Volume 82, Issue 11 - Themenheft: Berührungslose Strömungsmesstechniken / Jürgen Czarske

The measurement of fluids in the oil and gas industry requires a robust measurement of multiphase flows. Magnetic resonance as a measurement principle has multiple advantages over existing technologies (one single measurement principle, measurement performed from outside the pipe with no intruding sensors, full bore design, suited for producing wells and high sensitivity at high water liquid ratios). A magnetic resonance based multiphase flow meter which is capable of producing an image of the spatial distribution of a multiphase flow has been developed. This article describes the principles of magnetic resonance. Afterwards details of the technical implementation and the method by which the system determines multiphase flow composition are explained.

A novel technique for time- and space-resolved measurement of density fluctuation is presented. It is nonintrusive and based on laser Doppler vibrometry. The density fluctuations reveal information on dynamic heat release and fluid velocity. The significance of this technique is proven by recording thermo-acoustic oscillations in a model combustor.

Zusammenfassung Die Messung von Temperatur- und Geschwindigkeitsfeldern spielt eine wichtige Rolle sowohl in der Luftfahrt als auch in der Energie- und Verfahrenstechnik. Mit laseroptischen Verfahren können hochaufgelöste Messungen von Strömungen vorgenommen werden, aber üblicherweise sind Partikel für die Lichtstreuung einzubringen. In diesem Beitrag wird eine neuartige Methode vorgestellt, die keinerlei Streupartikel benötigt und eine gleichzeitige flächige Messung von Temperatur und Geschwindigkeit erlaubt. Die Methode basiert auf der spektralen Auswertung von gefilterter Rayleigh-Streuung. Durch die Verwendung einer kalibrierten analytischen Modellfunktion kann die Messunsicherheit des Systems reduziert werden.

Zusammenfassung Es wird die High Speed optische Kohärenztomografie (OCT) als alternatives und komplementäres Messverfahren für die Bildgebung des Blasensiedens an beheizten Oberflächen vorgestellt. Mit High Speed OCT können Dampfblasen räumlich und zeitlich hochaufgelöst visualisiert werden, wobei sich die Blasengeometrie mit einem Segmentierungs- und Trackingalgorithmus automatisiert quantifizieren lässt. Darüber hinaus ermöglicht die Doppler-OCT die simultane Messung der axialen Geschwindigkeitskomponente des Fluids.

The progressing miniaturisation and increasing power demand of microelectronic devices require efficient cooling systems to avoid thermal damage. Future cooling systems have to be capable of dealing with heat loads of more than 200 W/cm 2 , at small temperature differences. However, the convective heat transfer in microchannels is limited due to the laminar flow regime. Nanofluids, i. e. fluids with suspended particles of nanometer size, have been shown to enhance the heat transfer. Nevertheless, their potential was recently controversially discussed in the literature. Therefore, reliable experimental heat transfer investigations are necessary to understand the underlying physical phenomena and help to establish design rules for future microelectronic cooling systems. For this reason the aim of the current study was to design and test a platform for the characterization of the fluid flow and the heat transfer in a straight microchannel. The heat transfer using pure water and water with 30–60 nm Al 2 O 3 nanoparticles were investigated at two different volume concentrations, 1% and 2.5% and Reynolds numbers ranging from 70 to 300. The results imply that the experimental platform allows for reliable and reproducible measurements of heat transfer and its sensitivity to the appropriated fluid and the flow properties. It could be shown that the heat transfer coefficient can be enhanced by up to 5.5% using 2.5% water-Al 2 O 3 nanofluids compared to distilled water.

Flow control based on time-dependent magnetic fields is used in various industrial processes involving liquid metals, i. e. during the solidification process of silicon to improve the quality and efficiency of wafers. In order to investigate the interactions between spatiotemporal-varying magnetic fields and conductive fluids numerical simulations are performed. The numerical models are verified by model experiments with opaque low-melting alloys. A suitable measurement technique for flow mapping in such model experiments is ultrasound Doppler velocimetry. In contrast to conventional systems employing transducers with fixed sound field our approach is to use a phased array with the ability to focus and steer its acoustic field. We present the Phased Array Ultrasound Doppler Velocimeter (PAUDV) for flow mapping in magnetohydrodynamics. With its custom host software for control and signal processing experiments that are flexible regarding the experimental setup can be defined.

Zusammenfassung Die Klebetechnik gewinnt als zukunftsträchtige, variabel einsetzbare Fügetechnik immer mehr an Bedeutung. Um Ausschuss zu vermeiden und Prozesse steuern zu können, müssen zerstörungsfreie Qualitätssicherungsmaßnahmen in die Prozessketten integriert werden. Ultraschallbasierte Messkonzepte bieten hierfür eine mögliche Lösung zur Detektion von qualitätskritischen Lufteinschlüssen bei der Applikation von Kleberaupen.