Studies On Internal Absorption Distribution Of Thermal Radiation In Asymmetrically Illuminated Microscale Particle

In the real word,various microscale particles are often used as the main objects of studies and exposed to researchers for many engineering applications as well as all kinds of scientific researches,such as the raindrops,PM 2.5,the carbon particles in combustion systems,the thermal therapies in biological science and so on.The interaction of these particles with thermal radiation,such as absorption,emission and scattering,plays an important role in these engineering problems,and has become the focus of research in related fields.In engineering applications,most utilize geometric optics methods studying the radiation properties of large particles and the Mie’s theory for microscale particles.They focus on the overall properties of these particles,and the absorption has been treats as a surface interaction.However,there are certain applications,such as aerospace refrigeration,the phenomenon of micro-explosion and thermal therapies,for which the internal distribution of radiative energy absorption can be of critical importance.In this way,this study focus on the radiation absorption distribution in the particles.The finite-difference time-domain method(FDTD)is utilized to study the local absorption distribution in asymmetrically illuminated microscale spherical particles.The Mie’s theory is adopted to verify the accuracy of FDTD method.The results show that the scattering efficiencies obtained by these two methods are closely the same while the absorption efficiencies slightly differ at the studied parameters.The internal dimensionless absorption distribution function is defined to study the absorption distribution inside the particles.It shows that size parameter can be utilized to describe the influence of particles size on absorption distribution.When the particle size parameter is close to 1,the local radiation absorption distribution tends to be uniform.With the size parameter increases,there is an absorption peak inside the particle.The position of maximum absorption peak moves along the incident direction firstly,when it reaches the surface of the particle,it moves toward the direction against the incident direction.The value of maximum absorption peak changes significantly with size parameter of the particle.There are obvious interference fringes emerging inside the particle.The shape of the absorption distribution inside the particle differs slightly with different real part of complex refractive index,but the value of maximum absorption peak can be increased more than 30 times.When the imaginary part of complex refractive index increases,the absorption distribution changes from back-concentrated to front-concentrated.When k is close to 1,the local radiation absorption inside the particle is almost 0.The absorption distribution of two typical non-gray particles and a simple particle containing a core are studied.It shows that the core particle can significantly influence the absorption distribution of the basic particle.The absorption efficiencies can increase 30 times at the studied parameters.The absorption near the surface of core particle improves obviously.