Quote:
Originally Posted by JA
Hi Martin,
yes l think that is the crux of it. Even in ZWO's own literature for the 2600mc and 2600mc they state:
" *The Delta T 35℃ is tested at 30℃ ambient temperature. It might get down when the cooling system is working for a long time. Also, as the ambient temperature falls, the Delta T would also decrease."
So from each of those statements I would conclude:
1. Its limits are a Delta T of 35 ºC at an ambient temperature of 30ºC, so -5
ºC camera temperature.
2. After some/long time cooling (?) the camera temperature may go down further.
3. Delta T of 35 ºC is the maximum temperature drop possible. At say 20 ºC ambient who knows what's possible, but given their comment, a -15 ºC camera temperature is unlikely. As to whether even -10 ºC is possible, it may be a little too close to the limit which is what you may be finding. Perhaps even manufacturing variation between the Peltier coolers or fans in the devices is enough to account for the differences between the 2600mc and 2600mm. It is hard to be certain.
One thing though operating at higher relative humidity, means the ambient air used for the cooling has a greater water content. This means that importantly that the air, in the context of heat transfer, will have a higher film heat transfer coefficient, since typical film heat transfer coefficients for liquids are 1 to 2 orders of magnitude times higher than those for gases. Now the humid air may only contain a few grams of water per kilogram of dry air, so it won't be as extreme as a 1 to 2 orders of magnitude, but it's enough to make it different.
A higher film heat transfer coefficient means the cooler has more difficulty in lowering the Aluminium fin temperature (for a given heat flux) whilst transferring heat across the air film boundary layer at the Aluminium / air interface where most of the heat is being exchanged. This results in a slightly higher aluminum fin temperature than with dry air and thus a slightly reduced ability in transferring heat from the sensor.
Best
JA
PS: I was going to suggest exactly as Glen did that the use of an auxiliary fan might get you to where you want to be. That also gives me another thought along the lines of your thoughts of your (possibly) aging 2600mc camera and that is, perhaps the fan maximum airflow varies or is different either due to aging or other factors. You could possibly test the differences (or not) between your two cameras with an airflow meter. |
Thanks JA
Excellent evaluation
I just need a day to test without this horrible humidity at the moment
Cheers
Martin