Acoustic Modulation on Flame Synthesis of Carbon Nano-Materials

• Main Authors: De-HuaChung, 鍾德華
• Other Authors: Ta-Hui Lin
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/07693399052810230030

博士 === 國立成功大學 === 機械工程學系碩博士班 === 100 === Acoustically modulated ethylene jet diffusion flame was used in the synthesis of carbon nano-materials. The cold-flow axial velocity and gas concentration were simulated to search the suitable condition of synthesizing. The flame types were observed in an ethylene jet flow with mean velocity of 20 cm/s and acoustic frequency (f) of 0 ~ 80 Hz. Double-layer flame was formed at f = 10 ~ 20 Hz and 60 ~ 70 Hz because of resonance near the natural flickering frequency and acoustically resonant frequency, respectively. The former was caused by the flame/buoyancy coupling, while the latter was caused by the acoustics/fuel line coupling. However, the double–layer flame was only a single-layer flame, which was formed by the persistence of vision with quick change of flame diameter. There were shuttle-, cone- and mushroom-like flames observed in the instantaneous flames. The Schlieren images of vortices would be caught due to the change of refractive index, which was resulted in with heat transfer. The sequence of Schlieren images were determined by vortex growth in the cold flow simulation. The isopleths (cold flow simulation) of axial velocity and ethylene concentration matched respectively the vortical motions and Schiliren images in the flow field. It can help to analyze the suitable condition for flame synthesis. The carbon nano-onions (CNOs) were mainly deposited grape-likely on the Ni substrate. The amount of CNOs at f = 10 and 66 Hz were both formed much more those formed at f = 0 Hz (z = 5 and 10 mm). At the other frequency (f = 30 ~ 50 and 80 Hz), the amount of CNOs were less those at two resonant regions (f = 10 and 66 Hz), but more than those without acoustic modulation (f = 0 Hz). CNOs would be decreased with the decreasing of ethylene concentration, even carbon nanotubes (CNTs) would replace CNOs to be the main product at ethylene concentration 20% and f = 10 Hz.