The temperature measurement has great significance for the combustion diagnostics and the study of flame characteristics. In this paper, an optical sectioning tomographic (OST) technique for 3-D flame temperature measurement combined with light field imaging is proposed. First, the fundamental principle of light field OST is introduced in detail. Then, to determine the refocused depth, the point spread functions of the light field camera, and the relationship between the radiation intensity of flame and image gray value, the calibration works are carried out. Furthermore, the images of different sections of flame are acquired by the digital refocusing technology, and then the high-precision and real-time radiation intensity distribution of each section can be reconstructed using a tomographic reconstruction algorithm. Finally, in combination with the relationship between the image gray value and radiation intensity of flame, the 3-D flame temperature distribution can be calculated. The flame experiments of a candle and a single biomass particle in a fluidized bed under oxy-combustion conditions are performed to evaluate the light field OST system. Results show that the reconstructed results are in good agreement with the temperature distribution of the combustion flame. Compared with the traditional optical sectioning tomographic techniques, the light field OST has the advantages of simplicity of measurement system and fast response, and being suitable for 3-D temperature measurement of turbulent flame.

Optical Sectioning Tomographic Reconstruction of Three-Dimensional Flame Temperature Distribution Using Single Light Field Camera

Investigation of double-layer coating pigmented with CuO particles of different concentrations on aesthetic and thermal aspects

\n The history and progress in Monte Carlo methods applied to radiative energy transfer are reviewed, with emphasis on advances over the past 25 years. Unresolved issues are outlined, and comments are included about the outlook for the method as impacted by the advances in massively parallel and quantum computers.

The Past and Future of the Monte Carlo Method in Thermal Radiation Transfer

Application of the lattice Boltzmann method (LBM) recently proposed by Asinari et al. [ Asinari P , Mishra SC , Borchiellini R. A lattice Boltzmann formulation to the analysis of radiative heat transfer problems in a participating medium. Numer Heat Transfer B 2010; 57:126–146 ] is extended to the analysis of transport of collimated radiation in a planar participating medium. To deal with azimuthally symmetric radiation in planar medium, a new lattice structure for the LBM is used. The transport of the collimated component in the medium is analysed by two different, viz., flux splitting and direct approaches. For different angles of incidence of the collimated radiation, the LBM formulation is tested for the effects of the extinction coefficient, the anisotropy factor, and the boundary emissivities on heat flux and emissive power distributions. Results are compared with the benchmark results obtained using the finite volume method. Both the approaches in LBM provide accurate results.

Analysis of transport of collimated radiation in a participating media using the lattice Boltzmann method

The DRESOR method for transient radiation transfer in 1-D graded index medium with pulse irradiation

This paper extends the DRESOR (Distribution of Ratios of Energy Scattered by the medium Or Reflected by the boundary surface) method to radiative transfer in a variable refractive index medium. In this method, the intensity is obtained from the source term along the curved integration paths determined only by the variable refractive index, and the DRESOR values are calculated by the Monte Carlo method in which the propagation of the energy bundles are affected by Snell's law. With given temperatures on the black boundaries of a one-dimensional medium, the temperature distribution inside the medium with a variable scattering property is calculated under the condition of radiative equilibrium. It is shown that the DRESOR method has a good accuracy in the cases studied. For an isotropic-scattering medium with the same optical thickness, the scattering albedo has no effect on the temperature distribution, which can be obtained from the general equations and can be seen as an extension of what exists for a constant refractive index; however, the different refractive index causes obvious changes in the temperatures inside the medium. The effect of anisotropic scattering on the temperature distribution cannot be ignored, although it is still weaker than the effect caused by variation in the refractive index.

The DRESOR method for radiative heat transfer in a one-dimensional medium with variable refractive index

Equation-solving DRESOR method for radiative transfer in a plane-parallel, absorbing, emitting, and isotropically scattering medium with transparent boundaries

Distributions of ratios of energy scattered or reflected (DRESOR) method is a very efficient tool used to calculate radiative intensity with high directional resolution, which is very useful for inverse analysis. The method is based on the Monte Carlo (MC) method and it can solve radiative problems of great complexity. Unfortunately, it suffers from the drawbacks of the Monte Carlo method, which are large computation time and unavoidable statistical errors. In this work, an equation solving method is applied to calculate DRESOR values instead of using the Monte Carlo sampling in the DRESOR method. The equation solving method obtains very accurate results in much shorter computation time than when using the Monte Carlo method. Radiative intensity with high directional resolution calculated by these two kinds of DRESOR method is compared with that of the reverse Monte Carlo (RMC) method. The equation solving DRESOR (ES-DRESOR) method has better accuracy and much better time efficiency than the Monte Carlo based DRESOR (original DRESOR) method. The ES-DRESOR method shows a distinct advantage for calculating radiative intensity with high directional resolution compared with the reverse Monte Carlo method and the discrete ordinates method (DOM). Heat flux comparisons are also given and the ES-DRESOR method shows very good accuracy. [DOI: 10.1115/1.4025133]

Equation Solving DRESOR Method for Radiative Transfer in Three-Dimensional Isotropically Scattering Media

The DRESOR (Distribution of Ratios of Energy Scattered by the medium Or Reflected by the boundary surface) method is applied for radiative heat transfer in a one-dimensional medium with a nonlinear gradient index and gray boundary surfaces. In this proposed method, the DRESOR values calculated by the Monte Carlo method express quantitatively the impact of scattering on radiative transfer and the radiative intensity with high directional resolution of high precision can be easily obtained. With given media characteristics and boundary conditions, the temperature and radiative flux distributions inside the medium are calculated under the condition of radiative equilibrium. It is shown, in the cases studied, that the DRESOR method has a good accuracy. The temperature distributions have a node with different kinds of sine changed gradient index distributions under the same boundary emissivity. The impact of the gradient index on the radiative heat transfer is considerable, and the same as that of the ratios of its amplitude and average index. Besides, the effects of optical thickness, boundary emissivity and scattering phase function on radiative transfer also should be paid adequate attention.

https://iopscience.iop.org/article/10.1088/1742-6596/369/1/012004/pdf

Effects of nonlinear gradient index on radiative heat transfer in a one-dimensional medium by the DRESOR method

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The DRESOR method for radiative heat transfer in a one-dimensional medium with variable refractive index

Equation-solving DRESOR method for radiative transfer in a plane-parallel, absorbing, emitting, and isotropically scattering medium with transparent boundaries

Equation Solving DRESOR Method for Radiative Transfer in Three-Dimensional Isotropically Scattering Media

Effects of nonlinear gradient index on radiative heat transfer in a one-dimensional medium by the DRESOR method