Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.mrao.cam.ac.uk/projects/OAS/pmwiki/uploads/MROIFastTipTilt.TechMeet4/CameraThermalControlIssues.pdf Äàòà èçìåíåíèÿ: Fri May 21 12:35:39 2010 Äàòà èíäåêñèðîâàíèÿ: Sat Mar 1 04:13:10 2014 Êîäèðîâêà:

The MROI Fast Tip-Tilt/ Narrow-field Acquisition System (FTT/NAS) project
FLC & FTT/NAS Camera Thermal Control Issues

21 May 2010

FTT Technical meeting

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Environmental Requirements


FTT/NAS


Operational Temp Range:-5°C to + 20°C (goal -10°C to +20°C) Operational Humidity Range: 10% to 70% (goal 10% to 90%)



FLC


Operational Temp Range:-15°C to + 20°C Operational Humidity Range: 10% to 70% (goal 10% to 90%) Check these with UT spec.



Both


Surface temp any object `near' beam to be within 2°C of ambient

21 May 2010

FTT Technical meeting

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Camera Thermal Operation Scenarios


No enclosure


cooling fan running: not acceptable if the air temperature in the enclosure is lower than -5°C [0°C from camera spec] No control over humidity ­ dew point problems Start-up issues in cold weather allows some ventilation but otherwise allows the enclosure to warm up: not much better; no thermal or humidity control



Partial enclosure




Camera is placed in a thermally controlled enclosure


temperature is maintained at a few degrees below ambient but not below -5°C and preferably not below 0°C requires a camera enclosure cooling system that tracks a few degrees below ambient but with a low limit set point of ~0°C Dew point considerations eased.

21 May 2010

FTT Technical meeting

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Basic Calculations 1



Heat dissipation and surface temp If the cameras produce 10W convective heat dissipation in a passive enclosure the surface temperature would be approx:



Ts ­Tb = 10W/(2*0.375m2) = 13.3°C Assuming:


no forced cooling (wind) an enclosure of outer dimensions 250 x 250 x 250 mm a convective heat transfer coefficient of (average) 2 over the whole surface area. Excluding radiative cooling



May be OK for FLC (would need to check internal temperature) but is not OK for normal operations
FTT Technical meeting 4

21 May 2010


Basic Calculations 2








For convection cooling in no wind conditions the maximum amount of heat that can be allowed to escape the enclosure without the surface temperature increasing by more than 2°C is (very approximate): Q'= 2*0.375*2 = 1.5W Therefore, at least for the FTT/NAS arrangement we would need to extract ~8.5W by some kind of internal heat exchanger. Best done with a substantial T between the internal enclosure air and the cooling fluid to make heat exchange more efficient and to drive convection within. Coolant temperature of -5°C and an internal air temperature of +5°C would seem OK if the box insulation could be sufficient to allow a T of up to 18°C between internal and external air - otherwise have cooling track ambient.
FTT Technical meeting 5

21 May 2010


Test Results 1


Results from simple tests on Andor camera


Peltier off: camera head dissipation produces T = 2°C in airstream from camera fan compared with ambient temperature. Peltier on: set temperature of -85°C produces T = 8°C camera has a 50mm silent fan. These typically give an airflow of 7 to 10 cu. ft. per minute ( 0.21 to 0.3m3min-1)



Heat dissipated by the camera (approx.):


Heat gained by the air is:

21 May 2010

FTT Technical meeting

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Test Results 2


Approximate camera head dissipation by convection to air:



Peltier Operation
Peltier efficiency (CoP) for a 3-stage device with cold side temperature 85°C and a hot side temperature of 35°C is about 1% but this increases to about 5% if the hot side temperature is maintained at about 10°C. For room temperature ~20°C and fan operation giving an air-stream temperature of 8°C above ambient the hot-side temperature is likely to be ~35°C so the efficiency of the Andor unit is about 1%. The maximum power that the Andor unit delivers for the Peltier is 3A x 5V = 15W and so the maximum power removed at the cold side is about 0.15W which is composed of the detector dissipation and the thermal leakage to the assembly from the environment. Chip power is dominated by the output amplifiers (typically 30mW for the LS and 40mW for the HR amplifiers). Assuming both amplifiers are active this means ~50% of the heat removed is from the chip and the rest is heat transfer from the surroundings.

21 May 2010

FTT Technical meeting

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Camera Enclosure


Minimum size of enclosure is probably 250x250x250mm
Dichroic Corner cube reflector OAP M4 FTT/NAS Camera

Future AO system
21 May 2010

Optical bench is wider than shown here Automated Alignment System

FTT Technical meeting

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Derived requirements candidates


Camera Head


Camera must be enclosed At least 8W (TBC) to be removed by a fluid cooling system Cooling system to track -5°C (TBC) below ambient but to no less than -5°C. Camera must conduct no more than TBC W to optical table A maximum size of enclosure may be defined by other requirements/space envelope



Electronics


Dissipation in electronics rack


Computer (100W TBC) Other electronics we may need (25W TBC) Peltier/camera head enclosure chiller if located here (125W TBC)

21 May 2010

FTT Technical meeting

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Potential Design



Place camera in sealed, insulated enclosure. Use Peltier chiller circuit to extract heat from enclosure.




Pass chilled fluid through enclosure first and then into camera head Mount chiller in electronics rack (no more than 250W allowed to be dissipated so apportion this between chiller and computer plus any electronics. Otherwise need additional fluid/fluid heat exchanger and use telescope coolant.



Avoid heat being conducted to optical table. Mount as far away from beam as possible?


Helps with cable length issues May be able to allow T > 2°C surface temperature? Limit influence of any heat conducted into table
FTT Technical meeting 10

21 May 2010


Thermal Model 1


Schematic of simple cooling arrangement

21 May 2010

FTT Technical meeting

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Thermal Model 2


Equivalent circuit

21 May 2010

FTT Technical meeting

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Thermal Model 3

qo = m'cpT
21 May 2010

o
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FTT Technical meeting