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 | ||||
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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. |
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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) |
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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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