Search

Particle radiation significantly contributes to the overall heat transfer in pulverized solid fuel combustion. For a lower computational effort in numerical simulations, the particles are often assumed to be spherical without an internal structure. In particular, biomass particles deviate strongly from this shape assumption and consist of a structured porosity. To investigate the influence of these aspects, pulverized beech wood particles are modeled as realistic as possible, considering the asymmetric three-dimensional shape and tube-like pores. The numerically created particle is then used to calculate single-scattering properties (absorption-, scattering cross-section, and scattering phase function) by applying the discrete dipole approximation (DDA). Afterward, the shape and internal structure of the representative biomass particle are step-wise simplified, while comparing the impact on the radiation interaction with the detailed modeled particle. The calculations reveal that simplifications of the internal structure are acceptable as long as a similar shape is maintained. Here, an extruded ellipsis with no internal structure and an effective complex index of refraction indicates the best alternative and is recommended for future particle radiation simulations. While the deviations of the radiation cross-section between the extruded ellipsis and the realistic particle are below 10%, the deviations of the radiation cross-section between a sphere and the realistic particle are around 50%. The orientation averaged phase function of all particle models scatters more than 99.5% of the scattered radiation forward. Thus, a purely forward scattering model in combustion simulations is recommended. • Internal structure of biomass particles can be modeled by effective index of refraction. • Good Approximation of shape is mandatory. • Approximated shape has signifcant influence on radiative properties. • Spherical shape yields deviation to benchmark up to 60%. [ABSTRACT FROM AUTHOR]

Precise knowledge of the dependence of nano-object properties on their structural characteristics such as their size, shape, composition, or crystallinity, in turn, enables them to be finely characterized using appropriate techniques. Spectrophotometry and inelastic light scattering spectroscopy are noninvasive techniques that are proving highly robust and efficient for characterizing the optical response and vibrational properties of metal nano-objects. Here, we investigate the optical and vibrational properties of monodomain silver nanocubes synthesized by the chemical route, with edge length ranging from around 20 to 58 nm. The synthesized nanocrystals are not perfectly cubic and exhibit rounded edges and corners. This rounding was quantitatively taken into account by assimilating the shape of the nanocubes to superellipsoids. The effect of rounding on their optical response was clearly evidenced by localized surface plasmon resonance spectroscopy and supported by calculations based on the discrete dipole approximation method. The study of their acoustic vibrations by high-resolution low-frequency Raman scattering revealed a substructure of the T 2 g band, which was analyzed as a function of rounding. The measured frequencies are consistent with the existence of an anticrossing pattern of the two T 2 g branches. Such an avoided crossing in the T 2 g modes is clearly evidenced by calculating the vibrational frequencies of silver nanocubes using the Rayleigh-Ritz variational method that accounts for both their real size, shape, and cubic elasticity. These results show that it is possible to assess the rounding of nanocubes, including by means of ensemble spectroscopic measurements on well-calibrated particles.

A multilayer structure of microbial cells can result in multiple attenuations of electromagnetic waves, making the biological particles have a strong extinction ability. However, the influence of various morphologies on infrared band optical extinction performance of biomaterials is unclear. The combination of shape, dimension, and structure parameters is proposed to evaluate and enhance the optical extinction properties of artificial bioparticles. Combined with the preliminary work of our research group, four artificial biological particles were selected to simulate and calculate their extinction performance with different parameters theoretically based on the discrete-dipole approximation method. The results show the extinction properties of bioparticles with different shapes and dimensions in the 3.0 to 5.0 μm and 8.0 to 14.0 μm wavebands. It was found that the chain-shaped particles with more constituent spheres and a bending angle of 60 deg as well as the ellipsoid-shaped particles with an axis ratio of 1:2 exhibit better extinction properties in the above two bands. Among them, the regulation of extinction efficiency can reach ∼13.92 % and 18.16%. [ABSTRACT FROM AUTHOR]