A comprehensive review analysing the recent development in growth control enhancement of carbon nanotube synthesis in flame environment.

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A two‐dimensonal Tesla micromixer is experimentally characterized at varying Reynolds numbers (Re) and valve stages with the aim to acquire sufficiently high mixing performance. To ease fabrication, a simplified Tesla valve design is adopted. Results show two distinctive regimes of low and high Re. In the low‐Re regime, a steady incremental mixing was observed as the fluid passes by each valve, whereas an enhanced mixing was identified right in the first valve in the high‐Re regime. This is predominantly due to the amplified opposing flow from the helix branch which promotes stronger chaotic advection in the main microchannel. Interestingly, the measured mixing performance was found comparable to that of three‐dimensional passive micromixers reported in the literature.

Control improvement of carbon nanotubes synthesis in flames requires synergistic computational and experimental studies. The present study investigated distribution of carbon nanotubes growth region within methane diffusion flame using acid dipped nickel wire. The carbon nanotubes growth occurred in a narrow range between 4 to 6 mm height above the burner. Nickel wire oxidation in nitric acid within 90 seconds to 260 seconds favors formation of carbon nanotubes. Prediction of the carbon nanotubes growth region using multi-scale modelling method achieved a reasonable agreement with the experimental results though the region of no growth was not reproduced due to the exclusion of soot formation modelling.

Synthesis of carbon nanotubes in flames has become highly attractive due to its rapid, inexpensive, and simple method of production. The study of flame synthesis of carbon nanotubes revolves around the control of flame and catalyst parameters to increase the synthesis efficiency and to produce high quality nanotubes. The control parameters include flame temperature, concentration of carbon source species, catalyst type, equivalence ratio, and fuel type. Carbon nanotubes which are produced with rapid growth rate and possess high degree of purity and alignment are often desired. The present study reviews various optimization techniques from the advanced studies of chemical vapour deposition which are applicable for the synthesis of nanotubes in flames. The water-assisted and catalyst free synthesis are seen as possible candidates to improve the growth rate, alignment, and purity of the synthesized nanotubes. The state-of-the-art of the flame synthesis modelling at particle and flame scales are reviewed. Based on the thorough review of the recent experimental findings related to the catalytic growth of nanotube, possible refinement of the existing particle scale model is discussed. The possibility of two-way coupling between the two scales in computational fluid dynamics may be a major contribution towards the optimization of the flame synthesis.