Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2011. / Please refer to full text to view abstract.

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, 2010. / ENGLISH ABSTRACT: The purpose of this project is to investigate the method and accuracy of simulating axial ow fans with three-dimensional axisymmetric CFD models. Two models are evaluated and compared with experimental fan data. Veri cation data is obtained from a prototype fan tested in a facility conforming to the BS 848 standards. The ow eld over the blade surfaces is investigated further with a visualization experiment comprising of a stroboscope and wool tufts. Good correlation is found at medium to high ow rates and recommendations are made for simulation at lower ow rates as well as test guidelines at the fan test facility. The results and knowledge gained will be used to amend currently used actuator disc theory for axial ow fan simulation. / AFRIKAANSE OPSOMMING: Die doel van hierdie projek is om die metode en akkuraatheid om aksiaalvloeiwaaiers met drie-dimensionele BVM modelle te simuleer, te ondersoek. Twee modelle word geëvalueer en met eksperimentele waaiertoetse vergelyk. Veri- kasie data is verkry vanaf 'n prototipe waaier wat in 'n fasiliteit getoets is en wat aan die BS 848 standaarde voldoen. Die vloeiveld oor die lemoppervlaktes word ondersoek met 'n visualisering eksperiment wat uit 'n stroboskoop en wolletjies bestaan. Goeie korrelasie word gevind vir medium tot hoë massavloeie en aanbevelings word gemaak vir die simulasie by laer massavloeie met riglyne vir toetswerk in die toets-fasiliteit. Die resultate en kennis opgedoen sal gebruik word in die verbetering van huidige aksieskyfteorie vir numeriese aksiaalvloeiwaaier simulasies.

Thesis (MScEng)--Stellenbosch University, 2010. / ENGLISH ABSTRACT: This project originated when a team of scientists at the Gobabeb training and research and centre observed seed accumulation sites on the slope of sand dunes in the Namib Desert. Seeds that accumulate on the slip face of a sand dune provide food for small desert creatures that in turn attract larger animals, resulting in a small ecosystem on the side of the dune. Since wind is the primary transport of seeds throughout the Namib Desert it is of interest to investigate wind patterns over the dune. In this project it is therefore desired to look at seed dynamics and deposition as a result of near surface wind patterns around a three-dimensional dune geometry using computational fluid dynamics. The project is a joint venture between the University of Stellenbosch and the University of Namibia. This document presents the South African MScEng thesis part. The literature review shows the dominant winds in the Namib Desert to be from the south to westerly direction. Previous studies on air flow over dunes focussed on sand movement and were often limited to simplified two-dimensional geometries and steady state simulations. From these studies the basic flow features associated with dunes can be identified. Lastly, factors that influence particle dynamics around dune geometries are looked at. These particle studies mostly involve the movement of sand rather than seeds but still provide valuable insight. The project methodology is explained and includes the equipment used, the considerations taken into account, the simplifications made as well as the procedure followed when conducting field work and simulations. A section of an actual Namibian linear dune is mapped in order to obtain a geometry for the simulations. Flow measurements are carried out with a wind mast to obtain velocity profile inlet conditions for the simulations. Furthermore, seed sampling is done by the collaborating Namibian team of which the data is used to obtain an effective seed particle model. Lastly, simulations are carried out using primarily OpenFOAM-1.5. The simulations look at general near surface wind patterns, time dependant flow features and particle movement and seed deposition around and on the linear dune. The results show different wind profiles for different wind direction. It is also possible to see how the profile changes as the flow accelerates up the dune slope. Two-dimensional results provide the opportunity to compare results with previous studies as well as to provide the basis for looking at aspects such as differencing schemes, turbulence models and parallel computing before three-dimensional simulations are carried out. The importance of higher order differencing schemes are confirmed in the two-dimensional results. The turbulence models, however, produce very similar results. The results from the two- and three-dimensional results show typical flow features associated with dunes. Transient flow features and separation vortex structures can be identified from time dependant simulations. Furthermore, particle simulations reveal how particles tend to be trapped in the recirculation regions. The conclusions explain how the project objectives were achieved and provide recommendations for future studies related to this project. / AFRIKAANSE OPSOMMING: Die projek het ontstaan toe naforsers areas van saad akumulasie op die hellings van duine in Namibë opgelet het. Hierdie akumulasie van plant materiaal verskaf die voedsel vir klein diere op die duin wat ‘n klein ekosisteem tot gevolg het. Aaangesien die primêre vervoermiddel vir sade in die woestyn wind is beoog die projek om deur die wind patrone oor die duin beter te verstaan die saad verspreiding te beskryf. Die doel is dus om saad verspreiding en akumulasie te beskryf deur die wind patrone te bekyk wat die verspreiding tot gevolg het deur gebruik te maak van numeriese vloei dinamika. Die projek is ‘n saamgestelde projek tussen die Universiteit van Stellenbosch en die Universiteit van Namibië. Hierdie dokument behels die Suid Afrikaanse MScIng gedeelte van die projek. Deur die hersiening van literatuur word daar gesien dat die domineerende wind rigtings as suid tot wes beskryf kan word. Vorige studies wat verband hou met wind vloei oor duine wys dat die meeste op twee-dimensionele eenvoudige geometrië gefokus het met tyd onafhankike simulasies. Dit is egter moontlik om die resultate te gebruik om karakteristieke vloei patrone te identifiseer wat met duin wind patrone geassosieer kan word. Laastens word daar gekyk na die faktore wat partikel beweeging beïnvloed, maar hierdie studies sluit hoofsaaklik sand partikels in eerder as sade. Die motodologie beskryf die toerusting, oorwegings en prosedures wat gevolg is tydens veld werk asook simulasies. Tydens die veld werk is ‘n gedeelte van ‘n Namib lineêre duin gemeet en so gebruik om ‘n geometrie te maak wat vir simulasie doeleindes gebruik kan word. Daar is ook wind meetings gedoen met ‘n wind mas om wind profiele vir inlaat kondisies vir die simulasies te kry. Verder het saad bestudeering die nodige data verskaf om ‘n voledige saad partikel model op te stel wat in die simulasies gebruik kan word. Laastens kyk die simulasies veral na algemene vloei patrone, tyd afhanklike vloei effekte en ook partikel beweging in die vloei veld. Die resultate wys hoe wind profiele verskil wat van verskillende rigtings af waai. Dit is ook moontlik on te wys hoe die wind profiele verander soos die wind versnel teen die duin op. Tweedimensionele simulasies verskaf die geleentheid om te kyk na die effek van verkillende numeriese modelle, turbulensie modelle en ook multi-prosesseerder verwerking. Tydens die twee-dimensionele simulasies is die belangrikheid van hoër orde numeriese metodes besef. Die verkillende turbulensie modelle het egter klein verkille gewys. Alby die twee- en driedimensionele resultate wys karakteristieke vloei patrone wat met duine geasosieer kan word. Verder het tyd afhanklike simulasies gewys hoe wind patrone verander met tyd. Die partikel simulasies wys ook die beweging van partikels deur die wind en hoe dit neig om te akumuleer in die hersirkulasie gebied agter die duin. Die gevolgtrekkings wys dat al die doelstellings bereik is en maak voorstelle vir toekomstige studies wat met hierdie studie verband hou.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Axial flow fans used in large-scale air-cooled steam condensers (ACSCs) may operate under distorted inflow conditions. These conditions occur due to the prevailing wind conditions, the presence of buildings, and the location of the fan within the ACSC. Fans located on the periphery of the ACSC are affected the most due to their exposure to strong winds and the inner fans drawing in air past them. Distorted inflow conditions cause varying fan blade and gearbox loading conditions. The purpose of the investigation was to simultaneously measure the inlet air flow and the resultant blade and gearbox loading conditions of a single fan located on the periphery of a large-scale ACSC. Inlet and heat exchanger bundle outlet air flow velocities were measured using a combination of ultrasonic and propeller anemometers while blade loading was measured with strain gauges attached at the neck of the specific blade being monitored. Strain gauges were also attached to the low-speed fan shaft to measure gearbox loading. Measurements were recorded over a period of 8 days where it was found that increased wind resulted in increased air flow in the axial direction of the fan, which then caused a reduction in average blade loading. This was due to a decreased static pressure rise over the fan. The fan blade was found to vibrate at its own natural frequency of 6 Hz when excited by the variable aerodynamic loading. The aerodynamic loading was extracted from the measured data and was found to correlate well with previous experimental work performed by Bredell et al. (2006a). Shaft bending stresses and torque were found to oscillate at the fan’s rotational frequency of 2Hz with a large torque exerted on the shaft during fan start-up. / AFRIKAANSE OPSOMMING: Aksiaalvloeiwaaiers wat by groot lugverkoelde stoomkondensors gebruik word, werk dikwels onder verwronge inlaat lugvloei toestande wat geskied as gevolg van heersende winde, die teenwoordigheid van geboue en die posisie van die waaier in die kondensor. Waaiers wat geleë is op die rand van die kondensor word die meeste beïnvloed as gevolg van blootstelling aan die sterk winde en dwarsvloei wat deur die binneste waaiers geïnduseer word. Verwronge inlaat lugvloei veroorsaak gevolglik variërende waaierlem en ratkas belastingstoestande. Die doel van hierdie ondersoek was om terselfdetyd die inlaat lugvloei asook waaierlem en ratkas belastingstoestande van ’n enkele waaier wat op die rand van ’n grootskaalse lugverkoelde stoomkondensor geleë is, te meet. Waaier inlaat en warmteruiler uitlaat lugvloei snelhede is gemeet met ’n kombinasie van ultrasoniese- en skroefwindsnelheidsmeters terwyl die lem en ratkas belastings gemeet is met rekstrokies. Metings is oor ’n tydperk van 8 dae geneem. Die bevindinge toon dat ’n toename in windsnelheid ’n toename in aksiale lugvloei tempo, deur die waaier veroorsaak. ’n Afname in die gemiddelde lembelasting is waargeneem as gevolg van ’n afname in die waaier statiese druk. Daar is ontdek dat die waaierlem teen ’n natuurlike frekwensie van 6 Hz vibreer wanneer dit opgewek word deur die wisselende aerodinamiese belasting. Die aerodinamiese belasting is verkry uit die gemete data en vergelyk goed met die numeriese werk van Bredell et al. (2006a). Daar is ook bevind dat waaier-as buigspannings en wringkragte ossileer teen die waaier se rotasiefrekwensie van 2Hz met ’n groot wringkrag wat op die as uitgeoefen word wanneer die waaier aangeskakel word. iii

O presente trabalho trata do desenvolvimento de uma sonda de pressão para medição de magnitude e direção da velocidade em um escoamento de ar. Primeiramente, é feita uma pesquisa sobre métodos e instrumentos de medição de velocidade de escoamentos de ar, utilizando a literatura existente sobre os tipos de medidores e suas restrições e capacidades na medição de direção do escoamento. Em seguida, são escolhidos dois tipos de medidores capazes de atender aos requisitos de fabricação simples e robusta, sendo um deles aplicado a escoamentos bidimensionais (sensor de três orifícios, tipo prisma) e o outro, a escoamentos tridimensionais (sensor de cinco orifícios, tipo pirâmide). É feito o projeto detalhado destes medidores e define-se o método de fabricação dos mesmos, comparando o método da prototipagem rápida com a usinagem. Uma vez fabricados os sensores, são realizados ensaios de caráter investigativo para mensurar a faixa de ângulos de medição de cada sensor. De posse dos resultados, é feito um estudo sobre os coeficientes adimensionais utilizados para a definição do ângulo de escoamento a partir das medições de pressão realizadas pelo sensor. É proposto um novo conjunto de coeficientes adimensionais com os quais se determina uma faixa de medição de ângulos entre -25 e + 25 para a sonda tipo prisma e uma faixa entre -35 e + 35 para a sonda tipo pirâmide. Finalmente, são feitas as curvas de calibração para os sensores e se discute sobre suas aplicações na medição de velocidade de escoamentos de ar. / The present work deals with the development of a pressure probe for measuring magnitude and direction of velocity from an air flow. Initially, it is made a review of methods and instruments to measure air flow velocity, using the existing literature on kinds of instruments with their restrictions and capabilities on flow direction measurement. Secondly, two kinds of sensors are chosen based on the requirements of easy and robust manufacturing, being one of them applied to bi-dimensional flows (three-hole probe, prism type) and the other one for tri-dimensional flows (five-hole probe, pyramid type). The detailed design of these probes is made and the fabrication method is chosen comparing the fast prototyping method with machining. Once these sensors are manufactured, investigative tests are carried out in order to measure the flow angle range for each sensor. With these results, a study is made on the non-dimensional coefficients used for definition of flow angle from the pressure measurements from the sensor. A new set of non-dimensional coefficients is proposed and a flow angle range between -25 and + 25 is determined for the prism probe and a range between -35 and + 35 for the pyramid probe, Finally, the calibration curves are made for the two sensors, followed by a discussion on the applications on air flow velocity measurements.

O método de injeção de ar é utilizado para a descontaminação de solos e lençóis freáticos contaminados com Compostos Orgânicos Voláteis (VOCs). O ar injetado no solo na zona saturada, ao subir para a zona não saturada, volatiliza os contaminantes. A eficiência da remediação por esse método está diretamente ligada à região de solo em que ocorre o fluxo de ar. Essa região é denominada de zona de influência e é afetada por vários fatores tais como: tipo e estrutura do solo, permeabilidade e pressão de injeção. No presente trabalho foram realizados estudos de fluxo de ar em solos saturados em um modelo físico bidimensional com o objetivo de avaliar a zona de influência formada. Os ensaios bidimensionais têm por finalidade a visualização dessa zona de influência; para isso foi utilizado um tanque transparente feito de placas de acrílico. Para a realização dos ensaios foram utilizados três tipos distintos de solo, uma areia natural denominada de Areia Osasco, uma areia comercial e uniforme (Areia do IPT) e um solo residual utilizado para criar as lentes de baixa permeabilidade. Também foram realizados ensaios de laboratório para a caracterização dos solos em estudo, tais como: curva de retenção, índice de vazios máximo e mínimo, granulometria, permeabilidade a água e ao ar. Os ensaios realizados no modelo (tanque) mostraram, como visto na literatura, que a granulometria e a estrutura do solo são as principais responsáveis pela formação de caminhos preferenciais de ar no solo. A zona de influência formada durante a injeção de ar nos ensaios com a Areia Osasco não foi simétrica devido à heterogeneidade do solo, já a formada nos ensaios com a Areia do IPT foi simétrica por causa da uniformidade do solo. A Areia do IPT apresentou uma zona de influência mais estreita do que a da Areia Osasco, isso ocorreu em função da menor porosidade da Areia Osasco, pois quanto menor a porosidade maior a tortuosidade e maior a expansão lateral. Os ensaios com as lentes de baixa permeabilidade mostraram que pequenas variações na configuração do solo podem influenciar a eficiência do método já que a região logo acima das lentes não foi atingida pelo ar. O aumento da pressão de injeção durante os ensaios fez com que mais canais de ar fossem formados causando um aumento do tamanho da zona de influência. / The method of air sparging is used for remediation of soil and groundwater contaminated with Volatile Organic Compounds (VOCs). In this process the air is injected into the soil in the saturated zone to ascend to the vadose zone and volatilizes the contaminants. The efficiency of air flow remediation is directly linked with the region of soil in which the flow occurs. This region is called as zone of influence and is affected by several factors such as: type and structure of the soil, permeability and pressure of injection. In the present work the air flow in saturated soils was investigated using a bidimensional physical model to evaluate the zone of influence formed. The objective of the tests was to obtain informations about zone of influence. A transparent tank made by acrylic plates was used. For these tests it was used three different types of soil: natural sand, called Osasco sand, a commercial and uniform sand called IPT sand and a residual soil used to create the lenses with low permeability. Laboratory tests such as water retention, minimum and maximum voids ratio, water and air permeability were performed to characterize the soils used in this study. Tests performed in the model (tank) showed, like those in the literature, that the particle size and soil structure are mainly responsible to create the preferential paths of air in soil. The zone of influence formed during the injection of air in the tests with Osasco sand was not symmetrical due to the heterogeneity of the soil; on the other hand the test performed with IPT sand was symmetrical due to its uniformity. The IPT sand showed a narrower zone of influence than Osasco sand, this was due to the lower porosity of the Osasco sand. Lower porosity imply in higher tortuosity and greater lateral expansion. Testes performed with low permeability lenses within the sand showed that small variations in the structure of the soil can affect the efficiency of the method because the region immediately above the lens is not reached by the air. The increase in the pressure of injection during the experiments induced the formation of more air channels causing an increase in the size of the zone of influence.

Computational fluid dynamics (CFD) has become an attractive tool in understanding the characteristic of air flow in the human lungs. Inter-subject variations make subject-specific simulations essential for understanding structure-function relationship, assessing lung function and improving drug delivery. However, currently the subject-specific CFD analysis remains challenging due, in large part to, two issues: construction of realistic deforming airway geometry and imposition of physiological boundary conditions. To address these two issues, we develop subject-specific, dynamic lung models by utilizing two or multiple volume multi-detector row computed tomography (MDCT) data sets and image registrations in this thesis. A mass-preserving nonrigid image registration algorithm is first proposed to match a pair of three-dimensional (3D) MDCT data sets with large deformations. A novel similarity criterion, the sum of squared tissue volume difference (SSTVD), is introduced to account for changes in intensity with lung inflation. We then demonstrate the ability to develop dynamic lung models by using a pair of lung volumes to account for deformations of airway geometries and subject-specific boundary conditions. The deformation of the airway geometry is derived by the registration-derived deformation field and subject-specific boundary condition is estimated from regional ventilation in a 3D and one-dimensional (1D) coupled multi-scale framework. Improved dynamic lung models are then proposed from three lung volumes by utilizing nonlinear interpolations. The improved lung models account for nonlinear geometry motions and time-varying boundary conditions during breathing. The capability of the proposed dynamic lung model is expected to move the CFD-based interrogation of lung function to the next plateau.

No description available.

The longitudinal fluctuations at a point in the core of air flowing through a 15 cm. diameter pipe at a mean centerline velocity of 13.4 and 29.5 m/sec. were measured with a hot-wire anemometer. This signal, after analog to digital conversion, was stored in the form of digital samples on an ICT computer drum storage device. This method of data recording includes the effect of all eddy frequencies from DC upwards and the presence of large, slow eddies in the longitudinal direction became apparent in the subsequent autocorrelations. The longitudinal dispersion of a tracer material injected on the axis of the pipe was measured over short distances with pulses of approx. 20 msecs. duration of radioactive Krypton-85, detected at two downstream stations by small surface-barrier radiation detectors. By varying the separation of these two stations, an asymptotic mixing coefficient was established which was very much greater than the corresponding transverse mixing coefficient measured by other workers. The method proposed by Philip (4) for the prediction of the Lagrangian time autocorrelation from the Eulerian velocity measurements was examined with the correlation data of Baldwin and the data obtained in this investigation. The method applied to the unfiltered correlation data in the present measurements in a non-isotropic field to predict a longitudinal turbulent Peclet no. was found to predict a value in the region measured experimentally. When the present velocity data was filtered to remove the low-frequency components and give a turbulence intensity equal to that measured in a radial direction in previous dispersion measurements, the mixing coefficient predicted with Philip's method was found to agree very well with the transverse mixing coefficient reported in these investigations. A value is also suggested for the longitudinal Peclet number in the absence of the low frequency fluctuations. / Thesis (Ph.D.)-University of Natal, Durban, 1970.