Losses in the inlet section of counterflow wet-cooling towers

De Villiers, Eugene (1998-12)

One copy microfiche.

Thesis (MEng)--Stellenbosch University, 1998.

Thesis

ENGLISH ABSTRACT: The flow resistances in the inlet sections of counterflow wet-cooling towers are investigated and correlations are derived for inclusion in a one-dimensional tower performance model. The rain zone loss is modelled using analytical-numerical methods. Experimental verification of the model produces satisfactory confirmation of the method's general validity. Semi-empirical correlations are produced to predict the loss coefficient as a function of six dimensionless variables for both rectangular and circular cooling towers. In addition, a study is made of the heat and mass transfer in the rain zone and its influence on tower performance. The inlet loss coefficients for dry, isotropically packed, circular and rectangular counterflow cooling towers are determined experimentally and empirical correlations are formulated to fit this data. The inlet losses for isotropic-resistance-fill towers are found to be higher than those for orthotropic-resistance-fill towers. Computational fluid dynamics is used to investigate the dependence of the inlet loss coefficient on the rain zone characteristics. The rain zone loss generally dampens the inlet loss, but this coupling is indirect and necessitates a large amount of dependent variables. The numerical model is validated by means of experimental data for dry towers and it is found that the degree of accuracy achieved for circular towers exceeds that for rectangular towers. Consequently, the correlation derived to predict this occurrence for circular towers, can be applied more confidently than its rectangular counterpart. An example is presented wherein the improved accuracy iQ tower performance prediction, when applying this correlation, is shown. Additional measures for tower performance enhancement are also explored.

AFRIKAANSE OPSOMMING: 'n Studie is gemaak van vloeiweerstande in die inlaat seksie van nat teenvloei koeltorings met die oog op die afleiding van korrelasies om die verskynsels, vir gebruik in puntmodel koeltoring simulasies, te voorspel. Die reensone verlies is gemodelleer met behulp van 'n analities-numeriese metode. Die model is geverifieer met behulp van eksperimentele toetse. Semi-empiriese korrelasies word afgelei wat die verlies, as 'n funksie van ses dimensielose veranderlikes, vir beide ronde en reghoekige koeltorings, voorspel. Daar word ook 'n studie gemaak van die hitte en massa oordrag in die reensone en hoe dit koeltorings se termiese oordrags vermoe be'invloed. Die inlaat verlies vir droe, isotropies gepakte, ronde en reghoekige koeltorings is eksperimenteel bepaal en empiriese korrelasies is geformuleer om die data te pas. Daar is gevind dat die inlaat verlies vir isotropies gepakte torings hoer is as die vir ortotropies gepakte torings. Numeriese vloei dinamika is gebruik om die afuanklikheid van die inlaat verlies se grootte op die reensone se eienskappe te ondersoek. Die algemene tendens is vir die reensone om die inlaat verlies te demp, maar die afuanklikheid is indirek sodat 'n groot aantal veranderlikes benodig word om die demping te karakteriseer. Die numeriese model word geverifieer deur middel van eksperimentele data vir droe koeltorings en daar word tot die gevolgtrekking gekom dat ronde torings heelwat meer akuraat gemodelleer word as reghoekige torings. Dit veroorsaak dat die korrelasie wat afgelei is om die demping te voorspel vir ronde torings, met baie meer vertroue toegepas kan word as sy reghoekige eweknie. 'n Voorbeeld word gedoen om die verbeterde akuraatheid in koeltoring modellering, wat verkry kan word met behulp van die vergelyking, te wys. Bykomende matrieels, om torings se verkoelings vermoe te verbeter, word ook ondersoek.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/50986
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