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Optimizing the combustor geometry of micro thermophotovoltaic system can improve combustion conditions of the fuel and performance of the system. To accelerate the optimization process, a novel technique is proposed in this work by combining numerical simulation and machine learning. The influences of combustor geometric parameters on flame shape, wall temperature and combustor performance are investigated via numerical simulations which have been validated by experiment. Results show the length and diameter of inlet passage are important factors in affecting the flame shape. Also, all geometric parameters have great impacts on the performance of combustor. The data from simulations are then used to train the artificial neural network and the output of the network is compared with the simulations to determine whether the optimization is successful. Finally, the radiation power of combustor is optimized to 34.51 W from its initial value of 24.8 W using only 197 data samples. [Display omitted] • Effects of geometric parameter on flame shape and combustor performance are analyzed. • A novel technique by combining numerical simulation and machine learning is proposed. • The radiation power is improved to 34.51 W from its initial value of 24.8 W. [ABSTRACT FROM AUTHOR]

Hexamethyldisiloxane [HMDSO, (CH3)3‐SiOSi‐(CH3)3] is an important precursor for SiO2 formation during flame‐based silica material synthesis. As a result, HMDSO reactions in flame have been widely investigated experimentally, and many results have indicated that HMDSO decomposition reactions occur very early in this process. In this paper, quantum chemical calculations are performed to identify the initial decomposition of HMDSO and its subsequent reactions using the density functional theory at the level of B3LYP/6‐311+G (d, p). Four reaction pathways—(a) SiO bond dissociation of HMDSO, (b) SiC bond dissociation of HMDSO, (c) dissociation and recombination of SiO and SiC bonds, and (d) elimination of a methane molecule from HMDSO—have been examined and identified. From the results, it is found that the barrier of 84.38 kcal/mol and SiO bond dissociation energy of 21.55 kcal/mol are required for the initial decomposition reaction of HMDSO in the first pathway, but the highest free energy barrier (100.69 kcal/mol) is found in the third reaction pathway. By comparing the free energy barriers and reaction rate constants, it is concluded that the most possible initial decomposition reaction of HMDSO is to eliminate the CH3 radical by SiC bond dissociation. [ABSTRACT FROM AUTHOR]

Silica nanoparticles have been widely applied in many fields due to their excellent properties. SiO2 generation is crucial for silica particle formation, but in a swirling reactor the SiO2 generation is still unclear. In this study, numerical simulations are performed to investigate the SiO2 generation and distributions of temperature and velocity during silica particle synthesis using a swirling reactor. A computational model is first developed to describe the heat and mass transport in the swirling turbulent flame. Simulation models are validated with experimental data in the case without SiO2 chemistry. Then, effects of the fuel velocity and swirl number on SiO2 generation are investigated. Results show that most of the SiO2 molecules are generated in the region far away from reactor inlets and a relatively high SiO2 generation efficiency is obtained for a fuel velocity of 32.7 m/second. Distributions of the flame temperature, velocity and SiO2 concentration are found to vary with the swirl number and high chemical reaction rates for SiO2 generation are obtained when a swirl number of 0.5 is employed. Uncertainty analysis shows that the average relative errors of the results from different models are within 18%. [ABSTRACT FROM AUTHOR]

Abstract Large-size and high-purity fused silica glass fabricated by chemical vapor deposition (CVD) has been widely applied to many advanced optical systems. The deposition process is critical during fused silica glass synthesis. In this study, SiO 2 deposition at the substrate is modelled and analyzed. First, numerical simulations are performed with the computational fluid dynamics method to predict the flame feature. The gas temperature and velocity agree well with the experimental data. Then, the predicted distributions of gas temperature and concentrations are used as the input parameters to a two-dimensional soot dynamic model. The particle characteristics and particle deposition at the substrate are analyzed. It is found that the particle number density first increases and then decreases in the flame along the axial and radial directions. The predicted mean diameter of the particle is smaller than 50 nm near the substrate surface. The mechanism for SiO 2 deposition is different along the substrate surface. In the central region of substrate, the particle deposition is dominant, while in the exterior region the surface chemical deposition is more important. [ABSTRACT FROM AUTHOR]

With the development of modern optical systems towards large scale, the fused silica glass with a large size is receiving increasing attention. In this paper, multi-burner chemical vapor deposition technique was proposed to synthesize the large-sized fused silica glass, and an integrated computational model was used to describe the fluid flow, combustion and heat transfer in the furnace. The effects of various process parameters on the distributions of temperature and species were investigated. Based on the evaluation of temperature and key species concentrations on deposition surface, the size and quality of the synthesized fused silica glass were indirectly estimated. Results showed that reducing the deposition surface height and increasing the number of burners could improve the temperature and species concentrations on the deposition surface, while an increase in the number of furnace outlets led to their decreases. The use of two burners would lead to the formation of discontinuous glass regions at the current conditions and a circular glass structure was generated when employing three burners and deposition surface height of 0.5 m, based on the proposed temperature criterion. The combined process parameters of four burners, deposition surface height of 0.5 m, H 2 /O 2 equivalence ratio of 1.00 and two furnace outlets are be of advantage to synthesize the large-sized and high-quality fused silica glass at current sizes and structures of the furnace and burner. [ABSTRACT FROM AUTHOR]