Radiation Heat Transfer Characteristics Of Optical Large Particulate System

In nature and industrial production,many substances,product s are in particulate state.The radiation characteristics of particulate media have applications in atmospheric science and environment,remote sensing and nuclear.There are many applications using particulate media that the particles are densely packed,such as in many granular beds and fluidized bed.Radiative heat transfer in particulate systems is usually based on a continuous medium model,radiation transfer theory,which is analyzed by solving the radiation transfer equation.However,the classical radiative transfer equation is only applicable to sparse particle systems.For dense particle systems,the applicability of the traditional radiative transfer equation is doubtful because of the serious shadowing effect.At present,the problem of radiative heat transfer of dense optical large particle system lacks an effective analytical theory,and there is still a lack of understanding of its radiation heat transfer characteristics.In this paper,the radiative heat transfer characteristics of optical large particle systems are studied based on particle size radiation tra nsmission simulations.For systems composed of large optical particles,the analysi s of their radiative heat transfer can be based on the principle of geometrical op tics.In this paper,a method based on Monte Carlo method is developed to simulate the propagation of thermal radiation photons at the particle scale,and the particl e radiation distribution factor(RDF)is used to describe the spatial distribution of radiation heat transfer in the particle system.The Monte Carlo method based on the par ticle scale can effectively simulate the radiation heat transfer of the particle system,and can fully consider the shadowing effect between particles.Startin g from the particle energy balance equation,a calculation model of the RDF is established based on the Monte Carlo method,and a theoretical model of the RDF i s established through theoretical derivation.Based on the established calculation model,the radiation heat transfer characteristics of the particle system under the condition of two kinds of heat radiation light sources,that is particle radiation sources and laser light sources,are studied.The influence of different surface types,filling ratio,surface emissivity,and the radius of laser on the distribution of RDF.In this paper,we have derived the spatial distribution of RDF when particles are randomly arranged in the particle radiation source is deduced and verified by direct particle-scale simulation.It is revealed that when the particles are randomly arranged,the radial distribution of the RDF obeys the combination of the inverse square rate and the exponential attenuation.Under the same conditions,the distribution of RDF on the diffuse surface and the specular reflection surface is basically the same.When particles are randomly arranged in the case of a laser light source,the law of the RDF along the central axis is exponentially attenuated and approximates to the Bouguer's law.But when the particles are arranged regularly,the RDF does not decay exponentially because of the regularity of its distribution,and the RDF presents an anisotropic spatial distribution.