Dissertation (PhD)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The globalisation is increasing the complexity of product development in terms of product variants and the range of technologies implemented. It emphasises the requirement for developing various design information support systems for the world market. However, small and medium enterprises that employ a wide range of design procedures may not be able to afford customised information support systems, with the result that there is a need for flexible, i.e. easily adaptable, design support tools. Four case studies were carried out to investigate the requirements for an information support system aimed at the design process and design documents. They indicated that a design information support system aimed at supporting design teams in the pre-detail mechanical design phases should be able to adapt various design methods and handle design information in a flexible way. Flexible here means being applicable over a wide range of contexts and extendable without affecting data already captured. Ontology based approaches are widely applied where diverse information has to be handled. The development of the Internet today also makes a distributed design approach more and more popular for mechanical design. An internet-based design support system called DiDeas II (Distributed Design assistant) was developed here with an ontologybased approach implemented to provide distributed and flexible assistance during concept generation in small companies. The DiDeas II has separate server side and client side programs, which communicate through a TCP/IP connection. DiDeas II allows design teams to manage their design information according to various design methods, to decrease time-delays and to improve communication between team members. These benefits were confirmed in two case studies carried out to evaluate DiDeas II. Keywords: Distributed design; ontology; concept design, web-based system. / AFRIKAANSE OPSOMMING: Globalisering verhoog die kompleksiteit van produkontwikkeling, in terme van produk variante en die bereik van tegnologieë wat geïmplementeer word. Dit beklemtoon die behoefte om verskeie ontwerp-inligting-ondersteuningstelsels vir die wêreldmark te ontwikkel. Klein en medium ondernemings wat 'n wye spektrum ontwerpsprosedures gebruik, kan egter nie doelgemaakte inligting-ondersteuningstelsels bekostig nie, met die gevolg dat daar 'n behoefte vir maklik-aanpasbare ontwerp ondersteuningstelsels is. Vier gevallestudies is uitgevoer om die vereistes vir 'n inligting-ondersteuningstelsel gemik op die ontwerpproses en ontwerp dokumente, te ondersoek. Dit het aangetoon dat 'n ontwerp-inligting-ondersteuningstelsel, wat ontwerpspanne in die voor-detail meganiese ontwerp fases moet ondersteun, by verskeie ontwerpmetodes moet kan aanpas en ontwerpsinligting op 'n aanpasbare manier kan hanteer. Aanpasbaarheid in hierdie konteks beteken toepaslik oor 'n wye spektrum kontekste en uitbreibaar sonder om data wat alreeds ingevoer is, te beïnvloed. Ontologie-gebaseerde benaderings word wyd toegepas waar diverse inligting hanteer moet word. Die ontwikkeling van die Internet maak 'n verspreide-ontwerpbenadering meer en meer gewild vir meganiese ontwerp. 'n Internet-gebaseerde ontwerpondersteuningstelstel genaamd DiDeas II (Distributed Design assistant) is hier ontwikkel met 'n ontologie-gebaseerde benadering wat daarop gemik is om verspreide, aanpasbare hulp te verleen aan klein maatskappye gedurende konsep- ontwikkeling. Die DiDeas II stelsel het afsonderlike bediener en kliënt programme wat deur 'n TCP/IP verbinding kommunikeer. DiDeas II laat ontwerpspanne toe om hulle ontwerp inligting volgens verskeie ontwerpmetodes te bestuur, tydvertragings te verminder en om kommunikasie tussen spanlede te verbeter. Hierdie voordele is bevestig in twee gevallestudies wat uitgevoer is om DiDeas II te evalueer. Sleutelwoorde: Verspreide ontwerp; ontologie; konsepontwerp; web-gebaseerde stelsel.

Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: During the last 30 years I have been involved in the theory and practice of thermal engineering and in particular, in the areas of air-cooled heat exchangers and cooling towers for the power, refrigeration, process and petrochemical industries in South Africa and internationally. During this period, I have authored and co-authored more than 120 papers that were published in technical journals or presented at conferences nationally or internationally. Most of these papers are included in a manuscript entitled "Air-cooled Heat Exchangers and Cooling Towers", in which Ipresent a systematic approach to the thermal performance evaluation and design of industrial air-cooled heat exchangers and cooling towers. This original publication also includes the relevant practice applicable to the design of cooling systems, based on my experience as a consultant to industry. Design offices throughout the world presently follow our design methods, or at least employ many of our research results. Our work has furthermore contributed to the development of improved cooling system designs (e.g. new dephlegmator header designs), components (e.g. single-row flattened finned tubes) and product improvement and quality control (e.g. performance testing and measurement of thermal contact resistance between fin and tube during production). Many of our research findings have found application in the modification of existing cooling systems. The manuscript has also been used as reference work during the presentation of short courses to practising engineers and consultants in industry and to engineering graduates at the University of Stellenbosch. A two-volume edition of this manuscript was published by PennWell Corp., Tulsa, Oklahoma, USA in 2004. / AFRIKAANSE OPSOMMING: Gedurende die laaste 30 jaar was ek betrokke by die teorie en praktyk van lugverkoelde warmteoordraers en koeltorings vir die kragopwekkings-, verkoelings-, proses- en petro-chemiesenywerhede in Suid-Afrika sowel as in die buiteland. Gedurende hierdie periode was ek outeur en mede-outeur van meer as 120 publikasies wat in tegniese tydskrifte, of by plaaslike of oorsese konferensies aangebied is. Die meeste van hierdie publikasies vorm deel van 'n manuskrip getiteld "Air-cooled Heat Exchangers and Cooling Towers" waarin ek 'n sistematiese benadering tot die bepaling van die termiese vermoë en ontwerp van industriële lugverkoelde warmteoordraers en koeltorings aanbied. Hierdie oorspronklike publikasie bevat ook die relevante praktyk wat van toepassing is op verkoelingsaanlegte. Ontwerpkantore wêreldwyd volg tans hierdie ontwerpsmetodes, of gebruik ten minste baie van ons navorsingsresultate. Ons werk het verder bygedra tot die ontwikkeling van verbeterde verkoelingsaanlegte (bv. nuwe deflegmatore), komponente (bv. enkelbuisry platvinbuise ) en verbeterde produkte en kwaliteitskontrole (bv. toetsing van verkoelingsvermoë oftermiese kontakweerstand tussen vin en buis gedurende produksie). Baie van ons bevindinge het toepassing gevind in die modifikasie van verkoelingsaanlegte. Die manuskrip is ook as verwysing gebruik gedurende die aanbieding van kort kursusse aan ingenieurs in die praktyk en aan nagraadse studente aan die Universiteit van Stellenbosch. 'n Twee-volume uitgawe van die manuskrip is deur PennWell Corp., Tulsa, Oklahome, VSA in 2004 gepubliseer.

Thesis (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The findings of an investigation into the requirements of a support system for distributed conceptual design in small and medium enterprises are presented. Distributed conceptual design refers to the collaboration of spacially distributed design teams during the early stages of the product development process. Three main elements of a support system were identified. The first element, 'Design Methodology', places a framework for specification development, functional analysis, concept generation and concept evaluation at the designers' disposal. It systematically guides the users through the different steps of the design process. These steps can be performed either alone, or together with other team members. The users are also aided in documenting their steps in order to allow the team members or designers of followup projects to understand the decisions made. The second element, 'Communication and Information Transfer', co-ordinates the communication between the distributed designers and provides a platform for the exchange of design-related data, e.g. customer requirements, ideas, sketches, comments, and decisions. A case study was carried out to assess the use of various tools for communication and information transfer during synchronous and asynchronous collaboration. The case study is described and the results are presented and discussed. Both elements make use of a support service providing various 'Input Devices for Conceptual Design', the third element of a support system. While standard tools such as mouse and keyboard meet the requirements of subsequent stages of the design process, they are often impractical in creating or annotating sketches. Various low-cost input devices were investigated. A framework was developed to integrate the three elements into one support system. The 'Distributed Design Assistant', abbreviated as 'DiDeas', is an Internet-based system that allows simultaneous multi-user collaboration. A relational database is located on a central web-server and stores all design information entered into the system. The user interface was realized in the form of a collection of Microsoft Active Server Pages, which can be accessed platform-independently via a standard webbrowser. The development of the database structure and of the user interface is described in detail. A second case study was carried out to evaluate the Distributed Design Assistant. The case study is described and the results are presented and discussed. The low-cost system has proven to be a very useful tool for distributed conceptual design. The Distributed Design Assistant systematically guides novice and experienced designers through the stages of specification development and conceptual design. It facilitates the easy collection and the fast exchange of a large amount of textual and graphical information during these stages. Although the system is relatively simple, compared to professional product data management systems used in later stages of the design process, it strongly enhances the productivity of designers and distributed design teams. Keywords: Distributed Design, Conceptual Design, Systematic Product Development / AFRIKAANSE OPSOMMING: Die bevindinge van 'n ondersoek na die behoeftes van 'n ondersteuningstelsel VIr verspreide konsepsionele ontwerp in klein en medium ondernemings word aangebied. Verspreide konsepsionele ontwerp is die saamwerk van ruimtelik verspreide ontwerp spanne gedurende die aanvanklike fases van die produk ontwikkelingsproses. Drie hoof elemente van 'n ondersteuningstelsel is geïdentifiseer. Die eerste element, 'Ontwerpmetodiek' stel 'n raamwerk vir spesifikasie ontwikkeling, funksionele analise, konsep generasie en konsep beoordeling tot beskikking van die ontwerpers. Dit lei die gebruikers stelselmatig deur die verskillende stappe van die ontwikkelingsproses. Die stappe kan of alleen of tesame met ander lede van die span uitgevoer word. Die gebruiker word ook ondersteun met die dokumentasie van die stappe sodat die lede of ontwerpers van opvolgprojekte die besluite wat gemaak is, kan begryp. Die tweede element, 'Kommunikasie en Informasie Oordrag', koordineer die kommunikasie tussen die verspreide ontwerpers en bied 'n platvorm vir die uitruil van ontwerpinformasie, byvoorbeeld kliënte behoeftes, idees, sketse, kommentaar en besluite. 'n Gevallestudie is uitgevoer om die gebruik van verskeie gereedskapstukke vir kommunikasie en informasie-oordrag gedurende sinchrone en asinchrone samewerking te beoordeel. Die gevalle studie is beskryf en die resultate is bespreek. Altwee elemente maak gebruik van 'n ondersteuningsdiens wat verskeie 'Invoergereedskap vir Konsepsionele Ontwerp' voorsien, die derde element van die ondersteuningstelsel. Terwyl standard gereedskap, byvoorbeeld 'n rekenaar muis en sleutelbord, die behoeftes van die latere ontwerpsfases bevredig, is hulle dikwels onprakties vir die maak van sketse en byskrifte. Verskeie laekoste invoergereedskap is ondersoek. 'n Raamwerk is ontwikkel om die drie elemente in een ondersteuningstelsel te integreer. Die 'Distributed Design Assistant', verkort 'DiDeas', is 'n Internet-gebaseerde stelsel wat sinchrone multi-gebruiker samewerking moontlik maak. 'n Gekoppelde databasis is op 'n sentrale webbediener geplaas en versamel al die ontwerpinformasie wat in die stelsel ingevoer is. Die gebruikerintervlak is geskep as 'n versameling van Microsoft Active Server Pages. Toegang tot die stelsel is onafhanklik van die rekenaar bedryfstelsel en kan verkry word met 'n standard webblaaier. Die ontwikkeling van die databasisstruktuur en van die gebruikerintervlak is in detail beskryf. 'n Tweede gevallestudie is uitgevoer om die Distributed Design Assistant te beoordeel. Die gevallestudie is beskryf en die resultate is bespreek. Die laekoste stelsel het homself bewys as 'n baie nuttige werktuig VIr verspreide konsepsionele ontwerp. Die Distributed Design Assistant lei nuweling en ervare ontwerpers stelselmatig deur die spesifikasie ontwikkeling en konsepsionele ontwerp stappe. Dit fasiliteer die maklike versameling en die vinnige uitruil van 'n groot hoeveelheid teks en grafiese informasie gedurende hierdie stappe. Ofskoon die stelsel relatief eenvoudig is in vergelyking met professionele produkdata-bestuurstelsels, verhoog dit die produktiwiteit van ontwerpers en verspreide ontwerp spanne aansienlik.

Thesis (PhD) -- University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In the design of a modern natural draught wet-cooling tower (NDWCT), structural and performance characteristics must be considered. Air flow distortions and resistances must be minimised to achieve optimal cooling which requires that the cooling towers must be modelled two-dimensionally and ultimately threedimensionally to be optimised. CFD models in literature are found to be limited to counterflow cooling towers packed with film fill, which is porous in one direction only and generally has a high pressure drop, as well as purely crossflow cooling towers packed with splash fill. This simplifies the analysis considerably as the effects of flow separation at the air inlet are minimised and fill performance is determined using the method of analysis originally employed to determine the fill performance characteristics from test data. Many counterflow cooling towers are, however, packed with trickle and splash fills which have anisotropic flow resistances, which means the fills are porous in all flow directions and thus air flow can be oblique through the fill, particularly near the cooling tower air inlet. This provides a challenge since available fill test facilities and subsequently fill performance characteristics are limited to purely counter- and crossflow configuration. In this thesis, a CFD model is developed to predict the performance of NDWCTs with any type of spray, fill and rain zone configuration, using the commercial code FLUENT®. This model can be used to investigate the effects of different: atmospheric temperature and humidity profiles, air inlet and outlet geometries, air inlet heights, rain zone drop size distributions, spray zone performance characteristics, variations in radial water loading and fill depth, and fill configurations or combinations on cooling tower performance, for optimisation purposes. Furthermore the effects of damage or removal of fill in annular sections and boiler flue gas discharge in the centre of the tower can be investigated. The CFD modelling of NDWCTs presents various options and challenges, which needed to be understood and evaluated systematically prior to the development of a CFD model for a complete cooling tower. The main areas that were investigated are: spray and rain zone performance modelling by means of an Euler-Lagrangian model; modelling of air flow patterns and flow losses; modelling of fill performance for oblique air flow; modelling of air pressure and temperature profiles outside and inside the cooling tower. The final CFD results for the NDWCT are validated by means of corresponding one-dimensional computational model data and it is found that the performance of typical NDWCTs can be enhanced significantly by including protruding platforms or roundings at the air inlet, reducing the mean drop size in the rain zone, radially varying the fill depth and reducing the air inlet height. / AFRIKAANSE OPSOMMING: By die ontwerp van ‘n moderne natuurlike trek nat koeltoring (NTNK), moet strukturele en werkverrigtings eienskappe in ag geneem word. Wanverdeelde lugvloei en vloeiweerstande moet geminimaliseer word om optimale verkoeling te bewerkstellig, wat vereis dat die koeltorings twee-dimensioneel en uiteindelik driedimensioneel gemodelleer moet word om hulle te kan optimeer. Dit is gevind dat berekeningsvloeidinamika (BVD of “CFD” in engels) modelle in die literatuur, beperk is tot teenvloei koeltorings gepak met film tipe pakking, wat net in een vloeirigting poreus is en boonop gewoonlik ook ‘n hoë drukval het, sowel as suiwer dwarsvloei koeltorings met spatpakking. Hierdie vergemaklik die analise aansienlik omdat die effekte van vloeiwegbreking by die luginlaat verklein word en die pakking se werkverrigtingsvermoë bereken kan word met die analise metode wat oorspronklik gebruik is om die pakkingseienskappe vanaf toets data te bepaal. Baie teenvloei koeltorings het egter drup- (“trickle”) of spatpakkings met anisotropiese vloeiweerstand, wat beteken dat die pakking poreus is in alle vloeirigtings en dat die lug dus skuins deur die pakking kan vloei, veral naby die koeltoring se lug inlaat. Hierdie verskaf ‘n uitdaging aangesien beskikbare pakking toetsfasiliteite, en dus ook pakking karakteristieke, beperk is tot suiwer teenvloei en dwarsvloei konfigurasie. ‘n BVD model word in hierdie tesis ontwikkel wat die werkverrigtingsvermoë van NTNK’s kan voorspel vir enige sproei, pakking en reënsone konfigurasie deur van die kommersiële sagteware FLUENT® gebruik te maak. Hierdie model kan gebruik word om die effekte van verskillende: atmosferiese temperatuur- en humiditeitsprofiele, lug inlaat en uitlaat geometrië, lug inlaat hoogtes, reënsone druppelgrootteverdelings, sproeisone werkverrigtingskarakteristieke, variasie in radiale waterbelading en pakking hoogte, en pakking konfigurasies of kombinasies op koeltoringvermoë te ondersoek vir optimerings doeleindes. Verder kan die effekte van beskadiging of verwydering van pakking in annulêre segmente, en insluiting van ‘n stoomketel skoorsteen in die middel van die toring ondersoek word. Die BVD modellering van NTNK bied verskeie moontlikhede en uitdagings, wat eers verstaan en sistematies ondersoek moes word, voordat ‘n BVD model van ‘n algehele NTNK ontwikkel kon word. Die hoof areas wat ondersoek is, is: sproeien reënsone modellering mbv ‘n Euler-Lagrange model; modellering van lugvloeipatrone en vloeiverliese; modellering van pakking verrigting vir skuins lugvloeie; modellering van lugdruk- en temperatuurprofiele buite en binne in die koeltoring. Die BVD resultate word mbv van data van ‘n ooreenstemmende eendimensionele berekeningsmodel bevestig en dit is bevind dat die werkverrigting van ‘n tipiese NTNK beduidend verbeter kan word deur: platforms wat uitstaan of rondings by die luginlaat te installeer, die duppelgrootte in die reënsone te verklein, die pakkingshoogte radiaal te verander, en die luginlaathoogte te verlaag.

Thesis (PhD (Mechanical Engineering))--University of Stellenbosch, 1990. / Leaves printed on single pages, preliminary pages i- viii and numbered pages 1-1-R5. Includes bibliography, list of tables and figures and list of appendices. Digitized at 330 dpi black and white PDF format (OCR),using KODAK i 1220 PLUS scanner. / ENGLISH ABSTRACT: A numerical procedure for predicting the effect of inlet flow distortions on the performance of axial flow fans is proposed. The study is aimed specifically at fans of low solidity and low hub-to-tip ratios, which have attained some importance with the advent of large directly air-cooled power stations in certain arid regions of the world. The numerical model is an extension to cylindrical polar coordinates of the SIMPLEN algorithm that has been developed by the author previously. The algorithm is implemented in a computer code, FLOVAX, which solves the incompressible Navier-Stokes equations, augmented by the k-Ɛ model of turbulence, on a computational domain that is aligned with the cylindrical polar coordinate system. Several relatively simple flow problems are solved to verify the code: laminar stagnation flow, laminar flow near a rotating disk, turbulent flow near a propeller, turbulent flow through an abrupt axisymmetric expansion, and turbulent swirling flow in an annulus. Good agreement is obtained between the numerical solutions and the corresponding analytical, empirical or published experimental and numerical results. Some experimental results are also presented: measurements of shaft power, volume flow rate and static pressure rise were taken in a setup comprising an axial flow fan mounted in the wall of a wind tunnel. The wind tunnel was used to provide flow across the fan intake, thus establishing distorted inflow conditions. Detailed measurements of the velocity and static pressure distributions in the duct downstream of the fan rotor were also performed. It is clear from the results that flow across the intake of the test fan has a detrimental effect on its performance in that an increased amount of power is necessary to deliver the same flow rate as with no crossflow. In the numerical predictions, blade element theory is used to model the thrust and torque exerted by the fan blades on the air. The numerical results generally confirm the results of the experiment, although the increase in power is underestimated: an increase of only approximately half of the measured increase is predicted. Several recommendations for improvement of the numerical procedure are made. / AFRIKAANSE OPSOMMING: 'n Numeriese prosedure vir die voorspelling van die invloed van versteurings in inlaatvloei op die werking van aksiaalwaaiers word daargestel. Die studie is spesifiek gemik op waaiers van lae soliditeit en lae lempunt-tot-naafverhoudings. Waaiers van hierdie tipe het belangrikheid verwerf sedert die onlangse totstandkoming van groot lugverkoelde kragstasies in sekere droe werelddele. Die numeriese model is 'n uitbreiding na silindriese poolkoordinate van die SIMPLEN-algoritme wat voorheen deur die skrywer ontwikkel is. Die algoritme word geimplementeer in 'n rekenaarkode, FLOVAX, wat die onsamedukbare Navier-Stokes-vergelykings, aangevul deur die k-Ɛ-turbulensiemodel, oplos op 'n berekeningsgebied wat saamval met die silindriese poolkoordinaatstelsel. Verskeie relatief eenvoudige vloeiprobleme word opgelos ter verifikasie van die kode: laminere stagnasievloei, laminere vloei op 'n roterende skyf, turbulente vloei deur 'n propeller, turbulente vloei deur 'n aksiaalsimmetriese vernouing, en turbulente roterende vloei in 'n annulus. Goeie ooreenstemming tussen die numeriese oplossings en die ooreenstemmende analitiese, empiriese of gepubliseerde eksperimentele en numeriese resultate is verkry. Eksperimentele resultate word ook aangebied: metings van asdrywing, volumevloei en statiese drukstyging is geneem in 'n opstelling wat bestaan het uit 'n aksiaalwaaier wat in die wand van 'n windtonnel gemonteer is. Die windtonnel is gebruik om versteurde-invloei-toestande te genereer in die vorm van dwarsvloei oor die waaier-inlaat. Snelheids- en statiese drukverdelings in die kanaal stroom-af van die waaierrotor is ook gemeet. Dit blyk duidelik uit die resultate dat die dwarsvloei oor die inlaat van die toetswaaier 'n nadelige uitwerking het op die werking daarvan in die opsig dat meer drywing nodig is om dieselfde vloeitempo te handhaaf as wat die geval is sonder dwarsvloei. Vir die numeriese voorspellings word van lem-element-teorie gebruik gemaak om die stukrag en draaimoment wat deur die waaier op die lug uitgeoefen word, te modelleer. Die numeriese resultate bevestig oor die algemeen die eksperimentele resultate, alhoewel die drywingstoename onderskat word met sowat die helfte van die gemete toename. Verskeie aanbevelings ter verbetering van die numeriese prosedure word gemaak.

Thesis (MScEng)--Stellenbosch University, 2006. / ENGLISH ABSTRACT: The Stellenbosch University Compressor Code (SUCC) has been developed for the purpose of predicting the performance of axial flow compressors by means of axisymmetric inviscid throughflow methods with boundary layer blockage and empirical blade row loss models. This thesis describes the process of the implementation and verification of a number of stall prediction criteria in the SUCC. In addition, it was considered desirable to determine how certain factors influence the accuracy of the stall prediction criteria, namely the nature of the computational grid, the choice of throughflow method used, and the use of a boundary layer blockage model and a radial mixing model. The stall prediction criteria implemented were the di®usion factor limit criterion, de Haller's criterion, Aungier's blade row criterion, Aungier's boundary layer separation criterion, Dunham's, Aungier's and the static-to-static stability criteria. The compressors used as test cases were the Rofanco 3-stage low speed compressor, the NACA 10-stage subsonic compressor, and the NACA 5-stage and 8-stage transonic compressors. Accurate boundary layer blockage modelling was found to be of great importance in the prediction of the onset of stall, and that the matrix throughflow Method provided slightly better accuracy than the streamline curvature method as implemented in the SUCC by the author. The ideal computational grid was found to have many streamlines and a small number of quasi-orthogonals which do not occur inside blade rows. Radial mixing modelling improved the stability of both the matrix throughflow and streamline curvature methods without significantly affecting the accuracy of the stall prediction criteria. De Haller's criterion was over-conservative in estimating the stall line for transonic conditions, but more useful in subsonic conditions. Aungier's blade row criterion provided accurate results on all but the Rofanco compressor. The diffusion factor criterion provided over- optimistic predictions on all machines, but was less inaccurate than de Haller's criterion on the NACA 5-stage transsonic machine near design conditions. The stability methods performed uniformly and equally badly, supporting the claims of other researchers that they are of limited usefulness with throughflow simulations. Aungier's boundary layer separation method failed to predict stall entirely, although this could reflect a shortcoming of the boundary layer blockage model. / AFRIKAANSE OPSOMMING: Die Stellenbosch University Compressor Code (SUCC) is ontwikkel om die prestasie van aksiaalvloei kompressors te voorspel met behulp van aksisimmetriese nie-viskeuse deurvloeimetodes met grenslaagblokkasie en empiriese modelle vir die verliese binne lemrye. Hierdie tesis beskryf die proses waarmee sekere staakvoorspellingsmetodes in die SUCC geïmplementeer en geverifieer is. Dit was ook nodig om die effek van sekere faktore, naamlik die vorm van die berekeningsrooster, die keuse van deurvloeimetode en die gebruik van `n grenslaagblokkasiemodel en radiale vloeivermengingsmodel op die akuraatheid van die staakvoorspellingsmetodes te bepaal. Die staakvoorspellingsmetodes wat geïmplementeer is, is die diffusie faktor beperking metode, de Haller se metode, Aungier se lemrymetode, Aungier se grenslaagmetode en die Dunham, Aungier en die statiese-tot-statiese stabiliteitsmetodes. Die kompressors wat gebruik is om die metodes te toets is die Rofanco 3-stadium lae-spoed kompressor, die NACA 10-stadium subsoniese kompressor en die NACA 5- en 8-stadium transsoniese kompressors. Daar is vasgestel dat akkurate grenslaagblokkasie modelle van groot belang was om `n akkurate aanduiding van die begin van staking te voorspel, en dat, vir die SUCC, die Matriks Deurvloei Metode oor die algemeen 'n bietjie meer akkuraat as die Stroomlyn Kromming Metode is. Daar is ook vasgestel dat die beste berekeningsrooster een is wat baie stroomlyne, en die kleinste moontlike getal quasi-ortogonale het, wat nie binne lemrye geplaas mag word nie. Die numeriese stabiliteit van beide die Matriks Deurvloei en die Stroomlyn Kromming Metode verbeter deur gebruik te maak van radiale vloeivermengingsmodelle, sonder om die akkuraatheid van voorspellings te benadeel. De Haller se metode was oorkonserwatief waar dit gebruik is om die staak-lyn vir transsoniese vloei toestande, maar meer nuttig in die subsoniese vloei gebied. Aungier se lemrymetode het akkurate resultate gelewer vir alle kompressors getoets, behalwe die Rofanco. Die diffusie faktor metode was oor die algemeen minder akuraat as Aungier se metode, maar meer akkuraat as de Haller se metode vir transsoniese toestande. Die stabiliteitsmetodes het almal ewe swak gevaar. Dit stem ooreen met die bevindings van vorige navorsing, wat bewys het dat hierdie metodes nie toepaslik is vir simulasies wat deurvloeimetodes gebruik nie. Aungier se grenslaagmetode het ook baie swak gevaar. Waarskynlik is dit as gevolg van tekortkomings in die grenslaagblokkasiemodel.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: There are two methods generally used for heliostat field layout optimization: the field growth method and the pattern method. A third, less commonly used method also exists: the free variable method. Each of these three methods offers its own set of advantages and disadvantages. The purpose of this study is to explore the subject of heliostat field layout optimization and to examine the free variable method. In order to achieve this objective, optimization was conducted using the free variable method. To perform optimization, a technical model of the heliostat field was constructed using approximating functions from literature and geometric analysis. Results of this study indicated that the free variable method is possible using a gradient-based optimization algorithm. The free variable method was applied to redesign the field of a commercial plant, PS10, located in Spain. The original plant was improved by 1.2% in annual intercepted energy. The study has demonstrated some of the characteristics, advantages and pitfalls of the free variable method and has proved useful in contributing to the understanding of heliostat field layout optimization. The free variable method requires more research and development before it may be used commercially. / AFRIKAANSE OPSOMMING: Daar word oor die algemeen twee metodes gebruik om 'n heliostaatveld se uitleg te optimeer: die terreinvermeerderingsmetode (field growth) en die patroonmetode (pattern). 'n Derde, minder algemeen gebruikte metode bestaan ook: die vrye veranderlike metode (free variable). Elkeen van hierdie drie metodes bied sy eie voordele en nadele. Die doel van hierdie studie is om die onderwerp van heliostaat veld uitleg optimalisering te verken en die vrye veranderlike metode te ondersoek. Ten einde te hierdie oogmerk te bereik, is die optimalisering uitgevoer met gebruik van die vrye veranderlike metode. Om optimalisering uit te voer, is 'n tegniese model van die heliostaat veld gebou met behulp van benader funksies van letterkunde en geometriese analise. Resultate van hierdie studie het aangedui dat die vrye veranderlike metode moontlik is deur gebruik te maak van 'n gradientbebaseerde optimeeringslagoritme. Die vrye veranderlike metode is ook aangewend om die terrien van 'n kommersiele aanleg, PS10 in Spanje, te herontwerp. Die oorspronklike aanleg is in jaarlikse onderskep energie verbeter met 1.2%. Die studie het sommige van die eienskappe, voordele en slaggate van die vrye veranderlike metode getoon en het nuttige bewys om by te dra tot die begrip van heliostaat veld uitleg optimalisering. Die vrye veranderlike metode vereis meer navorsing en ontwikkeling voordat dit kommersieel gebruik kan word.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: A novel induced draft hybrid (dry/wet) dephlegmator (HDWD) is introduced which can enhance the performance of dry air-cooled condenser systems and a model is developed to simulate its performance. The HDWD consists of two stages of cooling with the steam flow in series and the air flow in parallel through both stages. The first stage consists of downwardly inclined finned tube bundles, similar to conventional air-cooled condenser bundles, and the second stage comprises horizontal bare tube bundles of which the outer surface can selectively be operated dry or wet by spraying it with deluge water. A comparison of the HDWD with other existing and new concepts reveals the significant advantages that this technology has over other technologies. This thesis is a continuation of the work done by Heyns (2008), who introduced a forced draft HDWD and investigated its performance, and Owen (2013), who conducted a parametric investigation on the induced draft HDWD to improve the basic design proposed by Heyns (2008). In his thermo-flow model, Heyns (2008) conducted a thermal analysis assuming equal air flow through both stages and a constant vapor temperature inside the bundles, while Owen (2013) solved the thermal, steam-side pressure drop and draft equations. Both their models make use of empirical correlations by Gaddis & Gnielinski (1985), Zukauskas (1987), Mizushina et al. (1967) and Niitsu et al. (1967) for the performance characteristics. The current model solves the thermal, steam-side pressure drop and draft equations of the HDWD with better accuracy in the steam-side pressure drop calculation. The airside heat and mass transfer and loss coefficient correlations found in literature were found to deviate significantly from each other resulting in uncertainty regarding their suitability. Based on the recommendations by Owen (2013), a bare tube test bundle with 19 mm outer diameter tubes arranged with a triangular pitch of 38 mm is therefore designed, manufactured and tested to investigate the performance characteristics of the bundle experimentally under dry and wet operating conditions to evaluate the correlations from literature. The experimental data confirmed the applicability of the correlations of Gaddis & Gnielinski (1985) and Zukauskas (1987) to predict the dry HDWD performance, since they deviated by 7% and 5% respectively from the experimental data in die applicable range. The heat transfer during wet operation is slightly over estimated within 5% with the correlations of Mizushina et al. (1967) in the range of application. The air-side pressure drop during wet operation is underestimated by 29 to 39% by Niitsu et al. (1967) and the correlation obtained from the experimental results is therefore used in the current model. Using the current HDWD model indicates significant performance enhancement using tubes with a smaller diameter in the delugeable bundle compared to the larger tubes of Heyns (2008) and agrees very well with the model of Owen (2013). / AFRIKAANSE OPSOMMING: ‘n Hibriede geïnduseerde trek deflegmator is voorgestel wat die werksverrigting van huidige lugverkoelde kondenserstelsels kan verbeter en ‘n model is ontwikkel wat die werksverrigting simuleer. Die deflegmator bestaan uit twee stadiums van verkoeling met die stoomvloei in serie en die lugvloei in parallel deur beide stadia. Die eerste stadium bestaan uit skuins, afwaartse finbuisbundels, soortgelyk aan konvensionele lugverkoelde kondenser-finbuisbundels, en die tweede stadium bestaan uit horisontale kaalbuisbundels waarvan die buite-oppervlak selektief droog of nat bedryf kan word deur dit met verkoelingswater te benat. ‘n Vergelyking tussen die deflegmator en ander huidige en nuwe konsepte toon merkbare voordele wat die tegnologie bo die ander tegnologië het. Die tesis is ‘n voortsetting van die werk van Heyns (2008), wie ‘n hibriede geforseerde trek deflegmator voorgestel en die werksverrigting daarvan ondersoek het, en Owen (2013) wat ‘n parametriese studie op die hibriede geïnduseerde trek deflegmator gedoen het om die basiese ontwerp voorgestel deur Heyns (2008) te verbeter. In sy termovloei-model, het Heyns (2008) die termiese analise ondersoek met die aanname van gelyke hoeveelhede lugvloei deur beide stadia met ‘n konstante damp-temperatuur binne die bundels, terwyl Owen (2013) die termiese, stoomkant-drukval and trekvergelykings opgelos het. Beide hul modelle maak van die empiriese korrelasies van Gaddis & Gnielinski (1985), Zukauskas (1987), Mizushina et al. (1967) en Niitsu et al. (1967) gebruik vir die werkverrigtingskarakteristieke. Die huidige model los die termiese, die stoomkant-drukval asook die trekvergelykings van die deflegmator op met verbeterde akkuraatheid van die stoomkant-drukval berekeninge. Die lugkant warmte- en massaoordrag en verlieskoëffisiënt korrelasies wyk baie van mekaar af wat lei tot onsekerhede rakende hul toepasbaarheid. Gebaseer op die voorstelle van Owen (2013) is ‘n kaalbuisbundel met 19 mm buite-diameter buise met ‘n driehoekige steek van 38 mm dus ontwerp, vervaardig en getoets om die werksverrigtingskarakteristieke van die bundel eskperimenteel te ondersoek onder droë en nat toestande om die korrelasies van die literatuur te evalueer. Die eksperimentele data bevestig die toepaslikheid van die korrelasies van Gaddis & Gnielinski (1985) en Zukauskas (1987) om die droë werksverrigting van die deflegmator te voorspel, aangesien hul met 7% en 5% onderskeidelik afwyk van die eksperimentele data in die toepaslike bestek. Die warmteoordrag tydens natwerking is ietwat oorskat binne 5% met die korrelasies van Mizushina et al. (1967) in die bestek van toepassing. Die lugkant-drukval tydens natwerking is onderskat met 29 tot 39% deur Niitsu et al. (1967) en die korrelasie verkry vanaf die eksperimentele resultate is dus gebruik in die huidige model. Deur gebruik te maak van die huidige model van die deflegmator dui merkbare werksverrigting verbetering aan deur van buise met ‘n kleiner diameter in die benatbare bundel te gebruik in vergelyking met die groter buise van Heyns (2008) en stem baie goed ooreen met die model van Owen (2013).

Thesis (MScIng)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Spier Estate - a wine estate in the Western Cape Province of South Africa - is engaged in a transition towards operating according to the principles of sustainable development. Besides changes in social and other environmental aspects, the company has set itself the goal to be carbon neutral by 2017. To this end, Spier is considering the on-site generation of electricity from renewable energy sources. This study was initiated to explore the technical and economic feasibility of a concentrating solar power plant for this purpose on the estate. The investigation was carried out to identify the most appropriate solar thermal energy technology and the dimensions of a system that fulfils the carbon-offset requirements of the estate. In particular, potential to offset the annual electricity consumption of the currently 5 570 MWh needed at Spier, using a concentrating solar power (CSP) system, was investigated. Due to rising utility-provided electricity prices, and the expected initial higher cost of the generated power, it is assumed that implemented efficiency measures would lead to a reduction in demand of 50% by 2017. However, sufficient suitable land was identified to allow electricity production exceeding today’s demand. The outcome of this study is the recommendation of a linear Fresnel collector field without additional heat storage and a saturated steam Rankine cycle power block with evaporative wet cooling. This decision was based on the system’s minimal impact on the sensitive environment in combination with the highest potential for local development. A simulation model was written to evaluate the plant performance, dimension and cost. The analysis was based on a literature review of prototype system behaviour and system simulations. The direct normal irradiation (DNI) data that was used is based on calibrated satellite data. The result of the study is a levelised cost of electricity (LCOE) of R2.741 per kWh, which is cost competitive to the power provided by diesel generators, but more expensive than current and predicted near-future utility rates. The system contains a 1.8 ha aperture area and a 2.0 MWe power block. Operating the plant as a research facility would provide significant potential for LCOE reduction with R2.01 per kWh or less (favourable funding conditions would allow for LCOE of R1.49 per kWh) appearing feasible, which results in cost competitiveness in comparison a photovoltaic (PV) solution. Depending on tariff development, Eskom rates are predicted to reach a similar level between 2017, the time of commissioning, and the year 2025. The downside is that the plant would not solely serve the purpose of electricity offsetting for Spier, which may result in a reduced amount of electricity that may be generated. Further studies are proposed to refine the full potential of cost reduction by local development and manufacturing as well as external funding. This includes identification of suitable technology vendors for plant construction. An EIA is required to be triggered at an early stage to compensate for its long preparation. / AFRIKAANSE OPSOMMING: Die Spier wynlandgoed in die Wes-Kaap Provinsie van Suid-Afrika is tans in ‘n oorgangsfase tot besigheids-praktyke gebaseer op volhoubare ontwikkeling. Afgesien van die sosiale en omgewingsaspekte het die groep hom ook ten doel gestel om koolstof neutraal te wees teen 2017. Ten einde hierdie doel te bereik, moet die maatskappy sy algehele elektrisiteitsverbruik vervang met hernubare bronne. Hierdie studie is dus geloods om die tegniese en ekonomiese uitvoerbaarheid van 'n gekonsentreerde sonkragstasie op die landgoed te ondersoek. Hierdie ondersoek is gedoen om die mees toepaslike sontermiese tegnologie en die grootte van 'n termiese sonkragstelsel te bepaal, wat aan die koolstof vereistes van die landgoed voldoen. Die potensiaal om die jaarlikse elektrisiteitsverbruik van 5 570 MWh met 'n gekonsentreerde elektriese sonkragstelsel te vervang, is ondersoek. Weens die toename in die elektrisiteitsprys en die verwagte hoërkoste van opgewekte elektrisiteit word aanvaar dat die implementering van voorgestelde doeltreffendheidsverbeteringe, sal lei tot 'n afname in die aanvraag na elektrisiteit van tot 50% teen die jaar 2017. Voldoende beskikbare grond is geïdentifiseer om genoeg elektrisiteit te produseer om die huidige vraag na elektrisiteit te oorskry. Die uitkoms van die studie is die aanbeveling van 'n lineêre Fresnel kollektorveld sonder addisionele warmte storing, asook 'n versadigde stoom Rankine sikluskragblok met ‘n nat-verdamping verkoelingstelsel. Die besluit is gebaseer op die stelsel se minimale impak op die omgewing, tesame met die hoogste potensiaal vir plaaslike ontwikkeling. 'n Simulasie is ontwikkel om die aanleg se werkverrigting, grootte en koste te evalueer. Die analise is gebaseer op 'n literatuuroorsig van 'n prototipe stelsel gedrag en stelsel-simulasies. Die direkte normale sonstralings data wat gebruik is, is gebaseer op gekalibreerde satelliet data. Die bevinding van die studie is 'n gebalanseerd koste van elektrisiteit van R2.74 per kWh, wat mededingend is met die koste van elektrisiteit wat deur diesel kragopwekkers verskaf word, maar is aansienlik duurder as die huidige en toekomstige voorspellings van Eskom-tariewe. Die stelsel bevat 'n 1.8 ha son kollektor oppervlakte en 'n 2.0 MWe krag-blok. Daarbenewens, sal die gebruik van die aanleg as 'n navorsingsfasiliteit die potensiaal hê om die gebalanseerd koste van elektrisiteit te verminder na R2.01 per kWh of minder (gunstig befondsing voorwaardes sal gebalanseerd koste van elektrisiteit van R1.49 per kWh tot gevolg hê), wat mededingend is met die koste van 'n fotovoltaïese alternatief. Daar word voorspel dat Eskom-tariewe dieselfde sal bly vanaf 2017, die jaar van inbedryfstelling van die aanleg, tot en met die jaar 2025. Die nadeel is dat die aanleg nie noodwendig uitsluitlik vir die opwek van elektrisiteit vir Spier gebruik sal word nie, en daarom kan dit lei tot 'n vermindering in die hoeveelheid elektrisiteit wat deur die aanleg opgewek word. Daar word voorgestel dat verdere studies onderneem word om die moontlikheid van koste-besparings vir die aanleg te ondersoek deur gebruik te maak van plaaslike ontwikkeling en vervaardiging, asook eksterne befondsing. Dit sluit die identifisering van geskikte tegnologie verskaffers vir die aanleg-kostruksie in. 'n Omgewingsimpakstudie, volgens die EIA regulasies, moet ook so gou as moontlik gedoen word aangesien dit n langsame proses is.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2008. / Low Cost Automation (LCA) is of immense importance to industry, and even more so for small scale industries. In implementing LCA determining cost effective and efficient actuator alternatives present challenges for design engineers. Most often decisions are experiential or entirely based on manufacturer recommendations. Experience based decisions are most often biased with respect to the engineers’ knowledge. Similarly, manufacturer recommendations are restricted to their own products and are as such also biased. Either way, sub-optimum drive alternatives may sometimes be chosen. This demonstrates the need for making better informed decisions based on more than experience and what is available for use. This thesis reports the development of an electric actuator selection procedure and aid for use in the early layout design phase. It provides readily accessible information on technically viable actuator options. Experiential knowledge of experts in the field, commercial information, as well as data obtained from experimentation was used in its development. Being orientated towards LCA, the procedure has been targeted at the application of electric motors and their associated control technologies but can be extended to hydraulic, pneumatic and other actuators. In achieving a wider applicability of the selection aid, a generic set of actuator properties descriptive of most actuators was formulated. An AC drives control evaluation was conducted for developing the selection procedure and aid. It provided a means to validate some selection aid rules associated with actuator controllability. Quantitative data on speed and positioning accuracies of common AC three phase motors and their associated inverter technologies were the targeted results of the experimentation.