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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Evaluation of detection methods for Legionella in industrial cooling water systems

Bartie, Catheleen 14 November 2007 (has links)
Please read the "Background" (p v) in the section 00front of this document Copyright 2002, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Bartie, C 2002, The life and career of the South African dramatric soprano Marita Napier, DPhil thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-11142007-125718 / > / Thesis (DPhil (Microbiology))--University of Pretoria, 2007. / Microbiology and Plant Pathology / unrestricted
42

Numerical modelling and sensitivity analysis of natural draft cooling towers

Dhorat, A., Al-Obaidi, Mudhar A.A.R., Mujtaba, Iqbal M. 12 April 2018 (has links)
Yes / Cooling towers are a relatively inexpensive and consistent method of ejecting heat from several industries such as thermal power plants, refineries, and food processing. In this research, an earlier model from literature was to be validated across three different case studies. Unlike previous models, this model considers the height of the fill as the discretised domain, which produces results that give it in a distribution form along the height of the tower. As there are limitations with the software used (gPROMS) where differential equations with respect to independent variables in the numerator and denominator cannot be solved, a derivative of the saturation vapour pressure with respect to the temperature of the air was presented. Results shown were in agreement with the literature and a parametric sensitivity analysis of the cooling tower design and operating parameters were undertaken. In this work the height of fill, mass flowrates of water and air were studied with respect to sensitivity analysis. Results had shown large variations in the outlet temperatures of the water and air if the mass flows of water and air were significantly reduced. However, upon high values of either variable had shown only small gains in the rejection of heat from the water stream. With respect to the height of the fill, at larger heights of the fill, the outlet water temperature had reduced significantly. From a cost perspective, it was found that a change in the water flowrate had incurred the largest cost penalty with a 1% increase in flowrate had increased the average operating cost by 1.2%. In comparison, a change in air flowrate where a 1% increase in flowrate had yielded an average of 0.4% increase in operating cost.
43

Dynamic modelling and operational optimisation of natural draft cooling towers

Dhorat, A., Al-Obaidi, Mudhar A.A.R., Mujtaba, Iqbal M. 28 October 2018 (has links)
Yes / Natural draft cooling towers are subjected to dynamic air temperature and humidity ratio of air throughout the day. Their performances based on steady state model is restricted to single air temperature and humidity ratio of air values and thus are not accurate. In this work, a dynamic model for a natural draft cooling tower is developed. Air temperature and relative humidity data for Johannesburg were acquired to develop dynamic correlations for these two parameters and are embedded in the process model together with the dynamic model of the collection basin of the tower. A simple algorithm is proposed to solve the resulting boundary value problem. Finally, the common perception that seawater/river water should be used instead of freshwater as cooling medium is tested via optimisation where the operating costs of the process for two cooling mediums is minimised. The freshwater has been found to be cost effective cooling medium.
44

Condition-based monitoring of natural draught wet-cooling tower performance-related parameters

Ehlers, Frederik Coenrad 12 1900 (has links)
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.
45

Experimental and numerical evaluation of anisotropic fill performance characteristics in cross- and counterflow

Grobbelaar, Pieter Jacobus 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The confidence level of modeling cooling towers, where oblique air flow within anisotropic fills takes place, is higher when the change in fill‟s performance cha-racteristics, dependent on the way that air flows through the fill, is better unders-tood. A trickle fill‟s performance characteristics in crossflow are compared to its per-formance characteristics in counterflow by doing crossflow fill tests that are per-formance comparable to counterflow tests with the same fill. In order to do these tests, an existing crossflow fill test facility is critically evaluated and improved. The difference between crossflow and counterflow trickle fill performance charac-teristics is found to depend on air mass velocity (Ga) and water mass velocity (Gw) and to be between 0 and 35% for the Merkel number (Me) and up to almost 200% for the loss coefficient. Additionally, the validity of a recently developed 2-dimensional evaporative cool-ing model is investigated by comparing its predictions to experimental results. The following conclusions are made: - For trickle fill and rain zone tests, the model, with the present assumptions, predicts the average temperature of the outlet air to within approximately 0.4 °C. - Currently, temperature profiles that are experimentally measured at the air and water outlets are subject to significant edge effects, which prevent a fair com-parison to model predictions. - The model predictions can be improved if local variations in Me and the redi-stribution of water by the fill are taken into account. / AFRIKAANSE OPSOMMING: Die betroubaarheid van die modellering van koeltorings, waar lug skuins deur anisitropiese pakking (of “fill” in Engels) vloei, is hoër indien die verandering in die pakking se verrigtingseienskappe, wat afhang van die manier waarop die lug deur die pakking vloei, beter verstaan word. „n Drup pakking (of “trickle fill” in Engels) se verrigtingseienskappe in kruisvloei word vergelyk met dié in teenvloei deur kruisvloei pakking toetse, wat direk vergelykbaar is met teenvloei toetse vir dieselfde pakking, te doen. Ten einde hieredie toetse te doen, word ʼn bestaande kruisvloei toets fasiliteit krities ondersoek en verbeter. Dit word bevind dat die verskil tussen die drup pakking se kruisvloei en teenvloei verrigtingseienskappe afhang van lug massa snelheid (Ga) en water massa snelheid (Gw) en 0 tot 35% is vir die Merkel getal (Me) en so groot as 200% is vir die verlies koëffisiënt. Verder word die geldigheid van ʼn 2-dimensionele nat-verkoelingsmodel wat onlangs ontwikkel is ondersoek deur die model se voorspellings te vergelyk met eksperimentele resultate. Die volgende gevolgtrekkings word gemaak: - Die model, met huidige aannames, voorspel die gemiddelde uitlaat lug temperatuur met ʼn afwyking van ongeveer 0.4°C. - Die temperatuur profiele wat eksperimenteel gemeet word by die lug en water uitlate is onderworpe aan noemenswaardige rand effekte, wat ʼn behoorlike vergelyk met model voorspellings verhoed. - Die model se voorspelling van die profiele kan verbeter word indien die lokale variasies in Me en die herverdeling van die water deur die pakking in ag geneem kan word.
46

Computer optimization of dry and wet/dry cooling tower systems for large fossil and nuclear power plants.

Choi, Michael Kam-wah. January 1978 (has links)
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
47

Die invloed van versteurde inlaatvloeipatrone op aksiaalwaaiers

Visser, J. G. J. 12 1900 (has links)
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.
48

The design of a single rotor axial flow fan for a cooling tower application

Bruneau, Phillippe Roger Paul, Von Backstrom, T. W. 12 1900 (has links)
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.
49

CFD investigation of flow in and around a natural draft cooling tower

Storm, Heinrich Claude 03 1900 (has links)
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.
50

Enhancement of cooling tower performance by manipulation of rain zone drop size

Oosthuizen, Henry Randolph 03 1900 (has links)
Thesis (MEng)--University of Stellenbosch, 1995. / AFRIKAANSE OPSOMMING: Die moontlikheid om die warmteoordrag in die reensone van 'n natuurlike trek nat koeltoring te vcrbeter deur die gemiddelde druppel diameter van die sproei te verminder is ondersoek. Eksperimentele wcrk was daarop gerig om tipiese druppelgrootte verspreidings onder druppakking te bepaal, asook die verkryging van werklike verrigtings-data vir verskiJlende pakking en reensone kombinasies in 'n koeltoring toetsfasiliteit. 'n Fotografiese metode wat gebruik maak van beeldverwerkingstegniekc is ontwikkel om die druppelgrootte verspreidings wat in die )meltoring toetsfasiliteit gevind word te bepaal. 'n Rekenaar simulasieprogram wat ontwikkel is deur Dreyer [940Rl] is verder gebruik om reensone verrigtingsdata ( oordragskarakteristieke en druppelgrootte verspreidings) teoreties te vcorspel, vir vergelyking met en evalusie van die eksperimentele resultate. Dit is bewys dat die plasing van 'n laag spatroosters reg onder druppakking die gerniddelde druppeldiameter in die reensone verrninder het, wat gelei het tot 'n ooreenstemmende toename in oordragskarakteristiek. Met die gebruik van 'n rekenaar simulasie program is bereken dat hierdie opstelling die termiese kapasiteit van 'n koeltoring met tot 5 % kan verbeter. / ENGLISH ABSTRACT: The possibility of improving the heat transfer in the rain zone of large natural draft wet cooling towers, by decreasing the mean drop diameter in this region, has been investigated. Experimental studies were aimed at determining typical drop size distributions under trickle packs and obtaining actual performance data for packing and rain zone combinations in a cooling tower test facility. A photography-based method, which utilizes image processing techniques, was develo!Jed t() determine the drop size distributions found in the test facility. A computer simulation program developed by Dreyer [94DRI] was used to theoretically predict rain zone performance data (i.e., transfer coefficients and drop size distribution data) for comparison with and evaluation of the experimental data. I: was found that by placing a layer of splash grids beneath a trickle pack the mean drop diameter in the rain zone was decreased, resulting in corresponding increases in transfer characteristic. Using a computer simulation program it was calculated that this arrangement could increase the thermal capacity of a large natural draft cooling tower by up to 5 %.

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