Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Polysulfone hollow-fibre membranes were fabricated via the dry-wet solution spinning technique. The objective was to demonstrate the influence of the various fabrication parameters on the diameter and mechanical properties of the hollow-fibre membranes and to optimize the spinning process by controlling these parameters with a computer control system. The effects of the operation parameters were investigated using an experimental design based on a fractional factorial method (Taguchi’s design of experiments). The parameters that were considered are the spinneret size, dope solution temperature, bore fluid temperature, coagulation bath temperature, dope extrusion rate, bore flow rate and the take-up speed. A new pilot solution spinning plant was installed and upgraded, and a computer control system, based on LabView, was developed to control, monitor and log the experimental data. The diameter of the hollow-fibres were determined using a scanning electron microscope (SEM) while the mechanical properties were measured using a tensile tester. The effects of diameter size and wall thickness of the hollow-fibres on the performance of the membranes were studied. The results showed the significance of the fabrication parameters that dominate the diameter and strength of the hollow-fibres. / AFRIKAANSE OPSOMMING: Polisulfoon holvesel membrane is met ‘n droë-nat oplossingspin proses vervaardig. Die doel hiermee was om die invloed van verskeie vervaardigingsparameters op die deursnee en meganiese eienskappe van die holvesel membrane te demonstreer asook om die spin proses te optimeer deur gerekenariseerde beheer van die aanleg. ‘n Eksperimentele ontwerp, gebaseer op ‘n gedeeltelike faktoriaal metode (Taguchi se eksperimentele ontwerp) is gebruik om die invloed van die vervaardigingsparameters te ondersoek. Die parameters wat oorweeg is, is spindop grootte, materiaal temperatuur, boorvloeistof temperatuur, stolbad temperatuur, materiaal ekstrusie tempo and opwen spoed. ‘n Nuwe oplossingspin loodsaanleg was geïnstalleer en opgegradeer en ‘n rekenaar beheerstelsel, gebaseer op LabView, is ontwikkel om die aanleg te beheer, moniteer en eksperimentele data te stoor. Die deursnee van die holvesel is gemeet met ‘n skanderingelektron mikroskoop (SEM) terwyl die meganiese eienskappe bepaal is met ‘n trektoets apparaat. Die effek van die deursnee en wanddikte van die holvesels op die werkverrigting van die membrane is ook bestudeer. Die resultate toon watter vervaardigingsparameters is beduidend vir die deursnee en sterkte van die holvesels.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / Although mass minimisation is an important application within structural optimisation, other applications include: (1) concept generation, (2) concept evaluation, (3) design for structural feasibility and (4) data matching. These applications, except data matching, are discussed and illustrated on a prototype design of the Karoo Array Telescope (KAT) antenna. The KAT passed through the design process and a full scale prototype was built, but was found to be too expensive. A detailed finite element model of the finalised design was considered as a test bed for reducing costs. Size-, shape- and topology optimisation are applied to three KAT components, while considering wind, temperature and gravity loads. Structural- and nonstructural constraints are introduced. Coupling of the structural optimisation code with an external analysis program to include non-structural responses and the parallelisation of the sensitivity calculations are presented. It is shown that if a finite element model is available, it is generally possible to apply structural optimisation to improve an existing design. A reduction of 2673 kg steel was accomplished for the existing KAT components. The total cost saving for the project will be significant, when considering that a large amount of antennas will be manufactured.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / This thesis investigates practical methods of modelling and control of the vertical motions of a hydrofoil assisted catamaran, the HYSUCAT. The aim of the control application is to reduce the motions, and consequently the motion sickness of the passengers. First, a potential flowcommercial program, POWERSEA,was used to model the system. This uses 2-D strip methods to model the planing hull-form of the vessel, and the Peter du Cane hydrofoil theory for modelling of the foils. These simulations are compared to experimental towing tank results, with fair agreement at lower speeds, but limited applicability at high speeds. Thus for the control design the agreement was insufficient. As an alternative, a simple coupled 2 degree-of-freedom spring - mass - damper model is proposed, for which the equations of motion are derived. This has 9 unknown parameters; three of these aremeasured directly, two are modelled, and the remaining four were identified using an experimental parameter estimation technique. Representative parameter values were calculated frommultiple experiments for application in the control design. The design of a control system was based on the above model. First, an output-weighted Linear Quadratic Regulator (LQR) was designed to obtain the full state feedback gains. A non-linear ’bang-bang’ control design was then implemented to try and speed up the response of the system. These control strategies, as well as no control, were applied in the towing tank in regular waves, with good results at low and medium frequencies. At the design point, 32% and 65% reductions in rms motions were achieved for pitch and heave, respectively. At high frequencies, though, not much improvement was achieved due to the bandwidth limitation of the control system. The LQR results were better overall (reduced motions) across the frequency range than the bang-bang controller, as well as having a lower added resistance in waves. The control design of the output-weighted LQR was then revised to be based on alternative outputs, as a possible improvement. However, a further two controller designs did not yield any noticeable improvement and were not developed further.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / This thesis is concerned with the testing of an “auscultation jacket” as a means of recording heart sounds and electrocardiography (ECG) data from patients. A classification system based on Neural Networks, that is able to discriminate between normal and abnormal heart sounds and murmurs, has also been developed . The classification system uses the recorded data as training and testing data. This classification system is proposed to serve as an aid to physicians in diagnosing patients with cardiac abnormalities. Seventeen normal participants and 14 participants that suffer from valve-related heart disease have been recorded with the jacket. The “auscultation jacket” shows great promise as a wearable health monitoring aid for application in rural areas and in the telemedicine industry. The Neural Network classification system is able to differentiate between normal and abnormal heart sounds with a sensitivity of 85.7% and a specificity of 94.1%.

Thesis (MScEng (Department of Mechanical and Mechatronic Engineering))--Stellenbosch University, 2006. / ENGLISH ABSTRACT: Wind conditions in South Africa determine the need for a small-scale wind turbine to produce useable power at windspeeds below 7m/s. In this project, a range of windspeeds, within which optimal performance o the wind turbine is expected, was selected. The optimal performance was assessed in terms of the Coefficient of Power(Cp), which rates the turbines blade's ability to extract energy form the avalible wind stream. The optimisation methods employed allowed a means of tackling the multi-variable problem such that the aerodynamic characteristics of the blade were ideal throughout the wind speed range. The design problem was broken down into a two-dimensional optimisaion of the airfoils used at the radial stations, and a three-dimensional optimisation of the geometric features of the wind rotor. by means of blending various standard airfoil profiles, a new profile was created at each radial station. XFOIL was used for the two-dimensional analysis of these airfoils. Three-dimensional optimisn involved representation of the rotor as a simplified model and use of the Blade Element Momentum(BEM) method for analysis. an existimg turbine blade, on which the design specifications were modelled, was further used for comparative purposes throughout the project. The resulting blade design offers substantial improvements on the reference design. The application of optimisation methods has successfully aided the creation of a wind turbine blade with consistent peak performance over a range of design prints. / Sponsored by the Centre for Renewable and Sustainable Energy Studies, Stellenbosch University

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The thesis was initiated by a Consulting Engineering Company (KV3) as a research project to investigate various options in which the efficiency and energy utilisation of conventional air conditioning systems may be enhanced by using alternative and renewable energy. Initially, eight options had been identified and through a process of determining the degree of commercialisation the alternative options were reduced to three. These options, referred to as the sustainable cooling alternatives, are active mass cooling, night flushing and roof cooling system. The roof cooling system comprised a roof-pond, roof-spray, pump and storage tank. The roof cooling system was mathematically and experimentally modelled. The roof cooling experiment was performed under a variety of weather conditions with the roof-pond and storage tank temperatures continuously recorded. The experimentally recorded temperatures were compared to the temperatures generated by the theoretical simulation calculations for the same input and weather conditions. Good agreement was found between the mathematical and experimental model. The largest discrepancy found between the simulated temperature and the experimental temperature was in the order of 1 ºC. A one-room building has been assumed to serve as a basis to which the sustainable cooling alternatives could be applied to for theoretical simulation. The one-room building had four façade walls and a flat roof slab. Night flushing, active mass cooling and the roof cooling system were applied to the one-room building such that the room air temperature and space cooling load could theoretically be simulated. The theoretical simulations were also repeated for the case where the roof-pond and roof-spray were applied as standalone systems to the one-room building. The theoretical simulation calculations were performed for typical summer weather conditions of Stellenbosch, South Africa. Under base case conditions and for a room thermostat setting of 22 ºC the peak cooling load of the one-room building was 74.73 W/m². With the application of night flushing between the hours of 24:00 and 07:00, the room cooling load was reduced by 5.2% by providing 3.9 W/m² of cooling and reducing the peak room temperature by 1.4 ºC. The active mass cooling system was modelled by supplying water at a constant supply temperature of 15 ºC to a pipe network embedded in the roof slab of the one-room building. The sea may typically be considered as a cold water source for buildings situated at the coast. The active mass cooling system reduced the peak cooling load of the one-room building by 50% by providing 37.2 W/m² of cooling and reducing the peak room temperature by 6.7 ºC. When the roof-spray and roof-pond systems were applied as standalone systems to the oneroom building, the peak cooling load of the one-room building could be reduced by 30% and 51% respectively. This is equivalent to 22.3 W/m² of peak cooling by the roof-spray and 38 W/m² of peak cooling by the roof-pond. The roof-spray reduced the peak room temperature by 3.71 ºC while the roof-pond reduced the peak room temperature by 5.9 ºC. Applying the roof cooling system to the one-room building produced 46 W/m² of peak cooling which resulted in a 61.1% reduction in peak cooling load. The roof cooling system reduced the peak temperature by 8 ºC. By comparing the sustainable cooling alternatives, the roof cooling system showed to be the most effective in reducing the one-room building peak cooling load. Over a 24 hour period the roof cooling system reduced the net heat entry to the one-room building by 57.3%. In a further attempt to reduce the peak cooling load, the sustainable cooling alternatives were applied in combinations to the one-room building. The combination of night flushing and roof-spray reduced the peak cooling load by 36% while a combination of night flushing and active mass cooling reduced the peak cooling load by 55%. Combining night flushing with the roof-pond also yielded a 55% peak cooling load reduction. The combination of roofpond, active mass cooling and night flushing provided 51 W/m² of cooling which corresponded to a 68% reduction in peak cooling load. Utilising the sustainable cooling alternatives in a combination in the one-room building gave improved results when compared to the case where the sustainable cooling alternatives were employed as standalone systems. It is illustrated by means of a sensitivity analysis that the ability of the roof cooling system to produce cool water is largely influenced by ambient conditions, droplet diameter and roofspray rate. Under clear sky conditions, an ambient temperature of 15 ºC, relative humidity of 80%, a roof-spray rate of 0.02 kg/sm² and a roof-pond water level of 100mm, water could be cooled at a rate of 113 W/m². The roof-spray energy contributed to 28 W/m² whilst the night sky radiation was responsible for 85 W/m² of the water cooling. It must however be noted that the water of the roof cooling system can never be reduced to a temperature that is lower than the ambient dew point temperature. / AFRIKAANSE OPSOMMING: Die tesis is geïnisieer deur ‘n Raadgewende Ingenieurs Maatskappy (KV3) as a navorsingsprojek om verskeie opsies te ondersoek waarmee die effektiwiteit en energie verbruik van konvensionele lugversorgingstelsels verbeter kan word deur middel van alternatiewe en hernubare energie. Agt opsies is oorspronglik geïdentifiseer en deur middel van ‘n proses waarby die graad van kommersialisering van hierdie alternatiewe maniere bepaal is, kon die opsies verminder word tot drie. Hierdie opsies, ook verwys na as die volhoubare verkoelingsalternatiewe, sluit in aktiewe massa verkoeling, dakverkoeling en nagventilasie. Die dakverkoelingstelsel bestaan uit dakwater, ‘n dakspuit, ‘n pomp en ‘n stoortenk. Die dakverkoelingstelsel is wiskundig en eksperimenteel gemodelleer. Die dakverkoelingseksperiment is uitgevoer onder ‘n verskeidenheid van weersomstandighede. Die dakwater asook die stoortenk se water temperatuur is voortdurend aangeteken. Dieselfde weer- en insetkondisies is gebruik vir die simulasie berekening en die temperature van die stoortenk se water en die dakwater is vergelyk met die temperatuurlesings van die eksperimentele werk. Die temperature van die eksperimentele lesings het goed vergelyk met die temperatuur simulasie berekeninge. Die grootste verskil tussen die simulasie en eksperimentele temperatuur was in die orde grootte van 1 ºC. ‘n Een-kamer gebou is aangeneem om as basis te dien waarop die volhoubare verkoelingsalternatiewe aangewend kon word vir teoretiese simulasie. Die een-kamer gebou het uit vier buite mure en ‘n horisontale beton dak bestaan. Nag ventilasie, aktiewe massa verkoeling en die dakverkoelingstelsel is toegepas op die een-kamer gebou en die kamer se verkoelingslas asook die kamer se lugtempertuur is teoreties gesimuleer. Die teoretiese simulasies is ook herhaal vir die geval waar die dakwater and dakspuitstelsel apart aangewend is op die een-kamer gebou. Die teoretiese simulasie berekeninge is uitgevoer vir tipiese somer weersomstandighede vir Stellenbosch, Suid Afrika. Onder basisgeval omstandighede, waar die een-kamer gebou gesimuleer is, sonder enige volhoubare verkoelingsalternatiewe en ‘n termostaat verstelling van 22 ºC, is die piek verkoelingslas bereken as 74.73 W/m². Met die toepassing van nagventilasie tussen die ure 24:00 en 07:00 was die piekverkoelingslas van die kamer verminder met 5.2% deur 3.9 W/m² se verkoeling te verskaf en die piekkamer temperatuur te verminder met 1.4 ºC. Aktiewe massa verkoeling is gesimuleer deur water teen ‘n konstante temperatuur van 15 ºC te verskaf aan ‘n pypnetwerk, geïnstalleer in the beton dak, van die een-kamer gebou. Geboue geleë aan die kus kan tipies seewater oorweeg as ‘n bron van koue water. Aktiewe massa verkoeling het die piekverkoelingslas van die een-kamer gebou verminder met 50% deur 37.2 W/m² se verkoeling te verskaf en die piekkamer temperatuur te verminder met 6.7 ºC. Wanneer die dakspuit- en dakwaterstelsel aangewend is op die een-kamer gebou as enkel staande stelsels, is die piekverkoelingslas verminder met 30% en 51% onderskeidelik. Dit is ekwivalent aan 22.3 W/m² se verkoeling vir die dakspuitstelsel en 38 W/m² se verkoeling vir die dakwaterstelsel. Die dakspuitstelsel het die piekkamer temperatuur verminder met 3.71 ºC terwyl die dakwaterstelsel ‘n 5.9 ºC verlaging in piekkamer temperatuur tot gevolg gehad het. Die dakverkoelingstelsel het 46 W/m² se piekverkoeling verskaf wat ‘n 61.1% vermindering in piekverkoelingslas tot gevolg gehad het. Die ooreenstemmende piek temperatuur vermindering is 8 ºC. Deur die verskeie volhoubare verkoelingsalternatiewe met mekaar te vergelyk, word getoon dat die dakverkoelingstelsel die mees effektiefste manier is om die een- kamer se piekverkoelingslas te verminder. Oor ‘n tydperk van 24 uur het die dakverkoelingstelsel die totale energievloei na die een-kamer gebou met 57.3% verminder. In ‘n verdere poging om die piekverkoelingslas te verminder, is die volhoubare verkoelingsalternatiewe toegepas in kombinasies op die een-kamer gebou. Die kombinasie van nagventilasie met die dakspuitstelsel het die piekverkoelingslas met 36% verminder, terwyl ‘n kombinasie van nagventilasie en aktiewe massa verkoeling ‘n 55% vermindering in piekverkoelingslas tot gevolg gehad het. Die kombinasie van dakwater en nagventilasie het ook ‘n piekverkoelingslas vermindering van 55% teweeggebring. Die kombinasie van dakwater, aktiewe massa verkoeling en nagventilasie het 51 W/m² se verkoeling veskaf, wat ooreenstem met ‘n 68% vermindering in piekverkoelingslas. Deur die volhoubare verkoelingsalternatiewe in kombinasies toe te pas op die een-kamer gebou, kon beter resultate verkry word toe dit vergelyk is met die geval waar die volhoubare verkoelingsalternatiewe as enkelstaande stelsels toegepas is. Dit is geïllustreer deur middel van ‘n sensitiwiteitsanalise dat die vermoë van die dakverkoelingstelsel om koue water te produseer, beïnvloed word deur buitelug kondisies, waterdruppel deursnee en dakspuit massa vloeitempo. Onder die oop hemelruimteomstandighede, ‘n buitelug temperatuur van 15 ºC, ‘n relatiewe humiditeit van 80%, ‘n dakspuit massa vloeitempo van 0.02 kg/sm² en dakwatervlak van 100 mm, kon water verkoel word teen ‘n tempo van 113 W/m². Die dakspuit gedeelte het 28 W/m² bygedra terwyl die nagruim radiasie sowat 85 W/m² se verkoeling verskaf het. Daar moet egter kennis geneem word dat die water temperatuur van die dakverkoelingstelsel nooit verminder kan word tot onder die buitelug doupunttemperatuur nie.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The valveless micropump holds great potential for the biomedical community in applications such as drug delivery systems, blood glucose monitoring and many others. It is also a critical component in many a lab-on-a-chip device, which in turn promises to improve our treatment and diagnosis capabilities for diseases such as diabetes, tuberculosis, and HIV/AIDS. The valveless micropump has attracted attention from researchers on the grounds of its simple design, easy manufacturability and sensitive fluid handling characteristics, which are all important in biomedical applications. The pump consists of a pump chamber with a diffuser and nozzle on opposing sides of the pump chamber. The flow into the diffuser and nozzle is induced by an oscillating piezoelectric disc located on top of the pump chamber. The nozzle and diffuser rectify the flow in one direction, due to different pressure loss coefficients. The design process however is complex. In this study, we investigate the characteristics of a diffuser / nozzle based micropump using detailed computational fluid dynamic (CFD) analyses. Significant parameters are derived using the Buckingham-Pi theorem. In part based on this, the respective shapes of the diffuser and of the nozzle of the micropump are selected for numerical investigation. Hence the influence of the selected parameters on the flow rate of the micropump is studied using three-dimensional transient CFD analyses. Velocity profiles from the CFD simulations are also compared to the Jeffery-Hamel solution for flow in a wedge shaped channel. Significant similarities exist between the data and the predicted Jeffery-Hamel velocity profiles near the exit of the diffuser. Three different diffuser geometries were simulated at three frequencies. The flow rate and direction of flow are shown to be highly sensitive to inlet and outlet diffuser shapes, with the absolute flow rate varying by as much as 200% for the geometrical perturbations studied. Entrance losses at both the diffuser inlet and nozzle inlet appear to dominate the flow resistance at extremely laminar flow conditions with the average Reynolds number of Reave ≈ 500. / AFRIKAANSE OPSOMMING: Die kleplosemikropomp hou groot potensiaal in vir die biomediese gemeenskap in toepassings soos medisyne dosering sisteme, bloed glukose monitering en baie ander. Dit is ook ’n kritiese komponent in “lab-on-chip” sisteme, wat beloof om die behandeling en diagnose van siektes soos suikersiekte, tuberkulose enMIV/VIGS te verbeter. Die kleplose mikropomp het tot dusver die aandag van navorsers geniet as gevolg van sy eenvoudige ontwerp, maklike vervaardiging en sensitiewe vloeistof hantering. Hierdie kenmerke is krities inmenige biomediese toepassings. Die pomp bestaan uit ’n pompkamer met ’n diffusor en ’n mondstuk aan teenoorstaande kante van die pompkamer. Vloei in die diffusor en mondstuk in word geinduseer deur ’n ossillerende piëso-elektiese skyf wat bo-op die pompkamer geleë is. Weens verskillende druk verlies koëffisinëte van die diffusor en diemondstuk word die vloei in een rigting gerig. Die ontwerp-proses is egter kompleks. In hierdie studie word die eienskappe van die diffusor /mondstuk ondersoek deur gebruik temaak van gedetailleerde numeriese vloei-dinamiese analises. Belangrike parameters word afgelei deur gebruik te maak van die Buckingham-Pi teorema. Gedeeltelik gebaseer hierop word die onderskeidelike vorms van die diffusor en die mondstuk van die mikropomp geselekteer vir numeriese ondersoek. Gevlolglik word die invloed van die geselekteerde parameters op die vloei tempo van diemikropomp ondersoek deur gebruik temaak van drie-dimensionele tyd afhanklike numeriese vloei-dinamiese analises. Snelheids profiele van hierdie simulasiesword vergelykmet die Jeffrey-Hamel oplossing vir die vloei in ’n wigvormige kanaal. Daar is oorwegende ooreenkomstighede tussen hierdie data en die voorspelde Jeffrey-Hamel snelheids profiele veral by die uitgang van die diffusor. Drie verskillende diffusor vorms is by drie frekwensies gesimuleer. Daar is bewys dat die vloei tempo en vloeirigting baie sensitief is vir inlaat- en uitlaat diffusor vorms en dat die absolute vloei tempo kan varieermet soveel as 200%vir die geometriese versteuringswat ondersoek is. Inlaat verliese by beide die diffusor inlaat en die mondstuk inlaat, blyk om die vloei weerstand te domineer waar die vloei uiters laminêr ismet ’n gemiddelde Reynolds getal van Regem ≈ 500

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: A reactor cavity cooling system (RCCS) is used in the PBMR to protect the concrete citadel surrounding the reactor from direct nuclear radiation impingement and heat. The speci ed maximum operating temperature of the concrete structure is 65 ±C for normal operating conditions and 125 ±C for emergency shut-down conditions. A conceptual design of an entirely passive RCCS suitable for the PBMR was done by using closed loop thermosyphon heat pipes (CLTHPs) to remove heat from a radiation heat shield over a horizontal distance to an annular cooling dam placed around the PBMR. The radiation shield is placed in the air space between the Reactor Pressure Vessel (RPV) and the concrete citadel, 180 mm from the concrete citadel. A theoretical heat transfer model of the RCCS was created. The theoretical model was used to develop a computer program to simulate the transient RCCS response during normal reactor operation, when the RCCS must remove the excess generated heat from the reactor cavity and during emergency shut-down conditions, when the RCCS must remove the decay heat from the reactor cavity. The main purpose of the theoretical model is to predict the surface temperature of the concrete citadel for di erent heat generation modes in the reactor core and ambient conditions. The theoretical model assumes a 1D geometry of the RCCS. Heat transfer by both radiation and convection from the RPV to the radiation heat shield (HS) is calculated. The heat shield is modelled as a n. The n e ciency was determined with the experimental work. Conduction through the n is considered in the horizontal direction only. The concrete structure surface is heated by radiation from the outer surface of the heat shield as well as by convection heat transfer from the air between the heat shield and the concrete structure surface. The modelling of the natural convection closed loop thermosyphon heat pipes in the RCCS is done by using the Boussinesq approximation and the homogeneous ow model. An experiment was built to verify the theoretical model. The experiment is a full scale model of the PBMR in the horizontal, or main heat transfer, direction, but is only a 2 m high section. The experiments showed that the convection heat transfer between the RPV and the HS cannot be modelled with simple natural convection theory. A Nusselt number correlation developed especially for natural convection in enclosed rectangles found in literature was used to model the convection heat transfer. The Nusselt number was approximately 3 times higher than that which classic convection theory suggested. An optimisation procedure was developed where 121 di erent combinations of n sizes and heat pipe sizes could be used to construct a RCCS once a cooling dam size was chosen. The purpose of the optimisation was to nd the RCCS with the lowest total mass. A cooling dam with a diameter of 50 m was chosen. The optimal RCCS radiation heat shield that operates with the working uid only in single phase has 243 closed loop thermosyphon heat pipes constructed from 62.72 mm ID pipes and 25 mm wide atbar ns. The total mass of the single phase RCCS is 225 tons. The maximum concrete structure temperature is 62.5 ±C under normal operating conditions, 65.8 ±C during a PLOFC emergency shut-down condition and 80.9 ±C during a DLOFC emergency shut-down condition. In the case where one CLTHP fails and the adjacent two must compensate for the loss of cooling capacity, the maximum concrete structure temperature for a DLOFC emergency shut-down will be 87.4 ±C. This is 37.6 ±C below the speci ed maximum temperature of 125 ±C. The RCCS design is further improved when boiling of the working uid is induced in the CLTHP. The optimal RCCS radiation heat shield that operates with the working uid in a liquid-vapour mixture, or two phase ow, has 338 closed loop thermosyphon heat pipes constructed from 38.1 mm ID pipes and 20 mm wide atbar ns. The total mass of the two phase RCCS is 198 tons, 27 tons less than the single phase RCCS. The maximum concrete structure temperature is 60 ±C under normal operating conditions, 2.5 ±C below that of the single phase RCCS. During a PLOFC emergency shut-down condition, the maximum concrete structure temperature is 62.3 ±C, 3.5 ±C below that of the single phase RCCS and still below the normal operating temperature of the single phase RCCS. By inducing two phase ow in the CLTHP, the maximum temperature of the working uid is xed equal to the saturation temperature of the working uid at the vacuum pressure. This property of water is used to limit the concrete structure temperature. This e ect is seen in the transient response of the RCCS where the concrete structure temperature increases until boiling of the working uid starts and then the concrete structure temperature becomes constant irrespective of the heat load on the RCCS. An increased heat load increases the quality of the working uid liquid-vapour mixture. Working uid qualities approaching unity causes numerical instabilities in the theoretical model. The theoretical model cannot capture the heat transfer to a control volume with a density lower than approximately 20 kg/m3. This limits the extent to which the two phase RCCS can be optimised. Recommendations are made relating to future work on how to improve the theoretical model in particular the convection modelling in the reactor cavities as well as the two phase ow of the working uid. Further recommendations are made on how to improve the basic design of the heat shield as well as the cooling section of the CLTHPs. / AFRIKAANSE OPSOMMING: 'n Reaktor lug spasie verkoelingstelsel (RLSVS) word in die PBMR gebruik om die beton wat die reaktor omring te beskerm teen direkte stralingskade en hitte. Die gespesi seerde maksimum temperatuur van die beton is 65 ±C onder normale bedryfstoestande en 125 ±C gedurende die noodtoestand afskakeling van die reaktor. 'n Konseptuele ontwerp van 'n geheel en al passiewe RLSVS geskik vir die PBMR is gedoen deur gebruik te maak van geslote lus termo-sifon (GLTSe) om hitte van die stralingskerm te verwyder oor a horisontale afstand na 'n ringvormige verkoelingsdam wat rondom die reaktor geposisioneer is. Die stralingskerm word in die lug spasie tussen die reaktor drukvat (RDV) en die beton geplaas, 180 mm vanaf die beton. 'n Teoretiese hitteoordrag model van die RLSVS was geskep. Die teoretiese model was gebruik vir die ontwikkeling van 'n rekenaar program wat die transiënte gedrag van die RLSVS sal simuleer gedurende normale bedryfstoestande, waar die oorskot gegenereerde hitte verwyder moet word vanuit die reaktor lug spasie, asook gedurende noodtoestand afskakeling van die reaktor, waar die afnemingshitte verwyder moet word. Die primêre doel van die teoretiese model is om the oppervlak temperatuur van die beton te voorspel onder verskillende bedryfstoestande asook verskillende omgewingstoestande. Die teoretiese model aanvaar 'n 1D geometrie van die RLSVS. Hitte oordrag d.m.v. straling asook konveksie vanaf die RDV na die stralingskerm word bereken. The stralingskerm word gemodelleer as 'n vin. Die vin doeltre endheid was bepaal met die eksperimente wat gedoen was. Hitte geleiding in die vin was slegs bereken in die horisontale rigting. Die beton word verhit deur straling vanaf die agterkant van die stralingskerm asook deur konveksie vanaf die lug tussen die stralingskerm en die beton. The modellering van die natuurlike konveksie GLTS hitte pype word gedoen deur om gebruik te maak van die Boussinesq benadering en die homogene vloei model. 'n Eksperiment was vervaardig om the teoretiese model te veri eer. Die eksperiment is 'n volskaal model van die PBMR in die horisontale, of hoof hitteoordrag, rigting, maar is net 'n 2 m hoë snit. Die eksperimente het gewys dat die konveksie hitte oordrag tussen die RDV en die stralingskerm nie met gewone konveksie teorie gemodelleer kan word nie. 'n Nusselt getal uitdrukking wat spesi ek ontwikkel is vir natuurlike konveksie in geslote, reghoekige luggapings wat in die literatuur gevind was, was gebruik om die konveksie hitteoordrag te modelleer. Die Nusselt getal was ongeveer 3 maal groter as wat klassieke konveksie teorie voorspel het. 'n Optimeringsprosedure was ontwikkel waar 121 verskillende kombinasies van vin breedtes en pyp groottes wat gebruik kan word om 'n RLSVS te vervaardig nadat 'n toepaslike verkoelingsdam diameter gekies is. Die doel van die optimering was om die RLSVS te ontwerp wat die laagste totale massa het. 'n Verkoelingsdam diameter van 50 m was gekies. Die optimale RLSVS stralingskerm, waarvan die vloeier slegs in die vloeistof fase bly, bestaan uit 243 GLTSe wat van 62.72 mm binne diameter pype vervaardig is met 25 mm breë vinne. The totale massa van die enkel fase RLSVS is 225 ton. Die maksimum beton temperatuur is 62.5 ±C vir normale bedryfstoestande, 65.8 ±C vir 'n PLOFC noodtoestand afskakeling en is 80.9 ±C vir 'n DLOFC noodtoestand afskakeling. In die geval waar een GLTS faal gedurende 'n DLOFC noodtoestand afskakeling en die twee naasgeleë GLTSe moet kompenseer vir die vermindering in verkoelings kapasiteit, is die maksimum beton temperatuur 87.4 ±C. Dit is 37.6 ±C laer as die gespesi seerde maksimum temperatuur van 125 ±C. Die RLSVS ontwerp kan verder verbeter word wanneer die vloeier in die GLTSe kook. Die optimale RLSVS stralingskerm met die vloeier wat kook, of in twee fase vloei is, bestaan uit 338 GLTSe wat van 38.1 mm binne diameter pype vervaardig is met 20 mm breë vinne. The totale massa van die twee fase vloei RLSVS is 198 ton, 27 ton ligter as die enkel fase RLSVS. Die maksimum beton temperatuur is 60 ±C vir normale bedryfstoestande, 2.5 ±C laer as die enkel fase RLSVS. Gedurende 'n PLOFC noodtoestand afskakeling is die maksimum beton temperatuur 62.3 ±C, 3.5 ±C laer as die enkel fase RLSVS en nogtans onder die maksimum beton temperatuur van die enkel fase RLSVS vir normale bedryfstoestande. Deur om koking te veroorsaak in die GLTS word die maksimum temperatuur van die vloeier vasgepen gelyk aan die versadigings temperatuur van die vloeier by die vakuüm druk. Hierdie einskap van water word gebruik om 'n limiet te sit op die maksimum temperatuur van die beton. Hierdie e ek kan gesien word in die transiënte gedrag van die RLSVS waar die beton temperatuur styg tot en met koking plaasvind en dan konstant raak ongeag van die hitte belasting op die RLSVS. 'n Toename in die hitte belasting veroorsaak net 'n toename in die kwaliteit van die vloeistof-gas mengsel. Mengsel kwaliteite van 1 nader veroorsaak numeriese onstabiliteite in die teoretiese model. The teoretiese model kan nie die hitteoordrag beskryf na 'n kontrole volume wat 'n digtheid het laer as ongeveer 20 kg/m3. Hierdie plaas 'n limiet op die optimering van die twee fase RLSVS. Aanbevelings was gemaak met betrekking tot toekomstige werk aangaande die verbetering van die teoretiese model met spesi eke klem op die modellering van konveksie in die reaktor asook die modellering van twee fase vloei. Verdere aanbevelings was gemaak aangaande die verbetering van die stralingskerm ontwerp asook die ontwerp van die verkoeling van die GLTSe.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / This paper describes a MEng thesis project for a MEng in Renewable Energy Systems program at the Centre for Renewable Energy Studies at the University of Stellenbosch, South Africa. The aim of this paper was to offer to SAB (South African Breweries), in Cape Town, a feasibility study for the possibilities of the usage of wind energy on site. The small scale wind power technology has a long history and has been in South Africa for more than a hundred years in the form of water pump wind mills. All wind mills have an absolute maximum power output defined by the Betz limit. The choice of a wind turbine depends not only on this, but also on the wind speed distribution, the power curve, the location and financing. The small scale turbines have many different design which are predominantly grouped in horizontal axis (HAWT) and vertical axis (VAWT) machines. The choice of turbine for SAB depends on the available wind energy, the available budget, the available space and the application. The aim of the measurements on site was threefold; find a correlation with existing weather stations in the area like at Cape Town International Airport, propose a turbine for SAB’s budget and research the possibility for installing the turbine on one of the buildings. This is also known as building integrated wind turbines. Wind speeds can increase over buildings due to venturi effects and it could therefore be viable to locate these acceleration zones and install a turbine there. The data analysis shows that the wind above the brewery is very well correlated with the wind at the airport. We can therefore use the average speed values of this station to predict average power production. This leads to the proposal of a 1kW or 3kW turbine from a South African manufacturer: Kestrel. Building integration is however not a good idea. The wind is too turbulent and can therefore not be used. This is mainly caused by the fact that the surroundings of the brewery are too high and irregularly shaped. This makes it difficult for the wind to “lower” in between the buildings and accelerate. The wind turbine for SAB is proposed to be installed on the highest point of the roof and based on the neighbouring average wind speed values. The wind turbine should be connected directly to the brewery’s grid with an inverter and would then solely function as an energy saver. Another important aspect is the promotional value in the energy efficiency strategy of SAB. / Centre for Renewable and Sustainable Energy Studies

Thesis (MScEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Air pollution is a major concern III the Cape Metropole. A major contributor to the air pollution problem is road transport. For this reason, a national vehicle emissions study is in progress with the aim of developing a national policy regarding motor vehicle emissions and control. Such a policy could bring about vehicle emission control and regulatory measures, which may have far-reaching social and economic effects. Air pollution models are important tools 10 predicting the effectiveness and the possible secondary effects of such policies. It is therefore essential that these models are fundamentally sound to maintain a high level of prediction accuracy. Complex air pollution models are available, but they require spatial, time-resolved information of emission sources and a vast amount of processing power. It is unlikely that South African cities will have the necessary spatial, time-resolved emission information in the near future. An alternative air pollution model is one that is based on the Gaussian Plume Model. This model, however, relies on gross simplifying assumptions that affect model accuracy. It is proposed that statistical and mathematical analysis techniques will be the most viable approach to modelling air pollution in the Cape Metropole. These techniques make it possible to establish statistical relationships between pollutant emissions, meteorological conditions and pollutant concentrations without gross simplifying assumptions or excessive information requirements. This study investigates two analysis techniques that fall into the aforementioned category, namely, Non-linear Time Series Analysis (specifically, the method of delay co-ordinates) and Singular Spectrum Analysis (SSA). During the past two decades, important progress has been made in the field of Non-linear Time Series Analysis. An entire "toolbox" of methods is available to assist in identifying non-linear determinism and to enable the construction of predictive models. It is argued that the dynamics that govern a pollution system are inherently non-linear due to the strong correlation with weather patterns and the complexity of the chemical reactions and physical transport of the pollutants. In addition to this, a statistical technique (the method of surrogate data) showed that a pollution data set, the oxides of Nitrogen (NOx), displayed a degree of non-linearity, albeit that there was a high degree of noise contamination. This suggested that a pollution data set will be amenable to non-linear analysis and, hence, Non-linear Time Series Analysis was applied to the data set. SSA, on the other hand, is a linear data analysis technique that decomposes the time series into statistically independent components. The basis functions, in terms of which the data is decomposed, are data-adaptive which makes it well suited to the analysis of non-linear systems exhibiting anharmonic oscillations. The statistically independent components, into which the data has been decomposed, have limited harmonic content. Consequently, these components are more amenable to prediction than the time series itself. The fact that SSA's ability has been proven in the analysis of short, noisy non-linear signals prompted the use of this technique. The aim of the study was to establish which of these two techniques is best suited to the modelling of air pollution data. To this end, a univariate model to predict NOx concentrations was constructed using each of the techniques. The prediction ability of the respective model was assumed indicative of the accuracy of the model. It was therefore used as the basis against which the two techniques were evaluated. The procedure used to construct the model and to quantify the model accuracy, for both the Non-linear Time Series Analysis model and the SSA model, was consistent so as to allow for unbiased comparison. In both cases, no noise reduction schemes were applied to the data prior to the construction of the model. The accuracy of a 48-hour step-ahead prediction scheme and a lOO-hour step-ahead prediction scheme was used to compare the two techniques. The accuracy of the SSA model was markedly superior to the Non-linear Time Series model. The paramount reason for the superior accuracy of the SSA model is its adept ability to analyse and cope with noisy data sets such as the NOx data set. This observation provides evidence to suggest that Singular Spectrum Analysis is better suited to the modelling of air pollution data. It should therefore be the analysis technique of choice when more advanced, multivariate modelling of air pollution data is carried out. It is recommended that noise reduction schemes, which decontaminate the data without destroying important higher order dynamics, should be researched. The application of an effective noise reduction scheme could lead to an improvement in model accuracy. In addition to this, the univariate SSA model should be extended to a more complex multivariate model that explicitly encompasses variables such as traffic flow and weather patterns. This will explicitly expose the inter-relationships between the variables and will enable sensitivity studies and the evaluation of a multitude of scenarios. / AFRIKAANSE OPSOMMING: Die hoë vlak van lugbesoedeling in die Kaapse Metropool is kommerwekkend. Voertuie is een van die hoofoorsake, en as gevolg hiervan word 'n landswye ondersoek na voertuigemissie tans onderneem sodat 'n nasionale beleid opgestel kan word ten opsigte van voertuigemissie beheer. Beheermaatreëls van so 'n aard kan verreikende sosiale en ekonomiese uitwerkings tot gevolg hê. Lugbesoedelingsmodelle is van uiterste belang in die voorspelling van die effektiwiteit van moontlike wetgewing. Daarom is dit noodsaaklik dat hierdie modelle akkuraat is om 'n hoë vlak van voorspellingsakkuraatheid te handhaaf. Komplekse modelle is beskikbaar, maar hulle verg tyd-ruimtelike opgeloste inligting van emmissiebronne en baie berekeningsvermoë. Dit is onwaarskynlik dat Suid-Afrika in die nabye toekoms hierdie tydruimtelike inligting van emissiebronne gaan hê. 'n Alternatiewe lugbesoedelingsmodel is dié wat gebaseer is op die "Guassian Plume". Hierdie model berus egter op oorvereenvoudigde veronderstellings wat die akkuraatheid van die model beïnvloed. Daar word voorgestel dat statistiese en wiskundige analises die mees lewensvatbare benadering tot die modellering van lugbesoedeling in die Kaapse Metropool sal wees. Hierdie tegnieke maak dit moontlik om 'n statistiese verwantskap tussen besoedelingsbronne, meteorologiese toestande en besoedeling konsentrasies te bepaal sonder oorvereenvoudigde veronderstellings of oormatige informasie vereistes. Hierdie studie ondersoek twee analise tegnieke wat in die bogenoemde kategorie val, naamlik, Nie-lineêre Tydreeks Analise en Enkelvoudige Spektrale Analise (ESA). Daar is in die afgelope twee dekades belangrike vooruitgang gemaak in die studieveld van Nie-lineêre Tydreeks Analise. 'n Volledige stel metodes is beskikbaar om nie-lineêriteit te identifiseer en voorspellingsmodelle op te stel. Dit word geredeneer dat die dinamika wat 'n besoedelingsisteem beheer nie-lineêr is as gevolg van die sterk verwantskap wat dit toon met weerpatrone asook die kompleksiteit van die chemiese reaksies en die fisiese verplasing van die besoedelingstowwe. Bykomend verskaf 'n statistiese tegniek (die metode van surrogaatdata) bewyse dat 'n lugbesoedelingsdatastel, die okside van Stikstof (NOx), melineêre gedrag toon, alhoewel daar 'n hoë geraasvlak is. Om hierdie rede is die besluit geneem om Nie-lineêre Tydreeks Analise aan te wend tot die datastel. ESA daarenteen, is 'n lineêre data analise tegniek. Dit vereenvoudig die tydreeks tot statistiese onafhanklike komponente. Die basisfunksies, in terme waarvan die data vereenvoudig is, is data-aanpasbaar en dit maak hierdie tegniek gepas vir die analise van nielineêre sisteme. Die statisties onafhanklike komponente het beperkte harmoniese inhoud, met die gevolg dat die komponente aansienlik makliker is om te voorspel as die tydreeks self. ESA se effektiwitiet is ook al bewys in die analise van kort, hoë-graas nie-lineêre seine. Om hierdie redes, is ESA toegepas op die lugbesoedelings data. Die doel van die ondersoek was om vas te stel watter een van die twee tegnieke meer gepas is om lugbesoedelings data te analiseer. Met hierdie doelwit in sig, is 'n enkelvariaat model opgestel om NOx konsentrasies te voorspel met die gebruik van elk van die tegnieke. Die voorspellingsvermoë van die betreklike model is veronderstelom as 'n maatstaf van die model se akkuraatheid te kan dien en dus is dit gebruik om die twee modelle te vergelyk. 'n Konsekwente prosedure is gevolg om beide die modelle te skep om sodoende invloedlose vergelyking te verseker. In albei gevalle was daar geen geraasverminderings-tegnieke toegepas op die data nie. Die akuraatheid van 'n 48-uur voorspellingsmodel en 'n 100-uur voorspellingsmodel was gebruik vir die vergelyking van die twee tegnieke. Daar is bepaal dat die akkuraatheid van die ESA model veel beter as die Nie-lineêre Tydsreeks Analise is. Die hoofrede vir die ESA se hoër akkuraatheid is die model se vermoë om data met hoë geraasvlakke te analiseer. Hierdie ondersoek verskaf oortuigende bewyse dat Enkelvoudige Spektrale Analiese beter gepas is om lugbesoedelingsdata te analiseer en gevolglik moet hierdie tegniek gebruik word as meer gevorderde, multivariaat analises uitgevoer word. Daar word aanbeveel dat geraasverminderings-tegnieke, wat die data kan suiwer sonder om belangrike hoë-orde dinamika uit te wis, ondersoek moet word. Hierdie toepassing van effektiewe geraasverminderings-tegniek sal tot 'n verbetering in model-akkuraatheid lei. Aanvullend hiertoe, moet die enkele ESA model uitgebrei word tot 'n meer komplekse multivariaat model wat veranderlikes soos verkeersvloei en weerpatrone insluit. Dit sal die verhoudings tussen veranderlikes ten toon stel en sal sensitiwiteit-analises en die evaluering van menigte scenarios moontlik maak.