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RESEARCH PAPERS

Computational Fluid Dynamics Simulation of a Tubular Aerosol Reactor for Solar Thermal ZnO Decomposition

[+] Author and Article Information
Christopher Perkins, Alan Weimer

Department of Chemical and Biological Engineering,  University of Colorado at Boulder, ECCH 111, Campus Box 424, Boulder, CO 80309-0424

J. Sol. Energy Eng 129(4), 391-404 (May 10, 2007) (14 pages) doi:10.1115/1.2769700 History: Received October 24, 2006; Revised May 10, 2007

Computational fluid dynamics simulations were performed to model solar ZnO dissociation in a tubular aerosol reactor at ultrahigh temperatures (19002300K). Reactor aspect ratios ranged between 0.15 and 0.45, with the smallest ratio base case corresponding to a reactor diameter of 0.02286m. Gas flow rates were set such that the Ar:ZnO ratio was greater than 3:1 and the system residence time was below 2s. The system was found to exhibit highly laminar flow in all cases (Re10), but gas velocity profiles did not seriously affect temperature profiles. Particle heating was nearly instantaneous, a result of the high radiation heat flux from the wall. There was essentially no difference between gas and particle temperatures due to the high surface area for conductive heat exchange between the phases. Calculation of ZnO conversion showed that significant conversions (>90%) could be attained for residence times typical of rapid aerosol processing. Particle sizes of >1μm negatively affected conversion, but sizes of 10μm still gave acceptable conversion levels. Simulation of reaction of product oxygen with the reactor wall showed that a reactor constructed of an oxidation-sensitive material would not be a viable choice for a high temperature solar reactor.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Aerosol reactor model geometry and boundary conditions

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Figure 2

Surface plot for a representative converged simulation of (a)z velocity, (b) gas temperature, (c) particle temperature, (d)ZnO concentration, and (e)O2 concentration (Twall=2000K, V̇gas=1SLPM, 1gL−1ZnO, 10μm particle size)

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Figure 3

Radial gas temperature profile at various axial positions for changing (a) wall temperature (V̇gas=1SLPM) and (b) inert gas flow (Twall=2000K)

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Figure 4

Fractional approach of average gas temperature to wall temperature for varying (a) wall temperature (V̇gas=1SLPM) and (b) tube diameter (V̇gas=1SLPM)

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Figure 5

Ratio of particle temperature to gas temperature at various axial positions for varying tube diameter and wall temperature (V̇gas=1SLPM)

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Figure 6

Fractional approach of average gas temperature to wall temperature for varying ZnO particle mass loading (Twall=2000K, V̇gas=1SLPM)

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Figure 7

Radial z-velocity profiles at various axial positions for changing (a) wall temperatures (V̇gas=1SLPM) and (b) inert gas flow (Twall=2000K)

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Figure 8

Exit conversion dependence on inlet superficial gas velocity for varying (a) wall temperature and (b) tube diameter

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Figure 9

Effect of particle mass loading on exit conversion of ZnO(V̇gas=1SLPM)

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Figure 10

Effect of ZnO particle size on exit conversion of ZnO(V̇gas=1SLPM)

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Figure 11

Variation of exit conversion with the diffusion distance z in the L’vov kinetic model (V̇gas=1SLPM)

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Figure 12

Corrosive wall conversion of O2 dependence on wall temperature for variation of (a) inlet inert gas flow rate and (b) tube diameter

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