This thesis focuses on investigating the stability, dynamics and physical mechanisms of thermocapillary flows undergoing phase change by means of direct numerical simulations and experiments. The novelty of the general approach developed in this work lies in the fact that the problems under consideration are addressed with novel fully-coupled transient two-phase flow models in 3D. Traditional simplifications are avoided by accounting for deformable interfaces and by addressing advection-diffusion mechanisms not only in the liquid but also in the gas. This strategy enables a realistic investigation of the interface energy and mass transfer at a local scale for the first time. Thorough validations of the models against theory and experiments are presented. The thesis encompasses three situations in detail: liquid layers in saturated environments, liquid layers in unsaturated environments and evaporation of liquid droplets. Firstly, a model grounded in the volume-of-fluid method is developed to study the stability of laterally-heated liquid layers under saturated environments. In this configuration, the planar layer is naturally vulnerable to the formation of an oscillatory regime characterized by a myriad of thermal wave-like patterns propagating along the gas-liquid interface, i.e. hydrothermal waves. The nonlinear growth of the instabilities is discussed extensively along with the final bulk flow for both the liquid and gas phases. Previously unknown interface deformations, i.e. physical waves, induced by, and enslaved to, the hydrothermal waves are reported. The mechanism of heat transfer across the interface is found to contradict previous single-phase studies since the travelling nature of the hydrothermal waves leads to maximum heat fluxes not at the points of extreme temperatures but somewhere in between. The model for saturated environments is extended in a second stage to assess the effect of phase change in the hydrothermal waves for the first time. New numerical results reveal that evaporation affects the thermocapillary instabilities in two ways: the latent energy required during the process tends to inhibit the hydrothermal waves while the accompanying level reduction enhances the physical waves by minimizing the role of gravity. Interestingly, the hydrothermal-wave-induced convective patterns in the gas decouple the interface vapour concentration with that in the bulk of the gas leading to the formation of high (low) concentrations of vapour at a certain distance above interface cold (hot) spots. At the interface the behavior is the opposite. The phase-change mechanism for stable layers is also discussed. The Marangoni effect plays a major role in the vapour distribution and local evaporation flux and can lead to the inversion of phase-change process, i.e. the thermocapillary flow can result into local condensation in an otherwise evaporating liquid layer. The third problem discussed in this thesis concerns with the analysis of evaporating sessile droplets by means of both experiments and 3D numerical modeling. An experimental apparatus is designed to study the evaporation process of water droplets on superheated substrates in controlled nitrogen environments. The droplets are simultaneously recorded with a CCD camera from the side and with an infrared camera from top. It is found that the contact line initially remains pinned for at least 70% of the time, period after which its behaviour changes to that of the stick-slip mode and the drop dries undergoing contact line jumps. For lower temperatures an intermediate stage has been observed wherein the drop evaporates according to a combined mode. The experimental work is complemented with numerical simulations. A new model implementing the diffuse-interface method has been developed to solve the more complex problems of this configuration, especially those associated with the intricate contact-line dynamics. Further insights into the two-phase flow dynamics have been provided as well as into the initial transient stage, in which the Marangoni effect has been found to play a major role in the droplet heating. For the first time, a fully-coupled two-phase direct numerical simulations of sessile drops with a moving contact line has been performed. The last part of this work has been devoted to the investigation of three-dimensional phenomena on drops with irregular contact area. Non-sphericity leads to complex three-dimensional drop shapes with intricate contract angle distributions along the triple line. The evaporation rate is found to be affected by 3D features as well as the bulk flow, which become completely non-axisymmetric. To the best of our knowledge, this work is the first time that three-dimensional two-phase direct numerical simulations of evaporating sessile drops have been undertaken.

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International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California / This paper introduces the essential points for designing a navigating system, and describes the modules of a typical vehicle navigator. This paper also gives a practical navigator example. Some experience for design is also mentioned.

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Thesis (MScAgric)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: In South Africa tomato production in greenhouses normally occurs out of season when conditions are unfavourable for production and for the pollination process. Pollination is of special importance and the backbone of production. High temperatures contribute to the formation of abnormalities in flower morphology such as splitting of the anther cone and style exsertion. Low temperatures inhibit growth of the anther cone and therefore the style is uncovered. The movement of pollen from the anther to the style is inhibited by the higher style position in relation to the anther cone. Under humid conditions the pollen tends to stick to the anther surface. Another factor contributing to the problem is the banning of European bumble bees in South Africa. Alternative methods of pollen transport have to be found. Truss vibration, honey bees and plant growth regulators (PGR) are the most popular alternatives. Truss vibration and the use of PGR's are labour intensive and honey bees tend to get disorientated inside a plastic greenhouse. During the first part of this study pollen from plants, grown at four different B-levels (0.02; 0.16; 0.32 and 0.64 mg rl) was germinated in vitro. It was kept at different temperatures and periods before incubating on different growth media. No proof was found that pollen from B-deficient plants germinated poorly. Germination of pollen decreased significantly after one week storage. Deterioration of pollen viability could be lowered by storage at 5°C. At least 10% sucrose is needed in the growth medium for in vitro germination but addition ofB had no positive effect. In a second phase of the study, the influence of the mentioned B application rates were tested. The experiment was done in a glasshouse where temperatures were mechanically regulated (22°C and 10°C day/night). Seedlings of the greenhouse tomato cultivar, Abigail, were planted in acid washed river sand. Plants were grown with the main stem trellised vertically and the side shoots removed weekly. Only the first, third and fourth cluster were used for this part of the study. The uptake of all the essential nutrient elements, fruit set, the relation of larger to smaller fruits, physical and chemical quality and fruit shelf life were evaluated. The application of B at higher rates increased the uptake of Ca and decreased K-uptake. Fruit set, fruit development, fruit color and shelf life were the best at a B-Ievel of 0.16 mg r'. At this rate the abortion of flowers was the least. The same plants were used for the second part of the study, using the third cluster. The influence of the same four B-Ievels, the relative humidity (RH) of the truss atmosphere and truss vibrations were tested. The second cluster was covered with a plastic bag. Dry {<I 0% relative humidity (RH)}, normal {60-7S% RH} and moist {8S-97% RH} air were constantly applied to the bags at ± 50 ml min-I. As a third factor, truss vibration was applied daily by means of an electric vibrator (polli-bee), The amount of flowers per cluster, fruits per cluster, fruit set, weight of the cluster (yield), fruit weight, seed production, fruit weight per amount of seeds formed and fruits with blossom-end-rot (BER) were evaluated. The application of higher B-Ievels, air with the normal RH and the vibration of the clusters positively affected fruit weight, weight of the cluster and fruit set. High RH increased the occurrence of BER, probably due to a lack of transpiration from the fruit surface and therefor a lack in Ca translocation. / AFRIKAANSE OPSOMMING: Die verbouing van kweekhuistamaties in Suid-Afrika geskied meestalonder toestande wat ongunstig is vir produksieprosesse en veral die bestuiwingsproses wat die basis van produksie is. Onder toestande van hoë temperature is die voorkoms van afwykings in die blommorfologie (gesplete meeldraadbuis en verlengde styl) algemeen. Net so, onder toestande van lae temperature, sal gebrekkige groei van die meeldraadkrans ook tot die blootstelling van die stempel lei. Die oordraging van die stuifmeel vanaf die helmknop na die stempel word hierdeur benadeel. Tydens humiede toestande mag vasklewing van stuifmeel aan die helmknoppe ook die beweging van stuifmeel belemmer. 'n Verdere faktor wat tot die probleem bydra is die verbod op die invoer van hommelbye uit Europa. Alternatiewe metodes vir oordraging van stuifmeel moet dus gevind word. Trosvibrasie, heuningbye en die gebruik van plantgroeireguleerders (PGR's) is die mees populêre alternatiewe. Trosvibrasie met 'n 'polli-bee' en die aanwending van PGR's is arbeidsintensief. Heuningbye ondervind navigasieprobleme in plastiek kweekhuise en is nie so effektief as hommelbye nie. Tydens die eerste fase van die ondersoek is stuifmeel vanaf plante, wat by vier verskillende Bvoedingspeile (0.02; 0.16; 0.32 en 0.64 mg rl) verbou is, versamel en in vitro ontkiem. Dit is by verskillende temperature en periodes opgeberg en op verskillende media vir ontkieming geïnkubeer. Geen bewyse kon gevind word dat stuifmeel vanaf B-gebrekkige plante swak ontkiem nie. Kiemkrag van stuifmeel het na sewe dae opberging betekenisvol verswak. Verswakking in kiemkrag kon beperk word deur die stuifmeel by SoC op te berg. 'n Ontkiemingsmedium met ten minste 10% sukrose is vir goeie in vitro ontkieming van stuifmeelkorrels nodig terwyl die byvoeging van B geen voordelige effek getoon het nie. Tydens die tweede gedeelte van hierdie ondersoek is die invloed van die genoemde vier B-voedingspeile ondersoek. Die ondersoek is in 'n glashuis, waarvan die temperature meganies beheer is (22°C en 10°C dag/nag), uitgevoer. Plantmateriaal van die kweekhuistamatiekultivar, Abigail, is in suurgewasde riviersand geplant. Hoofstamme is vertikaalopgelei en die sylote is een maal per week uitgebreek. Die eerste, derde en vierde bloeiwyses is vir die ondersoek gebruik. Die opname van al die essensiële voedingselemente (blaarontledings), vrugset, die verhouding van groot vrugte tot kleiner vrugte, fisiese en chemiese kwaliteite van die vrugte en die raklewe daarvan is ge-evalueer. Die toediening van B teen hoër peile het die opname van Ca ten koste van K bevoordeel. Die beste resultate ten opsigte van vrugset, vrugontwikkeling, vrugkleur en die houvermoë (raklewe) van die vrugte is verkry teen 'n B-toedieningspeil van 0.16 mg.l'. Vir die derde gedeelte van die ondersoek is die tweede tros van dieselfde aanplanting gebruik. Die invloed van die vier B-voedingspeile, relatiewe humiditeit (RH) van die omgewing rondom die tros en trosvibrasie is ondersoek. Die tweede bloeiwyse is met 'n deursigtige plastieksakkie bedek. Droë {dO% relatiewe humiditeit (RH)}, normale {60-75% RH} en vogtige {85-97% RH} lug is teen 50 ml min-1 oor die tros gestuur. Trosvibrasie is as derde faktor teen twee peile gebruik deur trosse daagliks met 'n elekriese vibreerder ("polli-bee') te vibreer. Die aantal blomme per tros, vrugte per tros, vrugset, trosmassa (opbrengs), vrugmassa, aantal sade, vrugmassa per saad en blom-end-verrotting (BER) is ge-evalueer. Die toediening van hoër B-voedingspeile, 60-75% RH lug en trosvibrasies het vrugmassa, trosmassa en vrugset bevoordeel. Hoë lugvog het die omvang van BER verhoog, waarskynlik weens 'n gebrek aan transpirasie vanaf die vrugoppervlakke wat aanleiding tot 'n beperking in translokasie van Ca kon gee.

Thesis (PhD)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Various experiments were undertaken over a period of five years to investigate the feasibility of initiating a large-scale programme of controlled apple breeding and selection for the improvement of climatic adaptation, using budbreak number (NB) as a practical criterion of selection. NB is preferred to time of budbreak as sole criterion on the grounds that early budbreak is associated with low NB under local conditions. Variation within and between adult and juvenile seedling families was investigated and the genetic control of the traits involved was assessed, as well as direct and correlated responses to selection. In initial experiments different rating criteria for NB as measure of chilling requirement were tested in association with vegetative and reproductive budbreak time and flowering duration, viz, a classification index based on number and distribution of budbreak (pDS grade), an index where shoot length with increased budbreak was included in the index calculation (pDS index) and bud break number expressed as number per 100 cm of shoot length (NB index). Variance analysis (ANOVA and Variance component analyses) detected significant variation within seedling families for budbreak time and NB, but estimates of genetic components of variance between families were generally low. High genetic variance among seedlings within families is most likely due to the high level of heterozygosity in the parental cultivars as is characteristic of vegetatively propagated crops. Intra-class correlation coefficients for clones within and between families indicate moderate genetic determination for NB with broad sense heritabilities around 30 percent. Realized heritabilities calculated from response to two-way truncation selection were between 40 and 60 percent. For budbreak time (reproductive and vegetative), the broad sense heritability averaged around 75 and 69 percent, respectively, indicating a high degree of genetic determination. Significant response to selection for NB of one-year-old shoots of young seedlings and from seedlings grown into adult trees showed that pre-selection for increased budbreak successfully identified seedlings genetically inclined to more and better distribution of budbreak within a set time of 21 days after initial budbreak. Correlated responses indicated additional advantages of practical and horticultural value, viz, uniformity and position of bud break, and the number and length of side shoots. In general, it is concluded from responses to two-way selection that utilizable genetic variance in NB is present within seedling families and thus that selection may successfully be applied as an early screening method for increased budbreak in adult trees. The NB index of intact one-year-old shoots under prevailing sub-optimal winter conditions is therefore proposed as criterion of selection for improvement of climatic adaptation, and combined selection utilizing genetic variation between and within crosses as the selection method. / AFRIKAANSE OPSOMMING: Verskeie proewe is oor 'n periode van vyf jaar uitgevoer om die toepaslikheid van 'n grootskaalse appelteel- en seleksieprogram vir die verbetering van klimaatsaanpasbaarheid te ondersoek met 'aantal knopbreke' (NB) as praktiese seleksiekriterium. NB word verkies bo tyd van knopbreek op grond daarvan dat vroeë knopbreek onder plaaslike toestande met lae NB gepaard gaan. Variasie binne en tussen volwasse en jong saailingfamilies en die genetiese beheer van die betrokke eienskappe is ondersoek, asook direkte en gekoreleerde seleksieresponsie. In die aanvangs-eksperimente is verskillende kriteria vir die kwantifisering van aantal knopbreke getoets as potensiële maatstawwe van die inherente kouebehoefte in appelsaailinge. Die tyd van vegetatiewe en reproduktiewe knopbreek en blomperiode is ook getoets. Die volgende indekse is gebruik: 'n klassifikasie-indeks om die aantal en verspreiding van knopbreke te beskryf (pDS graad), 'n indeks waar die lootlengte, met verhoogde aantal knopbreke, ingesluit is in die berekening van die indekswaarde (PDS indeks), en knopbreke uitgedruk as die aantal per 100 cm lootlengte (NB indeks). Variansie analise (ANOVA en variansie komponent analise) het betekenisvolle variasie binne saailingfamilies aangetoon vir tyd van, en aantal knopbreke. Ramings van genetiese komponente van variansie tussen families was relatief klein. Hoë genetiese variansie tussen saailinge binne families is waarskynlik te wyte aan die hoë vlak van heterosigositeit in die ouergenotipes, wat kenmerkend is van gewasse wat vegetatief voortgeplant word. Intraklas korrelasie koëffisiënte vir klone tussen en binne families het gedui op 'n middelmatige oorerflikheid in die breë sin (ongeveer 30 persent) vir aantal knopbreke. Verhaalde oorerflikhede wat bereken is vanaf responsie op twee-rigting atknottingsseleksie was tussen 40 en 60 persent. Vir tyd van knopbreek (vegetatief en reproduktief) was die breësin oorerflikhede ongeveer 75 en 69 persent, onderskeidelik, wat aanduidend is van 'n hoë graad van genetiese bepaling. Betekenisvolle responsie op seleksie vir NB van jong saailinge en saailingbome wat volwassenheid bereik het toon dat pre-seleksie vir knopbreke saailinge kan identifiseer wat geneties meer knopbreke en 'n beter verspreiding van knoppe binne 'n periode van 21 dae na die eerste knopbreek lewer. Gekorreleerde responsie op seleksie toon 'n addisionele voordeel van praktiese en tuinboukundige belang, naamlik, meer en langer sylote. In opsomming kan dit gestel word dat responsie op twee-rigting seleksie bruikbare genetiese variasie vir NB binne saailingfamilies ontgin het en dat seleksie vir verhoogde aantal knopbreke suksesvol toegepas kan word. Die NB indeks op een-jaar-oue hout word dus voorgestel as seleksiekriterium vir verbetering van klimaatsaanpasbaarheid onder plaaslike sub-optimale wintertoestande, en gekombineerde seleksie "combined selection" wat genetiese variasie binne en tussen kruisings benut as seleksiemetode.

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