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Browsing Energy by Subject "Carbon nanotubes"

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    Characterization of carbon nanotube growth region in flame using wire-based macro-imaging method
    (Universiti Teknologi Malaysia, 2019) Hamzah, Norikhwan
    Carbon nanotube (CNT) synthesis in flame has enormous potential as an energy-efficient and economical production method compared to the conventional catalytic chemical vapor deposition (CCVD) synthesis process. However, synthesis control remains a great challenge for flame synthesis due to the limited understanding on the effect of flame inlet condition toward CNT growth region in a heterogeneous flame environment and premature catalyst surface encapsulation by the amorphous carbon layer. The present study formulates a simple, yet accurate method called wirebased macro image analysis (WMA) for thorough growth region identification. The WMA method is employed to investigate the effects of reactant composition and aerodynamics on the spatial distribution of CNT growth region. Besides that, bend wire method is developed to provide cross-sectional analysis of the CNT growth region with focus on the amorphous carbon layer thickness (ACLT) at variable reactant concentration including fuel from 50% to 100% and oxygen from 19% to 27%, with addition of water vapor up to 0.14 mg/sec mass flow rate within the fuel stream. The CNT is synthesized on a 0.4 mm diameter pure nickel wire within the methane diffusion flame with a stainless-steel wire mesh placed on top and water vapor is introduced in a fuel stream using a bubbler mechanism. The CNT growth region is confined within the flame sheet, gradually shifts from flame front to flame centreline as height above the burner increases. The growth region is more sensitive towards the change in the oxygen concentration compared to that of the fuel concentration due to the significant change of flame height caused by the former. A segregation of growth region temperature with temperature difference of 100 ? that is observed between the upstream and downstream growth region is governed by the proximity with respect to the flame sheet. The ACLT reduces in lean flame due to the reduction in excess carbon concentration and the addition of water vapor remarkably reduces ACLT by 17% on average in any combination of inlet conditions due to the water-induced etching and oxidation of amorphous carbon on the catalyst surface. Development of the WMA and bend wire method leads to deeper fundamental understanding of CNT flame synthesis and further enhance possibility of highly efficient and economical CNT production process in the future.
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    Multi-scale modelling on the effects of flame parameters on carbon nanotube growth in non-premixed flames
    (Universiti Teknologi Malaysia, 2021) Zainal, Muhammad Thalhah
    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.