Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work reports an experimental investigation related to the drop-in process of HCFC22 in a commercial refrigeration system with a maximum capacity of 15 kW. Among the alternative refrigerants there are hydrocarbons (HCs) and synthetic refrigerants, HFC. The experimental facility is basically composed of analternative variable speed compressor (VSC), tube in tube heat exchangers and an electronic expansion valve (EEV). Different methodologies were addressed to this document. Initially, the systemoperated at the nominal frequency and has been configured to the same openning condition in the expansion valve. The limits of the refrigeration system were operated by factorial experimental designs. Therefore,there were presented response surfaces and metamodels, showing consistent tools to predict the cooling system behavior. Also, an analysis of the individual performance of each refrigerant was held in three different evaporation temperatures: -15ºC, -10ºC and -5ºC. All fluids, except R134a can be suitable to replace R22 in these specific applications. Both HCs and HFC32 provide the refrigeration capacity and COP greater than the original system. In addition, the environmental impact of each fluid was estimated by the TEWI method. HCs showed the lowest impacts, while HFC404A promoted the greatest damage to the environment. Finally, the analysis of the operating system with a Scroll compressor was made. Among the seven options to R22, only five refrigerants operated in stable condition. Moreover, even with handling system parameters, this class of compressors was less flexible to the proposed drop-in. In general, as a great technical contribution for refrigeration systems, this study found that, regardless of the installation capacity, the EEV/VSC pair functionality is an essential tool not only for the adaptation of an alternative fluid to the original compression cycle, as well as to reduce environmental impacts. / O presente trabalho relata uma investigação experimental do processo de drop-in(substituição direta) do HCFC22 em um sistema de refrigeração comercial com capacidade máxima de 15kW. Entre os refrigerantes alternativos testados, encontram-se hidrocarbonetos e refrigerantes sintéticos da classe HFC.A bancada experimental é composta, basicamente, de um compressor de velocidade variável(CVV) alternativo, trocadores de calor de tubos concêntricos e uma válvula de expansão eletrônica (VEE). Inicialmente, o sistema operou à frequência nominal e foiconfigurado à mesma condição de abertura no dispositivo de expansão. Posteriormente, os limites de cada refrigeranteforam explorados por meio de ferramentas estatísticas DOE,design of experiments. Nesta segunda etapa, foram apresentadas superfícies de respostas e metamodelos, que se mostraram ferramentas coerentes na previsão do comportamento do sistema de refrigeração.Em sequência,foirealizada uma análise do desempenho individual de cada refrigerante, em três diferentes temperaturas de evaporação: -15ºC, -10ºC e -5ºC. Todos os refrigerantes, com exceção do R134a, podem substituir o R22 nestas aplicações específicas. Ambos os hidrocarbonetos (HCs) e o HFC32 proporcionaram capacidades de refrigeração e COPs superiores ao sistema original. Em complemento, a estimativa dos impactos ambientais de cada fluidofoi estimada através do método TEWI, total equivalent warming impact. Os HCs apresentaram os menores impactos, enquanto o HFC404A promoveu os maiores danos ao meio ambiente.Por fim, realizou-se a análise do sistema operando com um compressor tipoScroll. Entre as sete opções ao R22, apenas cinco refrigerantes operaram em condições estáveis. Além disso, mesmo com a manipulação de parâmetros do sistema, esta classe de compressores mostrou-se menos flexível à proposta de drop-in.Em geral, como maior contribuição técnica aos sistemas de refrigeração, o presente trabalho comprovou que, independentemente da capacidade da instalação, a funcionalidade do par VEE/CVV é uma ferramenta essencial não só para a adaptação de um fluido alternativo ao ciclo de compressão original, como também para a reduçãodos impactos ambientais. / Doutor em Engenharia Mecânica

This thesis studies a droplet of ferrofluid impacting a liquid water pool. The ferrofluid is oil-based and therefore immersible in water. The shape of the ferrofluid drop at impact is changed by using an electromagnet underneath the liquid pool. The magnet is turned off by an external trigger just before the drop collides with the liquid pool surface, to stop the magnetic interaction. The prolate or oblate shape of the drop has an influence on the cavity formation and evolution after the impact. The experiments look specifically at the maximum depth and diameter of the cavity, as a function of the drop impact shape for the same impact velocity. This is done over a range of impact velocities. The prolate drops generate deeper cavities than spherical or oblate drops. Furthermore, a study is conducted on the jet formation that occurs during the cavity collapse to investigate the influence of droplet shape on the jet velocity.

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No / The local parameters for kerosene–water upward flow are measured in a vertical pipe of 77.8 mm inner diameter at 4200 mm from the inlet(L/D = 54) using hot-film and dual optical probes. The effect of superficial water velocity and volumetric quality on radial distribution of two-phaseflow parameters is investigated. The results show the following: (i) the profiles of volume fraction and drop frequency are very similar, and increasing superficial water velocity at low volumetric qualities (<18.6%) change the profile from a convex shape with peak at the pipe centreline to uniform then to concave shape with peak near the wall; (ii) the profiles of drop cut chord change from a parabolic shape with peak at centreline for lows uperficial water velocities to a flat shape at higher superficial water velocity, and the area-averaged drop diameter decreases with higher superficial water velocities for all volumetric qualities; (iii) velocity profiles for both phases have shapes similar to single phase flow, flatter at higher values of superficial water velocity and volumetric quality and centreline peaked at low superficial water velocities and volumetric qualities; (iv) the slip velocity decreases with radial distance having a peak at centreline and zero values near the wall; (v) introducing kerosene drops into single phasewater flow results in a sharp increase in turbulent intensity, particularly at low water velocity, and the difference between the single phase and two-phase flow turbulence intensities decreases with higher superficial water velocities and (vi) the results show that interfacial area concentration increased with higher volumetric quality and higher number of bubbles thereby increases the contact area between the two phases.

We analyze recordings of seismic events induced by underground mining operations at the Moonee Colliery, located in Australia, and at the Springfield Pike Limestone Quarry, located in the United States. The data were recorded underground in the vicinity of active mining operations and were initially used by the monitoring systems at the two mines to evaluate the potential for roof failure based on the temporal and spatial distribution of the seismic activity. In an earlier study, the roof failures at the two underground mine locations were found to be the result of two distinct failure processes, both of which were correlated with escalated seismic activity before the roof collapsed. In this study, we reexamine the recordings of these seismic emissions for a further assessment of the state of instability in the roof. We estimate the static seismic moment and radiated seismic energy for each recorded seismic event induced by mining operations at the two underground mine locations. These seismic source parameters are estimated from source spectra have been corrected for the instrument response, propagation effects and bandwidth limitations. The apparent stress, which provides an estimate of the stress drop (or stress release) associated with a seismic event, is then determined from the product between the modulus of rigidity and the ratio between the radiated seismic energy and static seismic moment. The validity of constant stress drop scaling for the seismic events at the two underground mine locations is tested. Estimation of the seismic source parameters indicate that the stress drop of the mining induced events increases over three orders of magnitude of increasing seismic moment (106 N·m ≤ M0 ≤ 109 N·m) and indicate a divergence from constant stress drop scaling. When these results are compiled with the results from seven other independent studies, which analyzed the seismicity associated with a variety of seismogenic environments, this trend is found to span over ten orders of magnitude of seismic moment (106 N·m ≤ M0 ≤ 1016 N·m). The observation that the mining induced events do not conform to constant stress drop scaling may assist in gaining a better understanding of the evolution of the roof failure process. We have found that the stress drop at one of the studied mines appears to increase through time prior to a roof collapse. More data are necessary to test this hypothesis. If this hypothesis is validated, it would have important implications for monitoring roof stability. Incorporation of near-real-time estimates of the stress drop into the existing seismic monitoring protocol may provide improved warning of imminent roof collapse hazards. / Master of Science

Bakgrund: Över 80 % av alla barn och ungdomar har någon gång varit aktiva i enidrottsförening men i 20-årsåldern är bara hälften kvar. Flickors drop outinom fotboll tenderar till att vara högre än vad det är för pojkar. I förlängningen lederdet till att ungdomslag får lägga ned då lagidrotter som fotboll kräver ett visst antalspelare för att kunna bedrivas. Organiserad idrott bidrar, specifikt för flickor, till en merpositiv framtidssyn och idrottande ungdomar har också visat sig hantera motgångar påett bättre sätt än de som inte idrottar. Syftet är att undersöka vilka orsaker som ökar risken för drop out från organiseradfotboll för flickor i åldern 10-17 år. Metod: Datainsamlingen bygger på enkätdata och för att besvara frågeställningarnaanalyserades svaren kvantitativt. Det stratifierade urvalet bestod av 275 flickfotbollsspelare från fotbollsklubbar i Sverige deltog. Resultat: Huvudfynden i studien är att det finns en skillnad i drop outs när det gällerålder då det är tydligt att äldre slutar i högre grad än yngre. Av de spelare som harmindre än 10 minuters resa till träning slutar 11,4% att spela, medan de som har 10minuter eller längre slutar 30,9%, alltså att om en spelare behöver resa 10 minuter ellerför att ta sig till träning så ökar risken för att spelaren slutar. Det är en större risk att enspelare slutar med fotboll om denne endast utövar fotboll. Det vill säga att om enspelare utövar minst en annan idrott så är det en mindre risk att individen slutar medfotboll. De spelare som har skattat lägre på skalan support slutar i högre grad att spela,medan de spelare som skattat högre är mer benägna med fortsatt utövande. Slutsats: Sammantaget verkar den här undersökningen visa att då det finns en konflikthos en aktiv så främjar det drop out. Konflikten kan gälla tidsåtgång, svårighet att kunna ta sig till och från träning eller huruvida vems ambition som ska styra antalet träningstimmar i veckan. Bristen på flexibilitet kan med stor sannolikhet vara en bidragande faktor till drop out. Nyckelord: Drop out, drop outs, Flickfotboll, Fotboll. Ungdomsidrott.

The Diploma thesis focuses on the drop-out of beginning teachers. Theoretical part elaborates on the phenomenon of drop-out, it describes the reasons why the beginning teachers leave and why they are the group of teachers which is the most threatened by drop-out. Furthermore, this part describes problems that beginning teachers have to deal with and the most frequent reasons for leaving the profession, their rate and consequences of drop-out. The end of the theoretical part presents options and suggestions that would help solve this problem. The empirical part of the thesis is realized by an on-line questionnaire and in-depth interviews. The research focuses on four main aspects: 1 - the motivation to study the teaching and to practise it, 2 - the main reasons for new teachers to leave, 3 - the possibilities to prevent drop-out and 4 - whether the respondents continue to work with children or not. Last but not least, the research focuses on the possibilities that would help respondents to stay in the profession. The results of the research confirm the reasons for quiting as described by literature. The qualitative description of the reasons for drop-outs provides a deeper understanding of how they interact in an institutional, interactive and cultural level. KEYWORDS Induction period, teacher...

The research topic of liquid drop interaction with solid surfaces is being actively pursued to gain in-depth understanding of several practical cases such as the impingement of fuel spray droplets on surfaces like combustion chamber walls and piston top of an I.C. engine, heat transfer via spray impingement, ink-jet printing, etc. In most of the cases, the physical and flow properties of the liquid drop/spray may be fixed whereas it may be possible to tune the physical and chemical properties of the solid surface thereby enabling to control the interaction process. The present work belongs to the study of liquid drop-solid surface interaction process with special focus on the physical characteristics of solid surface. The thesis reports an experimental study of the dynamics of millimetric water drops impacted onto the junction of dual-textured substrates made of stainless steel. The dual-textured substrates consisted of hydrophobic (textured) and hydrophilic (smooth) portions. The entire textured portion comprised of parallel groove-like structures separated by solid posts/pillars. Two dual-textured substrates, which differ only in the geometry of their textured portions, were employed. Surface topography features of the dual-textured substrates were characterized using scanning electron microscopy (SEM) and optical surface profilometer. The wetting behavior of the textured and smooth portions of the substrates, quantified in terms of the equilibrium, advancing, and receding contact angles adopted by a water drop on the surface portions, was characterized experimentally through the methods of sessile drop formation, captive needle volume addition, and drop evaporation under ambient conditions. Free-falling water drops were impacted from a height onto the junction between the hydrophobic (textured) and hydrophilic (smooth) portions of the dual-textured substrates. A set of twelve different impact experiments were conducted on each of the target substrates with drop impact velocity (Uo) ranging from 0.37 to 1.50 m/sec. The dynamics of drop impact were captured using a high speed camera with frame rate ranging from 3000 to 10000 frames per second. From the captured frames, the temporal variations of the impacting drop parameters were measured using a MATLAB-assisted program. A systematic analysis of experimental data revealed the existence of four distinct regimes of drop dynamics on the dual-textured substrate: (a) early inertia driven drop spreading, (b) primary drop receding, (c) secondary spreading on the hydrophilic portion, and (d) final equilibrium regimes. It is shown that the drop impact dynamics during the early inertia driven impact regime remains unaffected by the dual-texture feature of the substrate. A larger retraction speed of impacting drop liquid observed on the hydrophobic portion of the substrate makes the drop liquid on the higher wettability/hydrophilic portion to advance further (secondary drop spreading). The net horizontal drop velocity towards the hydrophilic portion of the dual-textured substrate decreases with increasing drop impact velocity. The available experimental results suggest that the movement of bulk drop liquid away from the impact point during drop impact on the dual-textured substrate is larger for the impact of low inertia drops. A semi-empirical model, based on the balance of the wettability gradient, contact angle hysteresis, and viscous forces acting on impacted drop liquid on the substrate, is formulated to predict the movement of bulk drop liquid away from the impact point (ξ). A satisfactory comparison between the model predictions and the experimental measurements is reported for the variation of ξ with Uo.

As drop-on-demand (DOD) applications continue to gain ground in desktop inkjet-printing, 3D printing, fluid mixing, and other areas the demand for higher frequency operations are beginning to push against the current physical boundaries in DOD technology. The current research is exploring the possibility of controlling drop volume and velocity at high frequency ranges where meniscus vibrations can occur between drop formations and affect drop formation characteristics. A periodic voltage is applied to a piezoelectric disk in order to generate pressure fluctuations in a single nozzle droplet generator, causing the fluid meniscus at the nozzle to vibrate. A single stronger pulse is then superimposed over the periodic waveform at different phases in order to drive drop ejection. The characteristics of the resulting drop, specifically the volume and velocity, are experimentally measured using a high speed camera with precise timing control. The results of these experiments are then compared to a lumped element model (LEM) developed for the droplet generator geometry used. Within the LEM model framework, special attention was given to the definition of a novel method by which one can measure drop volume within an electroacoustic circuit and also allow meniscus dynamics to affect present and future drop formations. Experimental results indicate a strong dependence of both drop volume and drop velocity on the phase of the vibrating meniscus at the start of drop formation. Positive meniscus displacements and momentums resulted in large drop volumes and velocities while negative displacements could reduce drop volume or altogether eliminate drop formation. Specifically, positive displacements and momentum of a vibrating meniscus could lead to drop volumes approximately 50% larger than the original drop volume without a vibrating meniscus. Meanwhile, negative meniscus displacements and momentums were shown to have the ability to completely prevent drop formation. Additional potential for drop characteristic control with a vibrating meniscus is discussed alongside observations on the stabilizing affect the vibrating meniscus appears to have on drop velocity as a function of time. Also, flow visualization of the drop formation is provided to demonstrate the added affect the meniscus vibrations have on the drop shapes and break-off profiles. The LEM model presented demonstrates qualitative agreement with the experimental model, but fails to quantitatively predict drop volumes. Sources of error for the LEM model and potential improvements are discussed. / Graduation date: 2012