Development of Two-Line Atomic Fluorescence for 2D-Temperature Measurement in the Flame Synthesis of Nanoparticles
Final Report Abstract
In the flame synthesis of nanoparticles, the temperature-residence time behaviour of the particles in the flame has a significant influence on the resulting particle size, structure and morphology. Due to the turbulent character of most technically relevant synthesis processes in flames, a non-contact measurement technique with high temporal and spatial resolution is urgently needed to improve the understanding of the process. Existing measurement techniques are only suitable to a limited extent for measurements in the heavily particle-laden environments during particle synthesis. In this project, the two-line atomic fluorescence (TLAF) method was further developed for temperature determination in the flame synthesis of indium(III) oxide nanoparticles. Optical parametric oscillators (OPOs) were developed for the excitation of the fluorescence signals, which are characterised by a particularly narrow-band emission even without external seeding by continuous-wave lasers. To calibrate the pulsed TLAF technique, a laminar burner suitable for aerosol delivery was developed with a matrix in the form of a hexagonal close-packed sphere arrangement, which is clogged by precursor deposits or burn inhomogeneously over time due to condensation on cooled burner walls, even over long periods of operation. A modular and flexible setup for calibration-free TLAF measurements with tunable continuous wave lasers was adapted to the calibration burner. Measurements were carried out at various heights above the burner surface and for various fuel-air ratios. For point measurements, the signal was recorded using photomultipliers, whereby very low standard deviations of the temperature of 34 K on average could be achieved. By expanding the lasers to light sheets, 2-dimensional calibration-free TLAF measurements could be performed using an ICCD camera. Finally, temperature fields in a turbulent diffusion burner for spray flame synthesis of indium oxide particles could be successfully determined using pulsed TLAF. By simultaneous measurement in the calibration burner with a common setup, effects such as pulse energy fluctuations of the OPOs and changes in the beam profile could be directly included in the evaluation. Although the experimental approach proved to be complex and laborious, the central goal of a 2-dimensional temperature measurement in flame processes for the synthesis of nanoparticles could be achieved.
Publications
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Versatile tunable narrowband laser source for optical temperature measurements in combustion processes, 37th International Symposium on Combustion, Dublin, Irland, 29.07.2018 – 03.08.2018
M. Labus, B. Münsterjohann, F.J.T. Huber, S. Will
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Development of a tunable solid state laser for temperature measurement in combustion processes, International Conference on Advanced Optical Technologies, Erlangen, Deutschland, 13.03.2019 – 15.03.2019
M. Labus, F.J.T. Huber, S. Will
