In this study, agitation of solutions using different impeller and tank geometry were investigated experimentally in terms of hydrodynamics, macromixing time and aeration characteristics. In the first set of experiments a cylindrical vessel equipped with two types of hydrofoil and a hyperboloid impeller or their combinations were used. Vessel and impeller diameters and water level were 300, 100 and 300 mm, respectively. At the same specific power consumption, 163 W/m3, the so called hydrofoil 1 impeller provided the shortest mixing time at 7.8 s. At the top hydrofoil 1 impeller submergence of 100 mm, the hyperboloid impeller combination of it was the most efficient by a mixing time of 10.0 s at 163 W/m3. Ultrasound Doppler velocimetry and the lightsheet experiments showed that the hydrofoil 1, hydrofoil 2 impellers and the stated impeller combination provided a complete circulation all over the tank. Macromixing measurements were performed in square vessel for Generation 5 low and high rib and Generation 6 hyperboloid impellers. Vessel length, impeller diameters and water level were 900, 300 and 450 mm, respectively. At the same specific power consumption, 88.4 W/m3, Generation 6 mixer provided the lowest mixing time at 80.5 s. Aeration experiments were performed in square tank for Generation 5 low rib and Generation 6 hyperboloid impellers equipped with additional blades. With increasing flow number, the differences between the performances at different rotational speeds became smaller for each type of mixer. At similar conditions the transferred oxygen amount of Generation 6 impeller was about 20% better.

Radiation therapy is administered to more than 50% of patients diagnosed with cancer. Mechanisms of interaction between radiation and tumour cells are relatively well understood on a molecular level, but much remains uncertain regarding how radiation interacts with the tumour as a whole. Recent studies have suggested that tumour response to radiation may in fact be regulated by endothelial cell response, consequently stressing the role of tumour blood vessels in radiation treatment response. As a result, various treatment regimens have been proposed to strategically combine radiation with vascular targeting agents. A great deal of effort has been aimed towards developing efficient vascular targeting agents. Nonetheless, no optimal method has yet been devised to strategically deliver such agents. Recent evidence suggesting that these drugs may “normalize” tumour blood vessels and enhance radiosensitivity, is supporting experiments where anti-angiogenic drugs are combined with cytotoxic therapies such as radiotherapy. In contrast, ultrasound-stimulated microbubbles have recently been demonstrated to enhance radiation therapy by biophysically interacting with endothelial cells. When combined with single radiation doses, these microbubbles are believed to cause localized vascular destruction followed by tumour cell death. Finally, a new form of ‘pro-angiogenics’ has also been demonstrated to induce a therapeutic tumour response. The overall aim of this thesis is to study the role of tumour blood vessels in treatment responses to single-dose radiation therapy and to investigate radiation-based vascular targeting strategies. Using pharmacological and biophysical agents, blood vessels were altered to determine how they influence tumour cell death, clonogenicity, and tumour growth, and to study how these may be optimally combined with radiation. Three-dimensional high-frequency power Doppler ultrasound was used throughout these studies to investigate vascular response to therapy.

Non-invasive and fast flow measurement techniques have had increasing importance for the last decades. Scientists are looking for such quick techniques to be able to monitor real velocities without disturbing flow itself. Ultrasound Doppler velocimetry (UDV) being one of such techniques promising with advantages of getting simultaneous velocity measurements from several points and of applicability for opaque liquids as well. UDV is a technique which is still being developed for new applications and analysis of complex flows. In this study effect of sinusoidal oscillating, turbulent (random) and viscoelastic fluid motions on UDV signals were investigated theoretically and experimentally. Obtained mathematical relations for random and viscoelastic motions were utilized to get statistics of flow and distribution of relaxation spectrum, respectively. Analytical analysis and numerical simulation of sinusoidal oscillating flow depicted that there is a critical value for the ratio of oscillation amplitude to oscillation frequency for a specified set of measurement parameters of UDV. Above this critical value UDV is not successful to determine mean flow velocity. Mathematical relations between velocity probability density function (PDF) &ndash / velocity auto correlation function (ACF) and UDV signal spectrum were obtained in the analysis v of flow with random velocity. Comparison of velocity ACFs from direct velocity measurements and from raw in-phase (I) and quadrature (Q) signals through derived relation, revealed that time resolution of UDV technique is not enough for getting a good velocity ACF and thus turbulence spectrum. Using I and Q signals rather than measured velocities to get velocity ACF, increased the time resolution in the order of number of pulses used for getting one velocity value (Nprn). Velocity PDF obtained from UDV spectrum was compared with the one obtained from measured velocities with the assumption of Gaussian PDF. Both velocity PDFs were consistent. Also some parameters of pipe turbulence from literature were compared with the presented findings from velocity ACF obtained from I and Q signals through derived relation. Results showed good compatibility. In the last part of the study, complex viscosity of a linear viscoelastic fluid mathematically related to spectrum of UDV for a pipe flow with small-amplitude oscillating pressure field. Generalized Maxwell model was employed to express complex viscosity terms. Zero frequency (mean flow) component of UDV spectrum was used to obtain an equation for relaxation viscosities of generalized Maxwell model. Results have revealed that UDV technique can also be used to probe some of viscoelastic material functions. In conclusion, UDV is relatively new but a promising technique for the measurement and analysis of complex flows in a non-invasive manner.

Bei einer Reihe bedeutsamer industrieller Prozesse, wie dem Stahl-Strangguss oder der Kristallzucht für die Photovoltaik, ist die Strömung flüssiger Metalle oder Halbleiter entscheidend für den Energieaufwand bei der Herstellung und die Qualität des Endproduktes. Eine gezielte, berührungslose Einwirkung von Lorentzkräften auf die heißen Schmelzen kann dabei die Ressourceneffizienz eines Prozesses signifikant steigern. Die komplexe Interaktion von elektrisch leitfähigen Fluiden und magnetischen Wechselfeldern wird dazu in der Magnetohydrodynamik (MHD) durch Experimente im Labormaßstab an niedrigschmelzenden Metallen untersucht. Die dabei auftretenden instationären, dreidimensionalen Strömungsfelder erfordern eine nicht-invasive, bildgebende Strömungsmesstechnik für opake Fluide mit hoher Orts- und Zeitauflösung, welche derzeitig nicht für die MHD zur Verfügung steht. Im Rahmen dieser Arbeit soll mit den Mitteln der Elektrotechnik eine für MHD-Modellexperimente geeignete Messtechnik basierend auf dem Ultraschall-Doppler-Prinzip geschaffen werden. Dabei wird der Ansatz verfolgt, die Komplexität eines Messsystems vom mechanischen Aufbau hin zur Rechentechnik zu verlagern, um durch die dort in jüngster Zeit verfügbaren Ressourcen neuartige Signalverarbeitungsmethoden und eine höhere Flexibilität zu ermöglichen. Mit dem Ultrasound Array Doppler Velocimeter (UADV) wurde ein flexibles Messsystem für MHD-Modellexperimente geschaffen, welches eine mehrkomponentige Mehrebenenmessung durch Sensordatenfusion von bis zu neun linearen Wandlerarrays im kombinierten Zeit- und Ortsmultiplex erreicht. Die Signalverarbeitung ist durch eine auf einem Field Programmable Gate Array implementierte Datenkompression onlinefähig. Sie reicht trotz geringer rechentechnischer Komplexität bis auf Faktor 3 an die fundamentale Grenze der Messunsicherheit, die Cramér-Rao-Schranke, heran. Das UADV wurde über ein Kalibrierexperiment mit interferometrischer Referenzmessung auf die SI-Einheiten zurückgeführt. Das UADV wurde an einer magnetfeldgetriebenen Strömung in einem kubischen Gefäß angewandt. Numerische Simulationen sagen dort nicht-deterministisch einsetzende Instabilitäten im Übergangsbereich des laminaren zum turbulenten Strömungsregimes vorher. Durch eine simultane Zweiebenenmessung mit hoher örtlicher (3 ... 5 mm) und zeitlicher Auflösung (Bildrate 11,2 Hz) bei gleichzeitig langer Aufnahmedauer (> 1000 s) konnten die Instabilitäten erstmals experimentell charakterisiert werden. Eine Hauptkomponentenanalyse identifizierte ein gekoppeltes Paar von Strömungsmoden, welche eine spontan anfachende harmonische Oszillation mit der Frequenz f = 0,072 Hz beschreiben und durch komplexe Wirbel gekennzeichnet sind. Die Analyse der Messunsicherheit für das gegebene Experiment ergab, dass diese mit σ v,rel = 13,9 % hauptsächlich durch das räumliche Auflösungsvermögen bestimmt wird. Das Schallfeld ist bei ultraschallbasierten Messverfahren ausschlaggebend für die Eigenschaften der Bildgebung. Mit dem Phased Array Doppler Velocimeter (PAUDV) wurde ein modulares Messsystem mit adaptiven Schallfeld aufgebaut, wobei durch digitale Strahlformung die örtliche und zeitliche Auflösung signifikant erhöht werden kann. Eine aktive Kontrolle des Schallfeldes ermöglicht zudem die Messung durch Objekte mit komplexen, unbekannten Ausbreitungseigenschaften. Mit dem Time Reversal Virtual Array (TRVA) wird dabei eine effiziente Methode zur Bildgebung vorgestellt und auf die Strömungsmessung durch einen Multimode-Wellenleiter angewandt. Damit kann die Beschränkung bildgebender Ultraschallmesstechnik hinsichtlich der Betriebstemperatur der Wandler umgangen und heiße Schmelzen industrieller und technischer Prozesse für nichtinvasive In-Prozess-Bildgebung zugänglich gemacht werden. / In many important industrial processes, such as continuous steel casting or crystal growth for photovoltaic silicon, the flow of liquid metals or semiconductors determines the energy consumption of the process and the quality of the product. Influencing the hot melts contactlessly through Lorentz forces for a targeted flow control can significantly improve the resource-efficiency of a process. The complex interaction of electrically conductive fluids and alternating magnetic fields is investigated in the field of magnetohydrodynamics (MHD) through laboratory-scale experiments in low melting metals. The emerging instationary, three-dimensional flows require a temporally and spatially high-resolved non-invasive flow imaging system, which currently is not available for MHD research. In this work, a flow instrumentation for MHD experiments based on the ultrasound Doppler principle is created through means of electrical engineering. The general approach is to shift the complexity of a system from mechanics over electronics to an algorithmic implementation in order to exploit the recent computational advances, enabling novel signal processing methods and increasing the flexibility. The ultrasound array Doppler velocimeter (UADV) has been created as a flexible instrumentation system for MHD experiments. It supports multicomponent, multiplane velocity measurements through sensor fusion of up to nine linear transducer arrays with spatiotemporal multiplexing. An online signal processing is realized through data compression on a field-programmable gate array (FPGA). It achieves an uncertainty as low as a factor 3 of the Cramér-Rao lower bound despite a low computational complexity of the algorithm. The UADV has been applied to a magnetically-driven flow in a cubic vessel. Numerical simulations predicted a non-deterministic instability in the transitory region between laminar and turbulent flow regimes. A simultaneous two-dimensional two-component flow measurement with high spatial (3 ... 5 mm) and temporal resolution (frame rate 11,2 Hz) over long durations (> 1000 s) allowed to characterize those instabilities experimentally for the first time. A principal component analysis identified a pair of coupled modes with a complex vortex structure that performs a spontaneously onsetting oscillation at f = 0,072 Hz. The measurement uncertainty for the experiment has been evaluated to be σ v,rel = 13,9 % and is primarily caused by the spatial resolution of the system. The properties of ultrasound-based imaging are primarily determined by the sound field. The phased array Doppler velocimeter (PAUDV) has been developed as a modular flow instrumentation system with an adaptive sound field, which allows to increase the spatial and temporal resolution. Furthermore, an active control of the sound field enables measurements despite a complex, unknown sound propagation. A method to image through strong aberrations efficiently has been proposed with the time reversal virtual array (TRVA). It has been applied to flow imaging through a multimode waveguide, thus allowing to circumvent the limitation of common ultrasound imaging systems regarding their maximum operating temperature. This paves the way for in-process flow imaging of hot, opaque liquids in technical and industrial processes.

This thesis presents an experimental study which investigates the behaviour of gas bubbles rising in a liquid metal and the related bubble-driven flow under the influence of external DC magnetic fields. The experimental configuration considered here concerns a cylindrical container filled with the eutectic alloy GaInSn. Argon gas bubbles are injected through a single orifice located at the container bottom in the centre of the circular cross-section. A homogeneous magnetic field was generated by a Helmholtz configuration of a pair of water-cooled copper coils. The magnetic field has been imposed either in vertical direction parallel to the main bubble motion or in horizontal direction, respectively. A vertical magnetic field stabilizes and damps the liquid metal flow effectively. The temporal variations of the fluid velocity with time become smaller with increasing magnetic induction. The velocity magnitudes are decreased, and the velocity distributions along the magnetic field lines are smoothed. The flow field keeps the axisymmetric distribution. A horizontal magnetic field destabilizes and enhances the flow within a range of moderate Hartmann numbers (100 < Ha < 400). The flow becomes non-axisymmetric due to the non-isotropic influence of the magnetic field. In the meridional plane parallel to the field lines, the flow changes its direction from a downward to an upward motion. Enhanced downward flows were observed in the meridional plane perpendicular to the field lines. The liquid velocity in both planes shows strong, periodic oscillations. The fluid motion is dominated by large-scale structures elongated along the magnetic field lines over the entire chord lengths of the circular cross-section.

This thesis presents an experimental study which investigates the behaviour of gas bubbles rising in a liquid metal and the related bubble-driven flow under the influence of external DC magnetic fields. The experimental configuration considered here concerns a cylindrical container filled with the eutectic alloy GaInSn. Argon gas bubbles are injected through a single orifice located at the container bottom in the centre of the circular cross-section. A homogeneous magnetic field was generated by a Helmholtz configuration of a pair of water-cooled copper coils. The magnetic field has been imposed either in vertical direction parallel to the main bubble motion or in horizontal direction, respectively. A vertical magnetic field stabilizes and damps the liquid metal flow effectively. The temporal variations of the fluid velocity with time become smaller with increasing magnetic induction. The velocity magnitudes are decreased, and the velocity distributions along the magnetic field lines are smoothed. The flow field keeps the axisymmetric distribution. A horizontal magnetic field destabilizes and enhances the flow within a range of moderate Hartmann numbers (100 < Ha < 400). The flow becomes non-axisymmetric due to the non-isotropic influence of the magnetic field. In the meridional plane parallel to the field lines, the flow changes its direction from a downward to an upward motion. Enhanced downward flows were observed in the meridional plane perpendicular to the field lines. The liquid velocity in both planes shows strong, periodic oscillations. The fluid motion is dominated by large-scale structures elongated along the magnetic field lines over the entire chord lengths of the circular cross-section.