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Two-Color/Two-Dye Planar Laser-Induced Fluorescence Thermography for Temperature Measurements at an Evaporating Meniscus

Fenner, Andreas J. C. (2017)
Two-Color/Two-Dye Planar Laser-Induced Fluorescence Thermography for Temperature Measurements at an Evaporating Meniscus.
Technische Universität Darmstadt
Ph.D. Thesis, Primary publication

Abstract

In the present work the applicability of 2c/2d PLIF-Thermography to evaporation processes is investigated. To analyze the applicability of 2c/2d PLIF-Thermography to evaporation processes a stationary evaporating liquid meniscus was chosen as test scenario. A stationary evaporating liquid meniscus was chosen because it is considered the simplest representation of the evaporation process which includes most of the physical phenomena. An experimental setup was designed and implemented which allowed the investigation of the applicability of the 2c/2d PLIF-Thermography to a stationary evaporating liquid meniscus. The setup enabled the investigations at a stationary evaporating liquid meniscus in a closed, single species system in a temperature range of 21 °C to 31 °C. A channel-based imaging spectrometer with two spectral channels was designed and implemented for the 2c/2d PLIF-Thermography. As detectors for the fluorescence signal sCMOS cameras were used. The channel-based imaging spectrometer had a spatial resolution of 14 μm per pixel. For the excitation of the fluorescent dyes a laser light sheet was generated by a high repetition rate pulsed frequency doubled Nd:YAG laser system which was synchronized with the detectors of the channel-based imaging spectrometer. Two dye combinations suitable for 2c/2d PLIF-Thermography in ethanol were investigated in detail regarding the influence of temperature, laser fluence, dye concentration, photobleaching, pressure and dissolved air/oxygen. The two dye combinations investigated were Rhodamine 6G combined with DCM and Rhodamine 6G combined with Pyridine 1. Based on the investigations the dye combination Rhodamine 6G and Pyridine 1 dissolved in ethanol was chosen for the investigations regarding the applicability of 2c/2d PLIF-Thermography to evaporation processes, because of its superior dependence on temperature. Experimental and data evaluation procedures for the calibration and the evaluation 2c/2d PLIF-Thermography measurement data were developed and implemented. An exponential and a second order polynomial approach for the calibration and evaluation of the 2c/2d PLIF-Thermography measurement data were implemented and compared with each other regarding the representation of the calibration data. The second order polynomial model showed a superior performance and therefore was chosen to be used for this work. With the settings used for the measurements in this work a confidence interval of 0.2 °C at a confidence level of 95 % could be reached for the 2c/2d PLIF-Thermography. The investigations at the stationary evaporating liquid meniscus revealed that a reliable application of the 2c/2d PLIF-Thermography to evaporation processes is not possible. Only for very low evaporation rates temperature measurements seemed to be possible. For higher evaporation rates the measured temperatures significantly deviated locally to higher temperatures which exceeded the applied evaporator temperature and therefore can be regarded as erroneous. The deviations were observed in and close to the region where the liquid-vapor interface meets the evaporator wall. In this region an increase of the fluorescence signal could be observed. This was most likely caused by the accumulation of fluorescent dyes induced by the evaporation process. An analysis regarding the origin of this deviations leads to the conclusion that they are most likely caused by a local violation of the assumption of a constant concentration ratio of the two dyes. The local dye concentration ratio is assumed to be shifted by the different diffusion rates of the two fluorescent dyes caused by the different diffusion coefficients of the two dyes used. Therefore any 2c/2d PLIF-Thermography application to evaporation processes would be compromised by the drawback that it cannot be guaranteed that the concentration ratio is locally constant.

Item Type: Ph.D. Thesis
Erschienen: 2017
Creators: Fenner, Andreas J. C.
Type of entry: Primary publication
Title: Two-Color/Two-Dye Planar Laser-Induced Fluorescence Thermography for Temperature Measurements at an Evaporating Meniscus
Language: English
Referees: Stephan, Prof. Dr. Peter ; Dreizler, Prof. Dr. Andreas
Date: 2017
Place of Publication: Darmstadt
Refereed: 15 November 2017
URL / URN: http://tuprints.ulb.tu-darmstadt.de/7004
Abstract:

In the present work the applicability of 2c/2d PLIF-Thermography to evaporation processes is investigated. To analyze the applicability of 2c/2d PLIF-Thermography to evaporation processes a stationary evaporating liquid meniscus was chosen as test scenario. A stationary evaporating liquid meniscus was chosen because it is considered the simplest representation of the evaporation process which includes most of the physical phenomena. An experimental setup was designed and implemented which allowed the investigation of the applicability of the 2c/2d PLIF-Thermography to a stationary evaporating liquid meniscus. The setup enabled the investigations at a stationary evaporating liquid meniscus in a closed, single species system in a temperature range of 21 °C to 31 °C. A channel-based imaging spectrometer with two spectral channels was designed and implemented for the 2c/2d PLIF-Thermography. As detectors for the fluorescence signal sCMOS cameras were used. The channel-based imaging spectrometer had a spatial resolution of 14 μm per pixel. For the excitation of the fluorescent dyes a laser light sheet was generated by a high repetition rate pulsed frequency doubled Nd:YAG laser system which was synchronized with the detectors of the channel-based imaging spectrometer. Two dye combinations suitable for 2c/2d PLIF-Thermography in ethanol were investigated in detail regarding the influence of temperature, laser fluence, dye concentration, photobleaching, pressure and dissolved air/oxygen. The two dye combinations investigated were Rhodamine 6G combined with DCM and Rhodamine 6G combined with Pyridine 1. Based on the investigations the dye combination Rhodamine 6G and Pyridine 1 dissolved in ethanol was chosen for the investigations regarding the applicability of 2c/2d PLIF-Thermography to evaporation processes, because of its superior dependence on temperature. Experimental and data evaluation procedures for the calibration and the evaluation 2c/2d PLIF-Thermography measurement data were developed and implemented. An exponential and a second order polynomial approach for the calibration and evaluation of the 2c/2d PLIF-Thermography measurement data were implemented and compared with each other regarding the representation of the calibration data. The second order polynomial model showed a superior performance and therefore was chosen to be used for this work. With the settings used for the measurements in this work a confidence interval of 0.2 °C at a confidence level of 95 % could be reached for the 2c/2d PLIF-Thermography. The investigations at the stationary evaporating liquid meniscus revealed that a reliable application of the 2c/2d PLIF-Thermography to evaporation processes is not possible. Only for very low evaporation rates temperature measurements seemed to be possible. For higher evaporation rates the measured temperatures significantly deviated locally to higher temperatures which exceeded the applied evaporator temperature and therefore can be regarded as erroneous. The deviations were observed in and close to the region where the liquid-vapor interface meets the evaporator wall. In this region an increase of the fluorescence signal could be observed. This was most likely caused by the accumulation of fluorescent dyes induced by the evaporation process. An analysis regarding the origin of this deviations leads to the conclusion that they are most likely caused by a local violation of the assumption of a constant concentration ratio of the two dyes. The local dye concentration ratio is assumed to be shifted by the different diffusion rates of the two fluorescent dyes caused by the different diffusion coefficients of the two dyes used. Therefore any 2c/2d PLIF-Thermography application to evaporation processes would be compromised by the drawback that it cannot be guaranteed that the concentration ratio is locally constant.

Alternative Abstract:
Alternative abstract Language

Zwei Farbstoffkombinationen, die für 2c / 2d PLIF-Thermografie in Ethanol geeignet sind, wurden im Detail hinsichtlich des Einflusses von Temperatur, Laserfluenz, Farbstoffkonzentration, Photobleichung, Druck und gelöster Luft/Sauerstoff untersucht. Die beiden untersuchten Farbstoffkombinationen waren Rhodamin 6G kombiniert mit DCM und Rhodamin 6G kombiniert mit Pyridin 1. Basierend auf den Untersuchungen wurde die Farbstoffkombination Rhodamin 6G und Pyridin 1 für die Untersuchungen zur Anwendbarkeit von 2c/2d PLIF-Thermografie auf Verdampfungsprozesse aufgrund ihrer höheren Temperaturabhängigkeit gewählt. Eine hohe Temperaturabhängigkeit war erforderlich, um die Anforderung hinsichtlich eine niedrigen Temperaturmessunsicherheit zu erfüllen. Für die 2c/2d PLIF-Thermografie wurde ein kanalbasiertes abbildendes Spektrometer mit zwei spektralen Kanälen entwickelt und implementiert. Als Detektoren für das Fluoreszenzsignal wurden sCMOS Kameras verwendet. Das kanalbasierte Bildgebungsspektrometer hatte eine räumliche Auflösung von 14 μm pro Pixel. Für die Anregung der Fluoreszenzfarbstoffe wurde ein Laserlichtschnitt mit einem frequenzverdoppeltem Nd:YAG-Laser mit hoher Wiederholrate erzeugt, der mit den Detektoren des kanalbasiertem abbildendem Spektrometer synchronisiert wurde.

Experimentelle Verfahren und Datenauswertungsverfahren für die Kalibrierung und die Auswertung von 2c/2d PLIF-Thermografie Messdaten wurden entwickelt und implementiert. Für die Kalibrierung und Auswertung der 2c/2d PLIF-Thermografie Messdaten wurden ein exponentieller Ansatz und eine polynomischer Ansatz zweiter Ordnung implementiert und miteinander verglichen. Der polynomische Ansatz zweiter Ordnung zeigte eine bessere Anpassung an die Messdaten und wurde daher als Kalibrierungsfunktion für diese Arbeit ausgewählt. Mit den für die Messungen in dieser Arbeit verwendeten Einstellungen konnte für die 2c/2d PLIF-Thermografie ein Konfidenzintervall von 0.2 °C bei einem Konfidenzniveau von 95 % erreicht werden. Um die Anwendbarkeit der 2c/2d PLIF-Thermografie auf Verdampfungsprozesse zu analysieren, wurde als Testszenario ein stationärer Verdampfungsflüssigkeitsmeniskus gewählt. Ein stationärer verdampfender Flüssigkeitsmeniskus wurde gewählt. Ein experimenteller Aufbau wurde entworfen und implementiert, der die Untersuchung der Anwendbarkeit der 2c/2d PLIF-Thermografie auf einen stationären verdampfenden Flüssigkeitsmeniskus erlaubte. Der Aufbau ermöglichte die Untersuchungen an einem stationären Verdampfungsflüssigkeitsmeniskus in einem geschlossenen Reinstoffsystem in einem Temperaturbereich von 21 °C bis 31 °C. Die Untersuchungen am stationären Verdampfungsflüssigkeitsmeniskus zeigten, dass eine zuverlässige Anwendung der 2c/2d PLIF-Thermografie auf Verdampfungsprozesse nicht möglich ist. Nur für sehr geringe Verdunstungsraten schienen Temperaturmessungen möglich zu sein. Bei höheren Verdampfungsgeschwindigkeiten weichen die gemessenen Temperaturen lokal deutlich zu höhere Temperaturen hin ab, die Temperatur der Verdampferwand überschritten und daher als fehlerhaft angesehen werden können. Die Abweichungen wurden in und nahe dem Bereich beobachtet, wo die Flüssigkeitsdampf-Grenzfläche auf die Verdampferwand zusammen treffen. In diesem Bereich konnte eine Erhöhung des Fluoreszenzsignals beobachtet werden. Dies wurde höchstwahrscheinlich durch die Anhäufung von Fluoreszenzfarbstoffen verursacht, die durch den Verdampfungsprozess induziert wurden. Eine Analyse über den Ursprung dieser Abweichungen führt zu dem Schluss, dass sie höchstwahrscheinlich durch eine lokale Verletzung der Annahme eines konstanten Konzentrationsverhältnisses der beiden Farbstoffe verursacht werden. Es wird angenommen, dass das lokale Farbstoffkonzentrationsverhältnis durch die unterschiedlichen Diffusionsraten der beiden Fluoreszenzfarbstoffe verschoben wird, die durch die unterschiedlichen Diffusionskoeffizienten der beiden verwendeten Farbstoffe verursacht werden. Daher würde jede 2c/2d PLIF-Thermografie-Anwendung auf Verdampfungsprozesse durch den Verdacht beeinträchtigt werden, dass nicht garantiert werden kann, dass das Konzentrationsverhältnis lokal konstant ist.

German
URN: urn:nbn:de:tuda-tuprints-70046
Classification DDC: 600 Technology, medicine, applied sciences > 620 Engineering and machine engineering
Divisions: 16 Department of Mechanical Engineering
16 Department of Mechanical Engineering > Institute for Technical Thermodynamics (TTD)
Date Deposited: 17 Dec 2017 20:56
Last Modified: 17 Dec 2017 20:56
PPN:
Referees: Stephan, Prof. Dr. Peter ; Dreizler, Prof. Dr. Andreas
Refereed / Verteidigung / mdl. Prüfung: 15 November 2017
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