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High Flux Solar Simulator and Solar Photo-Thermal Reactor:
Characterization and Design
Saroj Bhatta, Dassou Nagassou, and Juan Pablo Trelles
Department of Mechanical Engineering and Energy Engineering Graduate Program University of Massachusetts Lowell
ASME 2014 8th International Conference on Energy Sustainability Boston, MA, June 30 - July 2, 2014
Motivation: Solar Chemical Synthesis Solar Chemical
Synthesis:
Activation Energy
- Solar for targeted chemical reactions - Value-added products (e.g. solar fuels)
Solar Spectra
• Water splitting • Artificial
photosynthesis
artificial leaf 4 water splitting 3
3 http://www.sciencedaily.com/releases/2013/12/131213093310.htm 4 Nocera, D.G., Science 334(6056) (2011) 645-648
Photo-chemical Process
1 Pregger , T., Internat. J. Hydrogen Energy 34 (2009) 4256-4267 2 Chueh, W.C., 6 Sep. 2012, SPIE Newsroom. DOI: 10.1117/2.1201208.004440
Solar Intensity
methane cracking 1
Thermo-chemical Process
redox cycle 2
• Thermal decomposition
• Redox cycles
Photo- Thermo-chemical Process
Solar Intensity + Spectra
• Combines advantages (?) • New processes (?)
Solar Photo-Thermochemical Processes
• High temperature, but potentially lower than thermochemical • Photons on photocatalyst – promotion of molecules to excited
states (e.g. vibrational transitions, electronic excitation)
Reactants + Thermo-catalyst Products Solar Intensity
• High temperature à high reactivity • ~ Independent of heat source
Thermo-chemical:
Reactants + Photo-catalyst Products Solar Spectra
• Low temperature à low throughput • Depend on solar spectrum (e.g. UV)
Photo-chemical:
Reactants + Products
Solar Intensity + Spectra
Photo-Thermochemical: High-temperature
Photo-catalyst
Concentrating Solar Plants
a. Parabolic mirror with Stirling engine at Plataforma Solar de Almería , Spain b. Sierra Sun Tower, Lancaster, CA, USA c. CSP plant under the Jawaharlal Nehru National Solar Mission (JNNSM), India
b
a
c
d. University of Minnesota e. MIT f. ETH-Swiss Federal Institute of Technology
Solar Simulators
e
d
f
Ideal for lab R&D: • Simulate sun using different light source d. Xenon arc, e. Metal halide, f. Argon • Ellipsoidal reflectors
Solar fields: • Wide temperature range a. High (>1000o), b. Medium (~600o), c. Low (~400o) • Mirrors, parabolic reflectors, troughs
Solar Simulator @ UMass Lowell
Spectral Characterization: - 6.5 kW Xenon short arc lamp - 1.5 kW Metal halide lamp - Daylight (clear day, Lowell, MA)
Ø Xenon arc à better emulation of daylight in visible range
High-Flux Solar Simulator:
- 6.5 [kW] (variable) - Xe short arc Lamp - Magnetic stabilization - Ellipsoidal Reflector - Rectifier 80-170 [A], 110 [V]
Xenon Arc Lamp
Ellipsoidal reflector Anode
end
Horizontal alignment
Anode cable
Housing exit
Xenon Lamp Luminous Intensity Distribution
• Fills solid angle of 10 steradians • Small angular section à no luminous flux
Lamp Luminous Emission
• Lamp + reflector assembly • Most flux distribution covered by reflector • Regions with voids expected
Cathode Anode
Electrode gap (7.5 mm)
Ellipsoidal Reflector
Truncated Reflector Enclosure
Ray Tracing Analysis
Assumptions: • Point source • Specular reflection • Perfect alignment of optics
Target at focus: • All rays are focused at target center
Ray Tracing Analysis Intensity Distribution at Target
As target departs from focus: • Intensity distribution widens • Intensity decreases • Dark center spot start appearing
Dark spot
Stand & Cable shadow
Ray Tracing Analysis Intensity Distribution at Target
Intensity Mapping Procedure
• Target: Black flat plate with reference points
• Device: Camera + neutral density filter
• Position: Focused & aligned with center of intensity field
o Projective image transformation & processing à Matlab
l2
Set-up for Intensity Mapping
Simulator
Camera with Neutral Density
Filter
Target plane
Bench
l3
ϴ l1
Imaging Steps
Ø Procedure suitable for In-Field system evaluation e.g. intensity at target from parabolic concentrator
Intensity Distribution
Raw image at focal plane
Image Transformation and Processing
Final processed image
2 cm
Focal Focal + 1.6” Focal + 2.6” Focal - 1.6” Focal - 2.6”
Processed Image at Different Target Planes
0 0.5 1 Relative intensity
Mapped image
Ø Optical distortion away from focus
Photo-Thermochemical Reactor S-1 Reactor Schematic
S-1 Reactor @ UML
Characteristics: • Quartz interior (Reactor Integrity) • Reflective interior (Optical resonance cavity) • Gas flow <> Solar flux (Counter flow heat exchanger)
• Solar Flux: (in progress) Max: ~ 3000 [sun] Ave: ~ 300 [sun]
• Design Operating Temperature ~ 1000 [oC]
input gas
synthesized gas
Reactor Design Rationale Reactor – Simulator Operation:
Temperature distribution
Velocity distribution Ø Large recirculation à high
gas residence & mixing Ø No catalyst yet (porous)
catalytic monolith
l3 focal point
input gas
Rationale:
- High residence:
Photons (reflection) &
Gas (recirculation)
- Catalytic Monolith: “Optically-tuned” porosity High temp. photocatalyst
synthesized gas
Experimental Set-up
Cold Line Diagnostics:
• Spectrometer • Flow meters • Pressure gauges • Thermocouples • IR Thermometer • Gas analyzer
Process Schematic Set-Up
Hot Line
Rationale: • Two gas lines: natural separation high/low temp. • Extendible, open- and closed- loop operation
Reactor Operation Calibration Run
Radia?on in Inlet
Outlet
Probe in
Reflec1on Loss
Ongoing work: Ø Decomposition of CO2 Ø Metal foams + photocatalyst coatings Ø Reactor-scale fluid flow – radiation modeling
Simulator – Reactor Coupling
Loss
Reflec1on
Optical Resonance: High optical losses in the
absence of catalytic monolith
Summary and Conclusion
• Rationale: Solar Photo-Thermochemical Processing à combine advantages of high-temperature reactivity + photo-catalytic activation
• Simulator Characterization: – Spectral distribution: Xe vs. metal halide vs. daylight
– Intensity distribution: Analytical and experimental
• Photo- Thermo-chemical Reactor Design: Optical resonance + flow recirculation + “Optically-tuned” catalythic monolith à long residence photons & gas
• Ongoing: CO2 decomposition w. high-temperature photocatalysts
Thank You
Additional
17
ES-FuelCell2014-6829: High Flux Solar Simulator and Solar Photo-Thermal Reactor: Characterization and Design Chemical processing using solar energy for chemical synthesis is an appealing alternative to extend the reach of renewable energy utilization and to mitigate environmental emissions. High-flux solar simulators provide the flexibility to evaluate and optimize the design of concentrated solar energy utilization devices under laboratory conditions, before prototyping for in-field testing. The characterization of a 6.5 kW high-flux solar simulator at UMass Lowell is presented. The solar simulator is used for the design and evaluation of a novel reactor design for gas-phase solar photo-thermochemical processing. The high-flux solar simulator operates with a short arc xenon lamp coupled with a truncated ellipsoidal reflector to deliver high flux radiation onto a target. The spectral radiative intensity distribution from the simulator is compared with the intensity distribution from a metal halide lamp and evaluated against solar irradiance for Lowell, MA. Experimental results of intensity distribution over a target plane are contrasted against ray tracing calculations and used for the optimal dimensioning of the optical aperture of the solar photo-thermochemical processing reactor. The interior of the reactor resembles an optical resonant cavity that allows high residence time of solar photons and gas flow to promote gas-phase thermochemical as well as photochemical reactions, while permitting the testing of different catalytic monoliths. Experimental diagnostics of the reactor operation for gas-phase chemical processing are also presented.
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