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Enclosure Thermal Control. 25 August 2003 ATST CoDR. Dr. Nathan Dalrymple Air Force Research Laboratory Space Vehicles Directorate. Enclosure Thermal Control. Function: Suppress seeing. Seeing is caused by temperature differences. - PowerPoint PPT Presentation
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Enclosure Thermal Control
25 August 2003 ATST CoDR Dr. Nathan Dalrymple
Air Force Research LaboratorySpace Vehicles Directorate
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
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.
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
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.
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.
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
Shell Seeing, Seeing-Limited Error Budget
Blue contours: 50% encircled energy (arcsec)
Acceptable operating range
= 1600 nm
Shell Seeing, Coronal Error Budget
Blue contours: 50% encircled energy (arcsec)
Acceptable operating range
= 1000 nm
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.
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
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
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.
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
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
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
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.)
Skin Cooling System Flow Loop
Insert diagram here
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
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
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.)
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)
Flushing System Concept
42 vent gates
168 m2 flow area,each side
Flushing System Performance
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
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
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.