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Research Papers

Fluid Dynamics of a Transverse Jet Reactor for Zinc Aerosol Hydrolysis

[+] Author and Article Information
Julia Haltiwanger Nicodemus1

Engineering Studies, Lafayette College, Easton, PA 18042nicodemj@lafayette.edu

Jane H. Davidson

Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455jhd@me.umn.edu

This value for A′ was determined by fitting their collapsed data to Eq. 4; they do not give a value for A′.

1

Corresponding author.

J. Sol. Energy Eng 134(4), 041018 (Oct 25, 2012) (9 pages) doi:10.1115/1.4007726 History: Received March 30, 2012; Revised September 10, 2012; Published October 25, 2012; Online October 25, 2012

Abstract

A new concept for control of the flow field, and thus particle yield, in an aerosol reactor designed for the hydrolysis of Zn in the two-step Zn/ZnO solar thermochemical cycle for hydrogen production is described and evaluated. For the hydrolysis step, much attention has been given to Zn nanoscale reacting aerosols for their potential to increase conversion to ZnO and because they enable a continuous, controllable process. The success of this continuous process depends on achieving high particle yields in the reactor. A key challenge is to control the flow field in aerosol reactors to keep the particles entrained in the flow without deposition on the reactor wall. The ability of a new reactor concept based on transverse jet fluid dynamics to control the flow field and rapidly cool the Zn vapor is investigated. In the transverse jet reactor, evaporated Zn entrained in an Ar carrier gas issues vertically into the horizontal tubular reactor through which cooler $H2O$ and Ar flow. Particles are formed in the presence of steam at $∼450 K$. The trajectory of the jet is controlled via the effective velocity ratio, R, which is the square root of the ratio of the kinetic energy of the jet to that of the cross-flow. A computational fluid dynamics (CFD) model indicates that the trajectory of the jet can be controlled so that the majority of the Zn mass is directed down the center of the reactor, not near the reactor walls for R = 4.25 to R = 4.5. Experimentally, maximum particle yields of 93% of the mass entering the reactor are obtained at R = 4.5.

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Figures

Figure 4

Schematic of the modeling domain for the transverse jet reactor, including boundary conditions

Figure 5

Measured and numerically predicted temperatures along the line x = z = 0—the centerline of the evaporation tube extended up along the reactor diameter

Figure 6

Modeled temperature along a streamline originating from the center of the evaporation zone inlet

Figure 7

Streamlines originating from the jet inlet (gray-scale) and cross-flow inlet (colors) in the numerical model

Figure 8

Contours of constant zinc molar fraction in the plane of symmetry for numerical models corresponding to experiments 3, 6, 8, and 10

Figure 9

Yield, Y, versus effective velocity ratio, R, for all experiments. Y is maximized at 4.24≤R≤4.50 (dashed box)

Figure 10

Predicted and measured jet impact lengths for the transverse jet reactor

Figure 1

Conceptual drawing of the transverse jet zinc hydrolysis reactor

Figure 2

Schematic of the transverse jet reactor (not to scale), including the preheat zone, mixing zone, zinc evaporation zone, reaction zone, and cooling zone

Figure 3

Centerline temperature measurements in the transverse jet reactor for conditions matching experiment 4

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