No description available.

No description available.

This study investigates of the effect of nanoparticle volume fractions, NaCl concentration and pH on size of agglomerates, electrical conductivity and zeta potential of alumina nanofluids. The volume fractions used were 1, 2, 3 and 5 vol%. Different base fluids were prepared by adding NaCl (100, 300 and 500 ppm) or adjusting the pH (9, 7, 5 and 3). The results showed that the size of nanoparticle agglomerates was increased with an increase in nanoparticles concentration and NaCl concentration. Also, the electrical conductivity was increased with an increase in nanoparticle concentration and NaCl concentration. The size of nanoparticle agglomerates was 110 nm and the electrical conductivity was 290.2 μS/cm at pH 3 and 0 ppm, which was the highest value of electrical conductivity and smallest agglomerates nanoparticle size at 1 vol% with no salt. The highest value was 1830 μS/cm at pH 9 and 500 ppm of NaCl with 5 vol% of nanoparticles.

Particles in Saturn’s main rings range in size from dust to even kilometer-sized objects. Their size distribution is thought to be a result of competing accretion and fragmentation processes. While growth is naturally limited in tidal environments, frequent collisions among these objects may contribute to both accretion and fragmentation. As ring particles are primarily made of water ice attractive surface forces like adhesion could significantly influence these processes, finally determining the resulting size distribution. Here, we derive analytic expressions for the specific self-energy Q and related specific break-up energy Q⋆ of aggregates. These expressions can be used for any aggregate type composed of monomeric constituents. We compare these expressions to numerical experiments where we create aggregates of various types including: regular packings like the face-centered cubic (fcc), Ballistic Particle Cluster Aggregates (BPCA), and modified BPCAs including e.g. different constituent size distributions. We show that accounting for attractive surface forces such as adhesion a simple approach is able to: a) generally account for the size dependence of the specific break-up energy for fragmentation to occur reported in the literature, namely the division into “strength” and “gravity” regimes, and b) estimate the maximum aggregate size in a collisional ensemble to be on the order of a few meters, consistent with the maximum aggregate size observed in Saturn’s rings of about 10m. / Die Ringe des Saturns bestehen aus Myriaden von Teilchen, deren Größe von Mikrometern (Staub) bis hin zu Hunderten von Metern reicht. Die Ringteilchen bestehen hauptsächlich aus Eis, wobei attraktive Oberflächenkräfte wie Adhäsion und Gravitation zur Bildung von Aggregaten führen kann. Das Wachstum der Aggregate wird durch die Wirkung der Gezeitenkräfte und auch durch Kollisionen der Ringteilchen untereinander auf natürliche Weise begrenzt. Die Kollisionen der Ringteilchen führen zu Akkretion und Fragmentation, welche die resultierende Größenverteilung der Agglomerate schließlich bestimmen. In dieser Arbeit wurden Ausdrücke für die spezifische Eigenenergie Q der Aggregate und der in Relation stehenden spezifischen Fragmentationsenergie Q* analytisch hergeleitet. Diese Ausdrücke können für alle aus monomeren Teilchen bestehenden Agglomerate verwendet werden. Die analytisch gewonnenen Ergebnisse wurden mit numerischen Experimenten verglichen. In den numerischen Experimenten wurden verschiedene Agglomerattypen erzeugt: (i) Agglomerate mit kubischem Kristallsystem, (ii) ballistische Teilchenaggregate und (iii) modifiziert ballistische Teilchenaggregate. Für die ballistischen Teilchenaggregate wurden verschiedene Größenverteilungen der Konstituenten verwendet. Als Ergebnis lassen sich die erzeugten Aggregate gemäß ihrer Größe in zwei Gruppen einteilen. Während die kleinen Aggregate hauptsächlich durch die Kontaktkräfte (Adhäsion) zusammengehalten werden, dominiert bei großen Aggregaten (größer als einige Meter) die Gravitationskraft. D.h. wächst aus kleinen Teilchen ein Aggregat, so wird dieses zunächst durch die haftenden Kontakte zwischen den Teilchen zusammengehalten. Wächst das Agglomerat über eine bestimmte Größe, so ist es die Eigengravitation, die den Körper zusammenhält. Damit kann die maximale Gesamtgröße der Aggregate im Kollisionsensemble abgeschätzt werden. Der so bestimmte Wert von einigen Metern stimmt mit der aus Beobachtungen berechneten maximalen Größe der Ringteilchen von rund 10 Metern gut überein.

In the past few years, the prominent achievement of economy in Taiwan has been called the ¡§ Taiwan Experience¡¨ or ¡§The Miracle of Economy¡¨. Urban is not only the place that people gather to take economic activities and live in groups, but also the area that produce and consume goods. Now the modern economy has expanded as the type of urban economic. Nowadays, service industry which has been the major industry during the transition of industrial structure in Taiwan could be an illustration that Taiwan is in the age of Service Economy, the functions of a city are going to be more various and delicate, and the division of industry is tending to be more professional. Though the service industry that just serves customers in the past can¡¦t totally meet the needs of the public, the growth of its high specialization and output value bridges the gap for the problems resulted from the manufacturing industry. Most important, the producer service industry has become the main industry in the world. The purpose of this research is to understand the development in the present and tendency of producer service industry, and also to measure the space efficiency of producer service industry in 22 counties for three years by Data Envelopment Analysis(DEA). The research is divided into five parts: the first part includes research structure and literature review. The second part is to discuss and figure out the theory of DEA. The third part is to analyze the transition and development of producer service in present days. In the fourth part of the research measures the efficiency of producer service industry in 22 counties, in the mean time it estimates the relation of among efficiency, agglomerate economy, city scale, public investment, and the development of other industries by regression analysis and chi-square test. Then the conclusions and recommendations would be discussed to government that makes the plans of economy industry policy and the development of producer service industry. The conclusions of this research are: 1.The producer service industry in Taiwan grows rapidly, and the industry gathers in Taipei city which Location Quotient is more than one . In addition, Taipei city plays the most role for industry¡¦s output value, the numbers of employees and factories Moreover, the producer service industry in Taipei Metropolitan Area and other Metropolitan city gradually grows. Furthermore, the industry is expanding to the nearby metropolitan gradually. 2.The producer service industry and the industries in the producer service industry are influenced by Forward Linkage Effect. This shows that the industry grows rapidly following other industries development during the development of economy. 3.The producer service industry in Taipei city shows the excellent space efficiency. On the other hand, the some of 22 cities areas showed efficiency from 1986 to 1991, and the nearby metropolitan area also showed efficiency in 1996, especially in Taipei metropolitan area and in Kaohsiung metropolitan area. 4.The space efficiency of producer service industry shows remarkable relation with city scale, agglomerate economy and public investment. Additionally, the producer service industry also has the close relation with manufacturing industry and non-producer service industry during the development of industry.

Das thermische Spritzen ist geeignet Kompositschichten herzustellen, deren Einsatzgebiet hauptsächlich im Verschleißschutz liegt. Bisher lag der Schwerpunkt in der Untersuchung partikelverstärkter Schichten. Inhalt der vorliegenden Arbeit ist die Herstellung und Charakterisierung von C-kurzfaserverstärkten Schichten mit einer Aluminiummatrix. Als Spritzverfahren kamen das DC-Plasmaspritzen und das HF-Plasmaspritzen zur Anwendung. Die Aluminiumpulver und Kohlenstoffkurzfasern werden dafür agglomeriert. Gegenübergestellt wurden für beide Spritzverfahren die Mikrostrukturen der Schichten und das Verschleißverhalten. Die Kompositschichten können im Vergleich mit unverstärktem Aluminium ein deutlich verbessertes Verschleißverhalten aufweisen. Dies konnte in Gleit- und Schwingverschleißprüfungen nachgewiesen werden. Weiterhin wird auf eine für thermisch gespritzte Schichten charakteristische Fasereinbettung in die metallische Matrix hingewiesen, die zu einem speziellen Schädigungsmechanismus bei den Verschleißtests führt.

No description available.

The work in this thesis addresses the improvement of electrocatalyst performance in hydrogen PEM fuel cells. An agglomerate model for a catalyst layer was coupled with a one dimensional macroscale model in order to investigate the fuel cell performance. The model focuses on the agglomerate scale and the characteristic length in this study was 0.4 µm. The model was validated successfully with the experimental data. Based on the analysis of variance method at a 99% confidence level, the variation in the average fuel cell voltage was significantly sensitive to that in the volume fraction of electrolyte in an agglomerate. The effect of changing electrolyte film thickness was observed to have a significant impact only in the mass transport limited region, whereas the effect of changing agglomerate radius was found over the entire range of current density. An analysis comparing the effect of agglomerate shape at a constant platinum loading, a constant characteristic length and assuming the semi-finite structure was suitable for this study. Sphere, cylinder and slab agglomerate geometries were considered. The behaviour of the utilisation effectiveness was discovered to be strongly affected by the agglomerate shape. The improvement in the utilisation effectiveness was non-linear with current density. The advantage of the slab geometry in distributing reactant through the agglomerate volume was reduced and consequently the increase in utilisation effectiveness for slab-like agglomerates diminishes in the high current density region. At 0.85 Acm−2, the maximum improvement of the catalyst utilisation effectiveness in slab was 27.8% based on the performance in sphere. The improvement in fuel cell maximum power density achieved using slab-like agglomerate was limited to around 3%. The improvement in the overall fuel cell performance by changing the agglomerate shape was not significant. To achieve significant improvements in fuel cell performance will require changes to other features of the catalyst layer.

No description available.

The thesis investigates pipeline plugging mechanisms that have occurred during interim stabilization transfers at Hanford. A laboratory-scale saltwell pumping test loop was designed to evaluate a surrogate of Hanford Tank 241-SX-104 supernate. The effect of surrogate flow rate, cooling water flow rate and phosphate concentrations on plugging mechanisms was investigated. Critical parameters like particle and agglomerate size, velocity and bed growth rate were determined. Theoretical models were used to compare the experimental pressure rise and temperature drop of the surrogate in the channel. An operating region in which a plug would not form was developed, based on the experimental results. Experiments are also reported on plug remediation. Unplugging experiments at varying pump pressure heads and residence time of plug in the line were performed.