Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: This work entails a study of the control software of transportation systems for use in recon gurable manufacturing systems (RMSs). Various control approaches are considered, with the focus on enhancing recon gurability. The work is unique in the sense that the RMS is designed to manufacture small parts/products and is meant to be used in developing countries. Manufacturing systems that can ensure product quality and delivery, are a critical need in countries where the bulk of manufacturing systems function with manual labour. RMSs and holonic manufacturing systems (HMSs) are identi ed as concepts that can potentially compete with manual manufacturing systems. The competing system must thus have a low initial adoption risk, be able to adapt to changing product functionality and demands, and have a comparable throughput rate. IEC61311-3, IEC64199 function block and agent-based control architectures are evaluated. The control software is tested on an experimental conveyor system. The thesis shows that IEC61131-3 and IEC64199 architectures are advantageous in lower levels of control. IEC64199 function blocks provide human interface and development tools and simpli es the distribution of control. The human interface and development tools of IEC64199 function blocks may prove bene cial in providing system monitoring and rapid low skilled adaptation of the control system, increasing recon gurability of systems in under-developed countries. Unfortunately, the low maturity of the development environments for IEC64199 function blocks is a limitation. It is shown that an IEC64199 function block controller becomes complex as the actuator/sensor count exceed 10. Agent-based systems o er reliable control and powerful communication tools but requires a higher level of expertise than IEC64199 function blocks. Agent-based systems are proposed for the core high level control. Complex systems can be controlled with agents and intelligence can be added to control systems in a recon gurable way. For the recon gurable control of large manufacturing systems, agent-based control was found to be superior to IEC64199 function blocks. / AFRIKAANSE OPSOMMING: Hierdie werk behels 'n studie in die beheersagteware van vervoerstelsels vir die gebruik in herkon gureerbare vervaardigingstelsels. Verskeie benaderings word oorweeg, met die fokus op die verbetering van herkon gureerbaarheid. Die werk is uniek in die sin dat die herkon gureerbare vervaardigingstelsel ontwerp is vir die vervaardiging van klein onderdele/produkte en is bedoel vir die gebruik in die ontwikkelende lande. Vervaardigingstelsels wat die kwaliteit van die produk en a ewering kan verseker, is 'n kritieke behoefte in die lande waar die grootste deel van die vervaardiging met handearbeid gedoen word. Herkon gureerbare vervaardigingstelsels en holoniese vervaardigingstelsels is geïdenti seer as konsepte wat moontlik kan meeding met die handmatige produksie-stelsels. Die mededingende stelsel moet dus 'n lae aanvanklike aannemingsrisiko hê, in staat wees om te kan aanpas by die veranderende produk funksionaliteit en aanvraag, en 'n vergelykbare deurvloeikoers kan lewer. IEC61311-3, IEC61499 funksie-blok en agent-gebaseerde beheer argitekture word geëvalueer. Die beheer sagteware is getoets op 'n eksperimentele vervoerband stelsel. Die tesis toon dat IEC61131-3 en IEC61499 argitekture voordelig is in die laër vlakke van beheer. IEC61499 funksie-blokke voorsien menslike koppelvlak en ontwikkelings-gereedskap, en vereenvoudig die verspreiding van beheer. Die menslike koppelvlak en ontwikkelings-gereedskap van die IEC61499 funksieblokke is moontlik voordelig in die voorsiening van stelselmonitering en vinnige laag-geskoolde aanpassing van die beheer stelsel. Dit mag dus moontlik die herkon gureerbaarheid van stelsels, in onder-ontwikkelde lande, verhoog. Die lae vlak van volwassenheid van die ontwikkelingsomgewings vir IEC61499 funksie-blokke verlaag hul bruikbaarheid. Daar word aangetoon dat IEC61499 funksie-blok beheerders baie kompleks raak as die hoeveelheid van aktueerders en sensors meer as 10 raak. Agent-gebaseerde stelsels bied betroubare beheer, en kragtige kommunikasie-gereedskap, maar vereis 'n hoër vlak van kundigheid as IEC61499 funksie-blokke. Agent-gebaseerde stelsels word voorgestel vir die hoëvlak beheer. Komplekse stelsels kan beheer word met agente en intelligensie kan bygevoeg word om stelsels te beheer in 'n herkon gureerbare manier. Dit was gevind dat agent-gebaseerde beheer beter is as IEC61499 funksie-blok beheer vir die herkon gureerbare beheer van groot vervaardigings stelsels.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Traditionally nuclear reactor power plants have been optimised for electrical power generation only. In the light of the ever-rising cost of dwindling fossil fuel resources as well the global polluting effects and consequences of their usage, the use of nuclear energy for process heating is becoming increasingly attractive. In this study the use of a so-called cogeneration plant in which a nuclear reactor energy source is optimised for the simultaneous production of superheated steam for electrical power generation and process heat is considered and analysed. The process heat superheated steam is generated in a once-through steam generator of heat pipe heat exchanger with intermediate fluid while steam for power generation is generated separately in a once-through helical coil steam generator. A 750 °C, 7 MPa helium cooled HTMR has been conceptually designed to simultaneously provide steam at 540 °C, 13.5 MPa for the power unit and steam at 430 °C, 4 MPa for a coal-to-liquid fuel process. The simulation and dynamic control of such a typical cogeneration plant is considered. In particular, a theoretical model of a typical plant will be simulated with the aim of predicting the transient and dynamic behaviour of the HTMR in order to provide guideline for the control of the plant under various operating conditions. It was found that the simulation model captured the behaviour of the plant reasonably well and it is recommended that it could be used in the detailed design of plant control strategies. It was also found that using a 1500 MW-thermal HTMR the South African contribution to global pollution can be reduced by 1.58%. / AFRIKAANSE OPSOMMING: Tradisioneel is kernkragaanlegte vir slegs elektriese kragopwekking geoptimeer. In die lig van die immer stygende koste van uitputbare fossielbrandstohulpbronne asook die besoedelingsimpak daarvan wêreldwyd, word die gebruik van kernkrag vir prosesverhitting al hoe meer aanlokliker. In hierdie studie word die gebruik van ‘n sogenaamde mede-opwekkingsaanleg waarin ‘n kernkragreaktor-energiebron vir die gelyktydige produksie van oorverhitte stoom vir elektriese kragopwekking en proseshitte oorweeg ontleed word. Die oorvehitte stoom word in ‘n enkeldeurvloei-stoomopwekking van die hittepyp-hitteruiler met tussenvloeistof opgewek en stoom vir kragopwekking word apart in ‘n enkeldeurvloei-spiraalspoel-stoomopwekker opgewek. ‘n 750 °C, 7 MPa heliumverkoelde HTMR is konseptueel ontwerp vir die gelytydige veskaffing van stoom by 540 °C, 13.5 MPa, vir die kragopwekkings eenheid, en stoom by 430 °C, 4 MPa, vir ‘n steenkool-tot-vloeibare (CTL) brandstoff proses. Die simulasie en dinamiese beheer van ‘n tipiese HTMR mede-opwekkingsaanleg word beskou. ‘n die besonder word ‘n teoretiese model van die transiënte en dinamiese gedrag van die aanleg gesimuleer om sodoene riglyne te identifiseer vir die ontwikkeling van dinamiese beheer strategië vir verskillende werkstoestande van die aanleg. Daar was ook gevind dat die simulasie model van die aanleg se gedrag goed nageboots word en dat dit dus gebruik kan word vir beheer strategie doeleindes. Indien so ‘n 1500 MW-termies HTMR gebruik word sal dit die Suid Afrikaanse besoedling met 1.58% sal kan verminder.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Concentrating solar power technology is a modern power generation technology in which central receiver systems play a significant role. For this technology a field of heliostats is used to reflect solar irradiation to the receiver located on top of the tower. An extensive review has shown that contemporary receiver designs face geometric complexities, lack of thermal efficiency as well as issues with durability and cost. The purpose of this study is to develop a new receiver concept that can potentially reduce these issues. A parametric analysis was used to identify potential means of improvement based on an energy balance approach including sensitivities involved with convection and radiation heat transfer. Design criteria such as the use of headers to minimize pressure drop was also investigated. Based on these findings the hybrid pressurized air receiver was developed which is a combination of tubular and volumetric receiver technologies. The fundamental idea of the receiver was investigated by simulating the ray-tracing and coupled natural convection and radiation heat transfer. The ray-tracing results have shown that the use of quartz glass is a prospective solution to higher allowable flux densities, but with reflection losses in the order of 7 %. The coupled natural convection heat transfer simulation further revealed that the receiver concept effectively eliminates the escape of buoyant plumes and radiative heat losses are minimized. Empirical data was gathered from a medium flux concentrator and good agreement with the numerical results was obtained. The thesis therefore concludes that the research outcomes were met. Ongoing research aims to optimise the receiver concept for a 5MW pilot plant. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonkrag tegnologie is ’n moderne kragopwekkingstegnologie waar sentrale ontvangersisteme ’n beduidende rol speel. Vir hierdie tegnologie word ’n veld heliostate gebruik om sonstraling na die ontvanger wat aan die bopunt van die toring geleë is te reflekteer. ’n Omvattende hersiening het daarop gewys dat kontemporêre ontwerpe van die ontvangers ’n aantal geometriese kompleksiteite, ’n tekort aan termiese doeltreffendheid sowel as probleme in terme van duursaamheid en koste in die gesig staar. Die doel van die studie is om ’n nuwe ontvangerskonsep te ontwikkel wat moontlik hierdie probleme kan verminder. ’n Parametriese analise is gebruik om potensiële maniere van verbetering aan te dui wat gebaseer is op ’n energiebalans benadering; insluitend sensitiwiteite betrokke by konvektiewe en stralingswarmteoordrag. Ontwerpkriteria soos die gebruik van spruitstukke om drukverliese te minimaliseer is ook ondersoek. Gebaseer op hierdie bevindinge is die hibriede saamgepersde-lug ontvanger ontwikkel. Laasgenoemde is ’n kombinasie van buis- en volumetriese ontvangertegnologie. Die fundamentele idee van die ontvanger is ondersoek deur straalberekening asook die gelyktydige natuurlike konveksie en stralingswarmteoordrag te simuleer. Die straalberekeningsresultate het getoon dat die gebruik van kwarts glas ’n moontlike oplossing is om hoër stralingsintensiteit te bereik, maar met refleksieverliese in die orde van 7 %. Die gelyktydige natuurlike konveksie en stralingswarmteoordrag simulasie het verder aan die lig gebring dat die ontvangerkonsep die ontsnapping

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This thesis investigates the feasibility of the laser Doppler vibrometer (LDV) for use in the autonomous auscultation of the human heart. As a non-contact measurement device, the LDV could become a very versatile biomedical sensor. LDV, stethoscope, piezoelectric accelerometer (PA) and electrocardiogram (ECG) signals were simultaneously recorded from 20 volunteers at Tygerberg Hospital. Of the 20 volunteers, 17 were confirmed to have cardiovascular disease. 3 patients with normal heart sounds were recorded for control data. The recorded data was successfully denoised using soft threshold wavelet denoising and ensemble empirical mode decomposition. The LDV was compared to the PA in common biomedical applications and found to be equally accurate. The heart sound cycles for each participant were segmented using a combination of ECG data and a simplicity curve. Frequency domain features were extracted from each heart cycle and input into a k-nearest neighbours classifier. It was concluded that the LDV can form part of an autonomous, non-contact auscultation system. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die haalbaarheid daarvan om die laser Doppler vibrasiemeter (LDV) vir die outonome beluistering van die menslike hart te gebruik. As 'n kontaklose meettoestel kan die LDV werklik 'n veelsydige biomediese sensor word. Twintig vrywilligers by die Tygerberg Hospitaal se LDV-, stetoskoop-, piësoelektriese versnellingsmeter (PV)- en elektrokardiogram (EKG) seine is gelyktydig opgeneem. Uit die 20 vrywilligers was daar 17 bevestigde gevalle van kardiovaskulêre siektes. Die data van drie pasiënte met normale hartklanke is as kontroledata opgeneem. Geraas is suksesvol uit die opgeneemde data verwyder deur 'n kombinasie van sagtedrempelgolf en saamgestelde empiriese modus ontladingstegnieke. Die LDV was vergelyk met die PV vir algemene biomediese gebruike en daar was gevind dat dit vergelykbare akkuraatheid het. Die hartklanksiklusse van elke deelnemer is gesegmenteer deur EKG data en 'n eenvoudskromme te kombineer. Frekwensiegebiedskenmerke is uit elke hartsiklus onttrek en in 'n k-naastebuurpunt klassifiseerder ingevoer. Daar is tot die gevolgtrekking gekom dat die LDV deel van 'n outonome, kontaklose beluisteringstelsel kan uitmaak.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The RoboCup offers a research platform to advance robotics and multi-robot cooperation in dynamic environments. This project builds on work previously done to develop a research platform for multi-robot cooperation at Stellenbosch University. This thesis describes the development of an active ball handling system for a robot in the RoboCup Small Size League (SSL). This was achieved by building on the work done in the previous projects. The hardware for the kicker and dribbler mechanisms on the robot were implemented and tested to characterise their capabilities. The kicker was characterised to control the speed at which a ball is kicked and the dribbler for optimal control over a ball. More accurate movement was required and the Proportional Integral and Derivative (PID) controllers for translational and rotational movement on the robot were improved. The test results show an improvement in straight line trajectory tracking when compared to those of the previous controllers. Dribble control sensors were implemented on the robot for successful dribbling by the robot. This resulted in a significant improvement to the dribbling ability of the robot when these sensors are used. This dribbling ability was compared to the dribbling ability of the robot when no feedback was received from the sensors. Lastly a proposed curved trajectory tracking algorithm was tested by combining translational and rotational movement of the robot. This algorithm showed the capabilities of the robot to follow a curved trajectory with the improved translational and rotational controllers. / AFRIKAANSE OPSOMMING: Die RoboCup bied ’n navorsingsplatvorm om robotika en multi-robot samewerking in ’n dinamiese omgewing te bevorder. Hierdie projek bou voort op werk wat reeds gedoen is om ’n navorsingsplatvorm vir multi-robot samewerking aan die Universiteit van Stellenbosch te ontwikkel. Hierdie tesis beskryf die ontwikkeling van ’n aktiewe balhanteringsstelsel vir ’n robot in die RoboCup Klein Liga (KL). Dit is bereik deur voort te bou op die werk wat in vorige projekte gedoen is. Die hardeware vir die skopper- en dribbelmeganismes is geïmplementeer en getoets om hulle vermoëns te karakteriseer. Die skopper is gekenmerk deur die spoed waarteen ’n bal geskop word en die dribbler vir optimale beheer oor ’n bal. Meer akkurate beweging was nodig en die PID-beheerders vir translasie- en rotasiebeweging in die robot is verbeter. Die resultate van die toetse toon ’n verbetering in reguitlynbeweging in vergelyking met dié van die vorige beheerders. Dribbelbeheersensors is in die robot geïmplementeer vir suksesvolle dribbelbeweging deur die robot. Gevolglik is daar ’n aansienlike verbetering in die dribbelvermoë van die robot wanneer hierdie sensors gebruik word. Hierdie dribbelvermoë is vergelyk met die dribbelvermoë wanneer die robot geen terugvoer van die sensors ontvang nie. Laastens is ’n voorgestelde algoritme vir die robot om ’n geboë trajek te volg, getoets. Dit is bereik deur die translasie- en die rotasiebeweging van die robot te kombineer. Hierdie algoritme het die vermoë van die robot om ’n geboë baan te laat volg deur gebruik te maak van die verbeterde translasie- en rotasiebeheerders.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: A measurement device was developed to accurately determine the pneumatic power performance of an Oscillating Water Column (OWC) model in a wave flume. The analysis of the pneumatic power is significant due to the wave-topneumatic energy being the primary energy conversion process and where the most energy losses can be expected. The aim of the research study is to address the accurate pneumatic power measurement of unsteady and bidirectional airflow in OWC model experiments. The two fundamental measurements required for the pneumatic power measurement are the pressure difference over an orifice on the OWC model and the volumetric flow rate of air through the outlet. The designed, constructed and assembled measurement device comprised of a venturi flow meter, containing a hot-film anemometer, which could measure the pressure drop and the volumetric flow rate in one device. The assembled pneumatic power measurement device was calibrated in a vertical wind tunnel at steady state. The results from the calibration tests showed that the volumetric flow rate measurements from the pneumatic power measurement device was accurate to within 3 % of the wind tunnel’s readings. The pneumatic power measurement device was incorporated onto a constructed Perspex physical model of a simple OWC device. This assembled system was used as the test unit in the wave flume at Stellenbosch University (SUN). The results from the experimental tests underwent comparative analysis with three analytical OWC air-flow models which were simulated as three scenarios using Matlab Simulink. These results showed that the measurement device has the ability to measure the pneumatic power but there is difficulty in modelling the complex air-flow system of the OWC device. This results in varying levels of agreement between the experimental and simulated pneumatic power results. The research study has revealed that there is difficulty in designing an accurate device for a wide range of test parameters due to the variance in output values. The unsteady and bidirectional nature of the air flow is also difficult to accurately simulate using a one-dimensional analytical model. Recommendations for further investigation are for CFD systems to be used for the analysis of the air-flow in an OWC system and to be used to validate future pneumatic power measurement devices. / AFRIKAANSE OPSOMMING: ‘n Meetinstrument was ontwikkel om die pneumatiese kraglewering van ‘n model van die Ossillerende Water Kolom (OWK) golfenergie omsetter in ‘n golf tenk akkuraat te meet. Dit is belangrik om die omskakeling van golf na pneumatiese energie te analiseer siende dat die grootste energieverlies in dié proses plaasvind. Die doel van hierdie navorsingsprojek was om die akkurate pneumatiese kragmeting van variërende en twee-rigting vloei van lug in ‘n OWK model na te vors. Die twee fundamentele metings wat benodig word vir die pneumatiese kragbepaling is die drukverskil oor die vloei vernouing en die volumetriese vloeitempo van lug deur die uitlaat van die toetstoestel. Die spesiaal ontwerpte meettoestel wat gebruik is in die eksperiment het bestaan uit ‘n venturi vloeimeter wat ‘n verhitte-film anemometer bevat het wat die drukverandering en die volumetriese vloeitempo kan meet in ‘n enkele instrument. Die pneumatiese kragmeting was gekalibreer in ‘n vertikale windtonnel waarin ‘n konstante vloei tempo geïnduseer was. Die kalibrasieproses het bevestig dat die meettoestel metings lewer met ‘n fout van minder as 3 % wanneer dit vergelyk word met die bekende konstante vloei tempo soos bepaal in die windtonnel. ‘n Fisiese model van ‘n vereenvoudigde OWK golfenergie omsetter was ontwerp en gebou uit Perspex om as toetstoestel te gebruik vir die evaluering van die ontwerpte pneumatiese kraglewering meettoestel. Die toetse was uitgevoer in ‘n golftenk by die Universiteit Stellenbosch (SUN). The toetsresultate was vergelyk met drie ander OWK lugvloei modelle wat gesimuleer was deur om die analitiese modelle op te stel en te simuleer in Matlab Simulink. Die vergelyking van modellering resultate het gewys dat die meettoestel die vermoë het om pneumatiese krag te meet. Daar was wel komplikasies met die modellering van die komplekse lugvloei in die OWK toestel, die resultate het geen definitiewe ooreenstemming gewys tussen die eksperimentele en gesimuleerde pneumatiese krag resultate nie. Die navorsingsprojek het gewys dat daar komplikasies is om ‘n enkel toestel te ontwerp wat oor ‘n wye bereik kan meet weens die variasie van die verskillende parameters. Die variërende en twee-rigting lugvloei is ook moeilik om akkuraat te simuleer met ‘n een-dimensionele analitiese simulasie model. Aanbevelings vir verdere navorsing sluit in om die lugvloei in die OWK stelsel te modelleer en te analiseer in ‘n drie-dimensionele model om die lesings van ‘n pneumatiese krag meettoestel te bevestig.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The steam-side side operation of a practical air-cooled steam condenser is investigated using a combination of CFD, numerical, analytical and experimental methods. Particular attention is directed towards the vapor flow distribution in the primary condensers and dephlegmator performance. Analysis of the vapor flow in the distributing manifold, connecting the steam turbine exhaust to the air-cooled heat exchangers, highlights the importance of careful design of the guide vanes in the manifold bends and junctions. Improved guide vane design and configuration can reduce the steam-side pressure drop over the manifold and improve the vapor flow distribution, which may be beneficial to condenser operation. The vapor flow in the primary condensers is shown to exhibit a non-uniform distribution amongst the heat exchanger tubes. The vapor flow distribution is strongly linked to the distribution of tube inlet loss coefficients through the heat exchanger bundles. The non-uniform flow distribution places an additional demand on dephlegmator performance, over and above the demands of row effects in the case of multi-row primary condenser bundles. Row effects are shown to account for as much as 70 % of available dephlegmator capacity in this case. Simultaneously, inlet loss coefficient distributions can account for up to 30 % of dephlegmator capacity. In some situations then, the dephlegmator is fully utilized under ideal operating conditions and there is no margin of safety to cope with non-ideal operation of the primary condensers. The upstream regions of the primary condensers are therefore exposed to a high risk of undesirable noncondensable gas accumulation. Reduced dephlegmator capacity due to insufficient ejector performance may further compound this problem. Single-row primary condenser bundles eliminate row effects and thereby significantly reduce the demands on dephlegmator performance. The use of such bundles in the dephlegmator would also measurably reduce ejector loading. In light of the findings of this study, it is recommended that single-row bundles be considered as the primary option for future air-cooled condenser applications. A hybrid (dry/wet) dephlegmator concept is analysed and shown to be able to provide measurably enhanced dephlegmator performance when operating in wet mode, while consuming only a small amount of water. The enhanced dephlegmator cooling translates to an increase in total air-cooled condenser capacity of up to 30 % at high ambient temperatures in this case. The benefit of this enhanced cooling capacity to steam turbine output may be significant. The hybrid dephlegmator concept therefore offers a simple, cost-effective and sustainable solution to the issue of reduced air-cooled condenser performance during hot periods. Careful design of the first and second stage bundle configurations in the hybrid dephlegmator is necessary to avoid flooding in the first stage during wet operation of the second. Furthermore, the slightly poorer dry-operation performance of the hybrid dephlegmator results in increased risk of non-condensable gas accumulation in multi-row primary condensers. Again, single-row primary condenser bundles would lay rest to such concerns. / AFRIKAANSE OPSOMMING: Die bedryf aan die stoom-kant van ʼn praktiese lugverkoelde-stoomkondensor word ondersoek met behulp van 'n kombinasie van berekeningsvloeimeganika, numeriese, analitiese en eksperimentele metodes. ʼn Spesifieke fokus word geplaas op die dampvloeiverspreiding in die primêre kondensors asook die deflegmatorwerksverrigting. Ontleding van die damp vloei in die verdeelspruitstuk, wat die uitlaat van die stoomturbine aan die lugverkoelde-stoomkondensor koppel, beklemtoon die belangrikheid van noukeurige ontwerp van die leilemme in die spruitstukdraaie en aansluitings. Verbeterde leilemontwerp en opstelling kan die drukval aan die stoom-kant van die draaie en aansluitings verminder en die dampvloeiverspreiding verbeter. Dit kan gevolglik lei tot verbeterde werksverrigting van die kondensor. Die studie toon dat ʼn nie-eenvormige dampvloeiverspreiding in die warmteruilerbuise van die primêre kondensors bestaan. Die verspreiding van buisinlaat-verlieskoëffisiënte deur die bundels van die warmteruiler is sterk afhanklik van die voorgenome dampvloeiverspreiding. Die nie-eenvormige vloeiverspreiding veroorsaak 'n groter aanvraag na deflegmator-werksverrigting, bo-en-behalwe nog vereistes van ry-effekte in die geval waar multi-ry-bundels vir primêre kondensors gebruik word. Ry-effekte is verantwoordelik vir so veel as 70 % van die beskikbare deflegmator kapasiteit. Terselfdertyd kan die verspreiding van inlaat-verlieskoëffisiënte verantwoordelik wees vir tot 30 % van die deflegmator kapasiteit. In sommige gevalle is die deflegmator dus ten volle aangewend onder ideale bedryfstoestande, en bestaan daar geen band van veiligheid om nie-ideale werksverrigting van die primêre kondensor te hanteer nie. Sekere dele van die stroom-op primêre kondensors word dus blootgestel aan 'n hoë risiko vir die opbou van ongewenste nie-kondenseerbare gasse. Verder kan ‘n vermindering in deflegmator kapasiteit, weens onvoldoende werksverrigting van die vakuumpompe, dié probleem vererger. Enkel-ry-bundels vir primêre kondensors vermy ry-effekte en lei sodoende tot ʼn aansienlike vermindering in die aanvraag na deflegmator-werksverrigting. Die gebruik van sulke bundels in die deflegmator sou die vakuumpomplas ook meetbaar verminder. Uit die bevindinge van hierdie studie word dit aanbeveel dat enkel-ry bundels beskou word as die primêre opsie vir toekomstige lugverkoelde-kondensor aansoeke. ’n Konsep vir ’n hibriede-deflegmator (droog/nat) word ontleed. Die studie toon dat, deur hierdie konsep in die nat-modus te gebruik, ’n meetbare verbetering in deflegmator-werksverrigting gesien kan word, ten koste van net ʼn klein hoeveelheid waterverbruik. Die verbetering in verkoelingsvermoë van die deflegmator beteken ʼn toename van tot 30 % in die totale verkoelingsvermoë van die lugverkoelde-kondensor gedurende periodes wanneer hoë omgewingstemperature heersend is. Die voordeel van hierdie verbeterde verkoelingsvermoë op die werksuitset van die stoomturbine kan beduidend wees. Die konsep vir ’n hibriede-deflegmator bied dus 'n eenvoudige, koste-effektiewe en volhoubare oplossing vir warm atmosferiese periodes, wanneer die lugverkoelde-kondensor se verkoelingsvermoë afneem. Noukeurige ontwerp van die eerste en tweede fase bundelkonfigurasies in die hibriede-deflegmator is nodig om oorstroming in die eerste fase, tydens nat werking van die tweede fase, te verhoed. Verder veroorsaak die effens swakker werksverrigting, gedurende die bedryf van die hibriede-deflegmator in die droog-modus, ʼn verhoogde risiko vir die opbou van nie-kondenseerbare gasse in multi-ry primêre kondensors. Weereens sal enkel-ry-bundels in primêre kondensors hierdie probleem oplos.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The design, development and evaluation of a novel wave energy converter (WEC) device, called the ShoreSWEC, in a South African port development is presented. Based on the device requirements, site selection criteria were specified and applied to identify a suitable deployment location. A wave modeling procedure was developed to determine the operational wave conditions and available wave power resource at the selected location. The site was found to have a low mean annual average resource of approximately 2.3 kilowatt per meter wave crest (kW/m) due to its relatively sheltered location. The wave model was further used to determine design storm conditions and a structural stability analysis of the device was conducted. Experimental tests were performed to evaluate the hydrodynamic conversion efficiency of a single chamber of the device at its most conservative orientation, under a variety of wave energy conditions. The effect of a floor incline and an additional chamber on the performance of the system was investigated. The incline improved efficiency for low wave heights, making it ideal for the low wave power resource conditions of the site, whilst the multi-chamber system experienced increased performance at high wave periods. A comparison between the ShoreSWEC and a conventional oscillating water column (OWC) WEC showed that the OWC extracted 72% more energy, highlighting the sensitivity of performance on device orientation. A three-dimensional (3D) numerical model of the experimental setup was developed. The numerical model provided comparable water surface elevations inside the flume and chamber, yet predicted significantly higher internal chamber pressures and overall efficiency. The electricity generation potential of a 10 chamber ShoreSWEC at the specified location, approximated from the experimental results and 11 years of hindcast wave data, was found to be 6 kW on average for a 15 kW capacity system. Results of this study highlighted the need for greater understanding of the hydrodynamic characteristics of a full length device. Experimental tests in a 3D wave basin on a scaled full length ShoreSWEC model are therefore recommended. Once conducted, South Africa will be one step closer to the deployment of the full scale SWEC device. / AFRIKAANSE OPSOMMING: Die ontwerp, ontwikkeling en evaluasie van ‘n unieke golfenergieomsetter (GEO), genaamd die ShoreSWEC, in ‘n Suid-Afrikaanse haweontwikkeling word aangebied. Terrein evaluasie kriteria, gebaseer op die omsettervereistes, is ontwikkel en toegepas om die mees belowende terrein te identifiseer. ‘n Golfmodeleringsprosedure is ontwikkel om die operasionele golfkondisies en beskikbare golfdrywinghulpbron te bepaal. Daar is gevind dat die terrein ‘n lae gemiddelde golfdrywing van bykans 2.3 kilowat per meter golfkruin het as gevolg van die beskutte ligging. Die golfmodel is verder gebruik om ontwerpstormkondisies te bepaal en ‘n stabiliteitsanalise was op die toestel struktuur uitgevoer. Eksperimentele toetse van verskeie golfenergie kondisies is gedoen om die hidrodinamiese omsettingseffektiwiteit van ‘n enkel kamer van die toestel te bepaal teen sy konserwatiefste orientasie. Die effek van ‘n vloerhelling en ‘n addisionele kamer op die uitsette van die sisteem is ondersoek. Die helling het effektiwiteit verbeter vir lae golfhoogtes wat dit ideaal maak vir die lae hulpbron by die terrein, terwyl die veelvoudige-kamer-sisteem beter gevaar het by hoë golfperiodes. ‘n Vergelyking tussen die ShoreSWEC en ‘n konvensionele ossilerende waterkolom (OWK) GEO het gewys dat die OWK 72% meer energie onttrek. Dit beklemtoon die sisteem se sensitiwiteit vir die inkomende golfrigting. ‘n Drie-dimensionele (3D) numeriese model van die eksperimentele opstelling is ontwikkel. Die numeriese model het aansienlik hoër drukke binne die kamer, en gevolglik algehele effektiwiteit, voorspel as die eksperimentele toetse. Die elektriese opwekkingskapasiteit van ‘n 10 kamer ShoreSWEC by die terrein, gebaseer op die eksperimentele resultate en 11 jaar se golfdata, is bereken as 6 kW gemiddeld vir ‘n 15 kW kapasiteit stelsel. Die bevindinge van hierdie studie het die behoefte aan ‘n beter begrip van die hidrodinamiese eienskappe van ‘n vollengte sisteem beklemtoon. Eksperimentele toetse in ‘n 3D golfbak op ‘n geskaleerde vollengte ShoreSWEC model word dus aanbeveel. Sodra dit voltooi is, sal Suid-Afrika een stap nader wees aan die ontplooiing van ‘n volskaalse SWEC toestel.

Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Concentrating solar power plants are a promising means of generating electricity. However, they are dependent on the sun as a source of energy, and require thermal storage to supply power on demand. At present thermal storage – usually molten salt – although functional, is expensive, and a cheaper solution is desired. It is proposed that sensible heat storage in a packed bed of rock, with air as heat transfer medium, is suitable at temperatures of 500 – 600 °C. To determine if this concept is technically feasible and economically competitive with existing storage, rock properties, packed bed pressure drop and thermal characteristics must be understood. This work addresses these topics. No previously published data is available on thermal cycling resistance of South African rock, and there is limited data from other countries in the proposed temperature range for long-term thermal cycling, so samples were thermally cycled. There is rock which is suitable for thermal storage applications at temperatures of 500 – 600 °C. New maps of South Africa showing where potentially suitable rock is available were produced. Dolerite, found extensively in the Karoo, is particularly suitable. Friction factors were measured for beds of different particles to determine the importance of roughness, shape, and packing arrangement. Five sets of rock were also tested, giving a combined dataset broader than published in any previous study. Limitations of existing correlations are shown. The friction factor is highly dependent on particle shape and, in the case of asymmetric particles, packing method. The friction factor varied by up to 70 % for crushed rock depending on the direction in which it was poured into the test section, probably caused by the orientation of the asymmetric rock relative to the air flow direction. This has not been reported before for rock beds. New isothermal correlations using the volume equivalent particle diameter are given: they are within 15 % of the measurements. This work will allow a techno-economic evaluation of crushed rock beds using more accurate predictions of pumping power than could previously be made. Thermal tests below 80 °C show that bed heat transfer is insensitive to particle shape or type. A heat transfer correlation for air in terms of the volume equivalent diameter was formulated and combined with the E-NTU method. The predicted bed outlet temperatures are within 5 °C of the measurements for tests at 530 °C, showing that the influence of thermal conduction and radiation can be reasonably negligible for a single charge/discharge cycle at mass fluxes around 0.2 kg/m2s. A novel method for finding the optimum particle size and bed length is given: The Biot number is fixed, and the net income (income less bed cost) from a steam cycle supplied by heat from the bed is calculated. A simplified calculation using the method shows that the optimum particle size is approximately 20 mm for bed lengths of 6 – 7 m. Depending on the containment design and cost, the capital cost could be an order of magnitude lower than a nitrate salt system. / AFRIKAANSE OPSOMMING: Gekonsentreerde son-energie kragstasies is n belowende manier om elektrisiteit op te wek, maar hulle is afhanklik van die son as n bron van energie. Om drywing op aanvraag te voorsien moet hulle energie stoor. Tans is termiese stoor – gewoonlik gesmelte sout – hoewel funksioneel, duur, en n goedkoper oplossing word gesoek. Daar word voorgestel dat stoor van voelbare warmte-energie in n gepakte rotsbed met lug as warmteoordrag medium geskik is by temperature van 500 – 600 °C. Om te bepaal of dié konsep tegnies gangbaar en ekonomies mededingend met bestaande stoorstelsels is, moet rotseienskappe, gepakte bed drukval en hitteoordrag verstaan word. Hierdie werk spreek hierdie aspekte aan. Geen voorheen gepubliseerde data is beskikbaar oor die termiese siklus weerstand van Suid-Afrikaanse rots nie, en daar is beperkte data van ander lande in die voorgestelde temperatuurbereik, dus is monsters onderwerp aan termiese siklusse. Daar bestaan rots wat geskik is vir termiese stoor toepassings by temperature van 500 – 600 °C. Nuwe kaarte van Suid-Afrika is opgestel om te wys waar potensieel geskikte rots beskikbaar is. Doleriet, wat wyd in die Karoo voor kom, blyk om veral geskik te wees. Wrywingsfaktore is gemeet vir beddens van verskillende partikels om die belangrikheid van grofheid, vorm en pak-rangskikking te bepaal. Vyf rotsstelle is ook getoets, wat n saamgestelde datastel gee wyer as in enige gepubliseerde studie. Beperkings van bestaande korrelasies word aangetoon. Die wrywingsfaktor is hoogs sensitief vir partikelvorm en, in die geval van asimmetriese partikels, pakkings metode. Die wrywingsfaktor het met tot 70 % gevarieer vir gebreekte rots, afhanklik van die rigting waarin dit in die toetsseksie neergelê is. Dit is waarskynlik veroorsaak deur die oriëntasie van die asimmetriese rots relatief tot die lugvloei rigting, en is nie voorheen vir rotsbeddens gerapporteer nie. Nuwe isotermiese korrelasies wat gebruik maak van die volume-ekwivalente partikel deursnee word gegee: hulle voorspel binne 15 % van die gemete waardes. Hierdie werk sal n tegno-ekonomiese studie van rotsbeddens toelaat wat meer akkurate voorspellings van pompdrywing gebruik as voorheen moontlik was. Termiese toetse onder 80 °C wys dat die warmteoordrag nie baie sensitief is vir partikelvorm en -tipe nie. n Warmte-oordragskorrelasie vir lug in terme van die volume-ekwivalente deursnee is ontwikkel en met die E-NTU-metode gekombineer. Die voorspelde lug uitlaat temperatuur is binne 5 °C van die meting vir toetse by 530 °C. Dit wys dat termiese geleiding en straling redelikerwys buite rekening gelaat kan word vir n enkele laai/ontlaai siklus by massa vloeitempos van omtrent 0.2 kg/m2s. n Oorspronklike metode vir die bepaling van die optimum partikelgrootte en bedlengte word gegee: Die Biot-getal is vas, en die netto inkomste (die inkomste minus die bed omkoste) van n stoomsiklus voorsien met warmte van die bed word bereken. n Vereenvoudigde berekening wat die metode gebruik wys dat die optimum grootte en lengte ongeveer 20 mm en 6-7 m is. Afhangende van die behoueringsontwerp en koste, kan die kapitale koste n orde kleiner wees as dié van n gesmelte nitraatsout stelsel

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Central receiver power plants generate renewable electricity by exploiting the energy provided by the sun. The conditions experienced in the Northern Cape region of South Africa provide the ideal conditions for the development of these plants. Without a storage medium these plants have capacity factors in the range of 25-30%. The inclusion of a thermal energy storage medium provides the ability to increase the capacity factors of these plants. Although storage increases the costs, it results in better utilisation of the power block and a decrease in the levelised electricity cost (LEC). Eskom intends building a 100MWe central receiver dry cooled power plant in the Upington region. This research identifies the appropriate storage medium and ideal storage capacity to achieve the lowest LEC. A literature survey was performed to identify the different methods of storage that are available. The different storage methods were evaluated and the best storage medium for a central receiver power plant based on the developments of the various storage technologies was identified. To determine the costs associated with a central receiver power plant, data published by NREL was used. Different plant parameters were required to evaluate the costs. A power plant model based on efficiencies and energy balances was created to determine the required plant parameters. It provided the ability to determine the effect of changing different plant parameters on the LEC and estimate the plant output. The power block parameters were initially varied to determine the most efficient power block configuration. Once the most efficient power block configuration was identified the solar field and storage parameters were varied to determine the plant configuration which resulted in the lowest LEC. The most efficient power block configuration of 0.4206 was found for a system comprising of six feedwater heaters with the feedwater temperature of 230°C, main steam pressure 140 bar and an exit steam generator salt temperature of 290°C. A solar multiple of 3.0 with 16 hours of storage resulted in a LEC of R1.41/kWh with no system constraints. A capacity factor constraint of 60% resulted in a solar multiple of 1.8 with 8 hours of storage and a LEC of R1.78/kWh. / AFRIKAANSE OPSOMMING: Sonkragaanlegte met sentrale ontvangers wek hernubare elektrisiteit op deur sonenergie te ontgin. Die klimaat in die Noord Kaap-streek van Suid-Afrika is ideaal vir die oprigting van hierdie aanlegte. Sonder ’n bergingsmedium is die kapasiteitsfaktore van sulke aanlegte ongeveer 25-30%. Met die insluiting van ’n bergingsmedium vir termiese energie kan die kapasiteitsfaktore egter verhoog word. Hoewel berging aanlegkoste verhoog, lei dit terselfdertyd tot beter aanwending van die kragblok en ’n afname in die konstante eenheidskoste van elektrisiteit (LEC). Eskom beplan om ’n droogverkoelde kragaanleg van 100 MW met ’n sentrale ontvanger in die Upington-streek op te rig. Hierdie navorsing was dus daarop toegespits om die mees geskikte bergingsmedium en ideale bergingskapasiteit te bepaal om die laagste moontlike LEC uit die aanleg te verkry. ’n Literatuurstudie is onderneem om die verskeie beskikbare bergingsmetodes te bestudeer. Die verskillende metodes is beoordeel, waarna die beste bergingsmedium vir ’n kragaanleg met ’n sentrale ontvanger op grond van die ontwikkelings in die verskillende bergingstegnologieë bepaal is. Om die koste van ’n kragaanleg met ’n sentrale ontvanger te bepaal, is gepubliseerde data van die Amerikaanse Nasionale Laboratorium vir Hernubare Energie (NREL) gebruik. Verskillende aanlegparameters was egter nodig om die koste te beoordeel. Dié parameters is gevolglik bepaal deur ’n kragaanlegmodel op grond van doeltreffendheidsfaktore en energiebalanse te skep. Sodoende kon vasgestel word watter uitwerking veranderinge in die verskillende parameters op die LEC sou hê, en kon die aanleguitset geraam word. Die kragblokparameters is aanvanklik afgewissel om die doeltreffendste kragbloksamestel te bepaal. Nadat dít bepaal is, is die sonenergieveld en bergingsparameters weer afgewissel om vas te stel watter aanlegsamestel die laagste LEC tot gevolg sou hê. Die beste termiese benuttingsgraad is behaal vir ʼn stoom siklus met ses water verhitters en ʼn water temperatuur van 230 °C by die ketel se inlaat, ʼn stoom druk van 140 bar, en sout uitlaat temperatuur van 290 °C. ʼn Vermenigvuldigingsfaktor van drie vir die heliostaat veld, en 16 uur termiese energie storing gee ʼn opwekkingskoste van R 1.41/kW/h indien daar geen beperkings op die grootte of koste van die stelsel geplaas word nie. Indien die kapitaal uitgawe ʼn perk van 60 % op die kapasitiet van die stelsel plaas, verander die optimale ontwerpspunt na ʼn vermenigvuldigingsfaktor van 1.8, en die termiese stoorkapasitiet verlaag na 8 uur. In hierdie geval is die opwekkingskoste R 1.78/kWh.