EFFECT OF PARTICLE SCATTERING ON SPECTRAL ABSORPTIVE CHARACTERISTICS OF SEMITRANSPARENT FLUID LAYER
The effect of particle scattering on the absorptive characteristics of a semitransparent fluid layer is investigated by the Monte Carlo method. A one dimensional parallel plane model is used for the fluid layer. By the Fresnel's equation , the refraction and reflection of spectral radiation at the semitransparent and specular incident surface are considered along with the diffusive reflection at the opaque gray wall. Several kinds of typical scattering distributions are considered with the H-G phase function for the particles in the nongray absorbing semitransparent fluid. Taken as an example, a water layer containing particles is irradiated by an incident spectral radiation perpendicular to the surface. For the various scattering distributions, the overall spectral absorptivity of the water layer is presented along with the absorptive distribution for different positions inside the layer, which is described by a spectral absorptive distribution function introduced in this paper. By analyzing the calculated results, the influences on the absorptive characteristics of a semitransparent fluid layer are investigated , which come from the scattering distribution and albedo as well as the absorbing factor of the particles . From this investigation, the following conclusions are derived. First, particle scattering can greatly change both of the overall absorptive ability and the absorptive distribution function of a semitransparent fluid layer. The influences show multi-variable and nonlinear dependence on the fluid layer optical thickness and the absorptive factor, extinction coefficient, scattering phase function and albedo of particles. Second, the optical thickness of the fluid layer and the absorptive factor of particles exert an independent and monotonous influence that the increase of either can directly enlarge the absorptivity of the fluid layer. However,particle scattering affects the absorptive characteristics by changing transfer directions of radiation in the fluid layer, thus its influence depends on the fluid layer optical thickness and the absorbing ability of particles and therefore is dependent and nonmonotonous. Third,scattering distribution reacts differently under different scattering intensity . But for different scattering distributions, the absorptive distribution function reaches peak values almost at the same depth inside the fluid layer, and the peak occurrence moves toward the wall with decrease of scattering intensity.