Radiative Properties of Numerically Generated Fractal Soot Aggregates: The Importance of Configuration Averaging

2009 ◽  
Author(s):  
Fengshan Liu ◽  
Gregory J. Smallwood
Keyword(s):  
Primary Particle ◽  
Particle Diameter ◽  
Practical Interest ◽  
Aggregate Size ◽  
Small Variation ◽  
Radiative Properties ◽  
Fractal Aggregates ◽  
Cluster Aggregation ◽  
Fractal Parameters ◽  
Primary Particles

The radiative properties of numerically generated fractal soot aggregates were studied using the numerically accurate generalized multi-sphere Mie-solution method. The fractal aggregates investigated in this study contain from 10 to 600 primary particles of 30 nm in diameter. These fractal aggregates were numerically generated using a combination of the particle-cluster and cluster-cluster aggregation algorithms with fractal parameters representing flame generated soot. Ten different realizations were obtained for a given aggregate size measured by the number of primary particles. The wavelength considered is 532 nm and the corresponding size parameter of primary particle is 0.177. Attention is paid to the effect of different realizations of a fractal aggregate with identical fractal dimension, prefactor, primary particle diameter, and the number of primary particles on its orientation-averaged radiative properties. Most properties of practical interest exhibit relatively small variation with aggregate realization. However, other scattering properties, especially the vertical-horizontal differential scattering cross section, are very sensitive to the variation in geometrical configuration of primary particles. Orientation-averaged radiative properties of a single aggregate realization are not always sufficient to represent the properties of random-oriented ensemble of fractal aggregates.

scholarly journals Radiative Properties of Numerically Generated Fractal Soot Aggregates: The Importance of Configuration Averaging

2009 ◽  
Vol 132 (2) ◽  
Author(s):  
Fengshan Liu ◽  
Gregory J. Smallwood
Keyword(s):  
Primary Particle ◽  
Particle Diameter ◽  
Practical Interest ◽  
Aggregate Size ◽  
Small Variation ◽  
Radiative Properties ◽  
Fractal Aggregates ◽  
Cluster Aggregation ◽  
Fractal Parameters ◽  
Primary Particles

The radiative properties of numerically generated fractal soot aggregates were studied using the numerically accurate generalized multisphere Mie-solution method. The fractal aggregates investigated in this study contain 10–600 primary particles of 30 nm in diameter. These fractal aggregates were numerically generated using a combination of the particle-cluster and cluster-cluster aggregation algorithms with fractal parameters representing flame-generated soot. Ten different realizations were obtained for a given aggregate size measured by the number of primary particles. The wavelength considered is 532 nm, and the corresponding size parameter of primary particle is 0.177. Attention is paid to the effect of different realizations of a fractal aggregate with identical fractal dimension, prefactor, primary particle diameter, and the number of primary particles on its orientation-averaged radiative properties. Most properties of practical interest exhibit relatively small variation with aggregate realization. However, other scattering properties, especially the vertical-horizontal differential scattering cross section, are very sensitive to the variation in geometrical configuration of primary particles. Orientation-averaged radiative properties of a single aggregate realization are not always sufficient to represent the properties of random-oriented ensemble of fractal aggregates.

scholarly journals Morphology and Raman spectra of aerodynamically classified soot samples

2019 ◽  
Vol 12 (8) ◽  
pp. 4339-4346 ◽  
Author(s):  
Alberto Baldelli ◽  
Steven Nicholas Rogak
Keyword(s):  
Particle Size ◽  
Primary Particle ◽  
Particle Diameter ◽  
Size Control ◽  
Aggregate Size ◽  
Aerodynamic Diameter ◽  
Carbon Nanostructure ◽  
Transmission Electron ◽  
Primary Particles ◽  
Combustion Processes

Abstract. Airborne soot is emitted from combustion processes as aggregates of primary particles. The size of the primary particles and the overall aggregate size control soot transport properties, and prior research shows that these parameters may be related to the soot nanostructure. In this work, a laminar, inverted nonpremixed burner has been used as a source of soot that is almost completely elemental carbon. The inverted burner was connected to an electrical low-pressure impactor, which collected particles on stages according to the aerodynamic diameter, from 0.03 to 10 µm. The morphology was analyzed using a transmission electron microscope followed by image processing to extract projected area and average primary particle size for each aggregate (approximately 1000 aggregates analyzed in total for the nine impactor stages). Carbon nanostructure was analyzed using a Raman spectrometer, and five vibrational bands (D4, D1, D3, G, and D2) were fitted to the spectra to obtain an estimate of the carbon disorder. The average primary particle diameter increases from 15 to 30 nm as the impactor stage aerodynamic diameter increases. The D1, D3, D2, and D4 bands decreased (relative to the G band) with the particle size, suggesting that the larger aggregates have larger graphitic domains.

scholarly journals Morphology and Raman spectra of aerodynamically-classified soot samples

2019 ◽  
Author(s):  
Alberto Baldelli ◽  
Steven Nicholas Rogak
Keyword(s):  
Particle Size ◽  
Primary Particle ◽  
Particle Diameter ◽  
Size Control ◽  
Aggregate Size ◽  
Aerodynamic Diameter ◽  
Carbon Nanostructure ◽  
Absorption Bands ◽  
Primary Particles ◽  
Combustion Processes

Abstract. Airborne soot is emitted from combustion processes as aggregates of primary particles. The size of the primary particles and the overall aggregate size control soot transport properties, and prior research shows that these parameters may be related to the soot nanostructure. In this work, a laminar, inverted non-premixed burner has been used as a source of soot that is almost completely elemental carbon. The inverted burner was connected to an Electrostatic Low-Pressure Impactor, which collected particles on stages according to the aerodynamic diameter, from 0.3 to 10 μm. The morphology was analyzed using a Transmission Electron Microscope followed by image processing to extract projected area and average primary particle size for each aggregate (approximately 1000 aggregates analyzed in total for the 9 impactor stages). Carbon nanostructure was analyzed using a Raman spectrometer, and 5 absorption bands (D4, D1, D3, G, and D2) were fitted to the spectra to obtain an estimate of the carbon disorder. The average primary particle diameter increases from 15 to 30 nm as the impactor stage aerodynamic diameter increases. The D1, D3, D2, and D4 bands decreased (relative to the G band) with the particle size, suggesting that the larger aggregates have larger graphitic domains.

Optical Diagnostics and Radiative Properties of Simulated Soot Agglomerates

1991 ◽  
Vol 113 (4) ◽  
pp. 953-958 ◽  
Author(s):  
J. C. Ku ◽  
K.-H. Shim
Keyword(s):  
Optical Diagnostics ◽  
Forward Scattering ◽  
Radiative Properties ◽  
Weak Effect ◽  
Radiative Transport ◽  
Fractal Aggregates ◽  
Scattering Coefficients ◽  
Primary Particles ◽  
Accurate Relation ◽  
Number Of Particles

The effect of agglomeration on the optical diagnostics and radiative properties of simulated soot agglomerates is investigated, using results from the Jones solution. It is found that agglomeration has a very strong effect on scattering, but only a weak effect on extinction (≅ absorption). An accurate relation has been developed, based on near-forward scattering coefficients, for inferring the number of primary particles in soot agglomerates. General models for both total and differential scattering coefficients have also been established. These results are in general agreement with those predicted for fractal aggregates having a large number of particles. Because of the effect of agglomeration, scattering may not be negligible in treating radiative transport from soot agglomerates.

Numerical Study of Temperature and Incandescence Intensity of Nanosecond Pulsed-Laser Heated Soot Particles at High Pressures

2005 ◽  
Author(s):  
Fengshan Liu ◽  
David R. Snelling ◽  
Gregory J. Smallwood
Keyword(s):  
Soot Particle ◽  
High Pressures ◽  
Particle Diameter ◽  
Aggregate Size ◽  
Primary Particle Diameter ◽  
Time Resolved ◽  
Soot Particles ◽  
Nanosecond Pulsed Laser ◽  
Primary Particles ◽  
Laser Heated

Histories of temperature and incandescence intensity of nanosecond pulsed-laser heated soot particles of polydispersed primary particles and aggregate sizes were calculated using an aggregate-based heat transfer model at pressures from 1 atm up to 50 atm. The local gas temperature, distributions of soot primary particle diameter and aggregate size assumed in the calculations were similar to those found in an atmospheric laminar diffusion flame. Relatively low laser fluences were considered to keep the peak particle temperatures below about 3400 K to ensure negligible soot particle sublimation. The shielding effect on the heat conduction between aggregated soot particles and the surrounding gas was accounted for based on results of direct simulation Monte Carlo calculations. After the laser pulse, the temperature of soot particles with larger primary particles or larger aggregates cools down slower than those with smaller primary particles or smaller aggregates due to smaller surface area-to-volume ratios. The effective temperature of soot particles in the laser probe volume was calculated based on the ratio of thermal radiation intensities of the soot particle ensemble at 400 and 780 nm. Due to the reduced mean free path of molecules with increasing pressure, the heat conduction between soot particles and the surrounding gas shifts from the free-molecular to the transition regime. Consequently, the rate of conduction heat loss from the soot particles increases significantly with pressure. The lifetime of laser-induced incandescence (LII) signal is significantly reduced as the pressure increases. At high pressures, the time resolved soot particle temperature is very sensitive to both the primary particle diameter and the aggregate size distributions, implying the time-resolved LII particle sizing techniques developed at atmospheric pressure lose their effectiveness at high pressures.

Parametric Studies of a Spectrally Selective, Two-Layered, Porous, Volumetric Solar Collector

1992 ◽  
Vol 114 (3) ◽  
pp. 150-156 ◽  
Author(s):  
D. A. Kaminski ◽  
S. Kar
Keyword(s):  
Solar Collector ◽  
Cone Angle ◽  
Particle Diameter ◽  
Solid Particles ◽  
Solar Flux ◽  
Radiative Properties ◽  
Critical Parameters ◽  
Fluid Temperature ◽  
Spectrally Selective ◽  
Parametric Studies

A porous, packed bed, volumetric solar collector consisting of two dissimilar layers of spherical beads is numerically modeled. The bed is irradiated on the top surface by concentrated solar flux isotropic within a known cone angle. A gas stream perfusing the bed is heated by convection with the solid particles. The equation of radiative transfer, which accounts for absorption, emission, and linearly anisotropic scattering in the bed, is simplified by employing the P1 differential approximation. The bed materials are spectrally selective in the solar and infrared wavelengths. Sensitivity studies are used to identify the critical input parameters of the system, and a baseline configuration, which incorporates the key requirements of an efficient solar collector, is adopted. Parametric studies are conducted on the mass flow rate, incident solar flux, top layer porosity, solar absorptivity, particle diameter, and degree of back scatter. Tailoring of the particle and fluid temperature profiles and enhancing the efficiency of the collector by an appropriate selection of these critical parameters is demonstrated. Various high-temperature ceramics with suitable radiative properties are identified and their relative performance in the collector is assessed.

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