Dissertations / Theses on the topic 'Thermal bubble'

This thesis describes thermally induced bubble behaviour changes in liquid nitrogen (LN2) under electric fields. Cryogenic liquids such as LN2 have been used not only as the coolant but also as the electrical insulator in superconducting and cryogenic apparatus. However, bubbles are easily formed in these liquids by even moderate heating because of a narrow liquid temperature range and low boiling point. Bubbles are considered to be one of the factors causing a reduction of the electrical insulation level. Consequently, bubble behaviour in electric fields is of great interest primarily in the study of prebreakdown and breakdown phenomena in the presence of thermally induced bubbles. In addition, a bubble can appear and its behaviour changes in a fluid under the influence of an electric field, and this is the main reason for boiling heat transfer enhancement which is related to thermal stability and heat transfer efficiency. Studies including single bubble behaviour and bubble column behaviour as well as boiling heat transfer enhancement due to changes in bubble behaviour under electric fields using different electrodes have been completed. Free thermal bubble motion and related characteristics in LN2 under a conductor-plane electrode have been experimentally studied. A model for bubble motion in this non-uniform electric field has been developed and is described. Compared with theoretical results, the experimental measurements are in good agreement. An rimental study into the behaviour of thermal bubbles between two plane-plane inclined electrodes has been completed. Using a stainless steel mesh-to-plane electrode system, experimental investigations have been carried out to study the effect of uniform dc electric fields on the behaviour of a single thermal bubble in LN2. Bubble characteristics such as bubble growth, deformation and bubble departure frequency have been experimentally evaluated. Finally, the electric field effects on boiling heat transfer of LN2 have been experimentally assessed. The obtained data is applicable to the design of LN2 cooled high temperature superconductor power apparatus for both coolant and electrical insulation issues.

The thermal evolution of pyroclastic density currents (PDCs) is the result of entrainment of ambient air, particle concentration, and initial eruptive temperature, which all impact PDC dynamics and their hazards, such as runout distance. The associated hazards and opaqueness of PDCs make it impossible for in-situ entrainment efficiencies or concentration measurements that would provide critical information on the thermal evolution and physical processes of PDCs. The thermal evolution of explosive eruptive events such as volcanic plumes and pyroclastic density currents (PDCs) is reflected in the textures of the material they deposit. A multiscale model is developed to evaluate how the rinds of breadcrust bombs can be used as a unique thermometer to examine the thermal evolution of PDCs. The multiscale, integrated model examines how bubble growth, pyroclast cooling, and dynamics of PDC and projectile pyroclasts form unique pyroclast morphology. Rind development is examined as a function of transport regime (PDC and projectile), transport properties (initial current temperature and current density), and pyroclast properties (initial water content and radius). The model reveals that: 1) rinds of projectile pyroclasts are in general thicker and less vesicular than those of PDC pyroclasts; 2) as the initial current temperature decreases due to initial air entrainment, the rinds on PDC pyroclasts progressively increase in thickness; and 3) rind thickness increases with decreasing water concentration and decreasing clast radius. Therefore, the modeled pyroclast’s morphology is dependent not only on initial water concentration but also on the cooling rate, which is determined by the transport regime. The developed secondary thermal proxy is then applied to the 2006 PDCs from the Tungurahua eruption to constrain the entrainment efficiency and thermal evolution of PDCs. A three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model is coupled to topography and field data such as paleomagnetic data and rind thicknesses of collected pyroclasts to study the entrainment efficiency and thus the thermal history of PDCs at Tungurahua volcano, Ecuador. The modeled results that are constrained with observations and thermal proxies demonstrate that 1) efficient entrainment of air to the upper portion of the current allows for rapid cooling, 2) the channelized pyroclastic density currents may have developed a stable bed load region that was inefficient at cooling and 3) the PDCs had temperatures of 600-800K in the bed load region but the upper portion of the currents cooled down to ambient temperatures. The results have shown that PDCs can be heterogeneous in particle concentration, temperature, and dynamics and match observations of PDCs down a volcano and the thermal proxies. Lastly, the entrainment efficiencies of PDCs increases with increasing PDC temperature and entrainment varies spatially and temporally. Therefore, the assumption of a well-mixed current with a single entrainment coefficient cannot fully solve the thermal evolution and dynamics of the PDC.

This dissertation focuses on the effects of heating on superhydrophobic (SHPo) surfaces. The work is divided into two main categories: heat transfer without mass transfer and heat transfer in conjunction with mass transfer. Numerical methods are used to explore the prior while experimental methods are utilized for the latter. The numerical work explores convective heat transfer in SHPo parallel plate microchannels and is separated into two stand-alone chapters that have been published archivally. The first considers surfaces with a rib/cavity structure and the second considers surfaces patterned with a square lattice of square posts. Laminar, fully developed, steady flow with constant fluid properties is considered where the tops of the ribs and posts are maintained at a constant heat flux boundary condition and the gas/liquid interfaces are assumed to be adiabatic. For both surface configurations the overall convective heat transfer is reduced. Results are presented in the form of average Nusselt number as well as apparent temperature jump length (thermal slip length). The heat transfer reduction is magnified by increasing cavity fraction, decreasing Peclet number, and decreasing channel size relative to the micro-structure spacing. Axial fluid conduction is found to be substantial at high Peclet numbers where it is classically neglected. The parameter regimes where prior analytical works found in the literature are valid are delineated. The experimental work is divided into two stand-alone chapters with one considering channel flow and the other a pool scenario. The channel work considers high aspect ratio microchannels with one heated SHPo wall. If water saturated with dissolved air is used, the air-filled cavities of SHPo surfaces act as nucleation sites for mass transfer. As the water heats it becomes supersaturated and air can effervesce onto the SHPo surface forming bubbles that align to the underlying micro-structure if the cavities are comprised of closed cells. The large bubbles increase drag in the channel and reduce heat transfer. Once the bubbles grow large enough, they are expelled from the channel and the nucleation and growth cycle begins again. The pool work considers submerged, heated SHPo surfaces such that the nucleation behavior can be explored in the absence of forced fluid flow. The surface is maintained at a constant temperature and a range of temperatures (40 - 90 °C) are explored. Similar nucleation behavior to that of the microchannels is observed, however, the bubbles are not expelled. Natural convection coefficients are computed. The surfaces with the greatest amount of nucleation show a significant reduction in convection coefficient, relative to a smooth hydrophilic surface, due to the insulating bubble layer.

This thesis describes the development of a novel thermal desalination process based on the vapour transfer processes occurring in a water-filled bubble column. A strong focus on facilitating the involvement of local people and on promoting local capacity building by utilising simple technologies steers the research towards thermal desalination. The problem is addressed by first identifying alternative and previously unused water sources that can be utilised for sustainable water provision in remote places. The experimental analysis of a new desalination concept that combines a bubble column evaporator with a simple passive flatplate copper condenser is then provided. A comprehensive condenser assessment under a range of different physical conditions that examine the effects of external water cooling, partial insulation and aspects of air circulation on condenser performance is presented. Subsequently, for the purpose of mitigating high bubble column vapour temperatures without risking greenhouse plant survival in a prospective Bubble-Greenhouse, an alternative set of cooling and pre-condensing devices is assessed. Based on the findings, a conceptual Bubble-Greenhouse design that promotes a holistic sustainable approach to combined water provision and community development is then described. A prototype bubble evaporator is quantitatively and qualitatively assessed for the consistency of its performance and demonstrates a steady evaporation rate. The resulting data provides the basis for extrapolation of bubble evaporator capacity, both for relatively small standalone systems and for significantly up-scaled components that would operate in a Bubble-Greenhouse. In passive mode, condensate recovery rates of around 73% are achieved without the need for external cooling. Estimated by extrapolation, a standalone bubble desalination system with a 1m2 condenser may produce around 19 litres of distilled water per day. The common feature of the alternative set of cooling and pre-condensing devices is that they are easy to manufacture, of low energy demand and low investment cost and technically and operationally appropriate for local people in remote places. Under laboratory conditions, the passive copper tube concepts achieve water recovery rates of between 65-75% and the air cooled bubble condenser columns achieve condensate recovery rates of at least 50%. However, it emerges that a well designed latent heat recovery system is required to keep the energy demand of a thermal desalination system within acceptable limits, both technically and financially. Although the stacked evaporator-condenser bubble column array cannot demonstrate a significant cooling and condensing advantage over the flat-plate condenser, the concept facilitates the implementation of a heat recovery cycle. This attribute ultimately leads to the multistage evaporator-condenser module concept with an effective latent heat recovery system that is integrated into the horizontally stacked chambers, a key element of the Bubble- Greenhouse technology. The greenhouse desalination system is designed with a water production capacity of 8m3 per day. Due to the strongly reduced water demand of plants inside a humidified greenhouse, only a fraction is required for irrigation and the bulk of water is intended for human consumption. This study aims to contribute to the field of water service provision in remote communities, particularly by improving some of the shortcomings of conventional high-tech water treatment technologies that often fail in these situations. A comprehensive discussion posits the Bubble-Greenhouse concept in the context of these remote community water provision shortcomings and highlights how the proposed new treatment method aims to alleviate these. Consequently, the findings presented here may help to inform the essential transition from externally-led water service provision towards a self-determined community operated service, recommendations for future research and recommendations for implementation of a Bubble- Greenhouse field trial conclude the thesis.

Ziel dieser Arbeit war es, die Auswirkungen der im Kühlmittel von Leichtwasserreaktoren zur Reaktivitätssteuerung eingesetzten Borverbindungen auf Siedeprozesse – und damit indirekt auf die Wärmeabfuhr der Brennelemente – zu untersuchen. Bei den Siedeversuchen, die Gegenstand der vorliegenden Arbeit sind, wurde besonders auf eine realitätsnahe Annäherung an die Reaktorparameter Wert gelegt. Als Unterstützung zur Interpretation der Ergebnisse dienten eigene Messungen von signifikanten physikalischen Stoffdaten an wässrigen Borsäure- und Pentaboratlösungen. Die Siedeprozesse wurden in einer eigens für diese Analysen konzipierten und errichteten Versuchsanlage SECA unter Verwendung eines Leitfähigkeitsgittersensors sowie einer Hochgeschwindigkeitskamera bei Drücken von maximal 40 bar und Temperaturen bis zu 250 °C untersucht. Entsprechend der in den Untersuchungen gewonnenen Erkenntnis wird für reale Reaktoren fol-gendes angenommen: Die Anwesenheit von Borsäure hat keinen Einfluss auf großvolumige Sie-devorgänge im betrachteten Störfallszenario eines Druckwasserreaktors, und die Auswirkungen auf das unterkühlte Sieden sind vernachlässigbar gering. Es ist nicht zu erwarten, dass der Wärmeübergang von den Brennelementen an das Kühlmittel beeinflusst wird. Bei einer Einspeisung von Pentaborat in Siedewasserreaktoren kann jedoch davon ausgegangen werden, dass der Wärmeübergang durch eine Verkleinerung der Blasen verbessert wird. Weitere Untersuchungen bezüglich des Austrages von Pentaborat an der Phasengrenze sowie der Bildung von Schäumen sind jedoch notwendig, und es ist den Fragen nachzugehen, ob sich diese Schäume auch bei der Einspeisung von Pentaborat in einen Siedewasserreaktor bilden können und welche Auswirkungen diese auf die oberhalb des Kerns befindlichen Dampfabscheiderzyklone und Dampftrockner haben.

The most common way to exchange heat with the ground in Ground Source Heat Pump (GSHP) applications is with borehole heat exchangers (energy col-lectors in vertical wells). These boreholes contain the pipe with the secondary fluid of the GSHP and they are often filled with natural groundwater. It has been recently discovered that injecting air bubbles in the groundwater side of the boreholes increases the efficiency of the heat transfer. The aim of this thesis is to analyze the thermal changes in the borehole and the surrounding ground when bubbles are injected in the groundwater. Experiments are carried out through a distributed thermal response test along the borehole using two differ-ent rates of bubble injection. Temperature profiles of the secondary fluid and the groundwater are analyzed and calculations on the thermal resistances inside the borehole and the conductivity of the ground are made. Moreover, the validity of the line source conduction model is discussed under the above mentioned circumstances.

The master´s thesis deals with verification of thermal insulating property of thermoreflection foil insulations. The teoretical part of thesis focuses on the energy demand of buildings, the problems of heat transfer material, terms required for study of thermoreflection thermal insulation and experimental methods for determination of thermal insulating properties of insulators. In the next part the chapter is accompanied by an overview of the most common insulation materials which used in construction. The last part of teoretical part is devoted to the description of thermoreflect formation and analysis of the spread of thermal insulating layers of thermoreflection thermal insulation. The first part of thesis is devoted to the use of thermoreflection therm insulation in buildings. The second part of thesis is devoted to the design, assembly and calibration of the measuring device that uses a method of protected warm chamber. It is declared as a binding method of detection of the heat transfer performance of thermoreflection thermal insulation. The developed measuring device allows detection of endpoints in some direction of propagation of heat. Measurment of heat transfer coefficient devoted the third part of practical part. This part contains a description of the samples used for the measurement of the heat transfer coefficient. In the fourth chapter of the practical part are presented the results of the heat transfer coefficient measurments on selected samples of thermoreflection foil insulation. It is shown the characteristic of heat transfer coefficient of individual samples, the dependence of the heat transfer coefficient on the position of the sample in the measuring device and the recommendation of an appropriate use of sample in the works for the climatic conditions of the Czech republic. The work concludes the chapter of comparing and evaluating of all samples with practical recommendations.

Les mousses liquides sont utilisées dans de nombreux domaines de la vie quotidienne. Leur excellente capacité à dissiper de l'énergie en fait également des matériaux très utilisés dans le domaine militaire pour atténuer les ondes de souffle émises lors d'une explosion. Dans cette thèse, nous avons conçu un dispositif expérimental original nous permettant de visualiser la déformation d'une mousse liquide lors de l'impact d'une onde de souffle en sortie d'un tube à choc. Nous mesurons la surpression en plusieurs points de la mousse, sur une gamme de 5 à 50 kPa. Nous mettons en évidence une atténuation de pression qui augmente avec la taille des bulles puis sature, tous les autres paramètres, notamment la fraction liquide, étant maintenus constants. Ces résultats sont interprétés avec un modèle de dissipation thermique à l'échelle de la bulle suggérant l'existence d'un maximum d'atténuation pour une taille de bulles donnée. Nous caractérisons ensuite la vitesse de propagation de l'onde au sein de la mousse. Aux petites amplitudes, la vitesse suit le modèle de Wood, basé sur une propagation linéaire dans un milieu continu effectif. Aux plus hautes amplitudes, nous mettons en évidence l'apparition d'un régime non linéaire, avec une vitesse de propagation plus importante et une atténuation plus faible, ces deux phénomènes étant retrouvés à la fois théoriquement et numériquement. Près de la source, la mousse est détruite par le choc. Nous terminons notre étude avec des résultats plus qualitatifs sur la quantité de mousse détruite et la vitesse de propagation du front de rupture, visualisées pour la première fois dans une mousse tridimensionnelle
Liquid foams are used in various domains in our everyday life. Their excellent ability to dissipate energy makes foams widely used in the military domain to mitigate blast waves produced after an explosion. In this Thesis, we have designed an original experimental setup allowing us to image the deformation of a liquid foam after the impact of a blast wave exiting a shock tube. We also measure the overpressure in the foam, within a range of 5 to 50\,kPa. We evidence a pressure attenuation, increasing and then saturating at increasing bubble size, while all the other parameters of the foam, especially liquid fraction, are kept constant. Those results are interpreted with a thermal dissipation model at the bubble scale, suggesting the existence of a maximum dissipation for a given bubble size. We then characterise the wave velocity in the foam. At small amplitudes, the velocity follows Wood's model, based on linear propagation in an effective continuous medium. At greater amplitudes, we show the apparition of a non-linear regime, with a higher propagation velocity and a lower attenuation, those two features being captured theoretically and numerically. Close to the source, the foam is destroyed by the shock. We close our study with more qualitative results on the quantity of destroyed foam and the propagation velocity of the rupture front, which have been evidenced for the first time in a three-dimensional foam

Cette thèse s'inscrit dans un projet à long terme qui vise à renseigner les modèles moyennés diphasique grâce à la simulation numérique directe (SND) et se décompose en deux étapes. La première consiste à construire un équivalent de la simulation aux grand échelles (SGE) pour les écoulements diphasiques (appelé modèle ISS). Après avoir présenté les développements théoriques qui sont mis en œuvre, un ensemble de tests de validation est utilisé afin de caractériser le modèle et de déterminer son potentiel à fournir une solution pertinente à faible coût. La seconde étape se rapporte à l'utilisation de ce modèle afin de réaliser des simulations d'écoulements dispersés à bulles contenant plusieurs centaines d'inclusions. Nous nous sommes intéressés à différents cas se rapportant à des essaims monodisperses et bidisperses. Les résultats de ces simulations permettent de calculer les grandeurs moyennes relatives aux bilans de masse, de quantité de mouvement et d'aire interfaciale volumique (AIV). Celles-ci constituent le système d'équations qui régit l'écoulement moyen monodimensionnel, nous procédons ainsi à un test a priori du modèle complet. Dans un premier temps, nous nous sommes attachés à démonter la viabilité de nos mesures en vérifiant les bilans de masse et d'AIV. Ensuite, nous avons montré que l'une des difficultés de ce travail réside dans la définition des grandeurs moyenne à partir des grandeurs locales. Puis, nous avons montré que les hypothèses classiquement introduites sont valides pour des écoulements simples mais ne sont plus justifiées dans les cas plus complexes pour lesquels il est nécessaire d'ajouter des modèles supplémentaires. Enfin, nous avons confronté une corrélation usuelle de coefficient de traînée à nos mesures. Nous avons ainsi montré que cette corrélation donne de bons résultats dans les configurations monodisperses. À l'inverse, son utilisation dans les configurations bidisperses conduit à une surestimation des forces de traînée par le modèle moyenné testé
This work is a part of a long term project that aims at using two-phase Direct Numerical Simulation (DNS) in order to give information to averaged models. For now, it is limited to isothermal bubbly flows with no phase change. It could be subdivided in two parts : Firstly, theoretical developments are made in order to build an equivalent of Large Eddy Simulation (LES) for two-phase flows called Interfaces and Sub-grid Scales (ISS). After the implementation of the ISS model in our code called Trio_U, a set of various cases is used to validate this model. Then, special test are made in order to optimize the model for our particular bubbly flows. Thus we showed the capacity of the ISS model to produce a cheap pertinent solution. Secondly, we use the ISS model to perform simulations of bubbly flows in column. Results of these simulations are averaged to obtain quantities that appear in mass, momentum and interfacial area density balances. Thus, we processed to an a priori test of a complete one-dimensional averaged model. We showed that this model predicts well the simplest flows (laminar and monodisperse). Moreover, the hypothesis of one pressure, which is often made in averaged model like CATHARE, NEPTUNE and RELAP5, is satisfied in such flows. At the opposite, without a polydisperse model, the drag is over-predicted and the uncorrelated Ai flux needs a closure law. Finally, we showed that in turbulent flows, fluctuations of velocity and pressure in the liquid phase are not represented by the tested averaged model

Tse Wang Kong = 單泡聲致發光的熱輻射 / 謝宏岡.
Thesis submitted in: July 2003.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.
Includes bibliographical references (leaves 110-114).
Text in English; abstracts in English and Chinese.
Tse Wang Kong = Dan pao sheng zhi fa guang de re fu she / Xie Honggang.
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- General review of sonoluminescence --- p.1
Chapter 1.2 --- Thermal light emission models --- p.3
Chapter 1.3 --- Motivation and structure of this thesis --- p.7
Chapter 2 --- "Bubble-wall Dynamics, Hydrodynamics and Ionization" --- p.9
Chapter 2.1 --- Uniform bubble model --- p.9
Chapter 2.1.1 --- Bubble-wall dynamics --- p.9
Chapter 2.1.2 --- Equation of state of the gas --- p.10
Chapter 2.1.3 --- Temperature dynamics --- p.11
Chapter 2.1.4 --- Ionization --- p.12
Chapter 2.2 --- Computational fluid mechanics model --- p.13
Chapter 2.2.1 --- Bubble-wall dynamics --- p.13
Chapter 2.2.2 --- Hydrodynamics of the gas --- p.15
Chapter 2.2.3 --- Equation of State of the gas --- p.16
Chapter 2.2.4 --- Energy equation in the liquid --- p.17
Chapter 3 --- Thermal Radiation --- p.18
Chapter 3.1 --- Thermal electromagnetic fields --- p.20
Chapter 3.2 --- Generalized Kirchhoff's law --- p.22
Chapter 3.3 --- Thermal radiation from an absorbing object --- p.24
Chapter 3.4 --- Application to a slab --- p.26
Chapter 3.5 --- Application to a multilayered configuration --- p.29
Chapter 4 --- Absorption in a Multilayered Dielectric Sphere --- p.31
Chapter 4.1 --- Absorption cross-section for weakly absorbing sphere --- p.31
Chapter 4.2 --- Absorption cross-section for strongly absorbing sphere --- p.33
Chapter 4.3 --- Transfer matrix method --- p.33
Chapter 4.4 --- Calculation of the absorption cross-section --- p.39
Chapter 5 --- Collision Processes in a SL Bubble --- p.40
Chapter 5.1 --- Electron-ion Bremsstrahlung --- p.41
Chapter 5.2 --- Electron-ion Recombination --- p.43
Chapter 5.3 --- Electron-atom Bremsstrahlung --- p.43
Chapter 5.4 --- Effective Collision Frequency for a Maxwellian Plasma --- p.44
Chapter 6 --- Light Emission Models for a Sonoluminescing Bubble --- p.47
Chapter 6.1 --- The geometric optics model --- p.47
Chapter 6.2 --- The wave optics model --- p.48
Chapter 7 --- Thermal radiation from sonoluminescing bubbles --- p.50
Chapter 8 --- Effect of the light emission model --- p.53
Chapter 9 --- A more sophisticated model for collision processes --- p.58
Chapter 10 --- Effect of bubble temperature and water temperature --- p.65
Chapter 10.1 --- Effect of bubble temperature --- p.65
Chapter 10.2 --- Effect of water temperature --- p.68
Chapter 11 --- A more sophisticated hydro dynamic model --- p.70
Chapter 12 --- Degree of Strong Coupling and Summary --- p.94
Chapter 13 --- Conclusion --- p.98
Chapter 13.1 --- Summary --- p.98
Chapter 13.2 --- Suggestions for future work --- p.101
Chapter A --- Proof of the Reciprocity Theorem --- p.103
Chapter B --- Vector Spherical Harmonics --- p.105
Chapter C --- Collision frequencies and absorption coefficients --- p.107
Bibliography --- p.110

博士
國立清華大學
動力機械工程學系
95
A novel micromachined accelerometer based on micro thermal-bubble technology is proposed and demonstrated in this dissertation. Unlike the other techniques, the only moving element in this accelerometer is a small thermal-bubble created by using a high flux heater to vaporize the liquid contained in the micro chamber. The accelerometer consists mainly of a heating resistor, which creates a symmetrical temperature profile, and several pairs of temperature sensors placed symmetrically on either side of the heater. The bubble technology is employed due to the clear interface between thermal-bubble and working liquid, providing good thermal conduction and high density. The basic physical characteristics including the heat transfer and fluid flow behavior of this accelerometer have been analyzed and discussed in this work. The feasibility and performance of the proposed accelerometer are verified using numerical simulations and demonstrated experimentally using a designed test setup. The prototype devices indicate that a sensitivity of 200 mV/g for an operating power of 60 mW can be realized. The frequency response containing DI water is measured to be 200 Hz, and the corresponding noise equivalent acceleration is approximately 1 mg/Hz1/2. The results conclude that the presented design has better response and higher sensitivity comparing to its counterparts.

碩士
國立雲林科技大學
機械工程系碩士班
99
As technology advances, the development of micro-pumps are increasingly diverse, but the piezoelectric valve-less pump is still a problem of structural damage is not easy to replace. Although the research of valve-less micro thermal bubble pump has raised, but that did not have a lot of research and exploration guide. This study does some research about thermal bubble pump that change the pump size. The result is the flow rate is raised by changing pump size small to large, and get smaller pressure peak. At this situation that only change the surface tension to 2σ, 4σ, and 6σ. The results showed that the surface tension at 2σ get lower flow rate then original, and the surface tension at 2σ, 4σ, and 6σ no change obviously. The variation of peak pressure has increased to the positive direction with increasing surface tension. At this situation that only change the viscosity to 2μ and 4μ. The results showed that the viscosity at 2μ get lower flow rate then original, and the viscosity at 2μ and 4μ no change obviously. The variation of peak pressure has increased to the positive direction with increasing viscosity. Simulate changes frequency with the same watt and change watt setting with the same frequency, find the best situation is to find a fixed value of the bubble to grow is the best state of contraction.

碩士
國立臺灣大學
機械工程學研究所
84
In chapter 2, the stability problem of SHA is analyzed and an equation that demonstrates how some of the important specifications of amplifiers may affect the stability of closed-loop SHA is derived. In chapter 3, based on the fully differential "gain-enhanced unity-gain amplifier", a 8-bit, lOOMSamples/sec, fully differential CMOS SHA is designed and implemented by using an 0.8um, N-well, DPDM CMOS process. In chapter 4, a novel macromodel for SHA which includes its important characteristics is proposed.

碩士
國立成功大學
航空太空工程學系碩博士班
96
The focus of this study is to solve the problem of high pressure drop when fluid passes through the vapor line in micro capillary pumped loop, MCPL. In this study, MEMS technology is used to fabricate thermal bubble pump that has constant heat flux to investigate the mechanism of driving bubbles. By surface modification, the micro channel has hydrophilic and hydrophobic regions. The distribution of surface free energy will make bubbles move without external force. Because the TaAl alloy can’t stand the high temperature (630℃) of thermal fusion bonding, this study carries out a low temperature (180℃) bonding method. The device fabricates successfully by using PDMS as the intermediate layer between two substrates. In the experiment, observation of flow visualization is used to investigate the bubble phenomenon including nucleation, growth, and movement. Effects of different heater position with the same heat flux and different heat fluxes in the same position were compared. Furthermore, the effect of channel width is discussed. The result reveals that when channel width is 500micron, heater in the geometry change of channel (h2) is the best position to observe bubbles move or not. When 10V (93mW) is applied to h2, bubble will grow to 1000micron length and reach thermal equilibrium. However, at this state the bubble only oscillates. When channel width reduce to 100micron and 6.2V (76mW) is applied to the heater, the bubble will move forward continuously and have the effect of heat transfer.

碩士
國立成功大學
機械工程學系碩博士班
97
The target of this research is to establish an observation system of thermal bubble and to design and fabricate the micro-heater in order to discuss the thermal bubble behavior for combining the mixer in our Lab and helping to mix faster and good mixing efficiency. In fabrication of micro-heater, this research focus on the design of micro-heater and the choice of materials further. For design, we use single mask to fabricate the heater replacing several masks for saving the fabricating time. For the materials, we choose the Ta to be the material to replace polysilicon and expensive material Pt which were usually used in past. In the system of observation system, we design a flash observation system to substitute for the expensive high speed CCD for saving the money. Using high light LED to flash for freezing the thermal bubble instant behavior and using the ordinary CCD system to catch movie of bubbles. Finally, using the cutting soft to get the pictures of instant bubble behavior to know the bubble growth and shrink for the combination of our Lab mixer in the future. Finally, we’ll discuss bubble sizes between frequencies and voltages and the feasibility of observation system. We can know the micro-heater in this research can generate well bubbles in low frequencies. And the advantages of the micro-heater in this research, like low resistance, heat-resistant degree, and good heat dissipation, contribute to improve the heat dissipation and the strength of the Pt micro-heater for increasing the life of the heater.

碩士
國立雲林科技大學
機械工程系碩士班
97
With technology changing at such a rapid pace of modern micro-electronic components and the trend of chip-intensive and more rapid speed of operation with, more power required, it result in producing a more substantial amount of heat. In order to solve problems caused by heat generation of these small electronic components, the method of phase change liquid cooling may be a promising solution. In this study, the effects of static angle and change surface roughness are investigated to observe physics property and heat flux in the pool boiling. The bubble growth rate, boiling curves, bubble growth and depart diameter and steam bubble pressures are obtained by numerical simulations. Finally, this approach of numerical simulation of boiling is also applied on a simple micro-thermal bubble inkjet. The nozzle diameter is use as a parameter to observed shape and behavior of inkjet droplet. The results may be use as the design parameters for the next new inkjet design.

碩士
國立臺北科技大學
冷凍空調工程系所
93
In recent years, as the micro-system fabrication technology continues to advance, the production of many products has employed micro-system fabrication technology for mass production, thus, to reduce the cost and improve the product quality. Among the micro-system technology, micropump technology has gradually developed. Since the droplets dispersed by the micropump are minute, the droplet quality is consistent, and the amount of injection could be accurately controlled, it is feasible for application on electronics cooling. The developed micropump technology has been applied to wider fields. Thus, if the overall efficiency of micropump could be improved, the development of micropump could be enhanced. Therefore, this study discussed the use of micropump technology on cooling of heated surface, and the effect on refined micropump on overall injection and replenish efficiency. This study used CFD-RC commonly used in the micro-system field for analysis and simulation of the droplet injection speed, shape and path were simulated in the arrayed micropump. In the analysis of the droplet impacting the heated surfaced, the variables of fluid types, injection distance, droplet size, and hydrophile of the heated surface were analyzed by using CFD-RC to discuss the splash of the droplet when impacting the heated surface and the change of heat convection of the heated surface. The analysis of the refined micropump nozzle analyzed the droplet injection of different fluids and array effects. The results showed that as the hydrophile of heated surface improves (the contact angle decreases), the heated surface is more likely to disperse ethanol and the injection distance is larger. As the impacting force of the droplet on the heated surface increases, the droplet is more likely to splash on the heated surface, and is more effective in removing the surface heat. The refined nozzle is connected to coned channel and is affected by the channel, thus, the simulation results showed faster injection speed and better work fluid replenish efficiency than previous researches. The films shot with Schlieren show the evaporation of the droplet into gas upon impacting the heated surface. As for the refined micropump, in the simulation and experiment results, the shapes of the droplets were similar, and the injection speed of the convergent micropump【A】is 1m/s faster than that of divergent micropump【B】.

碩士
國立臺灣大學
應用力學研究所
96
Because the problem about energy need is more and more serious, all countries in Earth are researching the alternative energy. Fuel cell is very popular and important in many energy researches. In many kinds of them, DMFC has potential to miniaturize for the portable equipment above them. It has some advantage: no fuel reformer, low operation temperature, safe fuel storage and transport, and etc. It can be easy to carry on one’s person after miniaturization. In real experiment, it use only 3% ~ 10% solution of Methanol in water, so the energy density is very low. However, the total chemical reaction results in producing power, water and carbon dioxide. So if the water can be recycled to mix with methanol, the fuel concentration in cartridges may raise. The energy density is raised. How does the water and methanol be driven in miniaturized DMFC? A Micropump is wished to be used! The Voltage that DMFC outputs is very low. Few micropumps can be driven. So we choose micropump by thermal bubble actuated according to the properties of DMFC. In the meanwhile, it is looked forward to have high operation efficiency, so the valve-less design is also considered. Except the studies of the operation principles, this thesis focuses on the design issues and manufactures of the micropump. This micropump has three parts: (1) Thermal bubble actuator that is made by electric igniting device because it raises temperature fast in short time. It has low resistance, so it can be driven by low voltage. (2) Chamber where the phase of working fluid changes when it sucks heat transferred from actuator. (3) Nozzle-Diffuser channel that can rectify net flow in specified direction. This micropump chip is come true by MEMS and Anodic bonding successfully. In experiments, the peak power is fixed and the square wave or pulse function can switch the power supply and set the heating time. That is duty cycle. the flow rate and difference between them are be measured by changing the frequency or heating time. Then the average input power is discussed with the flow rate and frequency. According to the experiment that has been done, the maximum flow rate is 5.027μl/min under 10Hz operating frequency and 4375μs(about 0.044% duty cycle) and it consumes 67.2mW. When the operating frequency or heating time is raised, the flow rate isn’t guaranteed to raised, too. Preliminary result expresses that flow rates achieve the research before but consume lower power than them. In the future, the experiment is continued to gather more information to investigate the results.

碩士
雲林科技大學
機械工程系碩士班
99
In this paper, a single bubble in a square vertical tube boiling heat transfer factors and detachment of motor behavior research. Square vertical tube were simulated at different heating area, viscosity, boundary conditions, size of the physical phenomena of bubble formation, while the square vertical tube boundary settings are the same. Different heating areas of the nucleation of the bubble and out of time, the bubble formation diameter changes over time, comparing internal overpressure bubble, bubble formation free energy compared to the bubble generation frequency, bubble deformation, thermal and thermal flux relationship, and found that the larger heating surface area of the smaller heat flux, the smaller the bubble departure diameter, from the greater frequency of such phenomena. The viscosity of each of the different liquids and the size of the container border to observe the bubble from the heating surface after the offset of the central axis, the stability of the flow field, made a considerable viscosity of the liquid Reynolds number, the greater the smaller the bubble, the central axis offset the smaller, the smaller the bubble deformation, the flow chart can be observed that the two sides of the vortex bubble presents a symmetrical phenomenon; when the container the larger the bubble from the boundary after the central axis of the heating surface of the smaller offset by the flow chart can be observed that the two sides of the vortex bubble presents a symmetrical phenomenon.

碩士
國立中山大學
機械與機電工程學系研究所
100
The study applies the phase-field method to simulate the behavior between bubble and liquid-solid front in the solidification. During the process, the two-phase flow module is used to match up with temperature and phase-field function to determine the percentage of- solid, liquid, and gas- in the domain. The governing equations for mass, momentum and energy contain coefficients which are related to percentage of phases.The result show that the surface tension and the temperature difference will influence the shape of bubble and the velocity of solidification.

Xiao, Peng.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2008.
Includes bibliographical references (leaves 76-78).
Abstracts in English and Chinese.
ABSTRACT --- p.i
摘要 --- p.iii
ACKNOWLEDGEMENTS --- p.iv
TABLE OF CONTENTS --- p.vi
LIST OF FIGURES --- p.viii
LIST OF TABLES --- p.xi
Chapter CHAPTER ONE --- INTRODUCTION --- p.1
Chapter 1.1 --- The Thermal Characteristic of the CNT Heater --- p.1
Chapter 1.2 --- CNT-Based Micro Bubble Generation in a Static Droplet of Water --- p.2
Chapter 1.3 --- CNT-Based Micro Bubble Transportation in a Micro Channel --- p.4
Chapter 1.4 --- CNT-Based Micro Bubble Stimulation by Pulsed Current --- p.4
Chapter CHAPTER TWO --- THE THERMAL CHARACTERISTICS OF CARBON NANOTUBES --- p.6
Chapter 2.1 --- Temperature Coefficient of Resistance (TCR) of Our Typical CNT Heater --- p.7
Chapter 2.2 --- The Humidity Coefficient of the Resistance (HCR) for Our Typical CNT Heater --- p.13
Chapter 2.3 --- The Conclusion of the CNT Heater's Thermal and Humidity Characteristics --- p.18
Chapter CHAPTER THREE --- MICRO BUBBLE GENERATION WITH MICRO WATT POWER USING CARBON NANOTUBE HEATING ELEMENTS --- p.19
Chapter 3.1 --- Micro Electrode Fabrication --- p.19
Chapter 3.1.1 --- Methods for Metal Electrode Fabrication --- p.20
Chapter 3.1.2 --- Advantages and Disadvantages of Two Micro Fabrication Methods --- p.22
Chapter 3.1.3 --- The Fabrication of Micro Electrodes for Our CNT Heater --- p.24
Chapter 3.1.4 --- The Mask Design for Metal Electrode Fabrication --- p.26
Chapter 3.2 --- The Micro Bubble Generation Experimental Procedure --- p.28
Chapter 3.2.1 --- Initial Analysis of the Experimental Device --- p.28
Chapter 3.3 --- Theoretical Analysis of Bubble Generation Temperature on the CNT Heater --- p.31
Chapter 3.3 --- The Analysis of the Micro Bubble Generation Experimental Results --- p.35
Chapter 3.4 --- The Conclusion of Bubble Generation in a Static Droplet of Water --- p.44
Chapter CHAPTER FOUR --- CARBON NANOTUBE-BASED MICRO BUBBLE GENERATION IN A MICRO CHANNEL WITH DYNAMIC FLUID --- p.45
Chapter 4.1 --- Micro Channel Fabrication --- p.46
Chapter 4.1.1 --- Rapid Prototyping --- p.46
Chapter 4.1.2 --- PDMS Moulding --- p.47
Chapter 4.1.3 --- Irreversible Sealing --- p.49
Chapter 4.1.4 --- Mask Design --- p.50
Chapter 4.2 --- Experimental Setup --- p.51
Chapter 4.3 --- Experimental Procedure --- p.53
Chapter 4.4 --- Experimental Results --- p.55
Chapter 4.5 --- Conclusion for Bubble Generation in the Micro Channel with Dynamic Fluid --- p.59
Chapter CHAPTER FIVE --- CNT-BASED MICRO BUBBLE STIMULATION BY PULSED CURRENT --- p.60
Chapter 5.1 --- Attempt to Control the Micro Bubble Diameter --- p.61
Chapter 5.2 --- The Pulsed Current for Micro Bubble Departure in the Micro Channel --- p.63
Chapter 5.2.1 --- Manual Pulsed Current Stimulation for Micro Bubble Departure in the Micro Channel --- p.64
Chapter 5.2.2 --- The Pulsed Current Circuit for Micro Bubble Departure in the Micro Channel --- p.67
Chapter CHAPTER SIX --- FUTURE WORK AND SUMMARY --- p.70
Chapter 6.1 --- Future Work for Micro Bubble Generation Projects --- p.70
Chapter 6.1.1 --- The CNT-Based Micro Bubble Generation with Various Values of Input Current --- p.70
Chapter 6.1.2 --- The CNT Heater in the Zig-Zag Micro Channel --- p.71
Chapter 6.1.3 --- Summary --- p.72
APPENDIX A --- p.73
Fabrication Process --- p.73
Chapter I. --- Micro Electrode Fabrication --- p.73
Chapter II. --- Micro Channel Fabrication --- p.75
BIBLIOGRAPHY --- p.76

碩士
國立中央大學
機械工程研究所碩士在職專班
96
This study visualizes and measures the droplet ejection process of a high-resolution thermal-bubble inkjet printhead. A simple system utilizes the synchronization of the stroboscope, which consist of a set of optical lens, a function generator, and an image grabber, to record the droplets image at different delay time and analyze the length, flying speed and size of droplets. Also, the influences of voltage, pulse width, frequency, and the different viscosity of ink on droplet ejection process are discussed in order to know the relation between the inkjet signals and droplet ejection behavior, and then compare it with related records of documents. Finally, the signals of the inkjet printhead from a genuine printer are measured to investigate the relation of signal and the printing quality. This study finds that the voltage and pulse width are two key factors for providing stable heat flux, and by adjusting frequency one can adapt for various types of paper and printing effect. Further, during the lead time of developing inkjet printhead, this experimental system can be used to measure the correct signals and hence prevent heater burnout by misoperation. Moreover, this system can be utilized to adjust the frequency and change the ink characteristic in order to meet with the requirement of printing quality and to reduce the lead time and development costs.

碩士
國立成功大學
航空太空工程學系碩博士班
92
In this thesis, novel thermal bubble actuator has been designed and fabricated for bubble actuator studies. Micro platinum heaters and temperature sensors are integrated within the actuator to study the detailed dynamics of the thermal bubble actuator. Each actuator contains four sets of microheaters/microsensors in the firing chamber, and one set of microheater for the surface tension breaker at the nozzle exit. By actuating the microheater array, the bubble can be generated to eject the liquid droplet out of micro nozzle. According to the number of the microheater actuated, the volume of the liquid droplet can be controlled. Bubbles generated in the firing chamber not only function as a pump, but also serve as a flow regulator between the chamber and the liquid supply. This mechanism can eliminate the bottleneck design, which is use for hydrodynamics cross talk in a conventional inkjet printhead. 　　To investigate the dynamics of the novel thermal bubble actuator, a high speed microscopic imaging system was developed. The high-speed microscopic imaging system will help us diagnose the bubble nucleation, bubble growth and collapse, droplet breakup process, as well as the refilling process. From testing results of the experiment by using a commercial actuator HP ink-jet printhead, the performance of HPc6614d No.20 ink-jet printhead still has plenty of room to be improved. For example, the satellite droplets are found in HP printhead. Satellite droplets means non-uniform droplet sizes, which will degrade the printing quality. For the current thermal bubble actuator, surface tension breaker was design to manipulate the surface tension at the nozzle exit, which use to eliminate satellite droplets.

"The bubble rise characteristic is very important for the design of heat and masss transfer operations in chemical, biochemical, environmental, and food processing industries. The rate of heat and mass transfer is affected by the bubble size, pressure inside the gas phase, interaction between bubbles, rise velocity and rising trajectory. Research on bubble rise phenomena in non-Newtonian fluids is very limited and there is an increased demand for further research in this area since most of the industrial fluids are non-Newtonian in nature. This study investigated the bubble rise phenomena in water (Newtonian fluid) and various non-Newtonian stagnant fluids"--Abstract.

碩士
國立交通大學
機械工程系所
96
The present study purposes to experimentally examine the influence of liquid properties, hydrophilic conditions, and power on thermal bubble behavior. The CCD camera connected to a video recorder is utilized to visualize thermal bubble formation and growth process, and defined the advisable range for the application of bubble actuation for various viscosity of liquids, hydrophilic conditions, and power. Some significant physical parameters are define, and the thermodynamic behavior of thermal bubble is discussed in detail at various viscosity of liquids, hydrophilic conditions, power and various of the physical parameters. Experimental results show obvious influences of viscosity, hydrophilic conditions on the advisable range for application of bubble actuation. The instability of bubble formation and growth process take place for various hydrophilic conditions. Experimental results show the obvious influences of viscosity, hydrophilic conditions, and power on contact diameter between bubble and surface, height of the thermal bubble, and volume of the thermal bubble.

博士
逢甲大學
電機與通訊工程博士學位學程
101
This study presents the implementation of a thermal bubble actuated microfluidic chip with microvalve, micropump and micromixer, based on a simple process with SOI wafer. Only two photolithography processes were required to provide an effective means of manufacturing the vertical bulk microheater and high-aspect-ratio microchannel for microfluidic applications. The static and dynamic electro-thermal coupling behaviors of the proposed resistive silicon-based microheater were evaluated by finite element analysis to provide an applicable design. The feasibility of each actuation element has also been verified by experiments. Experimental results show that the sizes of thermal bubbles, at flow rates less than 4.5 μl/s, can be controlled steadily by applying the magnitude of direct current that meets the requirement of a microvalve to modulate flow rate. When applying an alternating current with high frequency to the microheater, thermal bubbles could grow cyclically and collapse rapidly, so the liquid stream could be regulated by the repeated volume change of thermal bubbles. A better pumping efficiency of flow rate 4.5 μl/s was obtained under the driving voltage with a frequency of 60 Hz and 30% duty ratio. The mixing test of the multi-layer fluidics with laminar flow also was successfully implemented by using the volume of thermal bubble to create turbulent flow in the fluids. With no moving parts, the proposed microfluidic chip is well designed with high performance and reliability.

The present study focusses on vortex breakdown (VB), which occurs in axially convected swirling flows and is characterized by the development of an internal stagnation point and regions of reverse flow. VB has been observed or utilized in a variety of situations including flow over delta wings, tornadoes, re whirls, turbomachinery, fuel injectors and combustors. Flows where VB is observed include swirling round jets with non-swirling and negligible co flow. The experimental study of Billant et al., (1998) has shown VB characteristics unique to this family of flows. In addition to the commonly observed bubble form of breakdown (BVB) the experiments revealed a new form, referred to as conical form of breakdown (CVB). Features of these forms (especially the latter) remain mostly unexplored. This serves as motivation for the present numerical investigation of VB in swirling jets. In this study, a survey of different VB states (laminar and turbulent) observed with varying flow parameters has been carried out using numerical simulations, along with investigations on hysteresis effects and bistability phenomenon. Previous theoretical models for VB have been assessed using these results. Helical instabilities that were observed to arise in the simulations have been examined using the tools of stability analysis. Three-dimensional numerical simulations were carried out using the open-source incompressible flow solver incompact3d in a Cartesian coordinate framework to study a swirling jet entering an adequately large domain to prevent con nement effects. The swirling jet was modelled using the axisymmetric and steady `Maxworthy' in flow pro le (Ruith et al., 2004), with the main control parameter as the swirl number, S, representing the relative rate of rotation in comparison to the centreline axial velocity of the jet. The Reynolds number (Re) was chosen based on the jet radius and centreline axial velocity. The long-time flow states achieved with varying S and initial conditions are reported for Re = 200 and 1000. For the latter case, where the flow transitioned to turbulence, large eddy simulations were carried out using the explicit fi ltering approach. Both local and global stability analyses have been performed to examine instabilities. Selective frequency damping and axisymmetric simulations using ANSYS Fluent have been used to compute base flows. For Re = 200, BVB and CVB were observed and could be clearly distinguished by the distinct spatial structure of the recirculation zone. These different VB forms could be further classi ed based on unique characteristics into different types. For BVB, the following types were identi ed{ steady one-celled BVB, one-celled BVB with spiral tail, pulsating BVB, two-celled BVB with spiral tail and asymmetric BVB. The categorization as one-celled and two-celled was based on the number of toroidal structures that could be identi fied within the bubble, while the pulsating BVB was observed to be an intermediate state between the two. The term `spiral tail' is used to denote the presence of a helical mode that developed in the wake of the bubble which had no signifi cant effect on the axisymmetric upstream portions of the bubble. In contrast, for the asymmetric BVB, a helical mode was present, which caused asymmetric motion of the entire bubble. Two types of CVB were identifi ed{ regular and wide-open{ the latter with an approximately radial expansion of the flow downstream to the stagnation point. Comparisons with different experimental results showed strong similarities in features for most flow states. Hysteresis studies established the coexistence of different types of BVB with the regular CVB in overlapping ranges of swirl numbers, confo rming that these are bistable forms. Remarkable differences in length scales involved for the two forms could be observed when comparing time-averaged flow structure. A hysteresis plot is provided based on the maximum radius achieved by a streamline starting from the in flow plane at an arbitrary radius. It was additionally seen that the two-celled BVB with spiral tail and asymmetric BVB coexist (along with regular CVB) over a small range of swirls. For Re = 1000, a transition to turbulence was observed, leading to some interesting differences in the flow states observed. At low swirls, the stagnation point occurred only intermittently in time, in contrast to the steady VB observed for equivalent S for Re = 200. For swirls above this, a two-celled BVB with a turbulent wake was observed for a large swirl range. The stagnation point at the bubble's nose was lost at swirls just above those for which BVB was observed. For this range, a spiral coherent structure was seen to arise intermittently in the bubble's wake, accompanied by streamwise oscillatory motions in the flow. At higher swirls, this motion was subdued and the spiral downstream of the bubble was lost, while the stagnation point at the bubble's nose eventually reappeared. The streamwise oscillations of the bubble being a common feature to all long-time flow states observed, these states are collectively referred to as oscillating BVB. For even higher swirls, turbulent regular and wide-open types of CVB were observed. Bistability of oscillating BVB and regular CVB, and additionally, between regular and wide-open CVB were established using hysteresis studies. The stark differences in length scales associated with the bistable bubble and conical forms were reduced due to turbulence, indicating that CVB might be misidenti ed as BVB at high Re. Indeed, it is speculated that some of the VB states reported in experimental studies of Liang and Maxworthy, (2005) are likely the CVB. The bistable regular and wide-open types of CVB were found to have considerable differences in the length scales of respective recirculation zones. The two VB states for which helical modes were observed, the BVB with spiral tail and asymmetric BVB, were examined using stability analysis. A closely related flow state to BVB with spiral tail is the spiral vortex breakdown (SVB). In previous studies, SVB was identi ed to arise due to the instability of a nonlinear steep global mode. Assuming weakly non-parallel flow, a local spatio-temporal analysis coupled with a WKBJ framework was used to show that the global mode associated with BVB with spiral tail differed from that of the SVB, with the linear frequency selection criterion (Chomaz et al., 1991) better predicting the global frequency. Using tools of global stability analysis, the asymmetric type of BVB was shown to arise due to a different unstable mode that has strong energy content in the bubble region. It was observed in the simulations that the base state was strongly modifi ed by the instability. The stability analysis using the mean flow made better predictions as compared to that based on the base flow for this type of BVB. Two theories developed by Benjamin, (1962) and Brown and Lopez, (1990) towards explaining VB were assessed. It was observed that the prediction from the former theory, that the flow becomes subcritical downstream of VB, was confi rmed based on simulation results. However, other aspects of the theory, which have not been scrutinized in previous studies displayed a trend opposite to that observed in the present simulations as well as other available experimental results. That is, the conjugate states predicted by the theory, modelling the flow downstream of VB, were found to better resemble the primary state upstream of VB with increasing swirl. This contradicts the observation that the bubble increases in size with swirl. Reasons for why the predictions display this trend, based on analogies to gasdynamic shockwaves, are provided. The theory of Brown and Lopez, (1990) was found to give qualitatively similar predictions for BVB, but deviated strongly from the numerical results for CVB. A major highlight of this study is the signifi cance of the initial conditions in determining the VB form or type achieved, with results showing the coexistence of three distinct pairs of long-time flow states in overlapping parametric ranges for swirling jets. Though emphasized by Billant et al., (1998), many later studies on swirling jets have generally neglected this aspect. Similarly, as this study shows, the CVB is a distinct form of VB that has not been clearly identifi ed in previous studies on swirling jets. These results might aid in better understanding features of the elementary flow confi guration of swirling jets and allow for more informed developments of design and control strategies in practical applications.

碩士
國立中山大學
機械與機電工程學系研究所
101
This study applies the phase-field method to simulate the behavior between bubble and liquid-solid front. Using the two-dimensional two-phase flow module and match up with temperature function to determine the solid, liquid and gas domain. The governing equations for the relative percentage of phases contain momentum, mass, energy and concentration equations. The result shows that the greater effect on the interface will easily influence the shape of bubble .

碩士
國立成功大學
機械工程學系碩博士班
90
One-dimensional bubbly flows through converging-diverging nozzles are investigated using a two-fluid model. Effects associated with both translational and radial relative motions between bubbles and liquid are incorporated. Calculation of a subsonic case is performed first and shows good agreement with experiments. The model is then applied to critical (or choked) flow situations studied previously by Muir and Eichhorn (1963). In their experiments, Muir and Eichhorn found larger critical pressure ratios (which are defined as the ratio of the pressure in the throat to that in the reservoir under choked conditions) and flow rates than homogeneous flow theory. They measured significant slip between phases which, therefore, was speculated to be responsible for these discrepancies. It is demonstrated in this paper that the phase relative velocity and mass flow rates can be predicted reasonably well (within the experimental uncertainly) using the present model, however, can not fully compensate the critical pressure ratio. Other important features of the critical flows are also explored, including the formation of compression shock waves present in the divergent part of the nozzle. Our computations show that the pressure ratio across the shocks agree very well with the Hugoniot relation established by Thang and Davis (1981). We also examine the sensitivity of the flow field to the value the effective viscosity employed in the Rayleigh-Plesset equation. In order to describe the effects of heat diffusion during the variation of bubble volume, we modify the Rayleigh-Plesset equation to in corporate the thermal damping into the present model. Both the subsonic flows and the supersonic flows are revisited. Results obtained show that the flashing instability of the bubbly flows can be stabilized by the thermal damping effects.

In this thesis, we explore some of the exciting physics of condensed matter systems manifested because of imperfection or disorder and interactions among the constituent particles. In phenomena like transport, e.g., electrical current; localization, e.g., confinement of electrons only within a small part of a system; entanglement (a correlation among the constituents particle); disorder and interaction play essential roles. These three properties are our main focus in the thesis. There are six chapters. In the first chapter, we introduce a few landmarks in the field to set the stage and give an overview of the works presented in the thesis. In the second chapter, we consider quasi-disordered or quasiperiodic systems in one, two, and three dimensions, where the quasi-disorder is deterministic but non-repeating throughout a lattice and considered from. Metal-insulator transitions in these systems are probed by calculating conductances and their change with system size. More specifically, we look at the systems from the perspective of single-parameter scaling theory. In the third chapter, we consider both the disordered and quasi-disordered systems with interactions. The systems show transitions from thermal to many-body localized phases, and we study them in Fock space, which is a natural description for an interacting system. We exploit the Fock space structure to calculate the propagator or Green’s function in an iterative way to push the system size accessible in the exact calculations. We define a length scale in Fock space, which can detect the phase transition and distinguish between the disordered and the quasi-disordered systems. In the fourth chapter, motivated by an experiment, we study the electrical current and noise therein in a disordered quantum Hall system in the proximity of a superconductor. To our surprise, the quantum Hall conductance plateau in the system comes with noise in the current as also observed in the experiment, and the calculated quantities match pretty well with the observed values. In the fifth chapter, we study the entanglement entropy of an interacting fermionic system using a new saddle-point approximation similar to a mean-field approximation. The approximation is based on a newly developed path integral approach for calculating the entanglement entropy. In the last chapter, we conclude the thesis by summarizing the important findings of our works presented in the thesis with some future directions.

博士
國立清華大學
奈米工程與微系統研究所
103
In this study, delay times of explosive dual microbubbles are controlled precisely to understand the complex and dynamic phenomenon of dual bubbles interactions. The interactions have been characterized in terms of maximal bubble size, sink/source flow, bubble pressure, and useful work. For DT = 0 μs, dual bubbles are produced simultaneously,and the produced pressures inhibit the growth ofeach other. The sizes of those are slightly smaller than thatof a single bubble. For DT = 2 μs, the pressure generated from the second (right) bubble affects the growth of the first (left) bubble in the beginning and poses the first bubble growth slower than the single bubble. When the first (left) bubble starts to collapse, the surrounding flow field induces a sink flow to promote the growth of the second (right) bubble. As the first (left) bubble rebounds, the peak pressure produced by the rebound leads to a rapid collapse of the second (right) bubble. For DT = 8 μs, the first (right) bubble keeps following the history of the single bubble because there is no influence from the second(right) one. As the first bubble rebounds in the same condition, the volume history of the second bubble drops and deviates from the original track of the single bubble. The dynamics of a high heat flux thermal bubble is constrained by the thermal energy carried on the bubble surface right after the bubble formation because of thermal isolation of vapor. This paper proposes a way by assigning time delays between dual bubbles to effectively transfer energy from one bubble into the other, thus breaks energy limitation that one single bubble can usually carry. Experiment result has demonstrated that the useful work as large as 40% can be transferred from one bubble into the other for the ignition time delay set between 2 and 3 μs in a dual bubble system. At the same time, the total extractable useful work in a dual bubble system is 20% higher than twice that of a single bubble system with the same input heat energy. This phenomenon opens up a new way to transfer or concentrate energies from distributed energy sources with limit energy density into a much higher one for higher power application.

博士
國立清華大學
化學工程學系
101
The therapeutic effectiveness of chemotherapy is optimal only when tumor cells have maximum drug exposure. A thermoresponsive liposomal formulation (ThermoDox; Lysolipid liposomes) rapidly releases DOX in regions where local tissue temperatures are elevated to at least 40 °C. Although Lysolipid liposomes have considerable therapeutic potential, roughly 50% of encapsulated DOX is released within 1 h in physiological environments. Lysolipid dissociation from liposomes, which is mediated by plasma proteins, is a highly likely cause of their intravenous instability. Thus, in study I, a thermoresponsive bubble-generating liposomal system that does not contain lysolipids was evaluated for its ability to trigger localized extracellular drug delivery. The key component in this liposomal formulation is encapsulated ammonium bicarbonate (ABC), which creates the transmembrane gradient needed for highly efficient DOX encapsulation. At an elevated temperature of 42 °C, ABC decomposition generates CO2 bubbles, creating permeable defects in the lipid bilayer that rapidly releases DOX and instantly increases the drug concentration locally. Because the generated CO2 bubbles are hyperechogenic, they also enhance ultrasound imaging results. Consequently, this novel liposomal system encapsulated with ABC may be able to monitor a temperature-controlled drug delivery process. Study II examined the feasibility of using this thermoresponsive bubble-generating liposomal system (ABC liposomes) for tumor-specific chemotherapy under mild hyperthermia. Incubation of ABC liposomes with rat whole blood resulted in a significantly smaller decrease in the retention of encapsulated DOX than that by Lysolipid liposomes, indicating superior plasma stability. Biodistribution study results demonstrate that the ABC formulation circulated longer than its Lysolipid counterpart. After the ABC liposome suspension was injected into mice with tumors that were heated locally, decomposition of the ABC encapsulated in liposomes facilitated immediate thermal activation for CO2 bubble generation, leading to increased intratumoral DOX accumulation. Consequently, the antitumor efficacy of ABC liposomes was superior to that of their Lysolipid counterparts. These analytical results indicate that this thermoresponsive bubble-generating liposomal system is a promising local drug delivery system activated at hyperthermia temperatures for tumor-specific chemotherapy. Since nonspecific distribution of therapeutic agents and nontargeted heating frequently cause undesirable side effects during cancer treatment, study III describes a novel liposomal system that can deliver both heat and a therapeutic agent, DOX, simultaneously into targeted tumor cells to exert its cytotoxicity intracellularly. A hybridized Mucin-1 aptamer was conjugated on the surface of test liposomes, which can function as a recognition probe to enhance their cell uptake, as well as a molecular beacon to signal when the internalized particles were maximized. Additionally, gold nanocages encapsulated in liposomes effectively converted near-infrared light irradiation into localized heat to directly damage cancerous cells and thermally trigger a high DOX release to reach the therapeutic threshold instantly. This combined treatment can significantly increase the drug potency, making it a promising approach for cancer therapy.

Taylor bubble flow in microchannel systems play an important role in many industrial applications such as two-phase flow micro heat exchangers, pulsating heat pipes, monolithic reactors, digital microfluidics, microscale mass transfer process, fuel cells, etc. Taylor bubble is formed in capillary tubes when gas-liquid or liquid-liquid flows with particular range of flow rate ratios. In this work, a 3D numerical study has been carried out using the volume-of-fluid (VOF) method on commercially available Ansys Fluent® for the formation of (i) isolated Taylor bubble and (ii) a train of Taylor bubbles, in a square channel of side 1.0 mm. At inlet of the capillary tube, gas and liquid flows in co-current flow arrangement neglecting the nozzle thickness. Constant thermo-physical properties are considered for solid and fluid. The flow is hydrodynamically developing at the inlet of the channel. Taylor bubble formed gets stabilized at the entry section of the fluid channel. The Taylor bubble then passes through a square channel (01 mm2 ) carved on a solid substrate of size 3×2×30 mm3 . The flow is hydrodynamically fully developed and thermally developing inside this channel. Constant heat flux is applied on the bottom wall of the substrate (3 × 30 mm2 ), while all other surfaces exposed to the ambient are insulated. To avoid the end effect, the fluid again passes through a capillary tube after it travels the full length of the substrate. Thus, three-dimensional Navier-Stokes and energy equations are solved simultaneously. No slip boundary condition is imposed on the inner walls of the channel. Sufficiently fine mesh considered near the boundary to capture liquid film surrounding a Taylor bubble interface near the wall. The liquid film is maintained without its breakup throughout the length of the channel. The numerical simulations are carried out for the substrate wall to fluid thermal conductivity ratio (ksf ∼ 10−646), ratio of substrate thickness to channel depth (δsf ∼ 1−3) and capillary number (Ca ∼ 0.005 − 0.007). The objective of this study is to explore heat transfer enhancement due to injection of Taylor bubbles in steady flow, which causes disturbance in the flow field at its head and tail, resulting in mixing in the fluid that shows reduction in wall temperature compared to single phase liquid flow in the channel. The axial variation of bulk fluid temperature shows a footprint of a Taylor bubble at its back end. The effect of bubble length and the frequency of bubble occurrence is also studied.

The high specific energy consumption from all existing seawater desalination methods has heightened the motivation for having more efficient and greener desalination processes to meet the future goals of sustainable seawater desalination. One of the promising thermally-driven desalination methods is the direct-contact spray evaporation and condensation (DCSEC) where the excess enthalpy between feed and equilibrium states of evaporator chambers is exploited with reasonably high flashing efficiency. Further improvements in energy efficacy of DCSEC are boosted by firstly the incorporation of micro/nano-bubbles (M/NB) where micro or nano size subcooled vapor are embedded in the sprayed liquid droplets of evaporator, thereby lowering the temperature brine in evaporator and minimizing the thermal equilibrium effect of brine. The presence of subcooled bubbles increased the available surface area for heat transfer. Secondly, the concept of an evaporator-condenser pair of DCSEC could be extended to a multi-stage arrangement where the latent heat of vapor condensing on the water droplets sprayed within the condenser is recovered. From the experiments, the effect of incorporating the (M/NB) in the DCSEC at optimum feed flow rate yields more than 34% increase in distillate production at feed temperatures greater 47oC and the cooling inlet temperature set at 35oC. The other salient improvement found from the experiments is the increase in performance ratio (PR) up to 3.3 for a 6-stage configuration. This quantum jump in the PR is attributed to the heat recovery effect by as much as 70% of the total heat input. Arising from the DCSEC design, the implicit benefits are the low capital and operational cost, i.e., low CAPEX and OPEX. The former savings is attributed zero physical interfaces such as tube-based heat exchangers or membranes, whilst the latter savings is contributed by significant lesser use of chemicals in the pre-treatment of seawater feed. Lastly, the accompanied benefit is the robustness of the DCSEC processes where it could within stand high salinity of the brine, typically as high as 200,000 ppm.