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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]

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]

This paper presents numerical studies of large-size and high-quality fused silica glass synthesis by SiCl 4 flame hydrolysis deposition method, specifically the correlation of uniformities of SiO 2 deposition and OH concentration with the optimal location of the substrate placement. A comprehensive computational model is developed to describe the complex turbulent reacting flow with the detailed SiCl 4 -H 2 -O 2 reaction mechanism. Numerical simulation is first conducted to obtain the characteristics of SiCl 4 hydrolysis flame without considering the substrate and the SiO 2 particle formation. The distribution of SiO 2 accumulation is then calculated. The potential region and location for placing substrate are initially determined based on the criterion of a uniform SiO 2 accumulation. Further, the effects of H 2 -O 2 equivalence ratio and the SiCl 4 flow rate on the distributions of the temperature, SiO 2 concentration and OH concentration are investigated. It is found that the H 2 -O 2 equivalence ratio is sensitive to the temperature and the OH concentration, and the flow rate of SiCl 4 mainly affects the temperature and SiO 2 concentration. This finding indicates that the H 2 -O 2 equivalence ratio and the flow rate of SiCl 4 have equally important roles in determining the optimal location for the deposition substrate placement. The presence of the substrate also changes the distributions of the temperature and compositions concentrations in the furnace. Adjusting the substrate location is an effective strategy to achieve optimal location with more uniform distributions of the SiO 2 accumulation and the OH concentration on the deposition surface. [ABSTRACT FROM AUTHOR]

• Transient heat flux can be predicted with machine learning algorithm. • The material temperature dependent parameters are not sensitive to the model. • The temperature changing trending is a necessary input of the model. • The predict model response time can achieve less than 1s with high accuracy. The traditional transient heat flux measuring instrument has harsh working conditions and high cost, which is not conducive to promoting the wide range of applications in the engineering manufacturing area. A novel transient heat flux measuring method based on Gradient Boosting Decision Tree (GBDT) algorithm is proposed in this paper. The new measurement method consists of a thermal receptor, a thermocouple, and a data processing device. The system can measure the heat flux absorbed by the thermal receptor through collecting the temperature tendency. This turns the complex problem of heat measurement into a simple problem of temperature measurement, which can greatly reduce the cost of measuring equipment. In this work, numerical simulation was also concerned, and related experiments were designed to verify the feasibility of the method. The GBDT method has demonstrated significant predictive accuracy in both cases. The relative errors of the model trained by the simulation data and the experimental data are 0.8% and 2.9%, respectively. The relative error of GBDT measurement method is less than 5.99% and the response time is 0.3s, which can meet most engineering needs. This work has broad application scenarios and commercial prospects. [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]