Nach einer kurzen technischen Beschreibung der Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW und der verwendeten Messtechnik werden die theoretischen Grundlagen zur Modellierung der Kondensation von Dampf in einer Wasserströmung erläutert. Dabei gehen die Autoren besonders auf die Auswahl geeigneter Modelle zur Beschreibung des Wärmeübergangs und der Zwischenphasengrenzfläche im Druckbereich zwischen 10 und 65 bar detailliert ein. Außerdem werden verschiedene Drift-Flux-Modelle auf ihre Tauglichkeit anhand von experimentellen Daten geprüft. Da Veränderungen thermodynamischer und strömungstechnischer Parameter hauptsächlich in axialer Richtung stattfinden, wurden diese Modelle in einen eindimensionalen Code eingebettet, mit dem der Strömungsverlauf entlang einer vertikalen Rohrleitung mit einer Länge von 8 m und einem Nenndurchmesser von 200 mm berechnet werden kann. Anschließend werden Aufbau und Funktion dieses Programms vorgestellt. Nachfolgend vergleichen die Autoren experimentelle und berechnete Strömungsverläufe bei der Kondensation von Dampf sowohl in einer unterkühlten Wasserströmung als auch nahe der Siedetemperatur. Dabei wird der Einfluss wichtiger Randbedingungen, wie z.B. Druck oder Primärblasengröße, auf die Kondensationsintensität analysiert. Eine Einschätzung der Fehlerbanden für die experimentellen Daten, die verwendeten Gittersensoren und die numerische Simulation schließen den Bericht ab.

<p>The aim of the present investigation is to increase theunderstanding of the role played by the solvent in inhibitingor enhancing crystal growth. Drowning-out crystallizationexperiments has been performed by the controlled addition ofwater or ethanol water mixtures to a saturated solution ofbenzoic acid in ethanol-water mixtures. Crystal habitcontrolling factors have been identified.Seededcrystallization experiments have been carried out to evaluatethe effect of solvent composition on crystal habit at constantsupersaturation. The solubility of benzoic acid inethanol-water mixtures at the working temperatures has beendetermined.</p><p>Electro-zone sensing determinations and microscopicmeasurements are used to characterize the final crystallineproduct. It has been found that the shape of the benzoic acidcrystals grown from ethanol-water solutions ranges from needlesto platelets. Platy particles possess a predominant basal plane(001), bound by (010) and (100) faces, while needles aredeveloped along the b-axis. Long needle-shaped particles havebeen produced at low initial bulk concentration and highethanol concentration in the feed. Small platelets are obtainedat high initial bulk concentrations and high waterconcentration in the feed.</p><p>The effect of solvent composition on the growth rate hasbeen evaluated at constant supersaturation. Seed crystals arecharacterized by image analysis measurement both before andafter each experiment. Length and width dimensions have beenmeasured on the particle silhouette. The growth rate, thesolid-liquid interfacial energy and the surface entropy factorfor the (010) faces (length dimension) and (100) faces (widthdimension) have been estimated. The interfacial energy andsurface entropy factor decreases in the direction of increasingethanol concentration due to increasing solubility.</p><p>The results suggest that at low ethanol concentration(xEtOH<60%) growth proceeds by screw dislocation mechanism,and adsorption of ethanol molecules may reduce the growth rate.As the ethanol concentration increases above a critical value(xEtOH ≥60%), the growth mechanism shifts to surfacenucleation and the growth rate increases with increasingethanol concentration. It has been suggested that the observedeffect of the solvent composition on crystal habit is theresult of two conflicting effects here referred as the kineticand interfacial energy effects. High interactions of the pairethanol-benzoic acid seem to be responsible of the growthretardation (kinetic effect) exerted by the solvent. On theother hand, increased ethanol concentration leads to reduceinterfacial energy and increasing surface nucleation whichmight contribute to enhance growth kinetics.</p><p><b>Keywords:</b>drowning-out crystallisation, solventcomposition, benzoic acid, solubility, crystal growth,interfacial energy, surface entropy factor, growth mechanism,crystal shape distribution.</p>

<p>Admixtures like reactants and byproducts are solublenon-crystallizing compounds that can be present in industrialsolutions and affect crystallization of the main substance.This thesis provides experimental and molecular modellingresults on the influence of admixtures on crystal nucleation ofvanillin (VAN). Seven admixtures: acetovanillone (AVA),ethylvanillin (EVA), guaiacol (GUA), guaethol (GUE), 4-hydroxy-acetophenone (HAP), 4-hydroxy-benzaldehyde (HBA), andvanillic acid (VAC) have been used in this study. Classicalnucleation theory is used as the basis to establish arelationship between experimental induction time andsupersaturation, nucleation temperature, and interfacialenergy. A novel multicell device is designed, constructed, andused to increase the experimental efficiency in thedetermination of induction times by using 15 nucleation cellsof small volumes simultaneously. In spite of the largevariation observed in the experiments, the solid-liquidinterfacial energy for each VAN-admixture system can beestimated with an acceptable statistical confidence. At 1 mole% admixture concentration, the interfacial energy is increasedin the presence of GUA, GUE, and HBA, while it becomes lower inthe presence of the other admixtures. As the admixtureconcentration increases from 1 to 10 mole %, the interfacialenergy also increases. The interfacial energies obtained are inthe range 7-10 mJ m^-2. Influence of admixtures on metastable zone widthand crystal aspect ratio of VAN is also presented. Theexperimental results show that the admixtures studied arepotential modifiers of the nucleation of VAN. Molecularmodelling by the program Cerius2 is used to identify the likelycrystal growth faces. Two approaches, the surface adsorptionand the lattice integration method, are applied to estimatequantitatively the admixture-crystal interaction energy on thedominating crystal faces of VAN,<i>i.e</i>., {0 0 1} and {1 0 0}. However, a simple and clearcorrelation between the experimental values of interfacialenergy and the calculated interaction energies cannot beidentified. A qualitative structural analysis reveals a certainrelationship between the molecular structure of admixtures andtheir effect on nucleation. The determination of the influenceof admixtures on nucleation is still a challenge. However, themolecular and crystal structural approach used in this thesiscan lead to an improved fundamental understanding ofcrystallization processes. Keywords: Crystallization,nucleation, vanillin, admixtures, additives, impurities,induction time, interfacial energy, molecular modelling,interaction energy.</p>

The thermoelectric effect was discovered well over a century ago, yet performance has not shown improvement until recent years. Prior work has shown that the thermoelectric effect can be enhanced by the use of microscale pieces of thermoelectric material. Conventional assembly techniques are inadequate to deal with parts of this size, making it necessary to find a suitable alternative before these devices can be made economically. Capillary self-assembly is a promising alternative to conventional techniques. This method employs the use of preparing substrates with areas of favorable surface tension to place and align parts. Still, many obstacles have to be overcome to adapt this process for use of constructing thermoelectric coolers. The goal of this work is to overcome these obstacles and assess the viability of self-assembly for fabricating these devices. In effort to make the method more effective a process for creating more uniform deposits of solder is also assessed. This work shows that microscale thermoelectric elements can be assembled into functional thermoelectric devices using self-assembly techniques through the assembly of coolers in experimental work.

Microelectronic devices are multilayered structures with many different interfaces. Their mechanical reliability is of utmost importance when considering the implementation of new materials. Linear elastic fracture mechanics (LEFM) is a common approach that has been used for interfacial fracture analyses in the microelectronics industry where the energy release rate parameter is considered to be the driving force for delamination and the failure criterion is established by comparing this with the interface toughness. However this approach has been unable to model crack-nucleation, which plays an important part in analyzing the mechanical reliability of chip-package systems. The cohesive interface modeling approach, which is considered here, has the capability to model crack nucleation and growth, provided interfacial parameters such as strength and toughness of the system are available. These parameters are obtained through the extraction of traction-separation relations, which can be obtained through indirect hybrid numerical/experimental methods or direct experimental methods. All methods of extracting traction-separation relations require some local feature of the crack-tip region to be measured. The focus in this doctoral work has been on the comparison of the two methods for a mode-I DCB experiment and on the development of a universal loading device to extract mixed-mode traction-separation relations at different mode-mix values. The techniques that have been adopted for the local measurements are infrared crack opening interferometry (IR-COI) and digital image correlation (DIC). Apart from the global measurements of load-displacement (P-[delta]), local crack-tip parameters were measured using IR-COI or DIC. The combination of global and local measurements gave the relations between the fracture driving force (energy release rate or J-integral, J) and crack opening displacements, which were used to obtain the local tractions. IR-COI is an extremely useful technique to image and measure local crack-tip parameters. However, as IR-COI is restricted to normal measurements, the loading device was configured to accommodate a DIC system in order to make both normal and tangential measurements. In addition to measurements, fracture surface characterization techniques such as atomic force microscopy (AFM), profilometry and X-ray photoelectron spectroscopy were used to observe the fracture mechanisms. / text

Physical scaling limits of microelectronic devices and the need to improve electrical performance have driven significant research and development into 3D architecture. The development of die stacks in first level packaging is one of the more viable short-term options for improved performance. Placement of memory die above or below processors in a traditional flip chip C4 package with through-silicon vias (TSVs) has significant benefits in reducing data and power transmission paths. However, with the electrical performance benefits come great thermal and mechanical challenges. There are two key objectives for this work. The first is understanding of the die-die interface resistance, R[subscript dd], composed of the back end of line (BEOL) layers and micro-C4 interconnects. The interfacial resistance between BEOL material layers, the impact of TSVs and the impact of strain on R[subscript dd] are subtopics. The second key objective is the understanding of package thermal and mechanical behavior under operating conditions, such as local thermal disturbances. To date, these topics have not been adequately addressed in the literature. It is found that R[subscript dd] can be affected by TSVs, and that the interfacial contributions predicted by theoretical sub-continuum models can be significantly different than measurements. Using validated finite element models, the significance of the power distribution and R[subscript dd] on the temporal responses of 2D vs. 3D packages is highlighted. The results suggest local thermal hotspots can greatly exacerbate the thermal penalty due to the R[subscript dd] and that no peaks in stress arise in the transient period from power on to power off. / text

Interfacial partitioning tracer tests (IPTT) are one method available for measuring air-water interfacial area (A(ia)).This study used the standard approach comprising tracer injection under steady unsaturated-flow conditions with a uniform water-saturation distribution within the column. Sodium dodecylbezene sulfonate (SDBS) and pentafluorobenzoic acid (PFBA) were used as the partitioning and nonreactive tracers, respectively. Three types of porous media were used for the study: a sandy soil, a well-sorted sand, and glass beads. Initial water saturations, S(w), were approximately 80%, 80%, and 26 % for the soil, sand, and glass beads, respectively. Water saturation was monitored gravimetrically during the experiments. The maximum interfacial areas (A(ia)/(1-S(w))) calculated from the results of the experiments are compared among the three porous media used in this work, and compared to previous air-water interfacial area studies.

The air-water interface in variably saturated porous media is recognized to influence interfacial retention of organic and inorganic contaminants, and mediate various mass-transfer processes. The formation and presence of water films commonly solvating the surfaces of soil/sediment grains in unsaturated systems, as well as their impact on flow and retention processes have been of sustained interest. X-ray microtomography was used to measure air-water interfacial area at multiple wetting-phase saturations for natural porous media. First, a study was conducted to evaluate image-processing procedures suitable for characterizing fluids and associated interfaces in natural porous media. A simple method was developed for the analysis of all phases in the system, using global threshold for phase identification and combination of binary files (M1). This method was then compared to a simultaneous multiphase segmentation approach using locally adaptive threshold selection (M2). Both methods were used to process data sets comprised of multiple drainage steps for water-saturated packed columns imaged via synchrotron x-ray microtomography. The results of both methods were evaluated based on comparison of values determined for porosity and specific solid surface area to independently measured porosity and specific solid surface areas. The results show both methods are suitable for determination of total air-water interfacial area, which requires characterization of only the non-wetting phase. Conversely, determination of capillary interfacial area requires characterization of all phases present and thus, is more sensitive to the challenges associated with image processing. The simultaneous multiple-phase segmentation (M2) method provides an integrated and consistent analysis of the phases, and anticipated to improve water-phase detection. Using the advanced segmentation approach, the air-water interfacial area is presented as a result of direct measurement of contact areas between the two fluids. This is in contrast to previously reported data, which were derived indirectly from calculations based on individually measured phase surface areas and conceptualizations of fluid distributions. The effects of these assumptions on the capillary interfacial behavior are evaluated. Results from this study confirmed the initial hypothesis that the behavior of fluid surface areas will affect the theoretical shape of the capillary curve. The results support the understanding of the capillary interfacial area behavior in response to changes in the configuration of fluid surface areas during a drainage cycle. Furthermore, results for the measured air-water interface allows for further identification of fluid domains, such as the relationship between film interfacial area, capillary domains (menisci), and the total-measurable interfacial area. Experiments were also conducted using aqueous-phase interfacial partitioning tracer tests for comparison. Results support the hypothesis that different methods provide characterization of different interfacial domains. Overall, this study provides an imaging-based approach for evaluation of water configuration, and presents a measurement-based framework for further understanding of the role of fluid-fluid interfaces in natural porous media.

In this work the nucleation kinetics of propane gas hydrate has been investigated experimentally using a stirred batch reactor. The experiments have been performed isothermally recording the pressure as a function of time. Experiments were conducted at different stirring rates, but in the same supersaturation region. The experiments showed that the gas dissolution rate rather than the induction time of propane hydrate is influenced by a change in the stirring rate. This was especially valid at high stirring rates when the water surface was severely disturbed. Addition of polyvinylpyrrolidone to the aqueous phase was found to reduce the gas dissolution rate slightly, however the induction times were prolonged quite substantially. The induction time data were correlated using a newly developed induction time model based on crystallization theory also capable of taking into account the presence of additives. In most cases reasonable agreement between the data and the model could be obtained. The results revealed that especially the effective surface energy between propane hydrate and water is likely to change when the stirring rate varies from very high to low. The prolongation of induction times according to the model is likely to be due to a change in the nuclei-substrate contact angle.

No description available.