Browsing by Author "Cordeiro, IMDC"

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    Atomistic characterisation of graphite oxidation and thermal decomposition mechanism under isothermal and non-isothermal heating scheme
    (Elsevier B. V., 2022-07) Cordeiro, IMDC; Yuen, ACY; Wang, W; Yang, W; Chan, QN; Yeoh, GH
    The oxidation of graphene-based material (i.e. graphite, graphene) is a reaction of immense importance owing to its extensive industrial application (i.e. nanocomposites, flame retardants, energy storage). Although immense experimental works were carried out for identifying the thermal degradation and oxidation process of graphene, they generally lack atomistic-level observation of the surface reactions, thermal formation pathways from solid to product volatiles and structural evolutions during oxidation. To analyse the favourable properties of graphene from its carbon-chain molecular structure viewpoint, it is essential to investigate graphene-based materials at an atomic level. This study bridges the missing knowledge by performing quantitative reactive forcefield coupled molecular dynamics simulation (MD-ReaxFF) to determine the oxidation kinetics of graphite under computational characterisation schemes with temperatures ranging from 4000 K to 6000 K. The kinetics parameters (i.e. activation energy) were extracted through proposed numerical characterisation methods and demonstrated good agreement with the thermogravimetric analysis experiments and other literature. Activation energy at 193.84 kJ/mol and 224.26 kJ/mol were extracted under the isothermal scheme by two distinct characterisation methods, achieving an average relative error of 11.3 % and 2.5 % compared to the experiment data, which is 218.60 kJ/mol. In comparison, the non-isothermal simulations yielded 214.53 kJ/mol, with a significant improvement on the average relative error of 1.86 %. © 2022 Elsevier B.V.
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    Numerical investigation of expandable graphite suppression on metal-based fire
    (Springer Nature, 2021-06-19) Cordeiro, IMDC; Liu, HR; Yuen, ACY; Chen, TBY; Li, A; Cao, RF; Yeoh, GH
    Aqueous suppression systems (i.e. fire sprinkler, water mist) have been extensively utilised for compartmental fire suppression due to their significant heat extraction ability. Nevertheless, challenges can be foreseen in suppressing water-reactive chemicals as a violent explosive reaction will be triggered, such as alkali metals (i.e. Na, Li) and alkali metal hydrides (i.e. LiH, LiAlH4). In this study, expandable graphite (EG) is proposed as a potential suppressant against alkaline metal fire due to its advantageous thermal properties and chemical stability. In-house user-defined functions (UDFs) are developed to characterise the particle expansion coupled with the heat and mass transfer process between EG and the fluid mixture. The model is incorporated in the large eddy simulation (LES) framework to study the temporal fire behaviours and the suppression effect of EG against the flame plume. The numerical model was validated by comparison of temperature profiles and expansion rate of EG particles along the suppression event against experimental results. The EG was found to be relatively effective in fire suppression compared to the same amount of natural graphite. Parametric analysis was conducted on a range of EG particle size between 400 µm—1000 µm to investigate the suppression mechanisms and the suppression efficiency of EG particles against metal fires. Within the range of the current study (400 µm—1000 µm), the EG particle diameter of 400 µm has achieved the most effective suppression performance and the suppression time of 2 s. It is observed that the smaller size of EG tends to be effective in fire suppression than the larger sizes. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021. This item has been added to APO for archival purposes. Springer Nature holds exclusive licence to publish. Usage is limited to academic research.
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    Simulation of competitive and cooperative egress movements on the crowd emergency evacuation
    (Elsevier, 2021-05-01) Cao, RF; Lee, EWM; Yuen, ACY; Chen, TBY; Cordeiro, IMDC; Shi, M; Wei, X; Yeoh, GH
    Empirical evidence suggests that evacuees tend to break down their well-coordinated motion and adopt competitive egress behaviour when they are confronting life-endangering situations (e.g., fire accident, earthquake). This phenomenon significantly influences crowd dynamics, and subsequently, the overall evacuation time. In this paper, a novel evacuation model has been developed, which takes the detailed cooperative and competitive egress movements of evacuees into consideration. The proposed model has been conducted to simulate crowd (i.e., with different proportion of competitive individuals within the crowd) evacuating from a single-exit compartment room (i.e., the exit width varies from 0.8 to 2.0m). Simulation results show that competitive evacuees exhibit an arc-shape formation in front of the bottleneck area (i.e., the exit). This is notably distinct from the cooperative evacuees generated shape formation. In addition, the evacuation performance (i.e., evacuation time, trajectories, density and flow rate) of competitive and cooperative evacuees over time are successfully captured for analysis. This study contributes to a better understanding of the crowd evacuation dynamics by considering the impact of competitive and cooperative egress movements. © 2021 Elsevier B.V.
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    Study of structure morphology and layer thickness of Ti3C2 MXene with small-angle neutron scattering (SANS)
    (Elsevier B. V., 2021-07-05) Yuen, ACY; Chen, TBY; Lin, B; Yang, W; Kabir, II; Cordeiro, IMDC; Whitten, AE; Mata, JP; Yu, B; Lu, HD; Yeoh, GH
    MXene is a class of 2D materials exfoliated from ternary carbide and nitride ceramics. During synthesis, etching and delamination conditions affect the quality, overall crystallinity, defects and surface functionalization of MXene flakes. In this article, the morphological structure of MXene (Ti3C2) nanosheets under temperature between 20 °C and 60 °C were investigated with the application of Small-Angle Neutron Scattering (SANS) combined with several complementary techniques, such as Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The SANS analysis enabled structural information to be obtained about the Ti3C2 nanosheets, which consists of layers of transition metal carbides in a multilayer lamella morphology. The results showed that a single Ti3C2 layer is approximately 11.4 – 11.8 Å (1.14 – 1.18 nm) in thickness with a 20.3 – 21.5 Å (2.03 – 2.15 nm) interstacking layer gaps. This results in a total thickness of approximately 32 Å (3.2 nm), which was consistent with the model-dependent lamella model analysis. Furthermore, the thickness of the Ti3C2 layer increased by approximately ~2 Å (0.2 nm) when the temperature increased from 20 - 40 to 50 - 60 °C. © 2021 The Author(s). Published by Elsevier B.V.