Huaichun Zhou

Simultaneous Measurement of Three-Dimensional Temperature Distributions and Radiative Properties Based on Radiation Image Processing Technology in a Gas-Fired Pilot Tubular Furnace

An on-line three-dimensional temperature measurement experiment was carried out in a gas-fired pilot tubular furnace. Four flame image detectors were utilized to obtain two (red and green) monochromatic radiation intensity distributions, which can be calculated by the DRESOR method based on the radiation image processing technology. Then a revised Tikhonov regularization method was developed to reconstruct three-dimensional temperature distributions from the green monochromatic radiative intensity. Meanwhile, a Newton method combined with a least-squares method was used to simultaneously reconstruct radiative properties from the red one. The two calculation procedures were performed alternately, forming an iterative algorithm to a simultaneous reconstruction of temperature and radiative properties. The reconstructed temperatures agreed well with those measured by thermocouples for different cases with different calorific values and components of gas. The largest relative error was less than 3%, which validated the effectiveness and accuracy of this reconstruction algorithm. Moreover, the nonuniform radiative properties for the flame and nonflame regions were determined to improve the accuracy of temperature measurement by a rigorous comparison test. Finally a set of reasonable fixed radiative properties for the media and walls was chosen for the on-line detection of temperature. The visualized temperatures obtained by the present method agreed reasonably with those measured by thermocouples for all cases, with the largest relative error less than 5%. The present method based on radiation image processing technology is reliable for on-line temperature measurement and shows a good accuracy for its application in the combustion industry.

The effect of BRDF surface on radiative heat transfer within a one-dimensional graded index medium

The traditional diffuse or specular surface assumption is insufficient to fully characterize a real surface.The BRDF surface is introduced into the radiative heat transfer problem for the first time.A Minnaert model for the BRDF surface is applied and the genetic algorithm is used to obtain the parameters of the proposed model.The DRESOR method and the RMC method are extended to solve the radiative heat transfer within a 1-D absorbing,emitting and scattering graded index medium with BRDF surfaces.The results obtained by the DRESOR method and the RMC method indicate the accuracy of the calculation.Compared with the corresponding diffuse surface,though the relative temperature difference of the BRDF surface is ±1.5%,the radiative flux increases significantly by±10.5%.This is enough to cause large error,which should be pay attention to in the radiative heat transfer problem.

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

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]

A Hybrid Partial Coherence and Geometry Optics Model of Radiative Property on Coated Rough Surfaces

Thermal and optical engineering applications of electromagnetic wave scattering from rough surfaces include temperature measurement, radiation heating process, etc. Most of the surfaces have random roughness and are often with coating material different from the substrate. However, the understanding of radiative properties of coated rough surfaces is not well addressed at this point. This paper presented a novel hybrid partial coherence and geometry optics (HPCGO) model to improve the generic geometry optics (GO) prediction by incorporating a previously developed partial coherence reflectance equation. In this way, HPCGO expands the applicable region of GO model and largely reduces the computation time of integrating different wavelength results in the regular hybrid model that considers coherence effect only. In this study, the HPCGO model is first compared with the more rigorous Maxwell equations solvers, the finite-difference time-domain (FDTD) method, and integral equation (IE) method. Then, the HPCGO model is applied to study the coherent effect of directional-hemispherical reflectance from coated rough surfaces. It is found the roughness of coated rough surface can cause partially coherent or noncoherent scattered light even if the incident light source is coherent. It also shows the reflected electromagnetic wave’s coherence effect reduces with increased coating thickness and surface roughness, besides the previously recognized incident wave-number bandwidth. The effect of reduce coherence in scattered wave is quantified. Finally a regime map, even limited in the roughness and coating thickness dimensionless parameter ranges, provides the region of validity of the HPCGO model. [DOI: 10.1115/1.4024466]

Analysis and Optimisation of Two-Dimensional Silicon Complex Grating With Different Ridge Heights or Groove Depths for Solar Cells

In this study, two kinds of two-dimensional (2D) complex gratings are proposed for a potential application as absorbing surfaces for solar cells in the visible and near-infrared wavelength regions, which are based on the superposition of multiple 2D simple gratings with different ridge heights for convex gratings or different groove depths for concave gratings, respectively. Silicon is selected as the complex grating material because it is common in micro/nanofabrication. Compared with one-dimensional (1D) gratings, the new structures present excellent radiative properties to rays from all directions. Besides, the new gratings can achieve satisfactory performance under both TM and TE waves, which cannot be easily obtained by 1D gratings. Furthermore, these two kinds of 2D complex gratings can both achieve higher absorptance in the whole of the interested spectral range by making full use of the microcavity resonance than 2D simple gratings with the same ridge height or groove depth. Taguchi method is employed as an efficient way of searching for the optimal profiles for the 2D complex gratings. The average spectral absorptance of the optimized structure for the 2D complex convex grating with two different ridge heights is above 0.93 within wavelength region from 0.3 to 1.1 μm for both TM and TE waves under normal incidence, which suggests that the proposed structures can be well suitable for solar absorber applications. The Finite-different time-domain (FDTD) method is used for all numerical calculations to obtain spectral absorptance of different structures.© 2013 ASME

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

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.