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Nanoparticle transport and deposition in boundary layer of stagnation-point premixed flames
- Source :
-
Powder Technology . Sep2012, p24-34. 11p. - Publication Year :
- 2012
-
Abstract
- Abstract: Nanoporous TiO2 thin films are deposited directly onto substrates by a one-step stagnation flame synthesis with organometallic precursors. The deposition mechanism in the stagnation-point boundary layer is intensively studied. For the first time, the radial profile of nanoparticle deposition flux is measured using a novel method of concentric collecting rings, which exhibits similar trend with the heat flux profile of stagnation-point flows. Then, we develop the mathematical model of nanoparticle transport and deposition in the stagnation-point boundary layer for further clarifying experimental results, especially the effects of substrate temperatures and in-situ produced particle sizes. Both thermophoresis in an inner part of boundary layer and thermal compression/expansion of the gas phase are found to play important roles in determining the deposition flux. The contribution of Brownian diffusion, determined by a thermophoretic Peclet number, is inappreciable compared to thermophoresis until particle diameter is as small as 2nm. The results in this work support a conclusion of size-independence of the thermophoretic velocity, implying that the rigid-body collision assumption of Waldmann''s formula is not accurate for small particles especially less than 10nm. This study can be generally applied to other deposition techniques of thin films. [Copyright &y& Elsevier]
Details
- Language :
- English
- ISSN :
- 00325910
- Database :
- Academic Search Index
- Journal :
- Powder Technology
- Publication Type :
- Academic Journal
- Accession number :
- 77338614
- Full Text :
- https://doi.org/10.1016/j.powtec.2011.12.035