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Research Papers

Transient Three-Dimensional Heat Transfer Model of a Solar Thermochemical Reactor for H2O and CO2 Splitting Via Nonstoichiometric Ceria Redox Cycling

[+] Author and Article Information
Justin Lapp

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

Wojciech Lipiński

Research School of Engineering,
Australian National University,
Canberra, ACT 0200, Australia
e-mail: wojciech.lipinski@anu.edu.au

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received May 13, 2013; final manuscript received December 17, 2013; published online January 31, 2014. Assoc. Editor: Prof. Nesrin Ozalp.

J. Sol. Energy Eng 136(3), 031006 (Jan 31, 2014) (11 pages) Paper No: SOL-13-1133; doi: 10.1115/1.4026465 History: Received May 13, 2013; Revised December 17, 2013

A transient three-dimensional heat transfer model is developed for a 3 kWth solar thermochemical reactor for H2O and CO2 splitting via two-step nonstoichiometric ceria cycling. The reactor consists of a windowed solar receiver cavity, counter-rotating reactive and inert cylinders, and insulated reactor walls. The counter-rotating cylinders allow for continuous fuel production and heat recovery. The model is developed to solve energy conservation equations accounting for conduction, convection, and radiation heat transfer modes, and chemical reactions. Radiative heat transfer is analyzed using a combination of the Monte Carlo ray-tracing method, the net radiation method, and the Rosseland diffusion approximation. Steady-state temperatures, heat fluxes, and nonstoichiometry are reported. A temperature swing of up to 401 K, heat recovery effectiveness of up to 95%, and solar-to-fuel efficiency of up to 5% are predicted in parametric studies.

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References

Figures

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Fig. 1

Schematic of solar thermochemical reactor realizing a nonstoichiometric ceria based redox cycle with solid–solid heat recovery [25]

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Fig. 2

Schematic of the computational domain: (a) horizontal cross section, and (b) vertical cross section. See the description of the subdomains AF in the text.

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Fig. 3

A sample cell of the structured cylindrical grid for the ceria and inert cylinders: (a) r–θ and (b) r–z cross sections

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Fig. 14

Effect of cylinder wall thickness on (a) heat recovery effectiveness and (b) maximum and minimum material-average temperatures

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Fig. 15

Effect of cylinder angular velocity on (a) heat recovery effectiveness and (b) maximum and minimum material-averaged temperatures

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Fig. 13

r–θ distribution of nonstoichiometry δ in the ceria cylinder at z = 0 for the case of increased thermal conductivity. The radial coordinate has been distorted by a ratio of 5.

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Fig. 12

r–θ distribution of temperature in the rotating cylinders at z = 0 for the case with increased thermal conductivity. The radial coordinate has been distorted by a ratio of 5.

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Fig. 11

Material-average value of δ as a function of the circumferential position for the baseline simulation case

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Fig. 10

r–θ distribution of nonstoichiometry δ in the ceria cylinder at z = 0 for the baseline simulation case. The radial coordinate has been distorted by a ratio of 5.

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Fig. 9

Outward net heat flux at the inner surface of the ceria cylinder as a function of the circumferential angle θ for the baseline simulation case: axially-averaged heat flux (solid line), heat flux at z = 0 (dashed line), and z = ± LD/2 (dotted line)

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Fig. 8

Temperature profiles along the reactor cavity wall measured from the aperture plane (x = 0) at selected circumferential positions φ for the baseline simulation case. φ = 0 corresponds to the angular location nearest to where the ceria cylinder enters the cavity.

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Fig. 7

Temperature distribution on the surface of the ceria cylinder as seen from the cavity aperture for the baseline simulation case

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Fig. 6

Circumferential temperature variations of the ceria cylinder at selected radial (1: r = r3, 2: r = (r3 + r4)/2, and 3: r = r4) and axial (solid lines: z = 0, dashed lines: z = ± LD/2) locations for the baseline simulation case

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Fig. 5

Material-average temperatures of the ceria (dashed line) and inert (solid line) cylinders as a function of the circumferential angle θ for the baseline simulation case. The directions of rotation are indicated by the arrows.

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Fig. 4

r–θ temperature distribution in the rotating cylinders at z = 0 for the baseline simulation case. The cavity-receiver is on the left-hand side of the plot, consistent with the arrangement shown in Fig. 2. The radial coordinate has been distorted by a ratio of 5:1.

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