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Research Papers

Computational Fluid Dynamics and Heat Transfer Analysis of Vortex Formation in a Solar Reactor

[+] Author and Article Information
Min-Hsiu Chien

Turbomachinery Laboratory,
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77840
e-mail: scottamm@tamu.edu

Nesrin Ozalp

Department of Mechanical Engineering,
KU Leuven, Celestijnenlaan 300B,
Leuven 3001, Belgium
e-mail: nesrin.ozalp@kuleuven.be

Gerald Morrison

Turbomachinery Laboratory,
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77840
e-mail: gmorrison@tamu.edu

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received September 6, 2014; final manuscript received March 14, 2015; published online June 23, 2015. Assoc. Editor: Ranganathan Kumar.

J. Thermal Sci. Eng. Appl 7(4), 041007 (Dec 01, 2015) (8 pages) Paper No: TSEA-14-1205; doi: 10.1115/1.4030697 History: Received September 06, 2014; Revised March 14, 2015; Online June 23, 2015

A hydrogen-producing solar reactor was experimentally tested to study the cyclone flow dynamics of the gas–particle two-phase phenomenon. Two-dimensional particle image velocimetry (PIV) was used to observe the flow and to quantify the vortex formation inside the solar reactor. The vortex flow structure in the reactor was reconstructed by capturing images from orientations perpendicular and parallel to the geometrical axis of the reactor, respectively. The experimental results showed that the tangential components of the fluid velocity formed a Rankine-vortex profile. The free vortex portions of the Rankine profile were synchronized and independent of the axial position. The axial components showed a vortex funnel of higher speed fluid supplied by a reversing secondary flow. According to the inlet channel design, the geometry dominates the flow dynamics. A stable processing vortex line was observed. As the vortex flow evolves toward the exit, the vortex funnel expands radially with decreasing tangential velocity magnitude peak as a result of the vortex stretching. An optimal residence time of the flow was found by changing the cyclone flow inlet conditions. The swirl number versus the main flow rate change was obtained. Upon completion of the experimental studies, a thorough numerical analysis was conducted to model the flow dynamics inside the solar reactor and to verify the results by comparison to the experimental results. Three turbulence models including the standard k–ϵ, k–ϵ renormalization groups (RNG), and Reynolds stress transport models were used. Computational fluid dynamics (CFD) simulations were coupled with heat transfer analysis via discrete ordinate (DO) model. Particle tracing in Lagrange frame was applied to simulate the particle trajectory. A comparison between the turbulence modeling results for the room temperature and high temperature cases, as well as the experimental results for room temperature cases is presented.

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References

Figures

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Fig. 1

Geometry of solar reactor: (a) cross-sectional side view, (b) internal channels of the inlets, and (c) top view [6]

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Fig. 4

Attenuation, absorption, and scattering coefficients of 0.05 μm particles across the spectrum

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Fig. 11

Flow velocity contours on cross-sectional planes of (a) entrance zone, (b) z = 0, (c) z = 25.4, (d) z = 50.8, (e) z = 76.2, and (f) z = 101.6 mm in the cylindrical zone at 1500 K, 1 atm

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Fig. 12

Flow velocity contours on (a) Y–Z and (b) X–Z cross-sectional plane of the reactor at 1500 K, 1 atm using 300 K wall screening gases at inlets

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Fig. 13

Flow velocity contours on cross-sectional planes of (a) entrance zone, (b) z = 0, (c) z = 25.4, (d) z = 50.8, (e) z = 76.2, and (f) z = 101.6 mm in the cylindrical zone at 1500 K, 1 atm using 300 K wall screening gases at inlets

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Fig. 16

Flow temperature contours on (a) Y–Z and (b) X–Z cross-sectional plane of the reactor at 1 atm using 300 K inlet gases heated by concentrated solar flux

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Fig. 2

Axial-symmetric mesh of the solar reactor geometry

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Fig. 3

Complex refractive index of acetylene, extracted from Dalzell and Sarofim [21]

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Fig. 5

Attenuation, absorption, and scattering coefficients of 1, 10, and 20 μm particles over the spectrum

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Fig. 6

Flow velocity contours in buffering channels of (a) main flow, (b) wall screen flow, and (c) window screen flow at 300 K

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Fig. 7

Flow velocity contours on (a) Y–Z and (b) X–Z cross-sectional plane of the reactor at 300 K, 1/3 atm

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Fig. 10

Flow velocity contours on (a) Y–Z and (b) X–Z cross-sectional plane of the reactor at 1500 K, 1 atm

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Fig. 14

Flow velocity contours on (a) Y–Z and (b) X–Z cross-sectional plane of the reactor at 1 atm using 300 K inlet gases heated by concentrated solar flux

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Fig. 15

Flow velocity contours on cross-sectional planes of (a) entrance zone, (b) z = 0, (c) z = 25.4, (d) z = 50.8, (e) z = 76.2, and (f) z = 101.6 mm in the cylindrical zone at 1 atm using 300 K inlet gases heated by concentrated solar flux

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Fig. 17

Particle tracking by DPM model in contour of (a) density and (b) temperature

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Fig. 8

PIV measurements at 300 K, 1/3 atm on cross-sectional planes at traverse positions from 0 to 4 in (101.6 mm) in the cylindrical zone: (a) flow velocity contours, (b) vorticity distribution, and (c) turbulent intensity distribution

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Fig. 9

Flow velocity contours on cross-sectional planes of (a) entrance zone, (b) z = 0, (c) z = 25.4, (d) z = 50.8, (e) z = 76.2, and (f) z = 101.6 mm in the cylindrical zone at 300 K, 1/3 atm

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