voordelig is om die dinamiese lembelasting te verminder. Omdat die presiese invloed wat windskerms het op LVKs nie goed gedokumenteer is nie, is ʼn beheerbare en herhaalbare eksperimentele ondersoek ʼn goeie metode om begrip van die onderwerp te verbeter. So ʼn eksperimentele ondersoek is gedoen op ʼn afgeskaalde LVK waaier ry met ʼn vaste platformhoogte, bestaande uit 3 waaiers, wat onderworpe was aan ‘n beheerbare kruisvloei met die doel om wind te simuleer. Deur hierdie toets opstelling te gebruik, kon die waaier se volumetriese vermoë en dinamiese lembelasting onder sterk kruisvloei ondersoek word en as ʼn maatstaf gebruik word om die veranderinge wat ʼn windskerm aan die waaier se volumetriese vermoë en dinamiese lembelasting aanbring mee te vergelyk. Die resultate het aangedui dat met toenemende kruisvloei neem die volumetriese vermoë van die randwaaier slegs af as gevolg van die formasie van ʼn vloei weg brekings gebied op die op stroom rand van die waaierinlaat. Dit het gelei tot ʼn beduidende verskil in die op- en afwaartse stroom invloei snelheidsprofiele van die waaier (loodreg met die lem) en gelui het tot ʼn toename in die dinamiese lem belasting. Die installasie van ʼn windskerm het die volumetriese vermoë van die randwaaier meestal negatief beïnvloed, aangesien die meerderheid van die inkomende vloei gedeflekteer was deur die windskerm en die vloei wat wel deur die windskerm beweeg het onvoldoende was. In die meeste gevalle het die windskerm egter gehelp om die verskil in op- en afwaartse snelheidsprofiele van die waaier se invloei te verminder, en daarmee saam die dinamiese lembelasting. Die toetse wat op die geskaleerde waaierry gedoen was, met en sonder ʼn windskerm, het baie soortgelyke tendense gelewer as wat bevind was op ʼn volskaalse LVK met dieselfde dimensielose platformhoogte, wat dus vertroue verleen aan die eksperimentele metodes wat in hierdie studie toegepas is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106058
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