Does the fan-behind-mirror/baffle arrangement so many folks are trying work as well as the Adler arrangement (where the fan blows over the primary) described in the S&T article? Has anyone compared?
Fan Questions
Started by nycdutch, 10/12/2003 12:00AM
Posted 10/12/2003 12:00AM
Opening Post
Posted 10/12/2003 03:47PM
#1
Ian,
That's a good question. That I cannot answer directly. Nonetheless, I feel the urge to pontificate
The fan behind the mirror with a baffle meets the basic tenants on which Adler based his quest for cooling and boudary layer control. It moves air across the entire face of the primary mirror. Certainly, Adler's implemetation moves more air and Adler did indicate in his article that the cooling was much more effective when he added the exhaust ports. That may infer that the rear fan/baffle method is not as effective and I would tend to agree from a purely analytical standpoint.
But, my qualitative data show that the rear fan/ring baffle method is very effective. As effective as Adler's side fans and exhaust ports? Dunno, but good enough for me to stop and not drill holes in my OTA.
Hope that was vague enough to not actually provide any useful information. I may run for political office and needed the practice.
Clear skies,
Tom
That's a good question. That I cannot answer directly. Nonetheless, I feel the urge to pontificate
The fan behind the mirror with a baffle meets the basic tenants on which Adler based his quest for cooling and boudary layer control. It moves air across the entire face of the primary mirror. Certainly, Adler's implemetation moves more air and Adler did indicate in his article that the cooling was much more effective when he added the exhaust ports. That may infer that the rear fan/baffle method is not as effective and I would tend to agree from a purely analytical standpoint.
But, my qualitative data show that the rear fan/ring baffle method is very effective. As effective as Adler's side fans and exhaust ports? Dunno, but good enough for me to stop and not drill holes in my OTA.
Hope that was vague enough to not actually provide any useful information. I may run for political office and needed the practice.
Clear skies,
Tom
Posted 10/13/2003 01:37AM
#2
OH OH OH... one more question...
What about dew? Does this arrangement make the mirror more susceptible to dew? Does the movement of the air actually help prevent dew? I guess it's comes down to a big compromise between the ideal from the perspective of dew: a temperature just above the ambient temperature (I think that's simplifying it -- whatever), and the ideal from a thermal management perspective: a mirror at the ambient temperature. Of course if your primary dews over you can't see anything anyway... What about using a dew prevention system WITH the fan?
OK... I need to finish my scope soon, so I can stop obsessing about details and actually observe LOL!
What about dew? Does this arrangement make the mirror more susceptible to dew? Does the movement of the air actually help prevent dew? I guess it's comes down to a big compromise between the ideal from the perspective of dew: a temperature just above the ambient temperature (I think that's simplifying it -- whatever), and the ideal from a thermal management perspective: a mirror at the ambient temperature. Of course if your primary dews over you can't see anything anyway... What about using a dew prevention system WITH the fan?
OK... I need to finish my scope soon, so I can stop obsessing about details and actually observe LOL!
Funding Member
