Multi-scale modelling on the effects of flame parameters on carbon nanotube growth in non-premixed flames
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Date
2021
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Universiti Teknologi Malaysia
Abstract
Flame synthesis is a rapid and cost-efficient method to produce carbon nanotube (CNT). However,the high uncertainty of CNT grow thregion in flames hinders up- scaling effort and essentially limits the broad application of CNT invarious industries. A comprehensive multi-scale model that predicts the CNT grow thregion in flame synthesis is deemedessential to address the problems.However,the existing state-of- the-art model still requires significant improvement in termsofaccuracy.Further more, the lack of systematic study on the carbon precursorand the stoichiometricmixture fraction zst hinders the improvement of growth control in flame synthesis.Therefore, the present study’s main goal was to refine further the available multi-scalemodel that couples computational fluid dynamics(CFD) and agrow thrate(GR) modeland investigate the effects ofcarbon precursor and zst on CNT growth in non-premixed flames. First,the published GR model was employed to investigate the dominant precursor for CNT growth and to assessthemethodsfordeterminingtheCNTgrowth region. Then,acoupledcomputationof the GR model and the CFD flame model was carried out.Adetailed chemistry simulation was employed in the CFD to improve the previous flame model based on simple chemistry.Effects of temperature and carbon source on CNT growth were described via thermodynamic analysis.Finally, a correlation for the CNT growth region was developed for no n-premixedflames with varying burner operating conditions.Extensive validation of the present multi- scale model demonstrated remark able accuracy improvement by 20% and 50% for temperature and CNT growth egion prediction,respectively,compared to the previous multi-scale model.Furthermore,the in accurate physics of the previous multi-scale model that failed to predict CNT growth with in the carbon-richregion was corrected in the present model.Investigation on thedominantcarbonprecursorusingtheGR model showedthathydrocarbon(acetyleneC2H2) andcarbonmonoxideCOwerethe precursors for CNT growth.On the other hand,thermodynamic analysis based on the presentmulti-scalemodelshowedthatlighthydrocarbons(methaneCH4, ethylene C2H4, and C2H2) were the potential precursors for CNT growth.Thesame analysis also indicated that carbon precursorf or CNT growth varied with the type of fuel employed.The effect of zst on CNT growth was demonstrated by the developed linear (zlb = 1:54zst + 0:11) and quadratic(zhb = zst ¹7 - 13zst )) correlations for the low and high boundaries of the CNT growth region,respectively.The said correlations showed that the CNT growth regione xpandsat0.050.25. The developed correlation sapply to various burner operating conditions as governed by the parameter zst . They are envisaged to cut down the required resources and time associated with finding the CNT growth region in future experimental start-upsand massproduction of CNT.
Description
Thesis (PhD (Mechanical Engineering))
Keywords
Carbon nanotubes