Experimental and Numerical Determination of Thermal Radiative Properties of ZnO Particulate Media

Abstract

The radiative characteristics of dependently scattering packed-beds of ZnO particles, applied in the design of high-temperature solar thermochemical reactors, were investigated experimentally. ZnO samples of varying thickness were exposed to a continuous beam of near monochromatic thermal radiation in the 0.5–1 μm wavelength range. The overall transmitted fraction measured as a function of sample thickness s obeys an exponential trend exp(−As), with the fit parameter A ranging from 4000±100 m−1 at 555 nm to 2100±100 m−1 at 1 μm. In the forward directions, the measured intensity distribution is approximately isotropic, whereas in the backward directions it is well approximated by a Henyey–Greenstein equation with asymmetry factors g≈−0.4 at 555 nm and g≈−0.1 at 1 μm. A Monte Carlo ray-tracing model of the experimental setup is employed to extract the extinction coefficient and the scattering albedo for the case of a nongray absorbing-scattering medium.