Enclosure Thermal Control 25 August 2003 ATST CoDR Dr. Nathan Dalrymple Air Force Research...
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![Page 1: Enclosure Thermal Control 25 August 2003 ATST CoDR Dr. Nathan Dalrymple Air Force Research Laboratory Space Vehicles Directorate.](https://reader036.fdocuments.net/reader036/viewer/2022062308/56649cd65503460f9499d23d/html5/thumbnails/1.jpg)
Enclosure Thermal Control
25 August 2003 ATST CoDR Dr. Nathan Dalrymple
Air Force Research LaboratorySpace Vehicles Directorate
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Enclosure Thermal Control
• Function: Suppress seeing
If a surface is the same temperature as the surrounding air, that surface introduces no seeing
Seeing is caused by temperature differences
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Requirements
1. Suppress enclosure seeing
a. Racine experiment: = 0.15 Ti - Te) 1.2
b. Ford analysis: = 0.012 Ts - Te 1.2
c. IR HB aerodynamic analysis: = TV, d. Bottom line: requirements on surface-air T, interior-
exterior T, and wind flushing
2. Provide passive interior flushing to equalize interior and exterior temperatures and to suppress structure and mirror seeing
Ref: Racine, Rene, “Mirror, dome, and natural seeing at CFHT,”
PASP, v. 103, p. 1020, 1991.
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Error Budgets
(nm) Exterior budget Interior budget
500 20 nm 10 nm
1600 0.07 arcsec 0.02 arcsec
1000 0.06 arcsec 0.025 arcsec
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IR Handbook Seeing Analysis
Given layer thickness and T, we can estimate .
zlG z
Hd2
0
222
Wavefront variance
Gladstone-Dale parameterFluctuating density Line-of-sight correlation length
Layer thickness
HlT
TGz2
10
22
Phase variance
2.01.0 H
lz
Surface-air temperature difference
)(1)exp(
)(33.3
s2
D
s
aberrationweak
aberrationstronglz
Blur angle
Strong/weak cutoff ~ 2 rad
Ref: Gilbert, Keith G., Otten, L. John, Rose, William C., “Aerodynamic Effects” in The Infrared and Electro-Optical Systems Handbook, v. 2, Frederick G. Smith, Ed., SPIE Optical Engineering Press, 1993.
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IR Handbook Seeing Analysis (cont.)
Layer thickness (mks units):
2.0
8.05.05.1
0392.0184.0V
L
V
TLH
L: upstream heated length (m)T: average temperature difference over upstream length (˚C)V: wind speed (m/s)
Buoyancy term Hydrodynamic term
Assume: If T < 0 then buoyancy term does not contribute to layer thickness.
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Shell Seeing, Diffraction-Limited Error Budget
Blue contours: rms wavefront error (nm)
Acceptable operating range, assuming no AO correction.
AO correction will extend the “green” area.
= 500 nm
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Shell Seeing, Seeing-Limited Error Budget
Blue contours: 50% encircled energy (arcsec)
Acceptable operating range
= 1600 nm
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Shell Seeing, Coronal Error Budget
Blue contours: 50% encircled energy (arcsec)
Acceptable operating range
= 1000 nm
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Dome Seeing (Inside/Outside Air T)
Correlation by Racine (1991)
Approximate error budget
Approximate T requirement
Need lots of passive flushing!
Ref: Racine, Rene, “Mirror, dome, and natural seeing at CFHT,”
PASP, v. 103, p. 1020, 1991.
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0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00
local time
seei
ng (
arcs
ec)
Shell seeing (arcsec)
Interior seeing (arcsec)
Dome seeing (arcsec)
IR Handbook aerodynamic treatment
Correlation of Racine (1991)
IR Handbook aerodynamic treatment
Good seeing from KE test
Ref: Racine, Rene, “Mirror, dome, and natural seeing at CFHT,”
PASP, v. 103, p. 1020, 1991.
BBSO Dome Seeing Experiments
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0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00
local time
seei
ng (
arcs
ec)
Shell seeing (arcsec)
Interior seeing (arcsec)
Dome seeing (arcsec)
Bad seeing from KE test
BBSO Dome Seeing Experiments
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A Nighttime Comparison: Gemini Dome
Gemini Thermal Tests: 11 - 14 Mar 2003Dome skin temperature [deg C]
-5
0
5
10
15
20
25
30
35
40
3/11 0:00 3/11 12:00 3/12 0:00 3/12 12:00 3/13 0:00 3/13 12:00 3/14 0:00 3/14 12:00 3/15 0:00
Top left (55 deg)
Middle left (36 deg)
Lower left (22 deg)
Top right (55 deg)
Middle right (36 deg)
Lower right (22 deg)
Air Temperature
1 Duct exhaust fan on, low-moderate wind (3 - 5 m/s)
T = -3 ˚C
Acceptable seeing observed with shell subcooled by 3 ˚C.
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Bottom Line Requirements
• Enclosure skin temperature needs to be subcooled by up to 3 ˚C
• Interior air temperature needs to be within 0.5 ˚C of ambient outside air
• Need large passive flowrate to flush interior
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Skin Energy Balance
We want to use this term to control the skin temperature
[~0 W/m2]
[377 W/m2]
[374 W/m2]
[98 W/m2]
[~100 W/m2]Quantities vary by location on dome and weather conditions
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Skin Thermal Control System Concept
Concept Features:1. White oxide paint
a. Large b. Small s
2. Chilled skina. Airb. Liquid (EGW)
3. Insulationprevents interior from beingchilled by skin coolant
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Shutter: air cooled, optional water cooling on lower endhair ~ 8 W/m2-KhH2O ~ 100 W/m2-K
Enclosure support wall: water cooled if presenthH2O ~ 100 W/m2-K
Oblique skin panels: air cooled, h ~ 5 W/m2-K
Sun-facing skin panels:
air or water cooledhair ~ 5 W/m2-KhH2O ~ 100 W/m2-K
Option: use fins on skin underside to increase effective area
Skin Thermal Control System Concept (cont.)
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Skin Cooling System Flow Loop
Insert diagram here
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MuSES Model Validation: Measured and Predicted Dome Skin Temperature
30 April 2003
0
5
10
15
20
25
30
9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00
Top left (55 deg)
Lower left (22 deg)
Air temperature
Elem 2749
Elem 2738
MuSES Modeling: Validation at Gemini North
Validation
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Skin Thermal Control System Performance
MuSES snapshot at 1430LT, 30 April 2003, Mauna KeaWind speed = 0.5 m/sAmbient air Te = 7 – 8 ˚CAir Cooling Only on SkinESW Water Cooled
Most of surface is acceptable
Sun-facing areasare ~ 5 ˚C hotter than ambient
Surfaces that see cold sky subcool
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MuSES snapshot at 1430LT, 30 April 2003, Mauna KeaWind speed = 0.5 m/sAmbient air Te = 7 – 8 ˚CAir & Water Cooling
Nearly all of surface is acceptably cool
Sun-facing areascooled with water
Surfaces that see cold sky subcool
Skin Thermal Control System Performance (cont.)
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Cooling Requirements
• Next steps:•Fan and system curves•Heat exchanger specs•Chiller specs•Time response of fluid volume
At peak heat load, surface cooling requires:• Air-cooled skin: 56 kW• Water-cooled skin: 18 kW• Lower shutter: 14 kW• Air-cooled shutter: 18 kW• Total for carousel: 106 kW• Enclosure support wall: 104 kW• Grand total: 210 kW (60 tons)
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Flushing System Concept
42 vent gates
168 m2 flow area,each side
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Flushing System Performance
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Active Interior Ventilation
• Gemini volume flowrate: 10 enclosure volumes/hour (150,000 m3/hr)• This flowrate on the smaller hybrid gives V ~ 0.2 m/s average • Directed flow can give V~0.5 – 1 m/s over much of structure
Fans may be mounted remotely or on carousel
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Active Ventilation Issues
• Fan blades heat air seeing• Require homogenizing screens, cooling coils
downstream of fans• May not be simple to mount all this on
carousel possible to mount remotely
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Shell Seeing Performance
Blue contours: rms wavefront error (nm)
Red: average T of skin, front skin, shutter, lower shutter, ESW
Most of the dome surface will give acceptable seeing
Back of shutter subcools. May need to add water cooling there as well.