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Presented By:
Benton Greene
TFAWS18-IN-21Characterization of a 50kW Inductively Coupled Plasma Torch for Testing of Ablative Thermal Protection Material
Benton Greene, Noel Clemens, Philip VargheseThe University of TexasAerospace Engineering and Engineering Mechanics
Thermal & Fluids Analysis Workshop
TFAWS 2018
August 20-24, 2018
NASA Johnson Space Center
Houston, TX
TFAWS Interdisciplinary Paper Session
Acknowledgements NASA Collaboratorso Stan Bouslog
o Steven Del Papa
o Luis Saucedo
o Chris Madden
o Hai Nguyen
UT Collaboratorso Philip Varghese
o Noel Clemens
Undergraduate Assistantso Daniel Cha
o Adarsh Patra
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 2
Research Motivation Atmospheric entryo Typical lunar return reentry velocity:
11 km/s
o ~10 metric ton reentry vehicle
o 500 GJ of kinetic energy
o 15 min from entry to landing
Thermal protectiono Ablative heat shields
• Rely on pyrolysis and mass loss
• Non-reusable
o Thermal soak
• Heat absorbed into TPS material
• Must be either cooled or ejected
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Research Motivation
5/20/2019 4
Ground testingo Replicate Mach number, heat flux,
pressure, and surface velocity gradient
o Understand chemistry of pyrolysis
o Develop computer models of heat shield mass loss and thermal soak
Difficult to replicate all parameters
Use different facilities to replicate specific features
Combine data in computational models
TFAWS 2018 – AUGUST 20-24, 2018
High-Enthalpy Flow Facilities Impulse facilitieso Gun tunnels, shock tubes, expansion tubes, Ludwieg tubes
o Use unsteady shock motion to generate high-enthalpy, high-velocity flow
o Run time on order of milliseconds
Arcjeto Use high-voltage discharge to superheat flow
o Run time virtually unlimited
o Metal electrodes contaminate flow
Inductively Coupled Plasma (ICP) Torcho Use fluctuating magnetic fields to superheat flow
o Run time virtually unlimited
o No metal electrodes in contact with flow
o Typically run at lower pressures than arcjets
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What is an ICP Induction coils fed with high-
voltage MHz AC power
Fluctuating magnetic field generates electric field necessary for gas breakdown
Gas injected into cooled quartz tube inside coil
Swirling motion of air keeps plasma ball away from walls
Superheated air forced through water cooled nozzle
5/20/2019 6TFAWS 2018 – AUGUST 20-24, 2018
Current Facility
COMPONENTS AND CAPABILITIES
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Current Facility
Water-Cooled
Insertion Arm
Torch Head
Control/Instrumentation
Cabinet
Plexiglas-Enclosed
Fume Hood
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Video of Startup
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 9
Torch Developed by Applied Plasma Technologies
Up to 50kW inductively coupled plasma
Coil voltage between 9 kV and 12 kV at 6 MHz
Plasma chambero Water-cooled quartz tube
o 250 mm in length
o 30 mm exit nozzle
Torch head tethered to power supply with flexible cable
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Traverse Table 3-Axis translation with 1 ton
capacity
Move torch with respect to a fixed optical diagnostic setupo Resolution: 0.5 mm
o Travel: 150 mm
Allows optical diagnostics to probe arbitrary locations in plume with no readjustment of optics
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Insertion Mechanism Developed by NASA
collaborators
Two water-cooled arms
Adjustable height above torcho 0 to 150 mm
Motorized insertiono Fast: 45° per second
o Slow scan: 1 mm resolution through plume diameter
Adapters for mounting instruments and test articles
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Testing Results
FLOW CHARACTERIZATION
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Operational Envelope
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Maximum Operating Voltage for Power Supply ComponentsH
igh C
oola
nt Tem
p
Bulk Enthalpy 𝑃𝑝𝑙𝑎𝑠𝑚𝑎 = 𝑉𝑎𝐼𝑎 − ሶ𝑚𝐻2𝑂𝑐𝑝Δ𝑇
Use 𝑃𝑝𝑙𝑎𝑠𝑚𝑎 to calculate bulk enthalpy of gas
𝑃𝑝𝑙𝑎𝑠𝑚𝑎 ≈ 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 for given voltageo Increased flow rate for given
voltage decreases bulk enthalpy of gas
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 16
Heat Flux Medtherm gardon gauge heat
flux sensoro Consists of a constantan foil
thermocouple junction
o Water cooled
o Outputs a voltage proportional to the incident heat flux
Slug calorimeter heat flux sensoro Type K thermocouple embedded in
copper slug
o One face of copper slug exposed to flow
o Heat flux related to slope of temperature rise
• 𝑞 =𝑚𝑐𝑝
𝐴ሶ𝑇
5/20/2019 17TFAWS 2018 – AUGUST 20-24, 2018
Gardon Gauge
Slug Calorimeter
Heat Flux (Gardon Gauge)
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Heat flux drops by ~0.9 W/cm2
every mm of axial distance
Heat Flux (Gardon Gauge)
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Heat flux peaks between 30 and
45 slpm flow rate
Heat Flux
ESTIMATED EXIT VELOCITY BULK ENTHALPY
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 20
0
10
20
30
40
50
60
70
80
90
10 20 30 40 50 60 70
Ve
locity (
m/s
)
Mass Flow (SLPM)
5500 K
6500 K
7500 K
Competing effects of velocity
increase and bulk enthalpy
decrease with flow rate
Heat Flux (Gardon Gauge)
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 21
Heat flux peaks between 30 and
45 slpm flow rate
Heat Flux (Slug Calorimeter)
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Heat Flux Calorimeter error based on
temperature slope goodness of fit
Measurements match within experimental error
Calorimeter reads slightly higher than Gardon gauge
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Heat Flux (Radial Variation) Radial profiles taken at 𝑉𝑎 =9.5 kV and various flow rates
Peak heat flux much higher than that measured by calorimeter due to difference in probe shape
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 24
Heat Flux (Radial Variation) Radial profiles taken at 𝑉𝑎 =9.5 kV and various flow rates
Peak heat flux much higher than that measured by calorimeter due to difference in probe shape
Slight drift in central peak with flow rateo Consistent trend for both voltages
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 25
Heat Flux (Radial Variation) Radial profiles taken at 𝑉𝑎 =9.5 kV and various flow rates
Peak heat flux much higher than that measured by calorimeter due to difference in probe shape
Slight drift in central peak with flow rateo Consistent trend for both voltages
Width of peak does not change with flow rate
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 26
Emission Spectroscopy OceanOptics HD2000+ USB
Spectrometero 200nm - 1200nm
o Calibrated with OceanOptics LS1-CAL tungsten calibration lamp
1mm diameter field of view
Emission spectra taken at 2mm intervals through plume diameter
Spectra are Abel inverted to obtain 𝐼(𝜆; 𝑟)
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 27
Emission Spectroscopy Capture spectrum from
narrow beam through plume at multiple radial locations
Fit symmetric polynomial in 𝑥 to intensity measurements, 𝐼(𝑥; 𝜆), for every 𝜆
Abel invert polynomial fit to get 𝐼(𝑟; 𝜆) and therefore 𝐼(𝜆; 𝑟)
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 28
Emission Spectroscopy
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Atomic Oxygen
Atomic Nitrogen
Emission Thermometry Use oxygen emission
Only 777nm and 615nm lines visible and non-overlapping with N emission
Fit line to Gaussian profile to determine intensity
Use intensity ratio of two lines to get temperature
𝑇 =𝜀𝑢2 − 𝜀𝑢1
𝑘 ln𝐼1𝐼2
𝐴2𝐴1
Δ𝜀2Δ𝜀1
𝑔𝑢1𝑔𝑢2
Eliminates need for absolute intensity
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 31
777 nm
615 nm
Emission Thermometry
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Emission Thermometry
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0.75
0.80
0.85
0.90
0.95
1.00
0.0 0.1 0.2 0.3 0.4 0.5 0.6
T/T
max
r/R
Laux
UT ICP 1
UT ICP 2
UT ICP 3
2
Comparison to Other Facilities
UT-Austin UVM4 VKI Plasmatron6
Ecole Centrale,
Paris3,5
Run time 1.5 hr 6 min >10 min
Max Heat Flux 225 W/cm2 85 W/cm2 350 W/cm2
Operating
Pressure500 kPa 10 kPa 1.5 kPa - 20 kPa 100 kPa
Flow Regime Subsonic Subsonic Subsonic/Supersonic Subsonic
Gas Composition Air, Ar Ar, Air, N2, CO2 Air, Ar Ar, Air
Flow Rate 20-75 slpm 0 to 50 slpm 800 slpm 70 slpm
Operating
Frequency6 MHz 2.7 MHz 400 kHz 4MHz
Operating Power 50 kW 30 kW 1.2 MW 50 kW
5/20/2019 TFAWS 2018 – AUGUST 20-24, 2018 34
Future Work Graphite and Teflon test
articleso Pyrometry to measure model
surface temperature
o LIF to measure species concentration near model surface
o Raman scattering to measure temperature and species concentration
Measure recession rates over a simulated heating cycle
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Questions?
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References1. C. Laux, T. Spence, C. Kruger, and R. Zare, “Optical Diagnostics of Atmospheric Pressure
Air Plasmas,” Plasma Sources Science and Technology, vol. 12, no. 2, pp. 125-138, 2003.
2. C. Laux, “Optical Diagnostics and Radiative Emission of Air Plasmas,” Mechanical Engineering, Stanford University, 1993.
3. M. E. MacDonald, C. M. Jacobs, C. O. Laux, F. Zander, and R. G. Morgan, “Measurements of Air Plasma/Ablator Interactions in an Inductively Coupled Plasma Torch,” J. Thermophys. Heat Transf., vol. 29, no. 1, pp. 12–23, 2014.
4. W. Owens, J. Uhl, M. Dougherty, A. Lutz, J. Meyers, and D. Fletcher, “Development of a 30kW Inductively Coupled Plasma Torch for Aerospace Material Testing,” in 10th AIAA/ASME Joint Thermophysics and Heat Transfer Conference, 2010, no. 4322.
5. C. Casses, P. Bertrand, C. Jacobs, et al., “Experimental Characterization of Ultraviolet Radiation in a High Enthalpy Plasma Torch Facility,” in 5th European Conference for Aerospace Sciences (EUCASS), 2013
6. B. Bottin, O. Chazot, M. Carbonaro, et al. “The VKI Plasmatron Characteristics and Performance,” The Von Kármán Inst for Fluid Dynamics, Rhode-Saint-Genese, Belgium, 2000.
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