Heat transfer consitutes one of the most crucial fields in space applications. Spacecrafts need to withstand very high thermal loads in their different missions and therefore the research about refrigeration systems becomes a paramount issue. Heat pipes are cooling devices which employ the phase change from liquid to vapor and viceversa in order to distribute the heat generated by some systems inside a space vehicle. For the better understanding of this process, a technique based on thermography has been developed for the characterization of the liquid layer which forms on the pipes when the vapor condenses. Hence, by thermal imaging it will be possible to measure the temperature and thickness of the liquid film. Thermography is an experimental methodology whose working principle is based on radiation heat transfer. Thus, a theoretical analysis has been performed and a mathematical model based on radiation has been elaborated. Afterwards, a physical arrangement has been built to calibrate, test and validate the model. For this purpose, the optical features of different materials are investigated to find the most suitable components. Aditionally, in order to measure and control the set up, a data acquisition module is included while hydraulic and electrical circuits are implemented, where a part of the hydraulic system is designed by CAD and manufactured. Once the physical arrangement is built, a calibration of the technique is carried out experimentally for verification of these optical properties and the differences are explained. Finally, some measurements are performed on the set up and the mathematical model is applied to the images in order to obtain the film temperature and thickness. After processing the data, it is proven that the technique provides acceptable results of temperature and thickness of a liquid water film. In addition, the uncertainty associated to the results falls within suitable limits and therefore the validity of this methodology is confirmed.
Il trasferimento di calore costituisce uno dei campi più importanti nelle applicazioni aerospaziali. I veicoli spaziali devono resistere a carichi termici molto elevati nelle loro diverse missioni e pertanto la ricerca sui sistemi di refrigerazione diventa un problema fondamentale. I tubi di calore sono dispositivi di raffreddamento che utilizzano il cambiamento di fase tra liquido a vapore e viceversa per distribuire il calore generato da alcuni sistemi all'interno di un veicolo spaziale. Per una migliore comprensione di questo processo, è stata sviluppata una tecnica basata sulla termografia per la caratterizzazione dello strato liquido che si forma sui tubi quando il vapore si condensa. Quindi, mediante le immagine termiche sarà possibile misurare la temperatura e lo spessore dello strato liquido. La termografia è una metodologia applicata il cui principio di funzionamento si basa sul trasferimento di calore per radiazione. Pertanto, è stata eseguita un'analisi teorica ed è stato elaborato un modello matematico basato sulla radiazione. Successivamente, è stata costruita un'attrezzatura da laboratorio in grado di realizzare un film di spessore e temperature note, per calibrare, testare e validare il modello. A tale scopo, vengono studiate le caratteristiche ottiche di diversi materiali per trovare i componenti più adatti. Inoltre, per misurare e controllare l'esperimento, viene utilizzato un sistema di acquisizione dati e anche sono implementati circuiti idraulici ed elettrici, dove una parte del sistema idraulico è progettata da CAD e fabbricata. Una volta costruita l'attrezzatura da laboratorio, viene eseguita sperimentalmente una calibrazione della tecnica per la verifica di queste proprietà ottiche e vengono spiegate le differenze. Infine, alcune misure sono fatte sul set up e il modello matematico viene applicato alle immagini al fine di ottenere la temperatura e lo spessore dello strato. Dopo aver elaborato i dati, è dimostrato che la tecnica fornisce risultati accettabili di temperatura e spessore di uno strato di acqua liquida. Inoltre, l'incertezza associata ai risultati rientra in limiti adeguati e pertanto viene confermata la validità di questa metodologia.
Development of a thermographic technique for liquid film characterization
BADENES PÉREZ, SARA
2018/2019
Abstract
Heat transfer consitutes one of the most crucial fields in space applications. Spacecrafts need to withstand very high thermal loads in their different missions and therefore the research about refrigeration systems becomes a paramount issue. Heat pipes are cooling devices which employ the phase change from liquid to vapor and viceversa in order to distribute the heat generated by some systems inside a space vehicle. For the better understanding of this process, a technique based on thermography has been developed for the characterization of the liquid layer which forms on the pipes when the vapor condenses. Hence, by thermal imaging it will be possible to measure the temperature and thickness of the liquid film. Thermography is an experimental methodology whose working principle is based on radiation heat transfer. Thus, a theoretical analysis has been performed and a mathematical model based on radiation has been elaborated. Afterwards, a physical arrangement has been built to calibrate, test and validate the model. For this purpose, the optical features of different materials are investigated to find the most suitable components. Aditionally, in order to measure and control the set up, a data acquisition module is included while hydraulic and electrical circuits are implemented, where a part of the hydraulic system is designed by CAD and manufactured. Once the physical arrangement is built, a calibration of the technique is carried out experimentally for verification of these optical properties and the differences are explained. Finally, some measurements are performed on the set up and the mathematical model is applied to the images in order to obtain the film temperature and thickness. After processing the data, it is proven that the technique provides acceptable results of temperature and thickness of a liquid water film. In addition, the uncertainty associated to the results falls within suitable limits and therefore the validity of this methodology is confirmed.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/151635