Zhi-Feng Huang

The Solution of Transient Radiative Transfer With Collimated Incident Serial Pulse in a Plane-Parallel Medium by the DRESOR Method

A time-dependent distribution of ratios of energy scattered by the medium or reflected by the boundary surfaces (DRESOR) method was proposed to solve the transient radiative transfer in a one-dimensional slab. This slab is filled with an absorbing, scattering, and nonemitting medium and exposed to a collimated, incident serial pulse with different pulse shapes and pulse widths. The time-dependent DRESOR values, representing the temporal response of an instantaneous, incident pulse with unit energy and the same incident direction as that for the serial pulse, were proposed and calculated by the Monte Carlo method. The temporal radiative intensity inside the medium with high directional resolution can be obtained from the time-dependent DRESOR values. The transient incident radiation results obtained by the DRESOR method were compared to those obtained with the Monte Carlo method, and good agreements were achieved. influences of the pulse shape and width, reflectivity of the boundary, scattering albedo, optical thickness, and anisotropic scattering on the transient radiative transfer, especially the temporal response along different directions, were investigated.

Existence of Dual-Peak Temporal Reflectance from a Light Pulse Irradiated Two-Layer Medium

The transport process of ultra-short light pulse propagation inside the nonemitting, absorbing, and scattering two-layer media is studied. Under the appropriate combination of the pulse width and scattering property of the probed medium, the temporal signal of the reflectance exhibits a direct correlation between the reflectance signal rise time and the location of the interface. The geometry under study is a two-layer structure. This study extends a prior work by authors, giving more extensive numerical simulations to rigorously test and revise the conditions of the optimal pulse width, which would reveal the dual-peak in the temporal reflectance signals.

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]

Improved Discrete Ordinates Method for Ray Effects Mitigation

A new and improved method based on the discrete ordinates scheme with infinitely small weights (DOS+ISW) is developed for radiative heat transfer in three-dimensional participating media. To demonstrate the effectiveness of the method, ray effects caused by 1) abrupt step changes in the boundary conditions and 2) the stepwise variation of the medium emissive power are discussed. In this work, angular quadrature sets with large number of discrete ordinate directions are chosen to mitigate ray effects, while at the same time keeping the computational time increase to a minimum. Comparing with the conventional discrete ordinates method, the difference is that intensities in these directions are calculated by DOS+ISW. Intensity with fine directional resolution calculated by this method is validated by comparing with that of Reverse Monte Carlo method. The large number of discrete ordinates directions used in the new method becomes computationally prohibitive in discrete ordinates method due to the increased computer memory and computation time requirements.© 2009 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.

A Hybrid Partial Coherence and Geometry Optics Model of Thin Film Optics on Coated Rough Surfaces

Thermal and optical engineering applications of electromagnetic wave reflectance from rough surfaces include temperature measurement, radiation heating process, etc. Most of the surfaces are random roughness and often with coating material different from the substrate. This paper presented a novel hybrid partial coherence and geometry optics (HPCGO) model to improve the generic geometry optics (GO) method 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. First, the HPCGO model is validated by more rigorous Maxwell equations solvers, for example, the finite-difference timedomain (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 partial or non-coherent scattered light even if the incident light source is coherent. It also shows the coherence effect reduces with increased incident wave-number bandwidth.