1. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Schematic of the vacuum aerosol reactor as a cross-sectional view, and an enlarged view of the graphite absorber tube showing the hot reaction zone and particle flow. The graphite tube radial and vertical axes are denoted by r and ζ, respectively.

2. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Temperature distribution at 1 mbar measured along the vertical axis of the graphite absorber tube as a function of different incident flux densities. The origin of the y-axis denotes the default temperature measurement position in experiments (at the focal point of HFSS and half-reflector height as shown in Fig. 1). The reaction zone is also defined with a length of 140 mm, and average temperature of the reaction zone is calculated along the height of the reflector (−70 mm < ζ < 70 mm) as such. Dashed lines indicate ± 1% error region of the thermocouple accuracy.

3. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Schematic layout of the experimental setup, showing the solar vacuum aerosol reactor at PSI's HFSS. Reactants are introduced by a rotary particle feeder (1) into the graphite absorber tube (2). Reaction products are precipitated on the condenser (3). Particles exiting the reactor are collected in a collection vessel (4) and entrained fine particles are withheld by means of filter paper (5). Inert Ar gas flows are controlled by mass flow controllers (FC), and the system pressure is recorded at the top of the reactor (P). Online gas analysis includes infrared (IR: CO, CO2, and CH4) and TC detectors (TC: H2) as well as a micro-gas chromatograph (GC). Additional instrumentation consists of needle valves to adjust system pressure (6) and Ar gas flow at p < 10 mbar (7). An overpressure relief valve (8) provides safety when the setup is pressurized at completion of experiment.

4. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Volume-based density (left) and cumulative (right) particle size distributions of activated charcoal (C), ZnO powder, and the blend of the two after stoichiometric mixing in a swing mill for 10 min

5. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Temperature at the focal height of the HFSS and molar flow rates of evolved gases for a typical pulsed feeding experiment at p = 100 mbar. Arrows denote gas species at select peak heights, where solid lines are CO, dashed lines are H2, and filled peaks are CO2. Segment (A) corresponds to three feed pulseswith m˙  = 0.68 g·min−1. Segments (B) and (C) correspond to two feed pulses with m˙ = 1.36 g·min−1 and m˙  = 2.04 g·min−1, respectively.

6. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Oxygen conversion for pulsed feeding experiments, investigating effect of system pressure, feed rate, and mean temperature TR of the reaction zone. Feed rates are indicated by marker type: solid markers denote low incident a flux density of 600 kW·m−2, with TR ∼1400 K; open markers denote a high incident flux density of 900 kW·m−2, with TR ∼ 1600 K. The error bars denote the standard deviation within feed pulses.

7. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Temperature at the focal height of the HFSS, incident flux density, and evolved gases CO, CO2, and H2 for a typical continuous feeding experiment at p = 10 mbar (experiment #8 in Table 2). Feeding intervals with feed rate m˙ = 0.68 g·min−1 for duration Δtf = 10 min are indicated by vertical dashed lines.

8. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Oxygen conversion (left) and particle Knudsen number (right) for continuous feeding experiments investigating the effect of system pressure and mean temperature of reaction zone TR. Flux density levels are indicated by marker type: squares refer to experiments at 600 kW·m−2 corresponding to reactor mean temperature TR ∼ 1400 K, circles to 900 kW·m−2 with TR ∼ 1600 K, and triangles to 1200 kW·m−2 with TR ∼ 1700 K, respectively. The error bars denote the standard deviation between two replicate experiments.

9. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Particle residence times in the reaction zone as a function of system pressure for spherical particles of different size. Equivalent particle diameters considered were taken from characteristic values of the reactant particle size distribution listed in Table 1.

10. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Mean particle velocity vp in the reaction zone and its ratio to the fluid gas velocity vg as function of system pressure for spherical particles of different size. Equivalent particle diameters considered were taken from characteristic values of reactant particle size distribution listed in Table 1.

11. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Oxygen conversion at 1 mbar nominal pressure and various incident flux densities for four flow conditions, two of which contain obstruction to particle flow within the reaction zone and one no argon sweep gas. Conversion increases with higher degrees of flow obstruction Φ.

12. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
Temperature at the focal height, incident flux density, and evolved gases for a long feeding experiment at p = 100 mbar. Feeding interval with m˙   = 0.68 g·min−1 for Δtf = 30 min is indicated by vertical dashed lines. The HFSS was shutdown simultaneously with the feeding system.

13. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
XRD patterns of ZnO reactant and product samples taken from the long-term feeding experiment, collected at different locations as shown in Fig. 3. Samples were taken from powder remaining in the particle feeder (1), graphite tube (2), condenser (3), particle collection vessel (4), and particle filter paper (5).

14. Date of download: 1/24/2018
Copyright © ASME. All rights reserved.
From: Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor
J. Sol. Energy Eng. 2016;138(2): doi: /
Figure Legend:
SEM images of collected samples from the long-term feeding experiment at different reactor locations described in Fig. 3. (a) Overview and (b) detail of precipitated reaction products on the condenser (location 3). (c) Overview and (d) detail of agglomerated particles collected in collection vessel (location 4) below the reactor. (e) Overview and (f) detail of fine particles collected from filter paper on the gas outlet (location 5).