we have reached ambient, so we can get an idea of how long it took to catch up from the graphat 8.45 pm, ambient was 17.5 and starting to flatten out. 1 hour and 15 minutes later it had stabilised at 17.1. the mirror in that time had dropped .8 of a degree.
so the old hour rule is pretty good!!!!
remember .5 of a degree difference or less is best!
i am the brand new owner of a 57mm hole on the side of my tube!. The mirror is out of the cell so that sharp metal filings did not produce pretty patterns on the mirror and I may as well clean it whilst it is out. Off to the shop for de mineralized water!
Have cut all protusions off the computer fan off and the square base sits very nicely into the 57mm hole!
I will drill some small vents later into the side of the tube later, once i have seen how this suction action will go. I reckon for tube strength, i will drill two sets of holes (small to start) 1/3 of the way around to the left and right to keep it symmetric.
The bottom bit of the fan is placed flush with the top of the mirror, so the boundary layer should be affected by the suction of the fan
Nice hot day and a chance of no clouds, so another temp run tonight!!!
Hi Davo. Your gamer than I am mate! Well done. I'll be HIGHLY interested in this experiment!! I've been wanting to do that for 2 years now! Looking forward to the results...especially between sucking & blowing! Is it variable speed??
I'm going to make a prediction & say you will have better results blowing rather than sucking.
If this experiment is SPECIFICALLY designed to get rid of the boundary layer, if the mirror is at ambient there IS no boundary layer to get rid of.
well, two fold:
1. i want to get the mirror quickly cooled to ambient in less than the hour that it roughly takes (from previous experiments) and in your case 4hrs!. ie if the temp is falling throughout the night, then the mirror will mean that i can start imaging sooner instead of waiting for the mirror to catch up.
2. now that i have a hole, it should also get rid of the dew that can now have easier access to the mirror!
Another thing I thought of..& no doubt you've thought of this also!...The AREA of the holes you've made. The holes on the opposite side of the fan should be a bigger area if you know what I mean? If it can't suck (or blow) thru those holes at the same rate as the fan it could start drawing from the air in the OTA setting up tube currents. (but it may do this in any case) I suggest you try it out without any cool down. Defocus on a star & you will plainly see the heat haze from the mirror & then kick in the fan while your viewing & see what happens...
i won't drill any extra holes yet, as at the end of the day, if there is enough air being sucked down the tube and from underneath (there a rather large air gaps in the mirror cell) and thus colder ambient air is being brought in from the outside to help cool the mirror through movement and convection, then i should be fine.
If i can get say a 10 minute or less lag to get the mirror within 1/2 degree then it is doing its job. If there is not enough air coming into the system, then more vent holes may be required.
To my mind, i will follow bird and not image whilst fans are on!
