Research Papers

Design and Characterization of a Novel Upward Flow Reactor for the Study of High-Temperature Thermal Reduction for Solar-Driven Processes

[+] Author and Article Information
H. Evan Bush, Robert J. Gill, Sheldon M. Jeter

George W. Woodruff School of
Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332-0405

Karl-Philipp Schlichting

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

Peter G. Loutzenhiser

George W. Woodruff School of
Mechanical Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332-0405
e-mail: peter.loutzenhiser@me.gatech.edu

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received February 13, 2017; final manuscript received May 18, 2017; published online July 18, 2017. Assoc. Editor: Marc Röger.

J. Sol. Energy Eng 139(5), 051004 (Jul 18, 2017) (11 pages) Paper No: SOL-17-1056; doi: 10.1115/1.4037191 History: Received February 13, 2017; Revised May 18, 2017

The design and characterization of an upward flow reactor (UFR) coupled to a high flux solar simulator (HFSS) under vacuum is presented. The UFR was designed to rapidly heat solid samples with concentrated irradiation to temperatures greater than 1000 °C at heating rates in excess of 50 K/s. Such conditions are ideal for examining high-temperature thermal reduction kinetics of reduction/oxidation-active materials by temporally monitoring O2 evolution. A steady-state, computational fluid dynamics (CFD) model was employed in the design to minimize the formation of eddies and recirculation, and lag and dispersion were characterized through a suite of O2 tracer experiments using deconvolution and the continuously stirred tank reactors (CSTR) in series models. A transient, CFD and heat transfer model of the UFR was combined with Monte Carlo ray tracing (MCRT) to determine radiative heat fluxes on the sample from the HFSS to model spatial and temporal sample temperatures. The modeled temperatures were compared with those measured within the sample during an experiment in which Co3O4 was thermally reduced to CoO and O2. The measured temperatures within the bed were bounded by the average top and bottom modeled bed temperatures for the duration of the experiment. Small variances in the shape of the modeled versus experimental temperatures were due to contact resistance between the thermocouple and particles in the bed and changes in the spectral absorptivity and emissivity as the Co3O4 was reduced to CoO and O2.

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Fig. 1

Exploded wireframe view of the UFR with (1) domed quartz tube, (2) alumina crucible, (3) o-rings, (4) stainless steel adapter, (5) stainless steel body, (6) cast clamps, and (7) gas/thermocouple feedthrough

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Fig. 2

Schematic of experimental setup: O2 and Ar tanks supplied gas to the reactor via flow controllers, driven by a pump downstream of the reactor outlet. A pressure transducer was used to monitor reactor operating pressure and products of reduction were measured via a mass spectrometer (MS) and gas chromatograph (GC). Labels A and B indicate locations at which the O2 flow controller and supply were connected for dispersion testing.

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Fig. 3

Mesh for UFR CFD and heat transfer modeling. The outer surface (left), outlet stem (top right), and sample crucible inside the reactor (bottom right) are depicted with annotations matching the boundary conditions in Table 3.

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Fig. 4

Average input (solid) and output (dash-dotted) dimensionless O2 concentration curves for dispersion tracer step tests. Gray regions indicate 95% confidence intervals. Curves were measured for step changes (a) from 0 to 0.2 LN/min and (b) from 0.2 to 0 LN/min flow controller settings with 60 s between changes to reach steady flow.

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Fig. 5

Residence time distribution of the reactor determined via the method of deconvolution (solid) and the CSTR in series model (dashed)

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Fig. 6

Three-dimensional streamlines originating from the three reactor inlets, as predicted by steady-state heat and mass transfer modeling of the UFR. Fluid velocity is defined by a logarithmic gradient on the streamlines and is higher near the inlets and outlet

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Fig. 7

Experimental results of Co3O4 reduction performed in UFR for HFSS input power (dashed), thermocouple temperature, (dashed), and Ar (solid, light) and O2 (solid, heavy) ion current

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Fig. 8

Modeled, smoothed sample surface heat fluxes for the center lamp of the HFSS in kW m−2, produced from the MCRT model modified for beam down configuration

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Fig. 9

Modeled steady-state temperature contours for a cross-sectional detail view of the crucible, sample, and neighboring fluid field for temperatures between 1100 and 1500 K

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Fig. 10

Modeled temporal temperature evolution averaged over the top surface (dotted), bottom surface (dashed), and bed (solid) compared with measured temporal temperatures (circles) for (a) the entire test and (b) the first 60 s of the test

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Fig. 11

Thermal reduction of Co3O4 as measured by mass spectrometer and gas chromatographer (solid) and corrected for dispersion (dashed), presented as (a) O2 molar flow rates and (b) Co3O4 to CoO conversion




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