Experimentally Determined Optical Properties of a Polydisperse Carbon Black Cloud for a Solar Particle Receiver

Abstract

Measured physical and optical properties of a stable polydisperse carbon black particle cloud at 532 nm and 1064 nm are reported. The particle cloud consisted of 99.7% spheroid primary particles (45–570 nm diameter) and 0.3% large irregularly shaped agglomerates (1.2–7.25 μm equivalent diameter). Although the numerical fraction of the agglomerates was only 0.2%, they contributed 60% to the cloud’s scattering cross section. The extinction coefficient, scattering coefficient and the scattering phase function were measured for both parallel and perpendicular polarized radiation at linear extinction coefficients ranging from 0.6 to 4.1 m−1. The cloud exhibited strong forward scattering, with 62% of all scattered energy in a forward lobe of 15° at 532 nm and 48% at 1064 nm. The scattering albedo was measured to 35% at 532 nm and 47% at 1064 nm. The dimensionless extinction coefficient was measured to 8.25 at 532 nm. The experimental data was compared to standard Mie theory by integrating the weighed contribution based on particle size, including agglomerates, according to the detailed measured population distribution. Neglecting the contribution of the agglomerates to the cloud’s optical properties was shown to introduce discrepancies between Mie theory and measured results. The results indicate that the-Mie theory can be used for estimating the optical properties of a partially agglomerated carbon black particle cloud for simulation of a solar particle receiver.