Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 1997. / A computer programme for the simulation of dilute phase pneumatic conveying of solids is presented. This includes positive pressure and vacuum pneumatic conveying. The characteristic conveying parameters such as the conveying absolute pressure, conveying air density, interstitial and average air velocity, particle velocity and voidage are calculated by integrating five differential equations that govern two-phase flow. The two-phase flow is approximated as one-dimensional along the pipe axis. Density and acceleration effects are accounted for. The integration is carried out by means of the Runge-Kutta-Fehlberg method yielding conveying parameter traces along the length ofthe pipeline. A new method is presented for the determination of the solids friction coefficient from the solids motion equation. This allows for a more accurate determination of the solids velocity in the pipeline when compared to currently used methods. The computer model results are compared to experimental results for cement and ice conveying yielding good correlation for the main output parameters. The theory for the scaling and calculation of Roots blower performance characteristics is presented. This is implemented in a Roots blower selection programme as an integral part of determining the prime air mover for the design of a pneumatic conveyor. The aim of providing a fast, user-friendly interface in terms of pipeline geometry input, simulation and data visualisation has been achieved by using the advantages of object orientated programming and the visual user interface of the DELPHI programming language.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / Shunt and shuffle in a vehicle drivetrain are two driveability related phenomena responsible for driver discomfort. They are experienced as a sharp jerk (shunt) followed by a series of longitudinal oscillations (shuffle) and are induced by a rapid change in engine torque. The use of drive‐by‐wire throttles in modern day vehicles enables the onboard electronic control unit to manipulate the driver’s torque demand befoe sending a revised torque demand signal to the engine. In this way a feedback control system can be used to ensure that the drivetrain follows the driver’s torque demand as quickly s possible without inducing shunt or shuffle.      In this project a drivetrain model was derived and its parameters experimentally determined. The accuracy of the model was validated using test data from a vehicle, and the conclusion was made that the model was an accurate vehicle simulation tool. A drivetrain controller was then designed and its performance simulated using the vehicle model. The simulations showed that the controller significantly reduced the shunt and shuffle in the drivetrain thereby improving drier comfort.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / The aerodynamic performance of an existing wind turbine blade optimised for low wind speed conditions is investigated. The aerodynamic characteristics of four span locations are determined from surface pressure measurements and wake surveys with a traversed five-hole probe performed in a low speed wind tunnel for chord Reynolds numbers ranging from 360,000 - 640,000. Two-dimensional modelling of the wind tunnel tests is performed with the commercial computational fluid dynamics code FLUENT. The predictive accuracies of five eddy-viscosity turbulence models are compared. The computational results are compared to each other and experimental data. It is found that agreement between computational and experimental results varies with turbulence model. For lower Reynolds numbers, the Transitional-SST turbulence model accurately predicted the presence of laminar separation bubbles and was found to be superior to the fully turbulent models considered. This highlighted the importance of transitional modelling at lower Reynolds numbers. With increasing angles of attack the bubbles were found to move towards the leading edge and decrease in length. This was validated with experimental data. For the tip blade section, computations implementing the k-ε realizable turbulence model best predicted experimental data. The two-dimensional panel method code, XFOIL, was found to be optimistic with significantly higher lift-to-drag ratios than measured. Three-dimensional modelling of the rotating wind turbine rotor is performed with the commercial computational fluid dynamics code NUMECA. The Coefficient of Power (Cp) predicted varies from 0.440 to 0.565 depending on the turbulence model. Sectional airfoil characteristics are extracted from these computations and compared to two-dimensional airfoil characteristics. Separation was found to be suppressed for the rotating case. A lower limit of 0.481 for Cp is proposed based on the experimental data. / Centre for Renewable and Sustainable Energy Studies

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The hydrodynamic characteristics of three typical ship-like hull sections, in different motions, are numerically investigated using FLUENT, 2009. These simple shapes, namely a v-bottom (triangle) hull, a at-bottom (square) hull and a round-bottom (semi-circle) hull, are investigated in uncoupled heave, sway and roll. The problem is described in two dimensions. A combination of numerical methods and models, found in literature, are used to conduct this investigation. Hull characterisation is achieved through the use of hull mass and damping coe cients. These numerically determined coe cients are compared to experimental work conducted by Vugts (1968). A good correlation between the numerical and experimental results exists for the heave and sway cases. By normalising the coe cients, different hulls are comparable to one another. The numerical models used are validated and veri ed. Roll motion remains largely unsolved for very large angles of roll (in excess of 11°). Different uid ow phenomena occurring around the hull sections have varying degrees of in uence on the motions of a hull. It is found that not one of the turbulence models investigated can be employed to globally solve each type of hull-motion case. Also, forced oscillations in computational simulations require considerably more computational time than free-decay oscillating hull simulations. / AFRIKAANSE OPSOMMING: Die hidrodinamiese karakteristieke van verskillende skeepsrompvorms, in verskeie bewegingswieë, is numeries ondersoek met behulp van FLUENT, 2009. Drie eenvoudige vorms ('n v-bodem (driehoek), plat-bodem (reghoek) en rondebodem (semi-sirkel) romp) is onderskeidelik ondersoek in opwieg, dwarswieg en rol. Die probleem is twee-dimensioneel. Daar is gebruik gemaak van 'n kombinasie van numeriese metodes en modelle, uit die literatuur, om die ondersoek uit te voer. Die rompe is gekarakteriseer met behulp van massa- en dempingskoëffi siënte. Hierdie numeries bepaalde koë ffisiënte is vergelyk met die eksperimentele werk van Vugts (1968). Daar bestaan 'n goeie korrelasie tussen die numeriese en eksperimentele resultate vir die opwieg en dwarswieg gevalle. Die koë ffisiënte is genormaliseer om die verskeie rompvorms te vergelyk. Die numeriese modelle is geverifi eer en valideer. Rolbewegings is onopgelos vir groot rolhoeke (groter as 11°). Die mate waartoe die romp se beweging beïnvloed word deur die verskillende vloei verskynsels wat om die rompe ontstaan, verskil. Daar is bevind dat geen van die turbulensie modelle gebruik kan word om alle skeepsbeweging-gevalle op te los nie. Gedwonge-ossilasie numeriese simulasies benodig meer berekeningstyd as vrye-verval ossilasie gevalle.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2008. / This study investigates practical passive methods to improve the seakeeping of a Hydrofoil Supported Catamaran (Hysucat). The Hysucat is a hybrid vessel combining hydrofoil efficiency with the stability of catamarans. The seakeeping of the Hysucat was initially investigated experimentally to determine what seakeeping improvements are inherent to the Hysucat design. The results showed that the seakeeping is improved by 5-30%. A passive suspension system for the main hydrofoil of the Hysucat was designed and tested. A concept development strategy was followed for the design of the suspension system as such a system had never been investigated previously. Detailed specifications for the design were developed and concepts that could satisfy the customer and engineering requirements were generated. Numerical simulation models for the Hysucat and the final concepts were derived assuming a simplified 2nd order system to describe the seakeeping dynamics of the demi-hulls. Unknown parameters were determined using parameter estimation techniques. Representative parameter values were calculated from multiple towing tank experiments. Theory describing the motion of a hydrofoil in an orbital velocity wave field was combined with the hull model to simulate the Hysucat as well as the suspension system concepts. The models indicated that the concept where the main hydrofoil was attached to a spring loaded arm, that was free to pivot in response to orbital waves, was the most feasible in damping out vertical transmitted accelerations. Experimental tests indicated that little improvement was achieved with the suspension system at low frequencies. At resonance the suspension system was effective in decreasing the heave of the vessel by up to 27%. The pitch and acceleration response results showed improvements at the higher encounter frequencies of up to 50%. The calm water resistance of the vessel increased by 10% over the Hysucat with rigidly attached hydrofoils; however was still 24% less than the hull without foils.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: One of the main challenges in using the Discrete Element Method (DEM) is to specify the correct input parameter values. In general, the models are sensitive to the input parameter values and accurate results can only be achieved if the correct values are specified. For the linear contact model, micro parameters such as the particle density, stiffness, coefficient of friction, as well as the particle size and shape distributions are required. Thus, there is a need for a procedure to accurately calibrate these parameters before any attempt can be made to accurately model a complete bulk materials handling system. Since the DEM is often used to model applications in the mining and quarrying industries, a calibration procedure was developed for materials that consist of relatively large (up to 40 mm in size) particles. A coarse crushed aggregate was used as the test material. Using a specially designed large scale shear box, the confined Young’s Modulus and internal friction angle of the material were measured by means of the confined compression test and the direct shear test respectively. The bulk (macro) density and porosity were also measured. The particle size distribution was measured while visual inspection was used to identify the different particle shapes. DEM models of the experimental set-up were developed and the input parameter values were varied iteratively until a close correlation between the experimental and numerical results was achieved. The resulting set of input parameter values were then verified through a series of anchor pull-out and angle of repose experiments and simulations. A good correlation between the experimental and numerical results was observed. In a study, independent of the calibration process, a half fraction factorial design was implemented to quantify the effect of the input parameter values on the bulk properties and to construct multiple linear regression models that relate the parameters to the bulk properties. The results were found to be in accordance with expected bulk behaviour, and can be used to develop advanced DEM calibration strategies. Based on the project outcomes, it was concluded that the developed calibration procedure performed satisfactorily and that the calibrated input parameters allow for the accurate modelling of the coarse aggregate. / AFRIKAANSE OPSOMMING: Een van die groot uitdagings in die gebruik van die Diskreet Element Metode (DEM) is om die korrekte invoer parameterwaardes te spesifiseer. Die modelle is in die algemeen sensitief vir die invoer parameterwaardes, en akkurate resultate kan slegs verkry word indien die korrekte waardes gespesifiseer word. Mikroparameters soos partikeldigtheid, styfheid, wrywingskoëffisiënt, die partikelgrootte verspreiding asook die partikelvorm verspreiding, word benodig vir die lineêre kontakmodel. ’n Prosedure word dus benodig om hierdie parameters akkuraat te kalibreer alvorens ’n volledige korrelagte materiaalhanteringstelsel akkuraat gemodelleer kan word. Aangesien die DEM gereeld in die modellering van myn- en gruisgroefbedryf toepassings gebruik word, is ’n kalibrasieprosedure ontwikkel vir materiaal wat bestaan uit relatief groot (tot 40 mm in grootte) partikels. Grofgebreekte klippe is as toetsmateriaal gebruik. Deur gebruik te maak van ’n spesiaal ontwerpte grootskaal-skuifboks is die ingeperkte Young se Modulus en die interne wrywingshoek van die materiaal gemeet deur middel van die ingeperkte kompressietoets en die direkte skuiftoets onderskeidelik. Die makro-digtheid en poreusheid is ook gemeet. Die partikelgrootte verspreiding is gemeet terwyl visuele inspeksie gebruik is om die verskillende partikelvorms te identifiseer. DEM modelle van die eksperimentele opstelling is ontwikkel en die invoer parameterwaardes is herhaaldelik gewysig totdat ’n goeie korrelasie verkry is tussen die eksperimentele en numeriese resultate. Die gevolglike stel invoer parameterwaardes is daarna geverifieer deur ’n reeks ankeruittrek- en natuurlike helling eksperimente en simulasies. In ’n studie, onafhanklik van die kalibrasieproses, is die half-fraksie faktoriaalontwerp geïmplementeer om die invoer parameterwaardes se effek op die makro eienskappe te kwantifiseer en om meervoudige lineêre regressiemodelle te ontwikkel wat die parameters met die makro eienskappe verbind. Die resultate was in ooreenstemming met die verwagte makro gedrag en kan gebruik word om gevorderde DEM kalibrasie-strategieë te ontwikkel. Daar is tot die gevolg gekom dat, gebaseer op die projekresultate, die ontwikkelde kalibrasieprosedure bevredigend presteer en dat die gekalibreerde invoer parameters die akkurate modellering van die grofgebreekte klippe toelaat.

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

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Thermoplastic composites (TPCs) have shown significant advantages over thermosetting composites. They have only been put into use recently and global knowledge in TPCs is often proprietary, therefore a study into the application, processing and properties is of importance. The aim of the study is to contribute knowledge in TPCs for South African industry and academic institutions. This thesis studies continuous fibre reinforced thermoplastics (CFRTPs), focussing on the autoclave processing of commingled CFRTPs. A literature study provided background knowledge to CFRTPs regarding processing techniques and mechanics. Flexural testing and impact testing were performed on a variety of CFRTPs and thermosetting composites (TSCs). These tests were performed to further understand CFRTPs as well as to compare CFRTPs and TSCs. The flexural testing revealed that CFRTPs have comparable strength and stiffness to the TSCs that were tested. They also revealed that pre-consolidated sheets showed better and more consistent properties than sheets made from commingled fabric. The impact testing revealed that the tested CFRTPs and TSCs had similar impact resistance even though thermoplastic composites are supposed to be more impact resistant. The tests also showed that thick unreinforced thermoplastics had much higher impact resistance than the reinforced materials. Manufacturing experiments were performed to establish sound processing methods of CFRTPs. It was realised here that the high temperatures required to process the materials require specific processing consumables and tooling. The experiments began by processing flat panels in a convection oven with vacuum bagging techniques. They then progressed to autoclave processing of parts with complex geometry. An airline seat backrest was chosen as the case study in the application of CFRTPs. This application requires structural strength and stiffness and also has strict fire, smoke, toxicity and heat release (FSTH) requirements. Its geometry was sufficiently complex to demonstrate the use of commingled CFRTP material. Backrests were made from both CFRTPs and TSCs so that a comparison could be made between the two types. The backrest was modelled using finite element methods (FEM) to determine an adequate lay-up. This lay-up was then used for both the CFRTP and TSC backrests to ensure similarity between the backrests of both materials. LPET (modified polyethylene terephthalate) was the chosen thermoplastic matrix as it was more attainable than PPS (polyphenylene sulphide) CFRTPs. The backrests of both materials were manufactured in an autoclave with a vacuum bag method and then assembled using adhesives and bonding jigs. Testing revealed that the stiffness and mass of the CFRTP backrests were very similar to the epoxy backrests. This implies that commingled CFRTPs can replace the use of TSCs in similar applications. A basic cost comparison was also performed to compare the manufacture of CFRTP backrests to TSC backrests. Further work is needed to optimise processing time of these materials to make them more competitive with TSCs. The processing time of commingled materials will probably never be as quick as that of press formed pre-consolidated sheets. Their ability to be formed into more complex parts does however make their use advantageous. / AFRIKAANSE OPSOMMING: Termoplastiese saamgestelde materiale (Engels: thermoplastic composites (TPCs)) toon beduidende voordele bo termoverhardbare saamgestelde materiale. Hulle word eers sedert onlangs benut en algemene kennis in TPCs is dikwels patentregtelik, dus is ’n studie van die aanwending, prosessering en eienskappe daarvan van belang. Die doel van hierdie studie is om ’n bydrae te lewer tot die kennis van TPCs vir die Suid-Afrikaanse industrie en akademiese instellings. Hierdie tesis ondersoek kontinue veselversterkte termoplastieke (Engels: continuous fibre reinforced thermoplastics (CFRTPs)) en fokus op die outoklaafprosessering van vermengde (Engels: commingled) CFRTPs. ’n Literatuurstudie het die agtergrondkennis rakende die prosesseringstegnieke en meganika van CFRTPs verskaf. Buigtoetsing en impaktoetsing is op ’n verskeidenheid CFRTPs en termoverhardbare saamgestelde materiale (Engels: thermosetting composites (TSCs)) uitgevoer. Hierdie toetse is uitgevoer om CFRTPs beter te verstaan asook om CFRTPs en TSCs te vergelyk. Die buigtoetsing het onthul dat CFRTPs ooreenstemmende sterkte en styfheid het as die TSCs wat getoets is. Dit het ook getoon dat vooraf-gekonsolideerde plate beter en meer konsekwente eienskappe getoon het as plate wat van vermengde materiaal gemaak is. Die impaktoetsing het onthul dat die CFRTPs en TSCs wat getoets is soortgelyke impakweerstand gehad het, selfs al is termoplastiese saamgestelde materiale veronderstel om meer impakweerstand te toon. Die toetse het ook getoon dat dik onversterkte termoplastieke veel hoër impakweerstand gehad het as die versterkte materiale. Vervaardigingseksperimente is uitgevoer om betroubare prosesseringsmetodes vir CFRTPs vas te stel. Daar is besef dat die hoër temperature wat vereis word om die materiale te prosesseer ook spesifieke prosesseringsverbruiksware en -gereedskap benodig. Die eksperimente het begin met die prosessering van reguit panele in ’n konveksie-oond met vakuumsaktegnieke. Daar is toe aanbeweeg na die outoklaafprosessering van onderdele met komplekse geometrie. Die rugleuning van ’n vliegtuigsitplek is gekies as die gevallestudie in die gebruik van CFRTPs. Hierdie toepassing vereis strukturele sterkte en styfheid en is ook onderhewig aan streng vereistes t.o.v. brand, rook, toksisiteit en hittevrystellimg (Engels FSTH). Die geometrie daarvan was kompleks genoeg om die gebruik van vermengde CFRTP-materiaal te demonstreer. Rugleunings is gemaak van beide CFRTPs en TSCs sodat ’n vergelyking tussen die twee tipes gemaak kon word. Die rugleuning is gemodelleer deur eindige element metodes (EEM) te gebruik om ’n aanvaarbare oplegging te bepaal. Hierdie oplegging is toe gebruik vir beide die CFRTP en TSC rugleunings om die gelykvormigheid tussen die rugleunings van beide materiale te verseker. LPET (Engels: modified polyethylene terephthalate) was die gekose termoplastiese matriks aangesien dit meer verkrygbaar was as PPS (Engels: polyphenylene sulphide) CFRTPs. Die rugleunings van beide materiale is vervaardig in ’n outoklaaf met ’n vakuumsakmetode en toe geintegreer deur die gebruik van kleefstowwe en setmate. Toetsing het getoon dat die styfheid en massa van die CFRTP rugleunings baie soortgelyk was aan die epoksie rugleunings. Dit impliseer dat vermengde CFRTP die plek van TSCs in soortgelyke gebruike kan inneem. ’n Basiese kostevergelyking is ook gedoen om die vervaardiging van CFRTP-rugleunings teenoor TSC-rugleunings te vergelyk.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: In the primary circuit components of high temperature reactors, various unwanted particles have been found. These particles include, for example, graphite and silver- 110 (110mAg). The silver-110 (110mAg) particles are radioactive, with a half-life of 253 days. The presence of radioactive particles in the primary circuit components constitutes an unwanted maintenance problem from a radiation hazard point of view. The development of a method to remove these particles from the helium stream is therefore needed. This thesis consideres two possible methods of removing silver from the helium stream, namely laser ablation of microparticles and electrostatic precipitation. These methods require the generation of silver ions or charged particles, the deflection of these particles in a helium gas stream passing through an electric field and the subsequent plate-out of these particles onto deflection electrodes. To find a suitable method of generating ions, various methods to generate the silver ions were investigated and evaluated. These methods include existing ion sources, thermionic, field and photoelectric emission and laser ablation of microparticles. No existing ion sources could be found which could be utilised in helium at high pressure. From calculations it was concluded that thermionic, field and photoelectric emission could also not be used to raise the energy of the emitted electrons sufficiently to ionize silver in a helium flight path. These methods were found not to be feasible ion sources in helium at high pressures. However, laser ablation of microparticles was found to constitute a feasible technology. Laser ablation was successfully utilised by Nichols et al. (2000) to deflect silver nanoparticles in an electric field across a two bar helium stream. An apparatus, similar to the one developed by Nichols et al. (2000), was designed and built. The apparatus included a silver insertion mechanism and tests with this apparatus were called the microparticle tests. To determine the efficacy of the silver insertion mechanism, the microparticle tests were done without the use of a laser. It was found that a laser was not necessary as microparticles collected on both the deflection electrodes. Dielectrophoresis was proposed as a possible explanation for the deflection and the plate-out of the mcroparticles. To theoretically model the deflection of the silver particles, two models were proposed, namely the deterministic and the stochastic deflection models. The latter describes the deflection of atoms, ions and polarized particles by using probability theory. From this model it was found that the Brownian motion force is far larger that the force created by the polarizibility of the atom due to an electric field. The deterministic deflection model describes the deflection of larger particles in a continuum. From this model it was found that a silver microparticle with a radius of 3 mm in a helium stream with bulk velocity of 0.0198 m/s would deflect 4.6 mm per helium flight path length of 140 mm. From these calculation it was found that the apparatus which had been built was not long enough to deflect and plate-out all the silver microparticles. The dielectrophoresis force on nanoparticles cannot be calculated, as the theory of dielectrophoresis is only valid for particles with diameter larger than 1 mm. Changes were therefore made to the apparatus to generate nanoparticles as their mobility is larger than that of microparticles. The nanoparticles were created by means of an arc discharge in helium; therefore tests with this modified apparatus were called the arc discharge test. The nanoparticles so created, deflected and deposited on both deflection electrodes. With the use of an atomic force microscope some of the particles could be classified as microparticles. According to the deterministic deflection model they should not have deflected. Combined with the fact that oxygen was in the plasma, due to the oxidation of the electrodes, a hypothesis of bipolar charging was thus proposed. The deterministic deflection model was used and supplemented with field and diffusion charging calculations, to support this hypothesis. A reasonable correlation between the theoretical model and this experimental results was obtained. Based on the arc discharge test, electrostatic precipitation was proposed as the indicated means of scrubbing silver and other particles such as graphite from a helium stream. It is recommended that a new apparatus be built and that the deterministic deflection model be used to predict the deflection of the particles. With this apparatus the uncertainties of breakdown voltage, the effect of thermionic emission and the size of the particles, all of which have been identified as being important, can then also be determined. / AFRIKAANSE OPSOMMING: In die primêre komponente van die kringloop van hoë temperatuurreaktors, was verskillende ongewenste partikels soos grafiet en silwer-110 (110mAg) teenwoordg. Silwer- 110 (110mAg) is radioaktief met ’n halfleeftyd van 253 dae. Vanuit ’n radiasie-risiko oogpunt word daar onderhoudsimplikasies geskep deur die teenwoordigheid van radioaktiewe partikels in die primêre komponente. Die ontwikkeling van ’n metode om hierdie partikels uit die heliumstroom the verwyder was dus nodig. Hierdie tesis ondersoek twee moontlike metodes van verwydering van silwer uit die heliumstroom, naamlik laser-ablasie van mikropartikels en elektrostatiese presipitasie. Hierdie metodes benodig die generasie van silwer ione of gelaaide partikels, die defleksie daarvan in ’n heliumstroom wat deur ’n elektriese veld vloei en die platering van die partikels op defleksie elektrodes. Om ’n geskikte metode the vind wat ione genereer was, verskillende metodes om die silwer ione te verkry, ondersoek en geëvalueer. Hierdie metodes sluit in bestaande ioonbronne, termioniese, veld en fotoëlektriese emissie en laser-ablasie van mikropartikels. Geen ioonbronne was gevind wat gebruik kan word in helium by hoë druk nie. Die gevolgtrekking is gemaak vanaf berekeninge dat termioniese, veld en fotoëlektriese emissie ook nie gebruik kan word om die energie van die voortgebronge elektrone genoeg te verhoog om silwer in ’n heliumstroom te ioniseer nie. Daar was gevind dat hierdie metodes nie geskik is as ioonbronne in helium by hoë druk nie. Daarenteen was laser-ablasie van mikropartikels gevind om ’n geskikte tegnologie voor te stel. Laser-ablasie van mikropartikels was suksesvol deur Nichols et al. (2000) gebruik om silwer nanopartikels te deflekteer in ’n elektriese veld oor helium van twee bar. ’n Apparaat soortgelyk aan Nichols et al. (2000) se eksperiment, was dus ontwerp en gebou. Die apparaat het ’n silwer insitmeganisme bevat en toetse met hierdie apparaat was die mikropartikel toetse genoem. Om die effektiwiteit van die insitmeganisme te bepaal, was toetse gedoen sonder opstelling van die laser. Daar was eksperimenteel gevind dat die laser nie nodig was nie, omdat mikropartikels op beide defleksie elektrodes geplateer het. Dielektroforese was voorgestel as ’n moontlike verduideliking vir deflektering en platering vir die silwer mikropartikels. Om die defleksie van silwer partikels teoreties te moduleer was twee modelle voorgestel, naamlik deterministiese en stogastiese defleksiemodelle. Laasgenoemde beskryf die defleksie van atome, ione en gepolariseerde partikels deur gebruik te maak van waarskynlikheidsteorie. Die stogastiese defleksiemodel dui aan dat die Brownian bewegingskrag veel groter is as die krag wat geskep word deur die polarisasie van ’n atoom as gevolg van ’n elektriese veld. Die deterministiese defleksiemodel beskryf die defleksie van groter partikels in ’n kontiuum. Met hierdie model was gevind dat silwer mikropartikels met ’n radius van 3 mmin ’n heliumstroom van snelheid van 0.0198 m/s, 4.6 mm sal deflekteer per 140 mm van heliumstroom lengte. Dit bewys dat die apparaat wat gebou was, se lengte onvoldoende was om al die silwer mikropartikels te deflekteer en te laat neerslaan. Die dielektroforese krag van nanopartikels kan nie uitgewerk word nie, omdat die dielektroforese model slegs geldig is vir partikels groter as 1 mm. Veranderings was dus aan die apparaat gemaak om nanopartikels te genereer omdat hul mobiliteit hoër is as die van mikropartikels. Die nanopartikels was geskep deur gebruik van ’n boogontlading in helium; daarom was toetse met hierdie gemodifiseerde apparaat die boogontladingstoets genoem. Die nanopartikels wat so geskep was, het gedeflekteer en het op beide elektrodes neergeslaan. Met die gebruik van ’n atomiese krag mikroskoop was dit gevind dat sommige van hierdie partikels mikropartikels was. Volgens die deterministiese defleksiemodel moes hul nie gedeflekteer het nie. Gekombineerd met die feit dat daar, weens oksidasie van die elektrodes, suurstof in die plasma was, was ’n hipotese van bipolêre lading voorgestel. Die deterministiese defleksiemodel is saam met die veld- en diffusielading gebruik om hierdie hipotese te staaf. ’n Redelike korrelasie tussen die teoretiese en eksperimentele data was gevind. Gebaseer op die boogontladingstoets, was elektrostatiese presipitasie voorgestel as ’n metode om silwer en ander partikels soos grafiet uit ’n heliumstroom te verwyder. Daar word voorgestel dat ’n nuwe apparaat gebou word en dat die deterministiese defleksiemodel gebruik word vir die bepaling van defleksie van die partikels. Deur die nuwe apparaat te gebruik kan die onsekerhede van deurslagspanning, effek van termioniese emissie en grootte van die partikels wat geidentifiseer is as belangrik, ook bepaal word.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / Cooling tower rain zone performance characteristics such as the loss coefficient and the Merkel number are evaluated and simulated. To this end the influence of drop diameter and drop deformation on the velocity, path length and cooling of single water drops are investigated. Experimental drop size and pressure drop data over a counterflow rain zone are presented and the effect of drop deformation on the pressure drop is investigated using the experimental data and CFD. Using the experimental drop size data and CFD, the performance uncertainty produced by using the Rosin-Rammler drop distribution function as opposed to the discrete drop distribution data is investigated. CFD models are developed to investigate the feasibility of modelling rain zones by assuming a constant drop diameter and to establish which diameter definition is the most representative of a particular polydisperse drop distribution. These models were used to validate the correlations for the rain zone performance characteristics proposed in literature.