Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Minimally Invasive Surgery (MIS) in human beings is performed by making small incisions in the abdominal region of the patient and inflating the abdominal cavity with CO2. This procedure enables the surgeon to manipulate long rigid surgical instruments inside the patient in order to perform the surgery. Unfortunately the current methods of insertion and assembly of MIS instruments limit the surgeon to only five (of a possible seven) Degrees of Freedom (DOF). Along with this, the surgeon’s movements are mirrored (called the Fulcrum effect) and scaled around the point of incision. Minimally invasive surgical robots attempt to alleviate these drawbacks by eliminating the Fulcrum effect, as well as improving dexterity and accuracy. These robots’ abilities to improve the surgeon’s hand-eye coordination, enables the surgeon to perform surgeries using their natural movements with reduced fatigue. As a result of this, the risk to both patient and surgeon is reduced. Existing MIS robotic systems are extremely expensive and large, and as a result they are not widely used. In this thesis a new, lower cost, seven DOF robotic manipulator is further developed. The thesis focuses on the external three DOF Secondary Slave Manipulator (SSM) and combines it with the Primary Slave Manipulator (PSM) that was developed by a previous Masters student. Tests done on the SSM showed that the manipulator has a minimum resolution of 0.7 ± 0.2 mm (mean ± standard deviation) on the shoulder joint’s yaw rotation and 0.5 ± 0.2 mm in pitch rotation. The linear actuator used for insertion has a minimum resolution of 0.2 ± 0.2 mm. A strength test was also conducted and showed that the manipulator is easily capable of producing a 10 N actuation force as required during Minimally Invasive Robotic Surgery (MIRS) procedures. In conclusion the complete system has potential as a viable alternative to the existing systems due to its accuracy and lower cost. Future work will include the development of a user interface and control system for the complete robot. / AFRIKAANSE OPSOMMING: Minimaal Indringende Chirurgie (MIC) op mense word uitgevoer deur klein insnydings in die pasiënt se buik te maak en dan die abdominale holte met CO2 te vul. Dit stel die chirurg in staat om lang, onbuigbare instrumente binne die pasiënt te manipuleer om sodoende die operasie uit te voer. Die manier waarop die MIC instrument ontwerp is en die pasiënt binnegaan, laat egter slegs vyf vryheidsgrade toe, terwyl die chirurg self sewe vryheidsgrade in sy handbewegings het. Verder veroorsaak hierdie instrumente ook dat die chirurg se aksies in spieëlbeeld vertolk word (Fulcrum effek) en geskaleer is. Chirurgiese robotika poog om hierdie nadele teen te werk deur die Fulcrum effek te verwyder, en ook om handvaardigheid en akkuraatheid te bevorder. Die robot se potensiaal om die chirurg se hand-oog koӧrdinasie te verbeter, maak dit moontlik vir die chirurg om op ’n meer natuurlike en gemaklike manier te werk te gaan en bring minder vermoeienis mee. Dit verminder die risiko’s vir beide die pasiënt en die chirurg. Bestaande robotiese stelsels is egter baie duur en groot, en word dus nie meer algemeen gebruik nie. In hierdie tesis word ‘n nuwe sewe-vryheidsgraad robotiese manipuleerder ontwikkel. Die tesis fokus op die eksterne drie-vryheidsgraad Sekondêre Slaaf Manipuleerder (SSM) en kombineer dit met die Primêre Slaaf Manipuleerder (PSM) wat deur ʼn vorige Meestersstudent ontwikkel is. Toetse wat uitgevoer is op die SSM het getoon dat dit ’n minimum resolusie van 0.7 ± 0.2 mm (gemiddeld ± standaard afwyking) op die skouer se afwyking en 0.5 ± 0.2 mm om die onderskeie skouer aslyne toon. Die linieêre aktueerder wat vir inlassing gebruik word het ’n minimum resolusie van 0.2 ± 0.2 mm. ’n Sterktetoets is uitgevoer en het getoon dat die manipuleerder maklik die nodige 10 N krag soos benodig in Minimaal Indringende Robotiese Chirurgie (MIRC) prosedures kan lewer. Ter afsluiting, die volledige stelsel het die potensiaal as lewensvatbare alternatief tot die bestaande stelsels vanweë die akkuraatheid en laer koste verbonde. Toekomstige navorsing kan moontlik die ontwikkeling van ʼn gebruikerkoppelvlak en beheerstelsel vir die volledige robot insluit.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In percutaneous procedures, where the surgeon inserts a needle into a target in the patient, it is challenging to access the target at the rst attempt. Repeated needle insertion attempts are highly undesirable, as they lead to increased theatre time, patient haemorrhage and radiation exposure. The proposal of this thesis was to develop a low-cost system to aid surgeons with the process of positioning and orientating the needle prior to insertion. The proposed system uses a stereo pair of images produced by a standard C-arm uoroscope. By applying computer vision techniques, such as triangulation, the desired needle position and orientation are determined from the set of images. An articulated manipulator is used to position and orientate the needle. The surgeon makes selections on the images, via a graphical user interface (GUI), to indicate the desired position and orientation of the needle. Following these selections, an algorithm determines the necessary angles for the manipulator. The surgeon then positions the manipulator accordingly. Results from tests on a phantom showed the system to be repeatable and accurate to 2 mm. This is less accurate than similar, existing systems which, reported accuracies of 0:25 and 1:21 mm. However, 2 mm accuracy is considered adequate as it allows a range of percutaneous procedures to be performed such as needle biopsy, regional anaesthesia, brachytherapy and percutaneous nephrolithotomy (PCNL). Tests on both a phantom kidney and a porcine kidney indicated that the system can function in a real percutaneous procedure and with an anatomical target. The total cost to develop the prototype system was R15 000. The accuracy of the proposed system and the time to gain access to the target indicate that the system can be a bene cial aid to surgeons when performing percutaneous procedures. As minimal X-ray imaging is required, patients will also be spared excessive radiation exposure and theatre time. / AFRIKAANSE OPSOMMING: In perkutane prosedures, waar die chirurg 'n naald in 'n teiken op die pasiënt invoeg, is dit moeilik om met die eerste probeerslag toegang tot die teiken te bekom. Herhaalde pogings om die naald in te voeg is hoogs ongewens, aangesien dit tot verlengde teatertyd, bloeding by pasinte sowel as stralingsblootstelling lei. 'n Laekostestelsel is ontwikkel om chirurge by te staan met die proses om die naald voor invoeging te plaas en te oriënteer. Die stelsel gebruik 'n paar stereobeelde wat deur 'n standaard-C-arm- uoroskoop voortgebring word. Met behulp van rekenaarsigtegnieke, soos triangulasie, word die gewenste naaldposisie en -oriëntasie uit die stel beelde bepaal. 'n Geartikuleerde manipuleerder word gebruik om die naald te plaas en te oriënteer. Die chirurg voer die vereiste invoerdata deur middel van 'n gra ese gebruikerskoppelvlak (GGK) in, waarna 'n algoritme die vereiste hoeke vir die manipuleerder bepaal. Die chirurg plaas dan die manipuleerder dienooreenkomstig. Die resultate van toetse op 'n fantoom toon dat die stelsel herhaalbaar en tot op 2 mm akkuraat is. Dit is minder akkuraat as soortgelyke, bestaande stelsels, wat 'n akkuraatheid van 0:25 mm en 1:21 mm onderskeidelik aangemeld het. Tog kan akkuraatheid van 2 mm as voldoende beskou word, aangesien dit 'n verskeidenheid perkutane prosedures moontlik maak, soos naaldbiopsies, regionale anestesie, bragiterapie en perkutane nefrolitotomie (PCNL). Toetse op 'n fantoomnier dui daarop dat die stelsel wél in 'n werklike perkutane prosedure kan funksioneer. Toetse op 'n varknier toon dat die stelsel wél ook met 'n anatomiese teiken kan werk. Die totale koste om die prototipe te ontwikkel was R15 000. Die akkuraatheid van die voorgestelde stelsel en die tydsduur om toegang tot die teiken te bekom, dui daarop dat die stelsel 'n nuttige hulpmiddel kan wees vir chirurge wat perkutane prosedures uitvoer. Aangesien minimale Xstraalbeelding vereis word, sal dit pasiënte ook oormatige stralingsblootstelling en verlengde teatertyd spaar.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The thesis evaluates control strategies for reconfigurable manufacturing systems by using a welding assembly cell as a case study. The cell consists of a pallet magazine, conveyor, feeder subsystem (comprising an articulated robot and singulation unit), welder subsystem (which uses a modular Cartesian robot), and inspection and removal subsystems. The research focuses on control strategies that enhance reconfigurability in terms of structure, hardware and software using agent-based control and the IEC 61499 standard, based on PC control. Reconfiguration may occur when a new product is introduced, as well as when a new subsystem is introduced or removed from the production cell. The overall control architecture is that the subsystems retain no knowledge of the product, but product information resides in the cell controller, while services offered by the subsystems are registered with the directory facilitator of the Java agent platform. The control strategies are implemented on the modular Cartesian weld robot and the cell controller for assembly cell. A layered architecture with low-level control and high-level control is used to allow separation of concerns and rapid changes in both hardware and software components. The low-level control responds in hard real-time to internal and external events, while the high-level control handles soft real-time actions involving coordination of control related issues. The results showed IEC 61499 function blocks to be better suited to low-level control application in distributed systems, while agents are more suited for high-level control. Modularity in software components enhances hardware and software scalability. Additionally, agents can support online reconfiguration of reconfigurable machines. / AFRIKAANSE OPSOMMING: Die tesis evalueer beheerstrategieë vir herkonfigureerbare vervaardigingstelsels deur gebruik te maak van ’n sweismonteersel as ’n gevallestudie. Die sel bestaan uit ’n palletmagasyn, vervoerbande, voersubstelsel (bestaande uit ’n geartikuleerde robot en singulasie-eenheid), sweissubstelsel (wat gebruik maak van ’n modulêre Cartesiese robot), en inspeksie- en verwyderingsubstelsels. Die navorsing fokus op beheerstrategieë wat herkonfigureerbaarheid verhoog in terme van struktuur, hardeware en sagteware met behulp van agent-gebaseerde beheer en die IEC 61499 standaard, wat gebaseer is op PC-beheer. Herkonfigurasie mag voorkom wanneer ’n nuwe produk in-gestel word, sowel as wanneeer ’n nuwe substelsel bygevoeg of verwyder word van die produksiesel. Die oorhoofse beheerargitektuur is dat die substelsels geen kennis van die produk hou nie, maar die produkinligting in die selbeheerder geberg, terwyl dienste wat aangebied word deur die substelsels wat geregistreer is by die gidsfasiliteerder van die Java agent platform. Die beheerstrategië is geïmplementeer op die modulere Cartesiese sweisrobot en die selbeheerder vir die monteersel. ’n Gelaagde argitektuur met ’n lae-vlak beheer en hoë-vlak beheer word gebruik om skeiding van oorwegings en vinnige veranderinge in beide hardeware en sagteware komponente toe te laat. Die lae-vlak beheer reageer hard intyds op interne en eksterne gebeure, terwyl die hoë-vlak beheer sag intyds die koördinering van beheerverwante kwessies hanteer. Die resultate het getoon dat IEC 61499 funksie-blokke beter geskik is vir lae-vlak beheer toepassing in verspreide stelsels, terwyl agente meer geskik is vir hoë-vlak beheer. Modulariteit in sagteware komponente verhoog hardeware en sagteware skaleerbaarheid. Boonop kan agente ook aanlyn herkonfigurasie van herkonfigureerbare masjiene ondersteun.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The Council for Scientific and Industrial Research has developed a vibration excitation system. The system is designed to excite the rotor blades of an axial compressor in the specified vibration mode and at the specified frequency. The vibration excitation system was tested on Stellenbosch University’s Rofanco compressor test bench. A two-way staggered fluid-structure interaction (FSI) model was created that was capable of simulating the vibration of the rotor blades excited by the system. The results of the FSI model were verified using available experimental data. It was concluded that the FSI model is able to recreate the vibration excited by the system to within the desired level of accuracy. In addition, the results of the FSI model showed that the vibration excitation system should be able to excite the blades in the selected vibration mode and at the selected frequency provided that the excitation frequency is close the natural frequency of the first bending mode. The results also suggested that a transient computational fluid dynamics model should be sufficient for the prediction of the aerodynamic forces acting on the rotor blades. Furthermore, a one-way staggered FSI model should be adequate for calculating the motions of the blades. / AFRIKAANSE OPSOMMING: Die Wetenskaplike en Nywerheidnavorsingsraad het ’n vibrasie-opwekkingstelsel ontwerp om die rotorlemme van ’n aksiaalvloei kompressor in die gespesifiseerde vibrasiemodus en teen die gespesifiseerde frekwensie op te wek. Die vibrasieopwekkingstelsel is met behulp van die Universiteit Stellenbosch se Rofanco kompressortoetsbank getoets. Daarna is ’n tweerigting vloeistof-struktuur-interaksie model geskep om die vibrasie van die rotorlemme, wat deur die stelsel opgewek is, te simuleer. Beskikbare eksperimentele data is gebruik om die resultate van die vloeistof-struktuur-interaksie model te bevestig. Die gevolgtrekking is gemaak dat die model wél die vibrasie van die lemme met die nodige akkuraatheid kan simuleer. Die resultate van die vloeistof-struktuur-interaksie model toon ook dat die stelsel die lemme in die gekose vibrasiemodus en teen die gekose frekwensie behoort te kan opwek, solank die opwekkingsfrekwensie na aan die natuurlike frekwensie van die eerste buigmodus is. Voorts dui die resultate daarop dat ’n berekeningsvloeimeganika model die aërodinamiese laste van die lemme sal kan voorspel. ’n Eenrigting vloeistof-struktuur-interaksie model behoort voldoende te wees om die beweging van die rotorlemme te bereken.

Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The coating thermal conductivity, the effective coated-tube thermal conductivity and the coating factor of three artificial protective coatings (APCs) applied to condenser tubes are experimentally evaluated. This testing broadens the limited available knowledge of these coatings, which is necessary for effective condenser refurbishment and operation. The coatings are applied to 25.4 mm brass tubes at thicknesses of 44, 46, 50, and 130 μm. Steady state heat transfer tests are performed on these tubes fitted in a double-pipe counter-flow heat exchanger, with heated water in the annulus and coolingwater inside the tube. The experimentally determined thermal conductivities of the coatings range from 0.5 to 2.3 W/m·K. The effective coated-tube conductivity and the coating factor depend on the tube material and size, as well as the coating thickness. A one-dimensional condenser model is used to parametrically investigate the relative overall effect on condenser performance. From these results, coating guidelines for Admiralty brass tubes are proposed in terms of the minimum and maximum coating conductivity and thickness. The effect of the coating on the thermal performance is equivalent to a Heat Exchange Institute (HEI) cleanliness factor of at least 0.85, when adhering to these guidelines. APCs provide a layer of protection against corrosion, erosion and fouling and can preferentially fill tube-wall pits. They can therefore be used to extend the condenser life-span effectively, but, to ensure minimal impact on the overall condenser performance, the coating thickness and conductivity must be carefully controlled and verified experimentally. / AFRIKAANSE OPSOMMING: Die termiese geleidingsvermoë, die effektiewe termiese geleidingsvermoë van bedekte buise en die bedekkingsfaktor van drie kunsmatige beskermingsbedekkingslae wat op kondensorbuise aangewend word, word eksperimenteel geëvalueer. Hierdie evaluering verbreed die beperkte beskikbare kennis oor sodanige bedekkingslae, wat nodig is vir effektiewe kondensor herinrigting en bedryf. Die lae word teen diktes van 44, 46, 50 en 130 μm in 25.4 mm geelkoperbuise aangewend. Warmteoordragstoetse by gestadigde toestande word gedoen op hierdie buise in ’n dubbelpyp-teenvloeiwarmteoordraer, met verhitte water in die annulus en verkoelingswater binne-in die buis. Die eksperimenteel bepaalde termiese geleidingkoëffisiënte wissel tussen 0.5 tot 2.3 W/m·K. Die effektiewe geleidingsvermoë en bedekkingsfaktor hang af van sowel die buis se materiaal en grootte sowel as die dikte van die bedekkings. ’n Eendimensionele kondensormodel word gebruik om die algehele effek van hierdie beskermingsbedekkingslae op kondensorwerkverrigting parametries te ondersoek. Riglyne ten opsigte van aanwending van beskermingslae vir buise van “Admiralty” geelkoper word verskaf in terme van die minimum en maksimum geleidingsvermoë en dikte van bedekkingslae. Met behulp van hierdie riglyne word ’n “Heat Exchange Institue” (HEI) ekwivalente skoonheidsfaktor van minstens 0.85 op ’n nuwe buis behaal. Hierdie kunsmatige bedekkingslaeslae bied beskerming teen korrosie, erosie en bevuiling en kan klein kuile in die buiswand vul. Hulle kan dus gebruik word om die lewensduur van die kondensator te verleng, maar hul dikte en geleidingsvermoë moet noukeurig beheer word en moet eksperimenteel geverifieer word.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The majority of power stations in South Africa are located in coal rich, but arid regions where wet-cooled condenser systems are not feasible from an environmental and economic perspective. Consequently the focus on power generation cooling has shifted towards dry-cooling systems using air-cooled steam condensers (ACSC). The steam passing through the ACSC units is cooled by an air-draught, mechanically induced by large diameter axial flow fans. Consequently the effectiveness of the cooling is impacted by the performance of these fans, which ultimately affects the overall efficiency of the power plant. However, due to the large diameters (> 10 m) of these fans, their performance is predicted based on small scale test results using the fan scaling laws. The objective of this project was to develop a methodology which accurately predicts the fan performance of more than one fan configuration using computational fluid dynamics (CFD) software and validating the results with experimental tests. Four fans were considered in this study of which three were scaled fan models of large air-cooled axial fans. The performance of the scaled fan models (L1-, L2- and N-fan) were measured in a type A, BS 848 standard fan test facility. The geometries of the fans were scanned three-dimensionally to obtain the models for simulation purposes. The other fan considered was an 8- bladed axial fan designed by Bruneau (1994) and referred to as the B-fan. Simulations were carried out for the L2-, N- and B-fan for different computational domains while implementing the multiple reference frames (MRF) and steady RANS approach. Three variations of the k-ε turbulence model were also investigated. Noticeable differences were found between the experimental and numerical results of the B-fan. Good correlations between the numerical and experimental fan static pressure, fan power and fan static efficiency were found for the two scaled model fans over a large operating range. The performance of the full scale fans, however, did not correlate well with the performance of the scaled models. It is concluded that accurate simulations of axial fans are possible although these domains require a large number of mesh elements. It is recommended that further research is carried out to investigate the relationship between full scale and small scale fan models. / AFRIKAANSE OPSOMMING: Die meerderheid steenkool kragstasies in Suid-Afrika is geleë in droë, maar steenkool ryke streke waar natverkoelde kondensor stelsels uit ʼn omgewings en ekonomiese perspektief nie geskik is nie. Die fokus in kragopwekking verkoeling het dus verskuif na droë-verkoelings stelsels en spesifiek die gebruik van lugverkoelde stoomkondensors (LVSKs). Die stoom in LVSK eenhede word verkoel deur atmosferiese lug wat meganies geïnduseer word deur groot aksiaalvloeiwaaiers. Die effektiwiteit van die verkoelingsproses word gevolglik beïnvloed deur die werksverrigting van hierdie waaiers wat uiteindelik die algehele effektiwiteit van die kragstasie beïnvloed. As gevolg van hierdie waaiers se grootte word hulle werksverrigting egter bepaal op grond van kleinskaal toetsresultate en deur gebruik te maak van die waaierskaleringswette. Die hoofdoelwit van hierdie projek was om ‘n metodiek te ontwikkel wat die werksverrigting van ʼn aksiaalwaaier akkuraat kan voorspel vir ʼn verskeidenheid opstellings, deur gebruik te maak van berekenings vloei meganika (BVM) sagteware en die resultate eksperimenteel te verifieer. Die projek het vier waaiers ondersoek waarvan drie van hierdie waaiers geskaleerde modelle van groot lugverkoelde aksiaalwaaiers was. Die werksverrigting van die geskaleerde waaiers (L1-, L2- en N-waaier) was met ‘n tipe A, BS 848 standaard waaier toetsfasiliteit gemeet. Die geometrie van dié waaiers was ook drie-dimensioneel opgemeet vir simulasie doeleindes. Die B-waaier, ‘n 8 lem aksiaalwaaier, wat ontwerp is deur Bruneau (1994) was slegs numeries ondersoek. Die L2-, N- en Bwaaier was gesimuleer in verskillende berekeningsdomeine deur gebruik te maak van die multi verwysingsraamwerk en gestadigde vloeiberekenings benaderings. Drie k-ε turbulensie modelle was ook ondersoek. Merkbare verskille tussen die eksperimentele en numeriese resultate van die Bwaaier was waargeneem. Goeie korrelasie tussen die eksperimentele en numeriese resultate van die geskaleerde waaiers vir ‘n wye bedryfsbestek was gevind. ‘n Vergelyking tussen die volskaal en kleinskaal waaiers se werksverrigting het egter beduidende afwykings aangetoon. Deur gebruik te maak van ‘n groot aantal selle in die berekeningsdomein was dit moontlik om ʼn verskeidenheid aksiaalvloeiwaaiers akkuraat te simuleer. Verdere navorsing wat die verhouding tussen volskaal en kleinskaal waaiers ondersoek woord aanbeveel.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This study describes the design and construction of a low-cost linear Fresnel solar concentrator. Ray-trace simulation models that analyse optical performance were developed and then used to perform sensitivity analyses of various characteristics of linear Fresnel concentrators. The design of a small-scale concentrator was optimised using the simulation models, after which the concentrator was constructed in the solar laboratory. The concentrator consists of a single-motor tracking system, flat primary mirrors and a low-cost secondary concentrator that approximates a compound parabolic concentrator. Testing revealed satisfactory performance that was comparable to the simulation models’ prediction. The construction of a low-cost solar concentrator that can replace existing thermal sources for the generation of power and process heat is thus achievable. / AFRIKAANSE OPSOMMING: Die ontwerp en konstruksie van 'n laekoste- lineêre Fresnel-sonkonsentreerder word in hierdie studie beskryf. Stralingsimulasiemodelle wat optiese werksverrigting analiseer is ontwikkel en gebruik om sensitiwiteitsanalises van die verskillende eienskappe van lineêre Fresnel-konsentreerders te doen. Die modelle is verder gebruik om die ontwerp van 'n kleinskaalse konsentreerder te optimeer, waarna die konsentreerder in die sonlaboratorium gebou is. Die konsentreerder bestaan uit 'n enkelmotorvolgingstelsel, plat primêre spieëls en 'n laekoste- sekondêre konsentreerder soortgelyk aan 'n saamgestelde, paraboliese konsentreerder. Toetsing dui bevredigende werksverrigting aan, vergelykbaar met wat die simulasiemodelle voorspel het. Dit is dus moontlik om 'n laekoste-sonkonsentreerder wat bestaande termiese bronne vir kragopwekking en proseshittegenerasie kan vervang, daar te stel.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Turbomachinery plays an important role in the efficiency of power generation and combustion processes used in the automotive and aerospace industries. The potential for fulfilling future energy needs has been identified in both civilian and military applications, for example micro gas turbines (MGTs) used in unmanned aireial vehicles (UAVs). The goal of this thesis was to build a performance testing facility for small-scale centrifugal compressors, for use in MGTs. The objectives of this study were mainly achieved through experimental work. In addition to the experimental work, numerical simulations using computational fluid dynamics (CFD) software were performed to substantiate the experimental results. The project methodology followed the process whereby a compressor performance map is constructed from experimental data and compared to map obtained from theoretical data. The test facility consists of a turbocharger fitted with an experimental compressor section. The turbocharger turbine is driven by unheated compressed air. Sensors, data acquisition and ancillary equipment required to perform performance test measurements, were obtained and installed on the test facility. Performance curves at three different rotational speeds were successfully obtained for the experimental compressor. When compared to the CFD results there was good qualitative agreement, although deviations in the results increased with rotational speed. In addition a second impeller design was tested which correlated well with the theoretical data. / AFRIKAANSE OPSOMMING: Turbomasjinerie speel 'n belangrike rol in die doeltre endheid van kragop- wekking en verbrandingsprosesse wat in die motor- en lugvaartbedryf gebruik word. Die potensiaal om in toekomstige energiebehoeftes te voorsien is in beide burgerlike en militêre toepassings uitgewys, byvoorbeeld mikrogastur- bines (MGT's) wat in onbemande vliegtuie (OLV's) gebruik word. Die doel met hierdie tesis was om 'n prestasietoetsfasiliteit vir kleinskaalse sentrifu- gale kompressors te bou wat in MGT's gebruik kan word. Die doelstellings van hierdie studie is hoofsaaklik deur eksperimentele werk behaal. Daarbe- newens is numeriese simulasies met gebruikmaking van sagteware vir bereke- ningsvloeidinamika (BVD) gedoen om die eksperimentele resultate te staaf. Die projekmetodologie volg die proses om 'n kompressorprestasiekaart uit eks- perimentele data op te stel en dit te vergelyk met 'n kaart wat uit teoretiese data bekom is. Die toetsfasiliteit bestaan uit 'n turboaanjaer wat met 'n eksperimentele kompressordeel toegerus is. Die turboaanjaer se turbine word deur onverhitte druklug aangedryf. Sensors, dataverwerwing en bykomstige toerusting, wat benodig is om prestasietoetsmetings mee te doen, is bekom en op die toetsfasiliteit geïnstalleer. Prestasiekrommes is vervolgens by drie verskillende omwentelingsnelhede suksesvol met die eksperimentele kompres- sor bekom. In vergelyking met die BVD-resultate was daar goeie kwalitatiewe ooreenstemming, ofskoon afwykings in die resultate vergroot het namate die omwentelingspoed toegeneem het. Daarby is 'n tweede stuwerontwerp getoets wat goed met die teoretiese resultate korreleer.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Carbon dioxide is a natural gas that has been used as a refrigerant as far back as the 1850s. It was then primarily used because it was easily obtainable and non-toxic. Due to the high operating pressure and relatively low critical temperature (and high critical pressure) of CO2, it was gradually phased out and replaced with hydrochlorofluorocarbons and chlorofluorocarbons. With the discovery of the greenhouse effect, greenhouse gasses and ozone depleting gasses, the Montreal Protocol and the Kyoto Protocol were placed into effect. These two protocols call for the reduction in use of certain greenhouse gasses and the complete exclusion of others. The focus turned to natural gasses that are more environmentally friendly and easier to come by. Carbon dioxide is one such gas. However, CO2 has a low critical temperature and high pressure, 33.98 °C and 73.77 bar respectively. CO2 refrigeration systems are more effective, have a greater coefficient of performance and have a greater operating temperature difference (over the gas-cooler) when used under transcritical conditions. It is preferred to have transcritical CO2 refriger-ation systems. The drawback of such a system is the extreme operating conditions. A special system must be designed, built and commissioned at the University of Stellenbosch. The system will demand the use or manufacture of unique, special-ised components. Most of the components utilised are extremely expensive and/or difficult to come by, or designed and manufactured specifically for this system. The CO2 system at the University of Stellenbosch is exceptional and stands out from conventional systems in that: - it can operate under both the subcritical and transcritical conditions; - it has multiple expansion units, which can be alternated, giving a total of four different operating configurations; - the system can run with fully automated controllers or as a static system; - the internal heat exchanger can be included or excluded from the system; - all the heat exchangers can run in counter flow or parallel flow; and - The system has multiple testing points, for both temperature and pressure, to give the operator accurate measurements to be used in comparison with design software, etc. Three simulation programs are given that describe the physical system. The first simulation program is a steady-state simulator used to aid in the design of the heat exchangers and the capillary tube. The second simulator is a steady-state program that determines the mass flow rate in the capillary tube. The third simulation is a transient program, programmed to determine the steady-state conditions of a sys-tem, given set initial conditions and a transient start-up. / AFRIKAANSE OPSOMMING: Koolstofdioksied is 'n natuurlike gas wat gebruik word as 'n verkoelingsmiddel so ver terug as die 1850's. Dit is toe hoofsaaklik gebruik omdat dit maklik verkrygbaar en nie giftig is nie. As gevolg van die hoë werksdruk en relatief lae kritiese temperatuur (en hoë kritiese druk) van CO2, is dit geleidelik uitgefaseer en vervang met hidrochloorfluoorkoolstof en chloorfluoorkoolstowwe. Met die ontdekking van die kweekhuiseffek, kweekhuisgasse en osoon-afbrekende gasse, is die Montreal-protokol en die Kyoto-protokol in werking gestel. Hierdie twee protokolle vereis die afname in die gebruik van sekere kweekhuisgasse en die algehele uitsluiting van ander. Die fokus het verskuif na natuurlike gasse wat omgewingsvriendeliker en makliker is om te bekom. Koolstofdioksied is so 'n gas. Maar CO2 het 'n lae kritiese temperatuur en hoë kritiese druk, 33.98 °C en 73.77 bar onderskeidelik. CO2 verkoelingstelsels is meer effektief, het 'n groter koëffisiënt van werksverrigting en het 'n groter bedryfstemperatuur-verskil (oor die gas-verkoeler) wanneer dit gebruik word onder transkritiese toestande. Dit is dus verkieslik om transkritiese CO2 verkoelingstelsels te hê. Die nadeel van so 'n stelsel is die relatief uiterste bedryfstoestande. 'n Spesiale stelsel moet ontwerp word, dikwels met die gebruik of vervaardiging van unieke, hoogs gespesialiseerde komponente. So 'n stelsel is ontwerp vir die Universiteit van Stellenbosch. Die meeste van die komponente wat gebruik is, is baie duur en/of moeilik om te bekom, of is spesifiek ontwerp en vervaardig vir hierdie stelsel. Die CO2-stelsel by die Universiteit van Stellenbosch is uitsonderlik en staan uit bo konvensionele stelsels deurdat: - dit kan funksioneer onder beide subkritiese en transkritiese toestande; - dit verskeie gasuitsettings-eenhede het, wat afgewissel kan word, wat 'n totaal van vier verskillende bedryfskonfigurasies gee; - die stelsel bedryf kan word met volle outomatiese beheerders of as 'n statiese stelsel; - die interne hitte-uitruiler óf in-, óf uitgesluit kan word van die stelsel; - al die hitte-uitruilers bedryf kan word in kontra-vloei of parallelle vloei; en - die stelsel verskeie toetspunte het, vir beide temperatuur en druk, wat die operateur akkurate metings gee om te vergelyk met die ontwerp sagteware, ens., wat gebruik word. Drie gegewe simulasieprogramme beskryf die fisiese stelsel. In een simulasie word 'n bestendige toestand-simulator gebruik om te help met die ontwerp van die hitteruilers en die kapillêre buis. Die tweede simulasie program is 'n bestendige toestands-program wat die algehele vloeitempo in die kapillêre buis bepaal. Die laaste simulasie is 'n vlugtige program, geprogrammeer om die tydelike toestande van 'n stelsel te bepaal, gegewe vasgestelde aanvanklike toestande en 'n kortstondige aanskakeling.

Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Patients in critical care with lung injuries need to be assisted with regards to breathing function, but current methods are not applicable for all situations. The most common method, Extracorporeal Membrane Oxygenation (ECMO) is an expensive procedure and requires trained staff to operate the equipment at all times. Lung injury may lead to the inability of the lungs to be perfused and the blood oxygenated by tracheal intubation, whereas mechanical ventilators can injure the lungs further. Especially at risk are preterm neonates, where congenital disorders or complications during birth render ECMO the only viable option. Respiratory Assist Catheters (RACs) could be used as an alternative because they do not place extra stress on the lungs, are easy to implement, cost-effective and are available for immediate use in clinical settings or in first aid situations. The development of such a device requires knowledge of possible oxygenation methods as well as the risks involved in implementing such a device. The possibility of oxygenating the blood via microbubbles by means of a RAC is promising due to the high gas transfer rates common in bubble oxygenators. It is the aim of this study to develop a prototype that could function as a RAC and to evaluate the feasibility of oxygenation by using microbubbles. The method used to design a prototype included selection of various materials and finalization of a design to be tested. The tests selected were in vivo tests and ex vivo tests using animal models to investigate the dissolution times of the microbubbles, as well as the physiological effects of an intravenously placed device. Measurements of oxygen saturation of the blood in arterial blood (SaO2), venous blood (SvO2) and pulmonary pressure allowed the oxygen transfer rates and risks involved to be evaluated, and also gave an indication regarding the formation dynamics of microbubbles in the blood. An in vitro test was also performed with the aim of determining the rate of dissolving of oxygen, and hence to give an indication regarding microbubble dissolution times. Mathematical simulations based on the dissolution rate of oxygen in venous blood confirmed the abovementioned results. The tests and simulations were analysed in order to evaluate the feasibility of intravenously oxygenating the blood using microbubbles. Approximate bubble dissolution times were an indicator of the feasibility of the concept and showed that very large bubble dissolution times renders intravenous bubble oxygenation unfeasible. These large dissolution times also lessen the possibility of implementing bubble oxygenation in an intravenous device. / AFRIKAANSE OPSOMMING: Pasiënte wat a.g.v. longbeserings in hoë-sorg behandel word het hulp nodig om asem te haal, maar bestaande metodes werk nie in alle omstandighede nie. Die mees algemene metode is ekstrakorporeale membraan suurstofverbinding (Extracorporeal Membrane Oxygenation (ECMO)), maar hierdie metode is duur en het voltyds opgeleide personeel nodig om dit te beheer. Longbeserings kan lei tot die onvermoë van die longe om bloed te ontvang en ook dat die bloed suurstof kry d.m.v. trageale intubasie. Meganiese ventilators kan die longe verder beskadig. Vroeggebore babas word blootgestel aan risiko’s veral waar oorerflike afwykings/steurnisse aanwesig is of komplikasies tydens geboorte en dus die EMCO die enigste lewensvatbare opsie maak. Kateters wat asemhaling aanhelp (Respiratory Assist Catheters (RACs)) kan as alternatief gebruik word aangesien dit nie ekstra spanning op die longe plaas nie, maklik is om te implementeer, koste-effektief is en beskikbaar is vir onmiddellike gebruik in kliniese omstandighede of in noodhulpsituasies. Die ontwikkeling van hierdie tipe toestel vereis kennis van moontlike suurstofverbindingsmetodes en ook die risiko’s verbonde aan die implementering van die toestel. Die moontlikheid om die bloed van suurstof te voorsien d.m.v. mikroborrels deur die RAC lyk belowend a.g.v. die hoë gasoordrag-koers wat algemeen is by borrel suurstofverbinders. Hierdie studie het ten doel om ʼn prototipe te ontwikkel wat kan dien as ʼn RAC en ook om die lewensvatbaarheid van suurstofverbinding met mikroborrels te bepaal. Die metode wat gebruik is om die prototipe te ontwerp sluit in die kies van verskeie materiale en die finalisering van die ontwerp wat getoets moet word. Die geselekteerde in vivo en ex vivo toetse is afgeneem deur gebruik te maak van dier-modelle om sodoende ondersoek in te stel na die oplossing van die mikroborrels en ook die fisiologiese gevolge van die toestel wat binne die aar geplaas is. Metings van die suurstofversadiging van bloed in slagaarbloed (SaO2), aarbloed (SvO2) en pulmonêre druk het toegelaat dat die koers en risiko’s verbonde aan suurstofoordrag geëvalueer word. Hierdie metings gee ook ’n aanduiding van die vormingsdinamika van die mikroborrels in die bloed. ’n In vitro toets is gedoen met die doel om die koers te bepaal van die oplossing van suurstof, en dus ’n aanduiding te gee van die tyd verbonde aan die oplossing van die mikroborrels. Wiskundige simulasies gebaseer op die oplossingskoers van suurstof in are het die bogenoemde toetse bevestig. Die toetse en simulasies is geanaliseer om die lewensvatbaarheid te bepaal om suurstof binne-aars te verskaf deur mikroborrels. Geskatte tye waarteen die borrels oplos is as aanduiding gebruik vir die lewensvatbaarheid van die konsep en ook die moontlike inwerkingstelling van die binne-aarse toestel.