Dissertationen zum Thema „Micro visualization“

Since the proliferation of CAD tools, visualizations have gained importance.. They provide invaluable visual feedback at the time of design, regardless whether it is fbi civil engineering or electronic circuit design-layout. Typically dynamic visualizations are produced in a two phase process: the calculation of positions and rendering of the image and its presentation as an animated video clip. This is a slow process that is unsuitable fbr interactive CAD visualizations, because the former two require finite element analysis Faster hardware eases the problem, but does not overcome it, because the algorithms are still too slow. Our MEMS CAD project works towards methods and techniques that are suitable for interactive design, with faster methods. The purpose of this PhD thesis is to contribute to the design of an interactive virtual prototyping of Micro Electro Mechanical Systems (MEMS) This research comprises the analysis of the visualization techniques that are appropriate for these tasks and identifying the difficulties that need to be overcome to be able to offer a MEMS design engineer a meaningful and interactive CAD design environment Such a VR-CAD system is being built in our research group with many participants in the team. Two particular problems are being addressed by presenting algorithms for truthful VR visualization methods: one is for displaying objects that are different in size on the computer screen. The other is modelling unsynchronized motion dynamics, that is different objects moving simultaneously at very high and vety low speed, by proposing stroboscopic simulation to present their dynamics on the screen They require specific size scaling and time scaling and filtering. It is these issues and challenges which make the design of a MEMS CAD tool different from other CAD tools. In the thesis I present algorithms for displaying animated virtual reality for MEMS virtual prototyping in a physically truthful way by using the simulated stroboscopic illumination to filter animated images to make it possible to show unsynchronized motion.. A scaling method was used to show or hide objects which cannot be shown simultaneously on the computer screen because of their large difference in size. The visualization of objects being designed and their animations is done with much consideration of visual perception and computer capability, which is rising attention, but not too often mentioned in the visualization domain.<br>Thesis (PhD Doctorate)<br>Doctor of Philosophy (PhD)<br>School of Information and Communication Technology<br>Full Text

Cette thèse porte sur la recherche sur la conception et l'utilisation de micro-visualisations pour l'exploration de données mobiles et pervasives sur des smartwatches et des trackers de fitness. Les gens portent de plus en plus de smartwatches qui peuvent suivre et afficher une grande variété de données. Mon travail est motivé par les avantages potentiels des visualisations de données sur les petits appareils mobiles tels que les brassards de suivi de la condition physique et les smartwatches. Je me concentre sur les situations dans lesquelles les visualisations soutiennent des tâches spécifiques liées aux données sur des smartwatches interactives. Mon principal objectif de recherche dans ce domaine est de comprendre plus largement comment concevoir des visualisations à petite échelle pour les trackers de fitness. Ici, j'explore : (i) les contraintes de conception dans le petit espace par le biais d'un atelier d'idéation ; (ii) le type de visualisations que les gens voient actuellement sur le visage de leur montre ; (iii) une revue de conception et l'espace de conception des visualisations à petite échelle ; (iv) et la lisibilité des micro-visualisations en considérant l'impact de la taille et du rapport d'aspect dans le contexte du suivi du sommeil. Les principaux résultats de la thèse sont, premièrement, un ensemble de besoins de données concernant un contexte d'utilisation touristique dans lequel ces besoins de données ont été satisfaits avec une richesse de conceptions de visualisation dédiées qui vont au-delà de celles couramment vues sur les affichages des montres. Deuxièmement, un affichage prédominant des données de santé et de forme physique, les icônes accompagnant le texte étant le type de représentation le plus fréquent sur les faces actuelles des smartwatchs. Troisièmement, un espace de conception pour les visualisations sur les faces de smartwatch qui met en évidence les considérations les plus importantes pour les nouveaux affichages de données sur les faces de smartwatch et autres petits écrans. Enfin, dans le contexte du suivi du sommeil, nous avons constaté que les gens effectuaient des tâches simples de manière efficace, même avec une visualisation complexe, à la fois sur les écrans de la smartwatch et du bracelet de fitness, mais que les tâches plus complexes bénéficiaient de la taille plus grande de la smartwatch. Dans la thèse, je souligne les opportunités ouvertes importantes pour les futures recherches sur la visualisation des smartwatchs, telles que l'évolutivité (par exemple, plus de données, une taille plus petite et plus de visualisations), le rôle du contexte et du mouvement du porteur, les types d'affichage des smartwatchs et l'interactivité. En résumé, cette thèse contribue à la compréhension des visualisations sur les smartwatches et met en évidence les opportunités ouvertes pour la recherche en visualisation sur les smartwatches<br>This thesis covers research on how to design and use micro-visualizations for pervasive and mobile data exploration on smartwatches and fitness trackers. People increasingly wear smartwatches that can track and show a wide variety of data. My work is motivated by the potential benefits of data visualizations on small mobile devices such as fitness monitoring armbands and smartwatches. I focus on situations in which visualizations support dedicated data-related tasks on interactive smartwatches. My main research goal in this space is to understand more broadly how to design small-scale visualizations for fitness trackers. Here, I explore: (i) design constraints in the small space through an ideation workshop; (ii) what kind of visualizations people currently see on their watch faces; (iii) a design review and design space of small-scale visualizations; (iv) and readability of micro-visualizations considering the impact of size and aspect ratio in the context of sleep tracking. The main findings of the thesis are, first, a set of data needs concerning a sightseeing usage context in which these data needs were met with a wealth of dedicated visualization designs that go beyond those commonly seen on watch displays. Second, a predominant display of health &amp; fitness data, with icons accompanying the text being the most frequent representation type on current smartwatch faces. Third, a design space for smartwatch face visualizations which highlights the most important considerations for new data displays for smartwatch faces and other small displays. Last, in the context of sleep tracking, we saw that people performed simple tasks effectively, even with complex visualization, on both smartwatch and fitness band displays; but more complex tasks benefited from the larger smartwatch size. Finally, I point out important open opportunities for future smartwatch visualization research, such as scalability (e.g., more data, smaller size, and more visualizations), the role of context and wearer's movement, smartwatch display types, and interactivity. In summary, this thesis contributes to the understanding of visualizations on smartwatches and highlights open opportunities for smartwatch visualization research

For the application of minichannel heat exchangers, it is necessary to have accurate design tools for predicting heat transfer and pressure drop. Until recently, this type of heat exchangers was not well studied, and in the scientific literature there were large discrepancies between results reported by different investigators. The present thesis aims to add to the knowledge of the fundamentals of single- and two-phase flow heat transfer and pressure drop in narrow channels, thereby aiding in the development of this new, interesting technology with the possibility of decreasing the size of electronics through better cooling, and of increasing the energy efficiency of thermal processes and thermodynamic cycles through enhanced heat transfer. A comprehensive experimental single-phase flow and saturated flow boiling heat transfer and pressure drop study has been carried out on vertical stainless steel tubes with inner diameters of 1.700, 1.224 and 0.826 mm, using R-134a as the test fluid. The heat transfer and pressure drop results were compared both to conventional correlations developed for larger diameter channels and to correlations developed specifically for microscale geometries. Contrary to many previous investigations, this study has shown that the test data agree well with single-phase heat transfer and friction factor correlations known to be accurate for larger channels, thus expanding their ranges to cover mini/microchannel geometries. The main part of the study concerns saturated flow boiling heat transfer and pressure drop. Tests with the same stainless steel tubes showed that the heat transfer is strongly dependent on heat flux, but only weakly dependent on mass flux and vapor fraction (up to the location of dryout). This behavior is usually taken to indicate a dominant influence of nucleate boiling, and indicates that the boiling mechanism is strongly related to that in nucleate boiling. The test data for boiling heat transfer was compared to several correlations from the literature, both for macro- and mini-channels. A new correlation for saturated flow boiling heat transfer of refrigerant R-134a correlation was obtained based on the present experimental data. This correlation predicts the presented data with a mean absolute deviation of 8%. The frictional pressure drop results were compared to both macro- and mini channel correlations available from the literature. The correlation suggested by Qu and Mudawar (2003) gave the best prediction to the frictional two-phase pressure drop within the studied ranges. A unique visualization study of saturated flow boiling characteristics in a vertical 1.332 mm inner diameter quartz tube, coated with a transparent heater has also been conducted. The complete evaporation process in a heated circular mini-channel has been studied visually in detail using high speed CCD camera. The study revealed the developments of the flow patterns and the behavior from bubble nucleation to the dry out of the liquid film. The bubble departure frequency, diameter, growth rate, and velocity were determined by analyzing the images. Finally, a flow pattern map for boiling flow in microchannels has been developed based on the test data.<br>QC 20100812

Microhemodynamics is the study of blood flow in small vessels, usually on the order of 50 to 100 µm. The in vitro study of blood flow in small channels is analogous to the in vivo study of the microcirculation. At this scale the Reynolds and Womersly numbers are significantly less than 1 and the viscous stress and pressure gradient are the main determinant of flow. Blood is a non-homogeneous, non-Newtonian fluid and this complex composition and behavior has a greater impact at the microscale. A key parameter is the shear stress at the wall, which is involved in many processes such as platelet activation, gas exchange, embryogenesis and angiogenesis. In order to measure the shear rate in these blood flows the velocity profile must be measured. The measured profile can be characterized by the maximum velocity, the flow rate, the shear rate at the wall, or a shape parameter reflecting the bluntness of the velocity profile. The technique of micro-particle image velocimetry (µPIV) was investigated to measure the velocity profiles of blood microflows. The material of the channel, the type of tracer particles, the camera used, and the choice in data processing were all validated to improve the overall accuracy of µPIV as a blood microflow measurement method. The knowledge gained through these experiments is of immediate interest to applications such as the design of lab-on-a-chip components for blood analysis, analysis of blood flow behavior, understanding the shear stress on blood in the microcirculation and blood substitute analysis. Polymer channels were fabricated from polydimethylsiloxane (PDMS) by soft lithography in a clean room. PDMS was chosen for ease of fabrication and biocompatibility. The contacting properties of saline, water, and blood with various polymer channel materials was measured. As PDMS is naturally hydrophilic, surface treatment options were explored. Oxygenated plasma treatment was found to be less beneficial for blood than for water. The choice of camera and tracer particles were validated. Generally, for in vivo studies, red blood cells (RBCs) are used as tracer particles for the µPIV method, while for in vitro studies, artificial fluorescent micro particles are added to the blood. It is demonstrated here that the use of RBCs as tracer particles creates a large depth of correlation (DOC), which can approach the size of vessel itself and decreases the accuracy of the method. Next, the accuracy of each method is compared directly. Pulsed images used in conjunction with fluorescing tracer particles are shown to give results closest to theoretical approximations. The effect of the various post-processing methods currently available were compared for accuracy and computation time. It was shown that changing the amount of overlap in the post-processing parameters affects the results by nearly 10%. Using the greatest amount of correlation window overlap with elongated windows aligned with the flow was shown to give the best results when coupled with a image pre-processing method previously published for microflows of water. Finally the developed method was applied to a relevant biomedical engineering problem: the evaluation of blood substitutes and blood viscosity modifiers. Alginate is a frequently used viscosity modifier which has many uses in industry, including biomedical applications. Here the effect of alginate on the blood rheology, i.e., the shape of the velocity profile and the maximum velocity of blood flow in microchannels, was investigated. Alginate was found to blunt the shape of the velocity profile while also decreasing the shear rate at the wall. Overall, the accuracy of µPIV measurements of blood flows has been improved by this thesis. The work presented here has extended the known methods and accuracy issues of blood flow measurements in µPIV, improved the understanding of the blood velocity profile behavior, and applied that knowledge and methods to interesting, relevant problems in biomedical and biofluids engineering.

Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, June 2003.<br>Thesis advisor(s): Kevin D. Jones, Max F. Platzer. Includes bibliographical references (p. 73-74). Also available online.

The aerodynamics phenomena of flapping motion in hover are considered in view of the future Micro Air Vehicle applications. The aim of this work is to characterize the vortex dynamics generated by the wing in motion using direct numerical simulation and experimental analysis then to propose a simplified analytical model for prediction of the forces in order to optimize the parameters of the motion leading to maximum force. A great number of cases are investigated corresponding to different angles of attack, location of start of change of incidence, location of start of change of velocity, axis of rotation, and Re number. The airfoil used is symmetrical. The flow is assumed to be incompressible and laminar with the Reynolds numbers between 500 and 2000. The experimental results obtained by the laser sheet visualization and the Particle Image Velocimetry (PIV) techniques are used in parallel with the direct numerical simulation results for the phenomenological analysis of the flow. The model developed for the aerodynamic forces is an indicial method based on the use of the Duhamel Integral and the results obtained by this model are compared with the ones of the numerical simulations.

Micro Air Vehicles (MAV’s) have small size and extreme maneuverability which makes them ideal for surveillance. Propulsion mechanisms include propellers, rotors, and flapping airfoils. Flapping motions, along with biologically-inspired wing profiles, are of interest due to their use of natural physics. Corrugated airfoil structures appears to have poor aerodynamic performance at higher Reynolds numbers, but serve well at Re<10,000. Understanding flow structures around corrugated profiles and comparing them to a standard airfoil will aid in understanding how these corrugated profiles perform well and have been adopted by some of nature’s most acrobatic flyers. Motivation for this investigation is to compare static flow visualizations of corrugated profiles to a standard National Advisory Committee for Aeronautics (NACA) airfoil from low to high angles of attack and further observe flow structure development of a pitching and plunging flat plate at a Re<10,000 and a Strouhal number relevant to natural fliers. The static visualization was conducted at Re=1,000 with a NACA 0012 airfoil and two corrugated models. The Pitch and Plunge Fixture (PPF) developed was constructed by simplifying flapping wings as a two degree of freedom motion in plunge (translation) and pitch (rotation). Results obtained from the PPF were compared with a numerical simulation.

Thesis (M.S.)--Worcester Polytechnic Institute.<br>Keywords: low reynolds; flight; flow visualization; low aspect ratio; micro air vehicles; planform; wings; mav; mavs. Includes bibliographical references (leaves 105-106).

A novel surface structure comprising dendritically ordered nano-particles of copper was developed during the duration of this thesis research project. A high current density electrodeposition process, where hydrogen bubbles functioned as a dynamic mask for the materials deposition, was used as a basic fabrication method. A post processing annealing treatment was further developed to stabilize and enhance the mechanical stability of the structure. The structure was studied quite extensively in various pool boiling experiments in refrigerants; R134a and FC-72. Different parameters were investigated, such as; thickness of the porous layer, presence of vapor escape channels, annealed or non-annealed structure. Some of the tests were filmed with a high speed camera, from which visual observation were made as well as quantitative bubble data extracted. The overall heat transfer coefficient in R134a was enhanced by about an order of magnitude compared to a plain reference surface and bubble image data suggests that both single- and two-phase heat transfer mechanisms were important to the enhancement. A quantitative and semi-empirical boiling model was presented where the main two-phase heat transfer mechanism inside the porous structure was assumed to be; micro-layer evaporation formed by an oscillating vapor-liquid meniscus front with low resistance vapor transport through escape channels. Laminar liquid motion induced by the oscillating vapor front was suggested as the primary single-phase heat transfer mechanism. The structure was applied to a standard plate heat exchanger evaporator with varying hydraulic diameter in the refrigerant channel. Again, a 10 times improved heat transfer coefficient in the refrigerant channel was recorded, resulting in an improvement of the overall heat transfer coefficient with over 100%. A superposition model was used to evaluate the results and it was found that for the enhanced boiling structure, variations of the hydraulic diameter caused a change in the nucleate boiling mechanism, which accounted for the largest effect on the heat transfer performance. For the standard heat exchanger, it was mostly the convective boiling mechanism that was affected by the change in hydraulic diameter. The structure was also applied to the evaporator surface in a two-phase thermosyphon with R134a as working fluid. The nucleate boiling mechanism was found to be enhanced with about 4 times and high speed videos of the enhanced evaporator reveal an isolated bubble flow regime, similar to that of smooth channels with larger hydraulic diameters. The number and frequency of the produced bubbles were significantly higher for the enhanced surface compared to that of the plain evaporator. This enhanced turbulence and continuous boiling on the porous structure resulted in decreased oscillations in the thermosyphon for the entire range of heat fluxes.<br>QC 20111111

Pulsating heat pipes (PHP) are very promising passive heat transfer devices, simply made of a capillary tube and characterized by high thermal performance and extraordinary space adaptability. One of the main advantages with respect to Thermosyphons (TS) is that PHPs can work also without gravity assistance, making such technology interesting also for space applications. Nevertheless, the global heat power input that they can absorb is limited due to the capillary dimensions of the tube. The actual literature shows that it would be theoretically possible to build a hybrid TS/PHP with an Inner Diameter larger than the capillary limit, evaluated in normal gravity conditions, that works indeed as a loop thermosyphon on ground and switches to the typical PHP slug/plug operation when microgravity occurs. The aim of the present work is to prove the feasibility of such hybrid two-phase passive heat transfer device concept by means of a complete multi-parametric experimental campaign. Therefore, during the first year of the doctoral thesis, a fully equipped hybrid TS/PHP experiment is designed and built at the Thermal Physics Laboratories of the University of Bergamo. Then, such device is tested both on ground and in hyper-micro gravity conditions during the 61th and the 63th ESA Parabolic Flight Campaign. A thorough thermo-hydraulic characterization is performed on ground, varying important parameters such as the heat power input, the inclination angle, the ambient temperature and the heating elements position. It is found that a strategic arrangement of multiple heaters may be used in order to enhance the flow motion and consequently the thermal performance. In micro-gravity, parabolic flight tests point out a PHP working mode. The sudden absence of buoyancy force activates an oscillating slug/plug flow regime, typical of the PHP operation, allowing the device to work in any orientation. Although the present work demonstrates the feasibility of the TS/PHP concept, and that a strategic position of the heating elements promotes the two-phase flow motion, further tests in prolonged micro-gravity conditions (i.e. onboard a sub-orbital flight or, even better, the International Space) can point out the effective heat transfer performance in weightlessness conditions.

The methodology of visualization of soft tissue is in biology and medicine a topic for many years. During this period there were approving many techniques how to achieve accurate and authentic image of the researched object or structure. X-ray computed tomography is very helpful to get this goal but is necessary to improve contrasting techniques as well as the techniques of image post-processing. This thesis deals with imaging soft tissue. Specifically, it focuses on mouse liver contrasting with the artificial resin Microfil. Thesis also describes image processing technique (thresholding and region growing) for the data of the measurement with the goal of the visualization of the sample in 3D.

Метою дипломної роботи є створення зручного web-інтерфейсу для візуалізації геопросторових даних в аграрному секторі. Об’єктом дослідження є геопросторові дані та методи їх відображення. Було виконано огляд існуючих програмних застосунків для візуалізації геопросторових даних, виявлено їх переваги та недоліки. Створено web-інтерфейс, що вирішує проблеми обробки та відображення геоданих для сільськогосподарського сектору. Створена програмна система може бути використана у роботі підприємців-аграріїв для автоматизації ведення стану полів. Загальний обсяг роботи: 50 сторінка, 20 ілюстрацій, 16 бібліографічних посилань та 3 додатки.<br>The purpose of the thesis is to create a convenient web-interface for visualizing geospatial data in the agrarian sector. The object of the study is geospatial data and methods for their reflection. A review of existing software applications for visualization of geospatial data was performed, their advantages and disadvantages were identified. A web-based interface has been created that solves the problem of processing and displaying location data for the agricultural sector. The created software system can be used in the work of entrepreneurs-agrarians to automate the state of the fields. Total volume of the paper: 50 pages, 20 illustrations, bibliography links and 3 appendixes.<br>Целью дипломной работы является создание удобного web-интерфейса для визуализации геопространственных данных в аграрном секторе. Объектом исследования является пространственные данные и методы их отражения. Было выполнено обзор существующих программных приложений для визуализации геопространственных данных, выявлены их преимущества и недостатки. Создан web-интерфейс, который решает проблемы обработки и отображения геоданных для сельскохозяйственного сектора. Создана программная система может быть использована в работе предпринимателей аграриев для автоматизации ведения состояния полей.

Diabetes is a rapidly increasing health problem. In a global perspective,approximately 415 million people suffered from diabetes in 2015 and this number ispredicted to increase to 640 million by 2040. To tackle this pandemic there is a needfor better analytical tools by which we can increase our understanding of the disease.One discipline that has already provided much needed insight to diabetes etiology isoptical molecular imaging. Using various forms of light it is possible to create animage of the analysed sample that can provide information about molecularmechanistic aspects of the disease and to follow spatial and temporal dynamics. The overall aim of this thesis is to improve and adapt existing andnovel optical imaging approaches for their specific use in diabetes research. Hereby,we have focused on three techniques: (I) Optical projection tomography (OPT),which can be described as the optical equivalent of x-ray computed tomography(CT), and two vibrational microspectroscopic (VMS) techniques, which records theunique vibrational signatures of molecules building up the sample: (II) Fouriertransforminfrared vibrational microspectroscopy (FT-IR) and (III) Ramanvibrational microspectroscopy (Raman). The computational tools and hardware applications presented here generallyimprove OPT data quality, processing speed, sample size and channel capacity.Jointly, these developments enable OPT as a routine tool in diabetes research,facilitating aspects of e.g. pancreatic β-cell generation, proliferation,reprogramming, destruction and preservation to be studied throughout the pancreaticvolume and in large cohorts of experimental animals. Further, a novel application ofmultivariate analysis of VMS data derived from pancreatic tissues is introduced.This approach enables detection of novel biochemical alterations in the pancreasduring diabetes disease progression and can be used to confirm previously reportedbiochemical alterations, but at an earlier stage. Finally, our studies indicate thatRaman imaging is applicable to in vivo studies of grafted islets of Langerhans,allowing for longitudinal studies of pancreatic islet biochemistry.viIn summary, presented here are new and improved methods by which opticalimaging techniques can be utilised to study 3D-spatial, quantitative andmolecular/biochemical alterations of the normal and diseased pancreas.

La miniaturisation continue et la complexité des dispositifs poussent les techniques existantes de nano-caractérisation à leurs limites. De ce fait, la combinaison de ces techniques apparait être une solution attrayante pour continuer à fournir une caractérisation précise et exacte. Dans le but de dépasser les verrous existants pour l’imagerie chimique 3D haute résolution à l’échelle nanométrique, nous avons concentré nos recherches sur la création d’un protocole combinant la spectrométrie de masse à ions secondaires de temps de vol (ToF-SIMS) avec la microscopie à force atomique (AFM). Ceci permet entre autre de corréler la composition et la visualisation en 3 dimensions avec des cartographies de topographie ou d’autres propriétés locales fournies par l’AFM. Trois principaux résultats sont obtenus grâce à cette méthodologie : la correction d’un ensemble de données ToF-SIMS pour une visualisation 3D sans artefacts, la cartographie du taux de pulvérisation locale permettant de mettre en évidence les effets liés à la rugosité et la présence d’interfaces verticales et la superposition des informations avancées ToF-SIMS et AFM. Quatre applications de la méthodologie combinée ToF-SIMS et AFM sont abordées dans cette thèse. La procédure de correction des données ToF-SIMS en 3D a été appliquée sur une structure hétérogène GaAs / SiO2. Les artefacts liés à la pulvérisation, notamment l’effet d’ombrage, ont été étudiés par le biais des cartographies de taux de pulvérisation sur des échantillons avec nano-motifs structurés et non structuré. Enfin, nous avons exploré la combinaison de l’analyse ToF-SIMS avec trois modes avancées de microscopie AFM : piézoélectrique (PFM), capacité (SCM) et conducteur (SSRM). Une première étude a notamment permis d’observer l’évolution et la modification chimique suite à l’application d’une contrainte électrique sur deux film mince piézoélectriques. Une deuxième étude s’est focalisée sur l’impact de l’implantation Ga lors de la préparation d’échantillons par FIB pour voir comment limiter l’effet de l’amorphisation sur la mesure électrique. Les aspects techniques de la méthodologie seront abordés pour chacune de ces applications et les perspectives de cette combinaison seront discutés<br>The continuous miniaturization and complexity of devices have pushed existing nano-characterization techniques to their limits. The correlation of techniques has then become an attractive solution to keep providing precise and accurate characterization. With the aim of overcoming the existing barriers for the 3D high-resolution imaging at the nanoscale, we have focused our research on creating a protocol to combine time-of-flight secondary ion mass spectrometry (ToF-SIMS) with atomic force microscopy (AFM). This combination permits the correlation of the composition in 3-dimensions with the maps of topography and other local properties provided by the AFM. Three main results are achieved through this methodology: a topography-corrected 3D ToF-SIMS data set, maps of local sputter rate where the effect of roughness and vertical interfaces are seen and overlays of the ToF-SIMS and AFM advanced information. The application fields of the ToF-SIMS and AFM combined methodology can be larger than expected. Indeed, four different applications are discussed in this thesis. The procedure to obtain the topography-corrected 3D data sets was applied on a GaAs / SiO2 patterned structure whose initial topography and composition with materials of different sputter rates create a distortion in the classical 3D chemical visualization. The protocol to generate sputter rate maps was used on samples with structured and non-structured nano-areas in order to study the possible ToF-SIMS sputtering artefacts, especially the geometric shadowing effect. Finally, we have explored the combination of ToF-SIMS analysis with three AFM advanced modes: piezoresponse force microcopy (PFM), scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM). Specifically, two main applications were studied: the chemical modification during electrical stress of a piezoelectic thin film and the recovery of initial electrical characteristics of a sample subjected to Ga implantation during FIB preparation. Technical aspects of the methodology will be discussed for each application and the perspectives of this combination will be given

The potential of Digital twin (DT) technology outside of the industrial field has been recognized by researchers who have promoted the vision of applying DTs technology beyond manufacturing, to purposes such as enhancing human well-being and improving quality of life (QoL). The expanded definition of DTs to incorporate living and nonliving physical entities into the definition of DTs was a key motivation behind the model introduced in this thesis for building health digital twins of citizens. In contrast with DTs that have been developed in more industrial fields, this type of digital twins modeling necessitates protecting each citizen's unique identity while also representing features common to all citizens in a unified way. In nature, DNA is an example of a model that is both unified, common to all humans, and unique, distinguishing each human as an individual. DNA’s architecture is what inspired us to propose a digital twin DNA (DT-DNA) model as the basis for building health DTs for citizens. A review of the literature shows that no unified model for citizens’ health has been developed that can act as a base for building digital twins of citizens while also protecting their unique identity thus we aim to fill this gap in this research. Accordingly, in this thesis, we proposed a DT-DNA model, which is specifically designed to protect the unique identity of each citizen’s digital twin, similar to what DNA does for each human. We also proposed a DT-DNA-based framework to build standardized health digital twins of citizens on micro, meso and macro levels using two ISO standards: ISO/IEEE 11073 (X73) and ISO 37120. To achieve our goal, we started by analyzing the biological DNA model and the influencing factors shaping health in smart cities. The purpose of the first is to highlight the DNA model features which provide the building blocks for our DT-DNA model. The purpose of the latter is to determine the main bases of our DT-DNA model of health DTs. Based on the analysis results; we proposed DT-DNA to model health DTs for citizens. In keeping with our DNA analogy, we have identified four bases, A, T, G, and C, for our unified and unique DT-DNA model. The A base in the proposed model represents a citizen’s anthropometric when we build the DT-DNA on an individual level and represents the city’s regulatory authorities when we build the DT-DNA on community and city levels. The T base represents different tasks included in the provided health data that are required to model citizens’ health DT-DNA on different levels. The G base represents the geographic and temporal information of the city, where the citizen exists at the time of data collection. The C base represents the context at the time of data collection. To proof the concept, we present our initial work on building health DTs for citizens in four case studies. The first two case studies are dedicated for health DTs at the micro level, the third case study is dedicated for health DTs at the meso level and the fourth case study is dedicated for health DTs at the macro level. In addition, we developed an algorithm to compare cities in terms of their community fitness and health services status. The four case studies provide promising results in terms of applicability of the proposed DT-DNA model and framework in handling the health data of citizens, communities and cities, collected through various sources, and presenting them in a standardized, unique model.

碩士<br>國立雲林科技大學<br>機械工程系碩士班<br>94<br>The objective of this study is to use a real time visualization technique to observe the effects of in-mold constraint on the shrinkage of a through hole array. Such a hole array can used in optical communication or optoelectronics applications. Precision control of roundness and position accuracy of the hole arrays are extremely important and directly related to diameter and pitch shrinkage of the hole arrays. In order to have through holes, pins are assembled within the cavity and result in anisotropic shrinkage of the through holes, or so called in-mold constraint shrinkage. To better understand the phenomena, a special designed mold was made to meet this attention. The molded part is a plate of 1mm thick. It has 3x3 through holes of 3mm in diameter. A endoscope behind a transparent quartz block was mounted upon the mold cavity to observe the live shrinkage inside the mold cavity. The melt front advancement can be captured by a high speed camera, respectively. In order to understand the effects of different processing conditions on the shrinkage of sampled hole diameter, Taguchi’s design method of experiments was applied to obtain meaningful results in less times of experiments. The numerical simulation results have shown the mold temperature is the most significant factor to holes’ shrinkage. Thermal shrinkage is about five times larger than the in-mold constraint shrinkage. The real time visualization helps us to observe live shrinkage in both with and without in-mold constraint cases. The pins inside the mold will stop the plastic to shrink and make the holes become elliptic during the in mold cooling. This makes that the dimension along the flow direction (x-direction) was found larger than the one in y-direction. Therefore lower shrinkage was found in the with in-mold constraint products. The in-mold constraint will result in higher residual stresses from the photo-elasticity measurement. It is because the polymer material is restricted to shrink and result in higher internal stresses within the molded parts. The presented work has increase our understanding of the shrinkage with and without in-mold constraint for molding a plate with through hole array. Future work may be extended to the cases of injection molded short fiber reinforced composites.

碩士<br>國立臺灣大學<br>機械工程學研究所<br>89<br>This study aims to investigate the formation of air bubbles at a submerged single micro-hole under non-constant pressure condition. A high-speed camera was used to visualize the process of bubble formation in order to calculate the detached bubble volume. The air pressure in the test chamber was recorded during each measurement. In the present experiment, pure water and 10%w.t. isopropanol solution were used as working fluids. The hole’s diameters with 60 mm, 90 mm, 126 mm, 210 mm, 580 mm and 1200 mm were respectively used for measurement. The liquid was drained out of the test chamber at a rate of 0.006 ml/sec, 0.01 ml/sec, 0.035 ml/sec, 0.05 ml/sec, and 0.1 ml/sec respectively. The effects of physical properties of liquids and the diameter of micro-holes on the bubble formation process and the detached bubble volume were discussed. The experimental results show that the liquid drained rate has no obvious effect on the detachment of a bubble volume, but can results in the formation of bubbles in pairs. The effects of the hole’s diameter and the properties of working fluids on the detached bubble volume are significant. Besides, the surface tension can not only increase the detached bubble volume, but can also delay the detachment time of the first generated bubble. In addition, a correlation has also been developed in the present study to obtain the relationship between a detached bubble volume, the physical properties of working fluids and the hole’s diameter. Moreover, the comparison with prior studies shows that the present proposed correlation lies in between the correlations for constant pressure condition and the constant flow condition.

碩士<br>國立中山大學<br>機械與機電工程學系研究所<br>102<br>In this study, we use an ultrasound micro-nozzle atomizer, made of piezoelectric ceramic material as the cooling system apparatus to observe the spray impinging on an ITO transparent heater. The working fluid is DI water and the main experimental parameters are the distance from nozzle to target, Z(30, 50, 70, 90, 100 mm), the temperature of the heater at the center point, Tc(25, 75, 125, 175, 225 oC), and nozzle diameter, dj(7, 10, 35 μm). The μPIV technique and a high speed camera are used to record the 2-D velocity distribution of a spray flow field on the side view and dynamic droplet size distribution on the lower view, respectively. In regard to the thermal characteristic, we use a data logger, T-type thermocouple wire and IR detector to record the surface temperature distribution on a transparent heater, and carry out an analysis of the heater’s temperature drop result from spray cooling. Finally, we develop a mini spray cooling system for CPUs or other electrical devices.

Visualization is used for stainless steel container wall and lid cross section characterization. Two specific types of containers are examined: 3013 and SAVY. The container wall examined is from a sample of the inner container of a 3013 container. The inner lid cross section examined is from a SAVY container. Laser confocal microscope data and photographic data are used to determine features of the surfaces. The surface features are then characterized by various feature statistics, such as, maximum depth, area, eccentricity, and others. The purpose of this pilot study is to demonstrate the effectiveness of using the methodology to detect potential corrosion events on the inner container surfaces. The features are used to quantify these corrosion events. An automatic image analysis system uses this methodology to classify images for possible further human analysis by flagging possible corrosion events. A manual image analysis methodology is used to determine the amount of MnS on the SAVY container lid cross section. Visualization is an integral component of the analysis methodology.

碩士<br>國立中山大學<br>機械與機電工程學系研究所<br>106<br>Due to the environmental issues have been concerned recently, much research about the fuel cells is widely discussed in various aspects; this study focuses on observations of the flow field, temperature field, and concentration field in an air-breathing direct methanol fuel cell stack, and their relationship with the performance. In this experiment, the distribution of momentum, heat, and mass transfer were established through the optical measurement method of μPIV and μLIF, and the objective of simultaneous for optical observation and performance measurement was achieved. From the experimental data, we obtained that the 2-cell stack had the power output up to 61.73mW/cm2; the CO2 bubbles and the vortex were also observed during operating. Further, the correlation of the Reynolds number (Re) with the friction factor (f), the Nusselt number (Nu), and the Sherwood number (Sh) are also obtained. By the conclusion, if the stack is constructed similarly by two or more cells, the influence of momentum, heat, and mass transfer, even the performance can be expected. That would provide a conception for design and further improve the application of micro direct methanol fuel cell stacks.

碩士<br>國立臺灣大學<br>機械工程學研究所<br>101<br>In this study, we employ a micro-schlieren system to observe Marangoni convection induced by concentration gradient during boiling of binary mixtures in square capillary tubes of various sizes. The effects of channel size, concentration of working fluids and mixture characteristic on boiling heat transfer are investigated experimentally. From the relation between refractive index gradient and grayscale ratio, we are able to quantify the concentration gradient near the vapor-liquid interface. The inner widths of square capillary tubes we use are 200 micrometer, 500 micrometer and 900 micrometer, and our working fluids are binary mixtures of 2-propanol/water, 2-butanol/water, 1-butanol/water, ethylene glycol/water, acetic acid/water and butyric acid/water. In general, binary mixtures can be classified into positive mixtures and negative mixtures. In this work, positive mixtures include 2-propanol/water and 2-butanol/water. Our experimental results reveal that both size of the square capillary and concentration play a prominent role in the heat transfer coefficients. Yet, heat transfer of 2-butanol/water mixtures is independent of size of capillary and varying concentration has no impact on the heat transfer of butyric acid/water mixtures. Results of this work confirm that the concentration induced Marangoni convection is significant to the boiling of binary mixtures. For 2-propanol/water and acetic acid/water mixtures, we find out that the Marangoni effect is particularly vital at low concentration. Heat transfer of 2-propanol/water mixture is enhanced at low concentration because the surface tension gradient acts to induce liquid motion towards the heated surface. Nevertheless, opposite trend is found for acid/water mixture. An interesting phenomenon, bubble oscillation, is discovered in smaller square capillary tube when concentrations are close to the azeotropic point and the mole fraction of liquid phase is higher than that of vapor. Usually, the schlieren patterns can be easily found in square capillary tubes of larger size. No schlieren phenomenon is observed in capillary of 200 micrometer in width. By comparing the refractive index derivatives with respect to temperature and concentration, we verify that the schlieren indeed corresponds to the concentration induced Marangoni convection. With the correlation of refractive index gradient and grayscale ratio, we are able to quantify the concentration gradients near the liquid-vapor interface during boiling of binary mixtures when the Marangoni convection is strong.

This thesis presents a performance evaluation of a micro horizontal axis wind turbine, investigates the use of particle image velocimetry (PIV) to capture the flow field around a rotating blade and to track water droplets in the flow. The testing was done in a low speed wind tunnel in a highly blocked configuration. The turbine was instrumented to measure rotational speed of the rotor, axial thrust and power output. Wind speed of the wake was measured with a Kiel probe. Performance characteristics were calculated and compared with the manufacturer’s published data and to power predictions by axial momentum theories. The turbine was shown to perform well and the manufacturer’s published data are accurate. Axial momentum theory over-predicts power by approximately 50%. It is shown that good PIV results can be obtained using a fog machine to seed the flow. Improved illumination and optics will be required to measure 3D flow close to the blade. Water droplets can be tracked but a shadowgraphy arrangement should be used to better visualize the droplets. The droplets also affect the rotational speed of the rotor such that capturing the blade in a consistent point in the field of view is problematic.

A body in a hypersonic flow field will experience very high heating especially during re-entry. Conventionally this problem is tackled to some extent by the use of large angle blunt cones. At the cost of increased drag, the heat transfer rate is lower over most parts of the blunt body, except in a region around the stagnation point. Thus even with blunt cones, management of heat transfer rates and drag on bodies at hypersonic speeds continues to be an interesting research area. Various thermal protection systems have been proposed in the past, like heat sink cooling, ablation cooling and aerospikes. The ablative cooling system becomes extremely costly when reusability is the major concern. Also the shape change due to ablation can lead to issues with the vehicle control. The aerospikes themselves may become hot and ablate at hypersonic speeds. Hence an alternate form of cooling system is necessary for hypersonic flows, which is more feasible, cost effective and efficient than the conventional cooling systems. Injection of a mass of cold fluid into the boundary layer through the surface is one of the potential cooling techniques in the hypersonic flight corridors. These kinds of thermal protection systems are called mass transfer cooling systems. The injection of the mass may be through discrete slots or through a porous media. When the coolant is injected through a porous media over the entire surface, the coolant comes out as a continuous mass. Such a cooling system is also referred as “transpiration cooling system”. When the fluid is injected through discrete slots, the system is called as “film cooling system”. In either case, the coolant absorbs the incoming heat through its rise in enthalpy and thus modifies the boundary layer characteristics in such a way that the heat flow rate to the surface is less. Injection of a forward facing jet (opposite to the freestream direction) from the stagnation point of a blunt body can be used for mitigating both the aerodynamic drag and heat transfer rates at hypersonic Mach numbers. If the jet has enough momentum it can push the bow shock forward, resulting in reduced drag. This will also reduce heat transfer rate over most part of the body except around the jet re-attachment region. A reattachment shock impinging on the blunt body invariably increases the local heat flux. At lower momentum fluxes the forward facing jet cannot push the bow shock ahead of the blunt body and spreads easily over the boundary layer, resulting in reduced heat transfer rates. While the film cooling performance improves with mass flow rate of the jet, higher momentum flow rates can lead to a stronger reattachment leading to higher heat transfer rate at the reattachment zone. If we are able to reduce the momentum flux of the coolant for the same mass flow rate, the gas coming out can easily spread over the boundary layer and it is possible to improve the film cooling performance. In all the reported literature, the mass flow rate and the momentum flux are not varied independently. This means, if the mass flow rate is increased, there is a corresponding increase in the momentum flux. This is because the injection (from a particular orifice and for a particular coolant gas) is controlled only by the total pressure of injection and free stream conditions. The present investigation is mainly aimed at demonstrating the effect of reduction in momentum of the coolant (injected opposing a hypersonic freestream from the stagnation point of a blunt cone), keeping the mass flow rate the same, on the film cooling performance. This is achieved by splitting a single jet into a number of smaller jets of same injection area (for same injection total pressure and same free stream conditions). To the best of our knowledge there is no report on the use of forward facing micro-jet array for film cooling at hypersonic Mach numbers. In this backdrop the main objectives of the present study are: • To experimentally demonstrate the effect of splitting a single jet into an array of closely spaced smaller micro-jets of same effective area of injection (injected opposite to a hypersonic freestream from the stagnation zone), on the reduction in surface heat transfer rates on a large angle blunt cone. · Identifying various parameters that affect the flow phenomenon and doing a systematic investigation of the effect of the different parameters on the surface heat transfer rates and drag. Experimental investigations are carried out in the IISc hypersonic shock tunnel on the film cooling effectiveness. Coolant gas (nitrogen and helium) is injected opposing hypersonic freestream as a single jet (diameter 2 mm and 0.9 mm), and as an array of iv micro jets (diameter 300 micron each) of same effective area (corresponding to the respective single jet). The coolant gas is injected from the stagnation zone of a blunt cone model (58o apex angle and nose radius of 35 mm). Experiments are performed at a flow freestream Mach number of 5.9 at 0o angle of attack, with a stagnation enthalpy of 1.84 MJ/Kg, with and without injections. The ratios of the jet stagnation pressure to the pitot pressure (stagnation pressure ratio) used in the present study are 1.2 and 1.45. Surface convective heat transfer measurements using platinum thin film sensors, time resolved schlieren flow visualization and aerodynamic drag measurements using accelerometer force balance are used as flow diagnostics in the present study. The theoretical stagnation point heat transfer rate without injection for the given freestream conditions for the test model is 79 W/cm2 and the corresponding aerodynamic drag from Newtonian theory is 143 N. The measured drag value without injection (125 N) shows a reasonable match with theory. As the injection is from stagnation zone it is not possible to measure the surface heat transfer rates at the stagnation point. The sensors thus are placed from the nearest possible location from the stagnation point (from 16 mm from stagnation point on the surface). The sensors near the stagnation point measures a heat transfer rate of 65 W/cm2 on an average without any injection. Some of the important conclusions from the study are: • Up to 40% reduction in surface heat transfer rate has been measured near the stagnation point with the array of micro jets, nitrogen being the coolant, while the corresponding reduction was up to 30% for helium injection. Considering the single jet injection, near the stagnation point there is either no reduction in heat transfer rate or a slight increase up to 10%. · Far away from stagnation point the reduction in heat transfer with array of micro-jets is only slightly higher than corresponding single jet for the same pressure ratio. Thus the cooling performance of the array of closely spaced micro jets is better than the corresponding single jet almost over the entire surface. • The time resolved flow visualization studies show no major change in the shock standoff distance with the low momentum gas injection, indicating no major changes in other aerodynamic aspects such as drag. · The drag measurements also indicate that there is virtually no change in the overall aerodynamic drag with gas injection from the micro-orifice array. · The spreading of the jets injected from the closely spaced micro-orifice array over the surface is also seen in the visualization, indicating the absence of a region of strong reattachment. · The reduction in momentum flux of the injected mass due to the interaction between individual jets in the case of closely spaced micro-jet array appears to be the main reason for better performance when compared to a single jet. The thesis is organized in six chapters. The importance of film cooling at hypersonic speeds and the objectives of the investigation are concisely presented in Chapter 1. From the knowledge of the flow field with counter-flow injection obtained from the literature, the important variables governing the flow phenomena are organized as non-dimensional parameters using dimensional analysis in Chapter 2. The description of the shock tunnel facility, diagnostics and the test model used in the present study is given in Chapter 3. Chapter 4 describes the results of drag measurements and flow visualization studies. The heat transfer measurements and the observed trends in heat transfer rates with and without coolant injection are then discussed in detail in Chapter 5. Based on the obtained results the possible physical picture of the flow field is discussed in Chapter 6, followed by the important conclusions of the investigation.

A body in a hypersonic flow field will experience very high heating especially during re-entry. Conventionally this problem is tackled to some extent by the use of large angle blunt cones. At the cost of increased drag, the heat transfer rate is lower over most parts of the blunt body, except in a region around the stagnation point. Thus even with blunt cones, management of heat transfer rates and drag on bodies at hypersonic speeds continues to be an interesting research area. Various thermal protection systems have been proposed in the past, like heat sink cooling, ablation cooling and aerospikes. The ablative cooling system becomes extremely costly when reusability is the major concern. Also the shape change due to ablation can lead to issues with the vehicle control. The aerospikes themselves may become hot and ablate at hypersonic speeds. Hence an alternate form of cooling system is necessary for hypersonic flows, which is more feasible, cost effective and efficient than the conventional cooling systems. Injection of a mass of cold fluid into the boundary layer through the surface is one of the potential cooling techniques in the hypersonic flight corridors. These kinds of thermal protection systems are called mass transfer cooling systems. The injection of the mass may be through discrete slots or through a porous media. When the coolant is injected through a porous media over the entire surface, the coolant comes out as a continuous mass. Such a cooling system is also referred as “transpiration cooling system”. When the fluid is injected through discrete slots, the system is called as “film cooling system”. In either case, the coolant absorbs the incoming heat through its rise in enthalpy and thus modifies the boundary layer characteristics in such a way that the heat flow rate to the surface is less. Injection of a forward facing jet (opposite to the freestream direction) from the stagnation point of a blunt body can be used for mitigating both the aerodynamic drag and heat transfer rates at hypersonic Mach numbers. If the jet has enough momentum it can push the bow shock forward, resulting in reduced drag. This will also reduce heat transfer rate over most part of the body except around the jet re-attachment region. A reattachment shock impinging on the blunt body invariably increases the local heat flux. At lower momentum fluxes the forward facing jet cannot push the bow shock ahead of the blunt body and spreads easily over the boundary layer, resulting in reduced heat transfer rates. While the film cooling performance improves with mass flow rate of the jet, higher momentum flow rates can lead to a stronger reattachment leading to higher heat transfer rate at the reattachment zone. If we are able to reduce the momentum flux of the coolant for the same mass flow rate, the gas coming out can easily spread over the boundary layer and it is possible to improve the film cooling performance. In all the reported literature, the mass flow rate and the momentum flux are not varied independently. This means, if the mass flow rate is increased, there is a corresponding increase in the momentum flux. This is because the injection (from a particular orifice and for a particular coolant gas) is controlled only by the total pressure of injection and free stream conditions. The present investigation is mainly aimed at demonstrating the effect of reduction in momentum of the coolant (injected opposing a hypersonic freestream from the stagnation point of a blunt cone), keeping the mass flow rate the same, on the film cooling performance. This is achieved by splitting a single jet into a number of smaller jets of same injection area (for same injection total pressure and same free stream conditions). To the best of our knowledge there is no report on the use of forward facing micro-jet array for film cooling at hypersonic Mach numbers. In this backdrop the main objectives of the present study are: • To experimentally demonstrate the effect of splitting a single jet into an array of closely spaced smaller micro-jets of same effective area of injection (injected opposite to a hypersonic freestream from the stagnation zone), on the reduction in surface heat transfer rates on a large angle blunt cone. · Identifying various parameters that affect the flow phenomenon and doing a systematic investigation of the effect of the different parameters on the surface heat transfer rates and drag. Experimental investigations are carried out in the IISc hypersonic shock tunnel on the film cooling effectiveness. Coolant gas (nitrogen and helium) is injected opposing hypersonic freestream as a single jet (diameter 2 mm and 0.9 mm), and as an array of iv micro jets (diameter 300 micron each) of same effective area (corresponding to the respective single jet). The coolant gas is injected from the stagnation zone of a blunt cone model (58o apex angle and nose radius of 35 mm). Experiments are performed at a flow freestream Mach number of 5.9 at 0o angle of attack, with a stagnation enthalpy of 1.84 MJ/Kg, with and without injections. The ratios of the jet stagnation pressure to the pitot pressure (stagnation pressure ratio) used in the present study are 1.2 and 1.45. Surface convective heat transfer measurements using platinum thin film sensors, time resolved schlieren flow visualization and aerodynamic drag measurements using accelerometer force balance are used as flow diagnostics in the present study. The theoretical stagnation point heat transfer rate without injection for the given freestream conditions for the test model is 79 W/cm2 and the corresponding aerodynamic drag from Newtonian theory is 143 N. The measured drag value without injection (125 N) shows a reasonable match with theory. As the injection is from stagnation zone it is not possible to measure the surface heat transfer rates at the stagnation point. The sensors thus are placed from the nearest possible location from the stagnation point (from 16 mm from stagnation point on the surface). The sensors near the stagnation point measures a heat transfer rate of 65 W/cm2 on an average without any injection. Some of the important conclusions from the study are: • Up to 40% reduction in surface heat transfer rate has been measured near the stagnation point with the array of micro jets, nitrogen being the coolant, while the corresponding reduction was up to 30% for helium injection. Considering the single jet injection, near the stagnation point there is either no reduction in heat transfer rate or a slight increase up to 10%. · Far away from stagnation point the reduction in heat transfer with array of micro-jets is only slightly higher than corresponding single jet for the same pressure ratio. Thus the cooling performance of the array of closely spaced micro jets is better than the corresponding single jet almost over the entire surface. • The time resolved flow visualization studies show no major change in the shock standoff distance with the low momentum gas injection, indicating no major changes in other aerodynamic aspects such as drag. · The drag measurements also indicate that there is virtually no change in the overall aerodynamic drag with gas injection from the micro-orifice array. · The spreading of the jets injected from the closely spaced micro-orifice array over the surface is also seen in the visualization, indicating the absence of a region of strong reattachment. · The reduction in momentum flux of the injected mass due to the interaction between individual jets in the case of closely spaced micro-jet array appears to be the main reason for better performance when compared to a single jet. The thesis is organized in six chapters. The importance of film cooling at hypersonic speeds and the objectives of the investigation are concisely presented in Chapter 1. From the knowledge of the flow field with counter-flow injection obtained from the literature, the important variables governing the flow phenomena are organized as non-dimensional parameters using dimensional analysis in Chapter 2. The description of the shock tunnel facility, diagnostics and the test model used in the present study is given in Chapter 3. Chapter 4 describes the results of drag measurements and flow visualization studies. The heat transfer measurements and the observed trends in heat transfer rates with and without coolant injection are then discussed in detail in Chapter 5. Based on the obtained results the possible physical picture of the flow field is discussed in Chapter 6, followed by the important conclusions of the investigation.

I visualized the flash-boiling atomization of liquid jets released into a low pressure environment at frame rates of up to five million frames per second. Such a high temporal resolution allowed us to observe for the first time the bubble expansion mechanism that atomizes the jet. To visualize the dynamics in detail, I focused closely to the outflow of the nozzle using a long distance microscope objective. I documented an abrupt transition from a laminar to a fully external flashing jet by systematically reducing the ambient pressure. I performed experiments with different volatile liquids and using nozzles with different inner diameters. The inner diameters of the nozzles varied from 30 to 480 µm. Perfluorohexane (PFnH) was our main working fluid, but also methanol, ethanol and 1-bromopropane were tested. Surprisingly, minimum intensity profiles revealed spray angles close to θs ~360°, meaning drops are ejected in all directions. Also, I measured speeds of bubble expansion up to 140 m/s. That is 45 times faster than the upper bound for inertial growth speed in complete vacuum from the Rayleigh-Plesset equation. I also calculated the trajectories of the ejected droplets as well as the drop speed distribution using particle tracking. I expect that our results bring new insight into the flash-boiling atomization mechanism.