Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The meteorological conditions at Eskom’s Majuba Power Station are measured, evaluated and trended in this dissertation. The results are used to evaluate the current natural draught wet-cooling tower (NDWCT) design- and performance test specifications and to compare these to the original design- and performance test specifications. The evaluation reveals that the design parameters for the NDWCTs at Majuba Power Station, a cooling system that was originally designed optimally, could have been determined differently and arguably more accurately by using the wet-bulb temperature (Tawb) as the main design variable instead of the dry-bulb temperature (Ta). A new technique to determine optimal NDWCT design and performance test conditions is consequently proposed. In order to satisfy the atmospheric conditions required for a successful NDWCT performance test, it is also proposed that the tests be undertaken between 12:00 and 14:00 during Summer. It is found that the NDWCT inlet Tawb, measured at specific heights, does not compare well to the far-field Tawb measured at the same heights when a Tawb accuracy of 0.1 K is required. It is proposed that a more representative far-field Tawb measuring height of 10 m should be used in future NDWCT designs as the NDWCT design temperature reference height. The industry-standard reference height should, however, still be used during temperature profile calculations. A parametric study of the water-steam cycle and wet-cooling system at Majuba indicates that during full load conditions, the generated output (Pst) is primarily dependent on the condenser saturation pressure (pc). The latter is reliant on Tawb, the temperature lapse rate (LRT) that is represented by the temperature profile exponent (bT), the main cooling water flow rate (mcw), atmospheric pressure (pa), and wind speed (VW). Using historical plant data relatively simple methods, enabling the quick and effective determination of these relationships, are proposed. The plant-specific and atmospheric parameters required for these analyses are also tabulated. Two NDWCT effectiveness models, one mathematical (Kröger, 1998) and one statistical artificial neural network (ANN) model are presented and evaluated. ANNs, which are not often used to evaluate NDWCT effectiveness, provide accurate NDWCT temperature approach results within 0.5 K of measured values for varying dependent variables. This motivates that an ANN, if set up and used correctly, can be an effective condition-monitoring tool and can be used to improve the accuracy of more empirical NDWCT performance models. The one-dimensional mathematical effectiveness model provides accurate results under NDWCT design conditions. The dependency of Majuba’s NDWCT to the rain zone mean drop diameter (dd) is evaluated by means of the one-dimensional mathematical model. A reduction in dd from 0.0052 m to 0.0029 m can reduce the NDWCT re-cooled water temperature (Tcwo) so that the rated pc is reduced by 0.15 kPa, which relates to a combined financial saving during peak and off-peak periods of R1.576M in 2013 and R1.851M in 2016. Similar improvements can result in higher savings at other wet-cooled stations in the Eskom fleet due to less optimally-designed wet-cooling systems. The proposed techniques should be considered in future economic evaluations of wet-cooling system improvements at different power stations. / AFRIKAANSE OPSOMMING: Die meteorologiese toestande by Eskom se Majuba-kragstasie is deur die navorser gemeet en -evalueer. Die resultate word gebruik om die Natuurlike-trek, Nat koeltoring (NTNKT) se ontwerp- en werkverrigting toetsspesifikasies te evalueer en vergelyk met die oorspronklike toetsspesifikasies. Die resultate dui daarop dat die ontwerpsparameters vir die NTNKTs by Majuba-kragstasie, ‘n verkoelings-sisteem wat aanvanklik optimaal ontwerp is, op ‘n ander, selfs meer akkurate manier bepaal kon word deur die natbol-temperatuur (Tawb) te gebruik as die hoof-ontwerpsparameter inplaas van die droëbol temperatuur (Ta).’n Nuwe tegniek wat gebruik kan word om akkurate NTNKT ontwerp- en werkverrigting toetsspesifikasies te bepaal word voorgestel. Die tydperk vir die mees optimale atmosferiese toestande, wanneer NTNKT-toetse uitgevoer moet word, word vasgestel as tussen 12:00 en 14:00 tydens Somermaande. Dit word bewys, vir ’n Tawb akkuraatheid van 0.1 K, dat die NTNKT inlaat-Tawb, gemeet by verskillende hoogtes, nie vergelykbaar is met Tawb wat ver van die NTNKT af op dieselfde hoogtes gemeet word nie. ’n Meer aanvaarbare hoogte van 10 m word voorgestel as die NTNKT ontwerpstemperatuur verwysingshoogte vir toekomstige NTNKT ontwerpe wanneer die Tawb ver van die NTNKT af meet word. Die industrie-standaard temperatuur verwysingshoogte moet wel steeds gebruik word tydens temperatuur-profielberekeninge. ’n Parametriese studie van die turbine se water-stoom siklus en die nat-verkoelingstelsel by Majuba dui daarop dat die generator se uitset (Pst) hoofsaaklik afhanklik is van die kondensator se druk (pc) gedurende vol-vrag toestande. Druk (pc) is weer afhanklik van Tawb, die temperatuur vervaltempo (LRT) wat voorgestel word deur die temperatuur profiel eksponent (bT), die verkoelingswater-vloeitempo (mcw), atmosferiese druk (pa) en windspoed (VW). Deur die gebruik van historiese data word redelike eenvoudige metodes voorgestel om dié verhoudings doeltreffend te bepaal. Die atmosferiese- en stasie-spesifieke parameters wat benodig word vir dié ontleding is ook getabuleer. Twee modelle vir NTNKT-effektiweit, ’n wiskundige (gebaseer op Kröger, 1998) en statistiese kunsmatige neurale-netwerk (KNN) model, word aangebied en geëvalueer. KNNe, wat nie gereeld gebruik word om NTNKTe se effektiwiteit te evalueer nie, lewer akkurate NTNKT temperatuur-benadering resultate binne 0.5 K van die gemete resultate vir wisselende afhanklike parameters. Dié resultate motiveer dat ’n KNN wat korrek opgestel is doeltreffend gebruik kan word om die toestand van NTNKTs te bepaal en om die akkuraatheid van ander NTNKT-modelle te verbeter. Die eendimensionele, wiskundige model lewer akkurate resultate onder NTNKT ontwerpspesifikasies. ’n Wiskundige NTNKT-model word gebruik om die afhanklikheid van Majubakragstasie se NTNKTe tot die reënsone druppelgrootte (dd) te bereken. 'n Vermindering in dd van 0,0052 tot 0,0029 m kan die NTNKT se afgekoelde watertemperatuur (Tcwo), van só 'n aard verlaag dat pc verminder met 0,15 kPa. Só kan ’n gesamentlike vol- en gedeeltelike vrag finansiële besparing van R1.576M in 2013 en R1.851M in 2016 behaal word. Soortgelyke verbeterings aan verkoelingstelsels sal lei tot meer en hoër besparings by ander Eskom nat-verkoelde stasies. Dié tegnieke moet in ag geneem word tydens toekomstige ekonomiese evaluasies van verbeterings tot nat-verkoelingstelsels by ander kragstasies.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: A 1.5 x 1.5 m2 counter-flow fill performance test facility is described in detail. Instrumentation was selected and installed in the cooling tower fill test facility and calibrated to ensure measurement accuracy. A facility control program was written to simplify the operation of the test facility via a user interface. The program calculates automatically the Merkel number and loss coefficients as measures of fill thermal and flow performance respectively. A spray frame was designed and manufactured to ensure uniform water distribution to the fill. The water distribution through different fills with varying fill heights and different water flow rates was measured. The water attached to the walls of the test facility was examined. Film, trickle and splash fills are tested in the upgraded test facility. The film and trickle fill performance determined during testing is deemed acceptable as these fills have minimal migration effects. Fills with poor distribution effects and large migration of water towards the walls of the test facility, like the splash fill tested, cannot to be tested accurately in a 1.5 x 1.5 m2 test section as the results do not represent the performance of the fill in a relatively large cooling tower. Other aspects examined were: • air flow uniformity • air fill bypass effects • location of water inlet and outlet temperature measurement points • location of pressure measurement probes. It was determined that, in the current test facility: • air uniformity is suitable for performance testing • air bypass effects can be ignored for open fills and can be minimised for dense fills by packing sponge between the fill and walls • water inlet and outlet temperatures should be measured in the pipe-work, resulting in a measurement method that is not influenced by the relative weightings of each thermocouple • pressure difference over the fill height measured by the pressure measurement tap is independent of its location on the fill outlet plane provided the pressure measurement points are perpendicular to the air stream and are not against the walls. / AFRIKAANSE OPSOMMING: 'n 1.5 x 1.5 m² Teenvloei pakking werkverrigting toetsfasiliteit word in detail beskryf. Instrumentasie is gekies en geïnstalleer in die koeltoring pakking toetsfasiliteit en gekalibreer om akkuraatheid te verseker. 'n Fasiliteit beheer program is geskryf om die gebruik van die toetsfasiliteit te vereenvoudig. Die program het ‘n vriendelike gebruikers intervalk. Die program bereken outomaties die Merkel-getal en verlies koëffisiënte as mate van pakking termiese- en vloeiwerksverrigting. 'n Sproeiraam is ontwerp en vervaardig om uniforme water verspreiding aan die pakking te verseker. Die water verspreiding deur verskillende pakkings met verskillende pakking hoogtes en water vloei snelhede is gemeet. Die water aangeheg aan die mure van die toetsfasiliteit is ook ondersoek. Film, druppel en spat pakkings word in die opgegradeerde toetsfasiliteit getoets. Die film- en druppelpakking werksverrigting bepaal tydens die toetse is aanvaarbaar, aangesien hierdie pakkings minimale migrasie effekte het. Pakking met swak verspreiding effekte en 'n groot migrasie van water na die wande van die toetsfasiliteit, soos gevind met die spatpakking toetse, kan nie met akkuraatheid in 'n 1.5 x 1.5 m² toets seksie getoets word nie omdat die resultate nie die werkverrigting van die pakking verteenwoordig in 'n relatief groot koeltoring. Ander aspekte wat ondersoek was: • lugvloei uniformiteit • lug omleiding effeckte • die posisie van water in- en uitlaat temperatuur meetpunte • posisie van die drukmeetapparaat. Dit is vasgestel dat, in die huidige toetsfasiliteit • lugvloei eenvormigheid geskik is vir prestasietoetsing • lug omleiding effekte kan geïgnoreer word vir oop pakkings en kan verklein word vir digte pakkings deur spons tussen die pakking en mure te pak • water inlaat- en uitlaattemperature behoort gemeet te word in die pypwerk en lei tot 'n metings metode wat nie beïnvloed word deur die relatiewe gewigte van elke thermokoppel nie • die druk verskil gemeet deur die drupmeetpunte oor die pakkinghoogte is onafhanklik van hul posisie op die pakkinguitlaatvlak op voorwaarde dat die drukmeetpunte loodreg is teen die lugstroom en nie teen die mure nie.

Thesis: M.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1978 / Includes bibliographical references. / M.S. / M.S. Massachusetts Institute of Technology, Department of Mechanical Engineering

Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. / Thesis (MEng)--Stellenbosch University, 1990. / ENGLISH ABSTRACT: The causes of disturbances in the flow patterns at the inlets of axial flow fans that are used in mechanical draft cooling towers and the effects of these disturbances on the fans, were investigated. A scale model of a part of a mechanical draft cooling tower used at a power station was built for the purpose of this study. In the cooling tower the axial flow fans are arranged in a matrix configuration. It was noted from the scale model that the boundary fan was subjected to the worst inlet disturbances and this had an adverse effect on the flow it produced. Geometric alterations like the use of guide vanes and rounded inlets improved the flow through the boundary fan considerably. It was found that the performance of the fans is a function of the number of fans used and the elevation of the fans. Several tests to determine the performance of the cooling tower confirmed the results obtained from the experiments on the scale model. It was also found that the speed and direction of the prevailing wind have a significant effect on the cooling tower. Experiments to investigate the effects of cross-flow at the inlet of a fan indicated an increased flow through the fan at low cross-flow velocities and that the flow decreased at high cross-flow velocities. / AFRIKAANSE OPSOMMING: Die invloed en oorsake van versteurde inlaatvloeipatrone op aksiaalwaaiers wat in meganiese-trek koeltorings gebruik word is ondersoek. 'n Skaaimodel van 'n deel van 'n meganiese-trek koeltoring wat by 'n kragstasie gebruik word is gebou vir die doel van die studie. Die aksiaalwaaiers wat in die koeltoring gebruik word is in 'n matrikskonfigurasie gerangskik. Vanaf die skaalmodel is waargeneem dat die randwaaier die ergste versteuring by die inlaat ervaar, en gevolglik minder vloei as die res van die waaiers in die opstelling lewer. Die vloei deur die randwaaier is verbeter deur verskillende geometriese wysigings soos leilemme en inlaatafrondings aan te bring. Daar is gevind dat die werking van die waaiers in die opstelling 'n funksie van die hoeveelheid waaiers asook die grondvryhoogte is. Om die werking van die koeltoring te bepaal is verskillende toetse daarop uitgevoer. Die resultate het die geldigheid van die skaalmodel bevestig. Daar is ook gevind dat die heersende windsterkte en rigting 'n definitiewe invloed op die koeltoring uitoefen. Die invloed van 'n dwarsvloei by die inlaat van 'n enkele waaier is ook eksperimenteel ondersoek. Die resultate toon dat daar 'n vermeerdering in vloei deur die waaier by lae dwarsvloeisnelhede plaasvind. Hoë dwarsvloeisnelhede veroorsaak egter 'n vermindering in vloei.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Thesis (MEng (Mechanical Engineering))--University of Stellenbosch, 1994. / 213 leaves printed on single pages, preliminary pages i-xix and numbered pages 1-116. Includes bibliography, list of tables, list of figures and nomenclature. / Digitized at 600 dpi grayscale to pdf format (OCR), using a Bizhub 250 Konica Minolta Scanner. / ENGLISH ABSTRACT: A design methodology for low pressure rise, rotor only, ducted axial flow fans is formulated, implemented and validated using the operating point specifications of a 1/6th scale model fan as a reference. Two experimental fans are designed by means of the design procedure and tested in accordance with British Standards 848, Type A. The design procedure makes use of the simple radial equilibrium equations, embodied in a suite of computer programs. The experimental fans have the same hub-tip ratio and vortex distribution, but differ in the profile section used. The first design utilises the well known Clark-Y aerofoil profile whilst the second takes advantage of the high lift characteristics of the more modern NASA LS series. The characteristics of the two designs are measured over the entire operating envelope and compared to the reference fan from which the utility and accuracy of the design procedure is assessed. The performance of the experimental fans compares well with both the reference fan as well as the design intent. / AFRIKAANSE OPSOMMING: 'n Ontwerpmetode vir lae drukstyging, enkel rotor aksiaal waaiers is geformuleer, toegepas en bevestig deur gebruik te maak van die ontwerppunt spesifikasies van 'n 1/6 skaal verwysingswaaier. Twee eksperimentele waaiers is ontwerp deur middel van die ontwerpmetode en getoets volgens die BS 848, Type A kode. Die ontwerpmetode maak gebruik van die eenvoudig radiale ewewigsvergelykings en 'n stel rekenaarprogramme. Die twee eksperimentele waaiers het dieselfde naaf-huls verhouding en werwel verdeling, maar verskil daarin dat verskillende vleuelprofiele gebruik is vir elkeen van die twee waaiers. Die eerste ontwerp maak gebruik van die bekende Clark-Y profiel terwyl die tweede die moderne NASA LS profiel gebruik. Die karakteristieke van die twee eksperimentele waaiers is gemeet oor die hele werkbereik en vergelyk met die verwysings waaier waardeur die geldigheid en akkuraatheid van die ontwerpmetode bepaal is. Die werkverigting van die eksperimentele waaiers vergelyk goed met die verwysingswaaier en bevredig die ontwerpsdoelwitte.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Cooling tower inlet losses and effective flow diameter under no crosswind conditions and the pressure distribution around a circular cylinder subjected to a crosswind are modelled using CFD. The CFD model used to evaluate the inlet losses is validated with data measured in an experimental cooling tower sector model and data obtained from literature. The effect of different inlet geometries on the inlet loss coefficient and the effective diameter are investigated in order to improve cooling tower inlet designs. CFD models are developed to investigate the pressure distribution around infinite and finite circular cylinders. The infinite cylinder is modelled with a smooth surface and a rough surface so that the results can be compared to experimental data from literature. Ultimately a finite cylinder model with a rough surface is developed and the results are compared to experimental data from literature. / AFRIKAANSE OPSOMMING: Koeltoring inlaatverlies en effektiewe vloei deursnit onder geen teenwind toestande en die drukverdeling rondom ‘n sirkelvormige silinder, onderworpe aan ‘n teenwind, word gemodelleer deur gebruik te maak van “CFD”. Die “CFD” model wat gebruik word om die inlaatverlies te evalueer is gevalideer met data verkry vanaf ‘n eksperimentele koeltoring sektor model. Verder word die “CFD” model gebruik in ‘n ondersoek om te bebaal wat die effek is van verskillende inlaat geometrieë op die inlaat verlies koeffisiënt en die effektiewe diameter sodat die inlaat geometrie van koeltorings verbeter kan word. ‘n “CFD” model word dan ontwikkel om die druk verdeling rondom ‘n sirkelvormige silinder te ondersoek. Die silinder word as oneindig gesimuleer met ‘n glade en ruwe wand sodat die resultate vergelyk kan word met eksperimentele data verkry vanaf literatuur. Die afdeling word afgesluit deur die silinder as eindig met ‘n ruwe wand te simuleer en dan word die resultate vergelyk met eksperimentele data verkry vanaf literatuur.

Thesis (MEng.) -- Stellenbosch University, 1988. / ENGLISH ABSTRACT: In this report various mathematical models for the thermal evaluation of evaporative coolers and condensers are presented. These models range from the exact model based on the work by Poppe [84P01] to the simplified logarithmic models based on the work of McAdams [54Mcl] and Mizushina et al. [67MI1], [68MI1]. Various computer programs were written to perform rating and selection calculations on cross-flow and counterflow evaporative coolers and condensers. Experimental tests were conducted on a cross-flow evaporative cooler to determine the governing heat and mass transfer coefficients. The experimentally determined coefficients were cqrrelated and these correlations are compared to the existing correlations. The two-phase pressure drop across the tube bundle was also measured and a correlation for two-phase pressure drop across a tube bundle is presented.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The performance of wet cooling towers can be improved by installing spray nozzles that distribute the cooling water uniformly onto the fill whilst operating at a low pressure head. In this thesis, three commercial spray nozzles are experimentally evaluated in terms of flow and pressure loss characteristics as well as water distribution patterns. The results of the evaluation process highlight the need for spray nozzles with enhanced performance characteristics. The theory required to implement the results of the evaluation process in the design of a cooling tower is presented and discussed. A systematic approach to enhance the performance of a spray nozzle through minor alterations is applied to one of the commercial spray nozzles that was evaluated. The fluid dynamics of an orifice nozzle, such as the effect of a change in pressure head, spray angle, spray height, orifice diameter and wall thickness on drop diameter and spray distance, is experimentally investigated and a model with which a spray nozzle can be designed is finally presented. Two prototype spray nozzles show that it is possible to enhance the performance of spray nozzles and thus wet cooling towers by means of the methods presented. / AFRIKAANSE OPSOMMING: Die werkverrigting van natkoeltorings kan verbeter word deur sproeiers te installeer wat die verkoelingswater uniform versprei op die pakking teen 'n lae pomp drukhoogte. In hierdie tesis word drie kommersiële sproeiers eksperimenteel geëvalueer in terme van vloei en drukverlies eienskappe sowel as water verdelings patrone. Die resultate van die evaluasie proses beklemtoon die behoefte aan sproeiers met verbeterde werkverrigtingseienskappe. Die teorie wat benodig word om die resultate van die evaluasie proses te implementeer in die ontwerp van 'n natkoeltoring word bespreek. 'n Stelselmatige benadering om die werkverrigtings van 'n sproeier te verhoog deur klein veranderinge aan die ontwerp aan te bring, word toegepas op een van die sproeiers wat getoets is. Die vloeidinamika van 'n plaatmondstuk, soos die effek van 'n verandering in drukhoogte, sproeihoek, sproeihoogte, gatdiameter en wanddikte op druppel diameter en sproeiafstand, is eksperimenteel ondersoek en 'n model word aangebied waarmee 'n sproeier ontwerp kan word. Twee prototipe sproeiers wys dat dit moontlik is om die werkverrigting van sproeiers, en dus ook natkoeltorings, te verbeter deur die metodes wat in die tesis aangebied word, toe te pas.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 1992. / The effect of cross-winds on the performance of natural draft dry-cooling towers is studied by means of isothermal model tests, a numerical simulation and full scale measurements. The action of the wind on such towers is found to be complex and is influenced by a number of different parameters including the wind speed, the shape of the approaching wind profile, the inlet diameter to the inlet height ratio of the tower, the tower height, the shape of the tower shell, the pressure loss coefficient of the heat exchangers and the amount of heat rejected by the tower. For a horizontal arrangement of the heat exchangers the wind effect on the tower is shown to be strongly dependent on both the shape and pressure loss coefficient of the tower supports. In practical cooling towers the heat exchangers are either arranged horizontally in the inlet cross-section of the tower or vertically around the circumference of the tower and the wind effect is found to be dependent on the particular layout. The wind effect on a tower is furthermore found to increase if the heat exchangers are arranged in the form of A-frames. Additional reductions in the heat rejection rate of the tower are caused by a non-uniform air temperature distribution inside the tower and flow distortions through the heat exchanger. Significant reductions in the wind effect on a cooling tower can be achieved by installing windbreak walls below the heat exchangers if the latter are arranged horizontally in the tower inlet.