The radiative characteristics of 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 factor g ≈ − 0.4 at 555 nm and g ≈ − 0.1 at 1 μm. A Monte Carlo ray-tracing model of the experimental set-up is employed to extract the extinction coefficient and the scattering albedo for the case of non-grey absorbing-scattering medium.

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