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Research Papers: Radiative Heat Transfer

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

[+] Author and Article Information
P. Coray

Solar Technology Laboratory, Paul Scherrer Institute, 5232 Villigen, Switzerland

W. Lipiński

Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455

A. Steinfeld1

Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland; and Solar Technology Laboratory, Paul Scherrer Institute, 5232 Villigen, Switzerlandaldo.steinfeld@ethz.ch

Underlined variables ($p̱$ and $u̱$) indicate local lens system coordinates. $u̱$ contains the slopes with respect to the optical axis and is not a unit vector.

In the subsequent text, the spectral subscript $λ$ will be omitted for brevity.

1

Corresponding author.

J. Heat Transfer 132(1), 012701 (Oct 23, 2009) (6 pages) doi:10.1115/1.3194763 History: Received June 02, 2008; Revised May 20, 2009; Published October 23, 2009

## 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.

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Copyright © 2010 by American Society of Mechanical Engineers
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## Figures

Figure 1

Experimental setup No. 1 with a rotary detector. Components: (No. 1) dual Xe-arc/Cesiwid-glowbar lamp, (No. 2) double monochromator, (No. 2′) monochromator exit slit, (Nos. 3 and 5) imaging lens pairs, (No. 4) sample, (No. 6) rotary detector, (No. 7) optical chopper, (No. 8) lock-in amplifier, and (No. 9) data acquisition system.

Figure 2

Experimental setup No. 2 with a fixed detector. Components: (Nos. 1–4 and 7–9) as in Fig. 1, (No. 6′) fixed detector.

Figure 3

Normalized volume-based particle size distribution function f(a) and the corresponding cumulative volume distribution function F(a) of ZnO particles as a function of particle radius a

Figure 4

Directions of emission from the monochromator exit slit: left—front view of the monochromator exit slit; right—cross section of the monochromator exit slit

Figure 5

Measured normalized signal q/q0 versus packed-bed thickness s. Data obtained with setup No. 2.

Figure 6

Measured normalized signal q/q0 as a function of viewing angle θ for different packed-bed thicknesses at λ=555 nm and 1000 nm. Data obtained with setup No. 1.

Figure 7

Measured data (points) versus Mie phase function based simulation (lines). The normalized signal q/q0 is plotted as a function of viewing angle θ for two sample thicknesses s. The wavelength is 555 nm. Further details in Table 1.

Figure 8

Measured data (points) versus model phase function based simulation (lines). The normalized signal q/q0 is plotted as a function of sample thickness s. The data were obtained with setup No. 2 (forward direction) at a wavelength of 1000 nm.

Figure 9

Measured data (points) versus model phase function based simulation (lines). The normalized signal q/q0 is plotted as a function of viewing angle θ. The data were obtained with setup No. 1 (backward direction) at a wavelength of 1000 nm.

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