Optical roughness BRDF model for reverse Monte Carlo simulation of real material thermal radiation transfer

Abstract

Optical roughness was introduced into the bidirectional reflectance distribution function (BRDF) model to simulate the reflectance characteristics of thermal radiation. The optical roughness BRDF model stemmed from the influence of surface roughness and wavelength on the ray reflectance calculation. This model was adopted to simulate real metal emissivity. The reverse Monte Carlo method was used to display the distribution of reflectance rays. The numerical simulations showed that the optical roughness BRDF model can calculate the wavelength effect on emissivity and simulate the real metal emissivity variance with incidence angles.

Bidirectional reflectance measurement of tungsten samples to assess reflection model in WEST tokamak

“…al. 16 , adopted in their BRDF model the optical roughness instead of surface roughness. The optical roughness (σ opt ) can be expressed as the ratio between surface roughness (σ 0 ) and wavelength (λ ):…”

“…17 , the surface can be classified in 3 regions following to the surface roughness: (i) Specular region when 0 < σ opt < 0.2 for which Bennett Law can be applied to get directional reflectivity (ii) Intermediate region when 0.2 < σ opt < 1 or which approximate models are needed to describe BRDF (iii) Geometric region when σ opt > 1 for which geometric optics law can be used. Su et al 16 presented a plot of the BRDF for five incidence angles and three optical roughness values: 0.1, 0.2 and 0.3 for a pure specular surface. As seen in figure 7 reported by Su et al 16 , the maximum of the BRDF value is increasing for increasing angle and the FHWM is increasing for higher σ opt .…”

“…Su et al 16 presented a plot of the BRDF for five incidence angles and three optical roughness values: 0.1, 0.2 and 0.3 for a pure specular surface. As seen in figure 7 reported by Su et al 16 , the maximum of the BRDF value is increasing for increasing angle and the FHWM is increasing for higher σ opt . For = 0.9 µm (wavelength at which the BRDF is presented in Figure 7), the σ opt values are 0.063, 0.2, 0.59 and 1.24 for M100, M101, M102 and M103, respectively.…”