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

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

Thesis (MScEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2008. / Aortic valve replacements are frequently performed during heart surgery. However, since this is quite a stressful procedure, many patients are turned down for medical reasons. Stented valves, designed and manufactured for percutaneous insertion, eliminate many of the risks involved in open-heart surgery, thus providing a solution to patients not deemed strong enough for open-chest aortic valve replacements. The aortic valve is a complex structure, and therefore numerical simulation is necessary to obtain flow and stress data to support the design of a prosthetic heart valve in the absence of viable physical measuring methods. To aid in the design of a prosthetic heart valve, various finite element valve models were created, and the fluid structure interaction (FSI) between the valves and the blood was simulated using commercial finite element software. The effect of the geometry of the leaflets on the haemodynamic behaviour over the cardiac cycle was investigated. It was found that leaflet dimensions should be chosen judiciously, because of their considerable effect on the stress distribution and performance of the valve. A simple leaflet geometry optimisation was done for a 20 mm and 26 mm valve, respectively, by means of existing geometry relationships found in the literature. Simulations were done to obtain the maximum leaflet attachment forces that can be used by a stent designer for fatigue loading, or to investigate the structural strength of the stent. These simulations were numerically validated. The effect of leaflet thickness and stiffness on resistance to opening, stress distribution and strain were investigated. Results showed that leaflet thickness has a greater effect on the performance of the valve than leaflet stiffness, and thereby validated the results of similar tests contained in the literature. After simulating over-, as well as under-dilation of a stented valve, it was found that problems associated with over-dilation can be minimised to a certain extent by increasing the coaptation1 region of the leaflets. A simple pulse duplicator was designed based on a four-element Windkessel model. The pulse duplicator was used to study the performance of the prototype valves by means of high-speed photography, the results of which were fed into one of the numerical finite element models and compared to real valve performance. Some of the prototype valves showed efficiencies of 88%.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2007. / This thesis is concerned with the simulation of the in vivo biomechanical performance of a cervical disc replacement. A representative (averaged) maximum range of motion (ROM), determined by measurement of 10 student participants (5 male, 5 female), was used as head motion input to a simulation model of the cervical spine containing a disc implant at the C5/C6 intervertebral level. Intradiscal pressure, relative applied force on the C5 vertebrae, bending moments and vertebral rotations were recorded. The force and motion components of the results obtained were critically evaluated against the ISO and ASTM experimental protocol standards, probing the representativeness of these standards to the actual in vivo behaviour of the cervical functional spinal unit. Further, the wear resulting from a lifetime (10 million cycles) of the ISO prescribed -and simulation determined input cycles was simulated using a linear wear model with a triangulation technique for volume lost due to wear, and compared to in vitro results in the literature. The inputs used for the wear model were determined from a validated non-linear static contact finite element method (FEM) model. The simulation “chain” shows great potential as a comparative tool for the preexperimental testing of spinal implant designs and may be used with relative success as an alternative to expensive prototype testing.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A wet-cooling tower fill performance evaluation model developed by Reuter is derived in Cartesian coordinates for a rectangular cooling tower and compared to cross- and counterflow Merkel, e-NTU and Poppe models. The models are compared by applying them to a range of experimental data measured in the cross- and counterflow wet-cooling tower test facility at Stellenbosch University. The Reuter model is found to effectively give the same results as the Poppe method for cross- and counterflow fill configuration as well as the Merkel and e-NTU method if the assumptions as made by Merkel are implemented. A second order upwind discretization method is applied to the Reuter model for increased accuracy and compared to solution methods generally used to solve cross- and counterflow Merkel and Poppe models. First order methods used to solve the Reuter model and crossflow Merkel and Poppe models are found to need cell sizes four times smaller than the second order method to obtain the same results. The Reuter model is successfully implemented in two- and three-dimensional ANSYS-Fluent® CFD models for under- and supersaturated air. Heat and mass transfer in the fill area is simulated with a user defined function that employs a second order upwind method. The two dimensional ANSYS-Fluent® model is verified by means of a programmed numerical model for crossflow, counterflow and cross-counterflow. / AFRIKAANSE OPSOMMING: ‘n Natkoeltoring model vir die evaluering van pakkings werkverrigting, wat deur Reuter ontwikkel is, word in Kartesiese koördinate afgelei vir ‘n reghoekige koeltoring en word vergelyk met kruis- en teenvloei Merkel, e-NTU en Poppe modelle. Die verskillende modelle word vergelyk deur hulle op ‘n reeks eksperimentele data toe te pas wat in die kruis- en teenvloei natkoeltoring toetsfasiliteit by die Universiteit van Stellenbosch gemeet is. Dit is bevind dat die Reuter model effektief dieselfde resultate gee as die Poppe model vir kruis- en teenvloei pakkingskonfigurasies sowel as die Merkel en e-NTU metode, indien dieselfde aannames wat deur Merkel gemaak is geїmplementeer word. ‘n Tweede orde “upwind” metode word op die Reuter model toegepas vir hoër akkuraatheid en word vergelyk met oplossingsmetodes wat gewoonlik gebruik word om kruis- en teenvloei Merkel en Poppe modelle op te los. Eerste orde metodes wat gebruik is om die Reuter model en kruisvloei Merkel en Poppe modelle op te los benodig rooster selle wat vier keer kleiner is as vir tweede orde metodes om dieselfde resultaat te verkry. Die Reuter model is suksesvol in twee- en driedimensionele ANSYS-Fluent® BVD (“CFD”) modelle geїmplementeer vir on- en oorversadigde lug. Warmte- en massaoordrag in die pakkingsgebied word gesimuleer mbv ‘n gebruiker gedefinieerde funksie (“user defined function”) wat van ‘n tweede orde numeriese metode gebruik maak. Die tweedimensionele ANSYS-Fluent® model word m.b.v. ‘n geprogrameerde numeriese model bevestig vir kruis-, teen- en kruis-teenvloei.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The focus of this project was on the potential application of waste heat recovery and utilisation (WHR&U) systems in pebble bed modular reactor (PBMR) technology. The background theory provided in the literature survey showed that WHR&U systems have attracted the attention of many researchers over the past two decades, as using waste heat improves the system overall efficiency, notwithstanding the cost of extra plant. PBMR waste heat streams were identified and investigated based on the amount of heat rejected to the environment. WHR&U systems require specially designed heat recovery equipment, and as such the used and/or spent PBMR fuel tanks were considered by the way of example. An appropriately scaled system was designed, built and tested, to demonstrate the functioning of such a cooling system. Two separate and independent cooling lines, using natural circulation flow in a particular form of heat pipes called thermosyphon loops were used to ensure that the fuel tank is cooled when the power conversion unit has to be switched off for maintenance, or if it fails. A theoretical model that simulates the heat transfer process in the as-designed WHR&U system was developed. It is a one-dimensional flow model assuming quasi-static and incompressible liquid and vapour flow. An experimental investigation of the WHR&U system was performed in order to validate the theoretical model results. The experimental results were then used to modify the theoretical heat transfer coefficients so that they simulate the experiments more accurately. Three energy conversion devices, the dual-function absorption cycle (DFAC), the organic Rankine cycle (ORC) and the Stirling engine (SE), were identified as suitable for transforming the recovered heat into a useful form, depending on the source temperatures from 60 ºC to 800 ºC. This project focuses on a free-piston SE with emphasis on the thermo-dynamic performance of a SE heat exchanger. It was found that a heat exchanger with a copper woven wire mesh configuration has a relatively large gas-to-metal and metal-to-liquid heat transfer area. Tube-in-shell heat exchanger configurations were tested, with the working fluid flowing in ten copper inner pipes, while a coolant flows through the shell tube. A lumped parameter model was used to describe the thermo-fluid dynamic behaviour of the SE heat exchanger. In order to validate the theoretical results, a uni-directional flow experimental investigation was performed. The theoretical model was adjusted so that it simulated the SE heat exchanger. It was found that after this correction the theoretical model accurately predicts the experiment. Finally, a dynamic analysis of the SE heat exchanger experimental set-up was undertaken to show that, although vibrating, the heat exchanger setup assembly was indeed acceptable from a vibrational and fatigue point of view. / AFRIKAANSE OPSOMMING: Die hoofoogmerk met hierdie projek was die moontlike aanwending van afvalhitteherwinningen- benutting-(WHR&U-) stelsels in modulêre-gruisbedreaktor-(PBMR-) tegnologie. Agtergrondteorie in die literatuurondersoek toon dat WHR&U-stelsels al menige navorser se belangstelling geprikkel het, hetsy vanweë die moontlike ekonomiese voordele wat dit inhou óf vir besoedelingsvoorkoming, bo-en-behalwe die koste van bykomende toerusting. Die PBMRafvalhittestrome is ondersoek en bepaal op grond van die hoeveelheid hitte wat dit na die omgewing vrystel. Om in die prosesbehoeftes van WHR&U-stelsels te voorsien, moet goed ontwerpte, doelgemaakte hitteherwinningstoerusting in ʼn verkoelings- en/of verhittingsproses gebruik word, dus is die PBMR as voorbeeld gebruik vir die konsep. ʼn Toepaslik geskaleerde WHR&U-stelsel is dus ontwerp, gebou en getoets om die geldigheid van die stelselontwerp te toon. Twee onafhanklike verkoelingslyne, wat van natuurlike konveksie gebruik maak, in die vorm van hitte-pype of termoheuwel lusse, was gebruik om te verseker dat verkoeling verskaf word wanneer die hoof lus breek of instandhouding nodig hê. ʼn Teoretiese model is ontwikkel wat die hitteoordragproses in die ontwerpte WHR&U-stelsel simuleer. Dié model was ʼn eendimensionele vloeimodel wat kwasistatiese en onsamedrukbare vloeistof- en dampvloei in die WHR&U-stelsel-lusse veronderstel. ʼn Eksperimentele ondersoek is op die WHR&U-stelsel uitgevoer ten einde die teoretiese model se resultate te bevestig. Die eksperimentele resultate was dus geneem om die teoretiese hitteoordragkoëffisiënte aan te pas sodat dit die eksperimente kon simuleer. Drie energieomsettingstoestelle, naamlik die dubbel funksie absorpsie siklus (DFAC), die organiese Rankine siklus (ORC) en die Stirling enjin (SE), is as geskikte toestelle uitgewys om die herwonne hitte op grond van brontemperature tussen 60 ºC en 800 ºC in ʼn bruikbare vorm om te sit. Hierdie tesis het op vryesuier-SE’s gekonsentreer, met klem op die hitteruiler. Meer bepaald is die termodinamiese werkverrigting van ʼn SE-hitteruiler ondersoek. Daar is bevind dat ʼn hitteruiler met ʼn geweefde koperdraadmaas-samestelling oor ʼn betreklik groot gas-totmetaal- en metaal-tot-vloeistof-oordragoppervlakte beskik. Die verhitter en verkoeler is in ʼn buis-in-mantel-vorm ontwerp, met die werksvloeistof wat deur tien koperbinnepype vloei en ʼn koelmiddel deur die mantelbuis. ʼn Saamgevoegde-parameter-model is gebruik om die termodinamiese gedrag van die SEhitteruiler te beskryf. Ten einde die teoretiese resultate te bevestig, is ʼn eenrigtingvloeiproefondersoek uitgevoer. Die teoretiese model is aangepas sodat dit die SE-hitteruiler kon simuleer. Ná die nodige verstellings is daar bevind dat die teoretiese model die proefneming akkuraat voorspel. Laastens was ʼn dinamiese ontleding van die SE-hitteruiler ook onderneem om te toon dat, hoewel dit vibreer, die hitteruiler proef samestel inderdaad veilig is.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / A small scale steam jet ejector experimental setup was designed and manufactured. This ejector setup is of an open loop configuration and the boiler can operate in the temperature range of Tb = 85 °C to 140 °C. The typical evaporator liquid temperatures range from Te = 5 °C t o 10 °C while the typical water cooled condenser presure ranges from Pc = 1 . 70 kPa t o 5. 63 kPa (Tc = 15 °C to 35 °C). The boiler is powered by by two 4kW electric elements, while a 3kW electric element simulates the cooling load in the evaporator. The electric elements are controlled by means of variacs. The function ... / Centre for Renewable and Sustainable Energy Studies

Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. / Thesis (MEng)--Stellenbosch University, 1990. / ENGLISH ABSTRACT: The causes of disturbances in the flow patterns at the inlets of axial flow fans that are used in mechanical draft cooling towers and the effects of these disturbances on the fans, were investigated. A scale model of a part of a mechanical draft cooling tower used at a power station was built for the purpose of this study. In the cooling tower the axial flow fans are arranged in a matrix configuration. It was noted from the scale model that the boundary fan was subjected to the worst inlet disturbances and this had an adverse effect on the flow it produced. Geometric alterations like the use of guide vanes and rounded inlets improved the flow through the boundary fan considerably. It was found that the performance of the fans is a function of the number of fans used and the elevation of the fans. Several tests to determine the performance of the cooling tower confirmed the results obtained from the experiments on the scale model. It was also found that the speed and direction of the prevailing wind have a significant effect on the cooling tower. Experiments to investigate the effects of cross-flow at the inlet of a fan indicated an increased flow through the fan at low cross-flow velocities and that the flow decreased at high cross-flow velocities. / AFRIKAANSE OPSOMMING: Die invloed en oorsake van versteurde inlaatvloeipatrone op aksiaalwaaiers wat in meganiese-trek koeltorings gebruik word is ondersoek. 'n Skaaimodel van 'n deel van 'n meganiese-trek koeltoring wat by 'n kragstasie gebruik word is gebou vir die doel van die studie. Die aksiaalwaaiers wat in die koeltoring gebruik word is in 'n matrikskonfigurasie gerangskik. Vanaf die skaalmodel is waargeneem dat die randwaaier die ergste versteuring by die inlaat ervaar, en gevolglik minder vloei as die res van die waaiers in die opstelling lewer. Die vloei deur die randwaaier is verbeter deur verskillende geometriese wysigings soos leilemme en inlaatafrondings aan te bring. Daar is gevind dat die werking van die waaiers in die opstelling 'n funksie van die hoeveelheid waaiers asook die grondvryhoogte is. Om die werking van die koeltoring te bepaal is verskillende toetse daarop uitgevoer. Die resultate het die geldigheid van die skaalmodel bevestig. Daar is ook gevind dat die heersende windsterkte en rigting 'n definitiewe invloed op die koeltoring uitoefen. Die invloed van 'n dwarsvloei by die inlaat van 'n enkele waaier is ook eksperimenteel ondersoek. Die resultate toon dat daar 'n vermeerdering in vloei deur die waaier by lae dwarsvloeisnelhede plaasvind. Hoë dwarsvloeisnelhede veroorsaak egter 'n vermindering in vloei.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / The project aimed at numerically modeling the flow and thermal processes occurring in a Volkswagen Citi Golf Chico underhood using computational fluid dynamics (CFD). The motivation for this investigation was to develop and demonstrate the capability of CFD as an automotive analysis tool. This would allow local automobile analysts and designers enhanced analyses of the thermal and flow conditions occurring in this com-pact environment, leading to improved local vehicles. A review of relevant literature indicated that the CFD community in South Africa is small with comparison to the international sector. The application of CFD to analyse automo-biles in South Africa is limited and practised by few. This experience requires develop-ment and refinement, such that South Africa may improve vehicles manufacture in the country. The review also indicated that CFD used in the international communities pro-vides good results, promoting simulation-based engineering. The experimental investigation involved parking a vehicle in the subsonic wind tunnel intake at the Mechanical Engineering Department in Stellenbosch. This tunnel is 3.7 m wide, 4 m long and 2.8 m tall, capable of wind speeds up to 90 m/s. Various equipment including thermocouples, a thermal imager and a hand held hot-wire anemometer pro-vided temperature and velocity measurements within the underhood. A pitot-static probe connected to a pressure transducer measured the wind tunnel velocities. The numerical investigation started with the creation of a three-dimensional geometry of the underhood from measurements taken of the vehicle. This geometry, created with Solid Edge version 14, formed the domain for automatically generating discretised grids using STAR-Design version 3.2. Subsequently, boundary conditions and numerical models were applied to the grids, which included simplified fan and radiator models. The analysis concluded with results obtained from the numerical CFD simulations, per-formed with STAR-CD version 3.24. The validity and accuracy of the numerical solutions was verified and quantified with the numerical results. The evaluation consisted of two test cases (wind tunnel speeds of 0 m/s and 5 m/s), each simulated at three different grid resolutions. Each simulation con-tinued until they fully converged to a single solution. The comparison of the three simu-lations from each case indicated that the results were grid independent. The final in-spection of the results in terms of y+ values and boundary conditions indicated that the models implemented were valid. The comparison of the numerical results for temperatures and fan inlet velocities with the experimentally measured data served as a measure to quantify the applicability of CFD for underhood investigations. The comparison between the two sets of results proved acceptable, with a maximum difference of 10%, indicating that CFD is capable of predicting temperatures and flow fields with reasonable accuracy. The numerical results indicated that while the vehicle travels at higher velocities, the underhood remains well ventilated. The underhood tends to trap the hot air from the radiator and other heat sources when the vehicle remains stationary, causing the air to heat further. This can be addressed by the installation of vents in the side panels near the top of the underhood environment. This should allow the hot air to escape, possibly resulting in a significant reduction of the underhood temperatures. Momentum and energy source terms modelled the effects from the fan and radiator. These models worked well for both cases, but improvement is necessary. Special at-tention should be given to the condition where the radiator fan obstructs the flow through the radiator. A further result of the project was the establishment of a flexible foundation for conduct-ing numerical simulations on automobiles. It allows for the inclusion of additional com-ponents and the implementation of more advanced models for representing effects from various engine components.

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2006. / Cooling tower spray nozzle performance characteristics such as the water distribution onto the fill material, air side pressure drop, pump head, drop size distribution and heat transfer in the spray zone were investigated experimentally and theoretically. The aim was to evaluate and simulate the performance characteristics of new and existing types of cooling tower spray nozzles with emphasis on the spray zone. Two medium and two low pressure type spray nozzles were tested and the results analysed. Single nozzle water distribution data obtained from tests was used to predict the water distribution obtained from four evenly spaced nozzles by superposition. The results were compared to data obtained from corresponding four nozzle tests. Computer codes and CFD models were developed to predict the drop trajectories, water distribution, total heat transfer and pressure drop for single nozzles and four nozzle grids. This was compared to correlated data found in literature. The performance characteristics expected from an ideal nozzle was discussed and compared to actual nozzle performance characteristics.