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URN: urn:nbn:de:bsz:25-opus-88204
URL: http://www.freidok.uni-freiburg.de/volltexte/8820/


Schmitt, Martin

Detektion von Schichtbelegungen innerhalb von flüssigkeitsgefüllten Rohren und Behältnissen durch Modenkonversion von Lambwellen

Detection of deposition within liquid-filled tubes and containers by mode conversion of Lamb waves

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Kurzfassung in Deutsch

Die Detektion von Schichtbelegungen innerhalb von flüssigkeitsgefüllten Rohren und Behältnissen ist in vielen technischen Anlagen und Geräten von großer Bedeutung. Durch den Einsatz eines online messenden Schichtbelegungssensors können Reinigungszyklen effizient gestaltet, Wartungszyklen reduziert und Rohrverschluss vermieden werden.

In dieser Dissertation wird erstmalig das akustische Messprinzip der Modenkonversion von Lambwellen zu Druckwellen in der angrenzenden Flüssigkeit zur Detektion von Schichten innerhalb von flüssigkeitsgefüllten Rohren und Behältnissen untersucht. Zur Qualifizierung des Messverfahrens werden Versuche mit verschiedenen Schichten an Laufstrecken und flüssigkeitsgefüllten Rohren und Behältnissen durchgeführt und diese mit Berechnungsergebnissen verglichen. Ferner werden die Dispersion von Lambwellen, die Abstrahlung von Druckwellen in die angrenzende Flüssigkeit und die Reflexion dieser an der fest-flüssig Grenzfläche theoretisch und experimentell untersucht.

Dieses neuartige Messprinzip hat den entscheidenden Vorteil, dass kein Sensorelement in das Rohr oder Behältnis eingebaut werden muss. Hierdurch können Sterilität und Reinigungsfähigkeit beibehalten werden.


Kurzfassung in Englisch

The detection of deposition within liquid-filled tubes and containers is very important in many technical plants and devices. The application range spreads from water supply systems over food plants to the chemical industry. An optimization of cleaning and maintenance cycles requires on-line sensors for deposition detection.

In this thesis, the acoustical approach of deposition detection by mode conversion of Lamb waves is investigated for the first time. Single phase transducers are attached to the exterior side of tubes and containers. Selectively excited Lamb waves on the vessel produce pressure waves inside the adjacent liquid. On the opposite side the pressure waves themselves are able to excite Lamb waves, which are detected by a second locally attached single phase transducer. Furthermore, the residual Lamb waves on the emitter wall are detected by a third single phase transducer forming a delay-line together with the emitter. The genesis of a deposition on the inner side of the vessel results in a change of the transmission times and the amplitudes of the measured signals by the two receiving transducers. With this new measurement approach no sensor element has to be insert into the tube or container, which is necessary for applications with high needs of sterility and cleanability.

In order to characterize this novel measurement concept, measurements and calculations were performed.

In the field of calculations, the dispersion of Lamb waves in multilayers and contact to half-spaces is modelled by the global-matrix-method. The results are verified by dispersion measurements. The attenuation, caused by the emission of pressure waves into the adjacent liquid is compared to the viscosity of the fluid and the material damping of the plate. For common technical liquid-solid combinations the attenuation by the emission of pressure waves is very dominant compared to the other ones.

The influence of a liquid layer and a liquid half-space in contact to Rayleigh and Lamb waves on the phase velocities and the attenuation coefficients are calculated and discussed for technically common liquid-solid combinations. Schlierenoptic and sound field measurements by a membrane hydrophone show good agreement between the measured and the calculated emission angles and phase velocities.

A comparison of the calculated results of the normal-mode-theory and the elastic potential theory or the global-matrix-method for the attenuation coefficient of Rayleigh and Lamb waves shows good conformance. The normal-mode-theory is recommended for the design and optimization of sensors and actuators based on the emission of pressure waves by Rayleigh and Lamb waves.

By Schlierenoptic images within a container structure multireflection was observed. A lateral displacement of the nonspecular reflection is observable in the Schlieren figures. The measured specular reflection angle agree with calculations. The measured non-specular displacement differs from the calculated result of the inhomogeneous wave theory, which can be justified with the ideal conditions of the theory and the non-ideal conditions in the experiment.

Dispersion, propagation, emission and reflection investigations are merged together in order to explain the measurement results on deposition detection within liquid-filled tubes and containers. Layers of gelatine, correction fluid, adhesive tape, acrylic lacquer and nickel are accurately coated and measured on delay-lines. In vessels consisting of glass, steal or plastic, layers of gelatine, correction fluid and adhesive tape are measured. A comparison of the measurement results of the delay-lines with the calculated results of bending wave theory, perturbation theory, global-matrix-method and finite-element-method shows a enormous variation. These are evoked by the idealized approaches in the theories and the unknown material parameters, which strongly depend on temperature and frequency. The container and tube measurements show significant layer sensitivities in the measured run-times and amplitudes. For the technical realization of the measurement concept the Lamb wave transmission time of the signal on the emitter wall should be taken into account. The run-time of the wave propagation through the liquid shows strong cross-sensitivity in temperature, concentration and streaming velocity.

This thesis introduces first results for the concept of layer detection inside liquid-filled tubes and containers by Lamb wave excitation. Further investigations for an optimization of the measurement arrangement and for an increase in the layer sensitivity are necessary in the future. Especially for the application of biofouling detection this measurement concept seems to be promising.


SWD-Schlagwörter: Dünne Schicht , Akustischer Sensor , Schallwelle , Dispersion <Welle> , Reflexion <Physik> , Abstrahlung , Modenwandlung , Dünnwandiges Rohr , Contain
Freie Schlagwörter (deutsch): Schichtbelegung , Behältnis , Lamb Welle , akustische Volumenwelle, akustische Oberflächenwelle
Freie Schlagwörter (englisch): deposition , mode conversion , Lamb wave , tube , container
PACS Klassifikation *43.40.Le , *43.60.Vx , *43.35.Ns , 68.35.Iv , 68.60.Bs
Institut: Institut für Mikrosystemtechnik
Fakultät: Technische Fakultät (bisher: Fak. f. Angew. Wiss.)
DDC-Sachgruppe: Technik
Dokumentart: Dissertation
Erstgutachter: Reindl, Leonhard Michael (Prof. Dr.)
Quelle: RF MEMS and Applications Vol. 13, Der Andere Verlag, ISBN: 978-3-86247-298-7
Sprache: Deutsch
Tag der mündlichen Prüfung: 14.06.2012
Erstellungsjahr: 2012
Publikationsdatum: 04.12.2012
Bemerkung: Dissertation ist auch als Buch in der Reihe RF MEMS and Applications Vol. 13, Der Andere Verlag, ISBN: 978-3-86247-298-7 erhältlich.
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