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Technical Briefs

# Modeling of a Multitube High-Temperature Solar Thermochemical Reactor for Hydrogen Production

[+] Author and Article Information
S. Haussener

Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland

D. Hirsch, C. Perkins, A. Weimer

Department of Chemical Engineering, University of Colorado, Boulder, CO 80309-0424

A. Lewandowski

National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401-3393

A. Steinfeld

Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland; Solar Technology Laboratory, Paul Scherrer Institute, 5232 Villigen, Switzerland

1 sun corresponds to a solar radiative flux of $1 kW/m2$.

J. Sol. Energy Eng 131(2), 024503 (Mar 25, 2009) (5 pages) doi:10.1115/1.3097280 History: Received August 08, 2007; Revised November 18, 2008; Published March 25, 2009

## Abstract

A solar reactor consisting of a cavity-receiver containing an array of tubular absorbers is considered for performing the ZnO-dissociation as part of a two-step $H2O$-splitting thermochemical cycle using concentrated solar energy. The continuity, momentum, and energy governing equations that couple the rate of heat transfer to the Arrhenius-type reaction kinetics are formulated for an absorbing-emitting-scattering particulate media and numerically solved using a computational fluid dynamics code. Parametric simulations were carried out to examine the influence of the solar flux concentration ratio (3000–6000 suns), number of tubes (1–10), ZnO mass flow rate (2–20 g/min per tube), and ZnO particle size $(0.06–1 μm)$ on the reactor’s performance. The reaction extent reaches completion within 1 s residence time at above 2000 K, yielding a solar-to-chemical energy conversion efficiency of up to 29%.

###### FIGURES IN THIS ARTICLE
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Copyright © 2009 by American Society of Mechanical Engineers
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## Figures

Figure 1

Solar reactor configuration consisting of a cylindrical cavity containing an array of absorber tubes. The shadowed rectangle indicates the aperture. The dashed line indicates the x-y-plane used for the 2D clip.

Figure 2

(a) Real and imaginary part, n and κ, of the refractive index of ZnO. (b) Scattering and absorption efficiencies, Qλs and Qλa, for 1 μm and 0.06 μm diameter ZnO particles.

Figure 3

Fractional factorial design parameters: cavity radius rc, absorber tube radius ra, and help circle radius rh

Figure 4

Temperature field (in kelvin) for a specularly-reflecting cavity with four absorber tubes. Baseline parameters: C=4500 suns, rc=0.12 m, ra=0.0227 m, rh=0.096 m, and ṁZnO=6 g/min per tube.

Figure 5

Pareto charts on (a) the solar-to-chemical energy conversion efficiency (in percent) and (b) the average absorber tube temperature (in kelvin). The two lines indicate the boundary for 5% and 10% probability of type 1 error. Factor numbers denote (1) dp, (2) specularly/diffusely-reflecting cavity, (3) C, (4) ṁZnO, (5) window aspect ratio, (6) rc, (7) rh, (8) Ntubes, (9) dp∗ specularly/diffusely-reflecting cavity, (10) dp∗C, (11) dp∗ṁZnO, (12) dp∗ window aspect ratio, (13) dp∗rc, (14) dp∗rh, and (15) dp∗Ntubes.

Figure 6

Contour plots for ηsolar-to-chemical (%) as a function of (a) ṁZnO and Ntubes, (b) ṁZnO and C, (c) C and Ntubes. In each plot, the high level of the third parameter is kept constant (C=5392 suns, Ntubes=6, and ṁZnO=7.16 g/min/tube).

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