Water cooling on a moving/rotating telescope (a really big telescope)

[ngc]

Hi all,

Apologies if this is the wrong place to ask, but I have an unusual (or so I think) problem to solve.

I need to liquid cool a camera on that's on a moving/rotating platform (on a really big telescope), that will move in pretty much all orientations, upside down etc.

I am currently using something called an Oasis UC160 liquid chiller to cool the camera in the lab. It provides a steady temperature to camera and works very well in a stationary position. However, it will not function on this moving platform since the reservoir cannot operate in any other position than upright.

Does anybody know if an alternative reservoir exists which I could use in conjunction with my liquid chiller?

(the telescope is a bit too big to place the chiller/reservoir on the ground, tubing would get in a mess )
Thanks!

[tikker]

7 minutes ago, ngc said:

However, it will not function on this moving platform since the reservoir cannot operate in any other position than upright.

Wouldn't not turning the telescope upside down not be an easier solution? You only need to move it along two axes, either alt/az (azimuthal mount) or ra/dec (equatorial mount) and avoid moving it through zenit.

7 minutes ago, ngc said:

the telescope is a bit too big to place the chiller/reservoir on the ground, tubing would get in a mess

Can you mount it on the mount? You'll very often have trouble with cables. That's why observatories impose limitations and rules to how you can slew the telescope.

[ngc]

It is an equatorial mount telescope, where the telescope takes up ~6m*6m*6m of space.  Afraid I can't choose not to be upside down - our stars of interests (for science) mean the telescope will eventually be in a position which would cause a leak/pump malfunction for the chiller.

[ngc]

26 minutes ago, tikker said:

Can you mount it on the mount? You'll very often have trouble with cables. That's why observatories impose limitations and rules to how you can slew the telescope.

Just saw this.  It is maybe an option (perhaps a last resort) - but there's some uncertainty that the tubing will still get tangled or get hooked on to something as it changes position

[For Science!]

Its not a great solution, but perhaps a dual-pump mount like for the EKWB dual D5 would mean even if it is upside down, at least one pump will still be upright and may be enough to keep it operational. 

[brob]

Is a Peltier cooler an option?

[porina]

Really curious what the set up is! Did some astro imaging in the past but nothing on this scale.

 

As for the cooler, I have to wonder, do you really need something that powerful? Is an air cooled solution not sufficient?

[tikker]

1 hour ago, ngc said:

It is an equatorial mount telescope, where the telescope takes up ~6m*6m*6m of space.  Afraid I can't choose not to be upside down - our stars of interests (for science) mean the telescope will eventually be in a position which would cause a leak/pump malfunction for the chiller.

 

48 minutes ago, ngc said:

Just saw this.  It is maybe an option (perhaps a last resort) - but there's some uncertainty that the tubing will still get tangled or get hooked on to something as it changes position

Doesn't necessarily have to be the immediate mount of the telescope, I meant more the supporting structure like the pillar attaching it to the ground. I think giving it plenty of tubing and cable-managing that may be the most straightforward way. I've operated an equatorial telescope for a while and cabling was also an issue. The way we managed it was to not allow travel through zenit (although I don't think any observatory let's you do this, not wise anyway) and not allowing more than a certain amount of rotation along a certain axis. Like, if you were at 360* RAand wanted to slew to an object at 5* RA you'd have to go backwards the entire way, otherwise the cabling simply got twisted up too much.

36 minutes ago, porina said:

As for the cooler, I have to wonder, do you really need something that powerful? Is an air cooled solution not sufficient?

Air cooled can work, but the colder the CCD the better if you want to go deeper. It limits the amount of so-called "dark current", which produces noise proportional to the temperature of the sensor. Besides cold you therefore ideally also want a stable detector temperature moreso.

[porina]

8 minutes ago, tikker said:

Air cooled can work, but the colder the CCD the better if you want to go deeper. It limits the amount of so-called "dark current", which produces noise proportional to the temperature of the sensor. Besides cold you therefore ideally also want a stable detector temperature moreso.

I get that, been there before without the cooling part. That was too spendy for my level of interest. Still recall the fun of creating dark frames to try and subtract noise. My point remains, just how far can you get with air if the logistics of water are getting too complicated?

 

It might be easier to visualise potential solutions if we can see the physical setup where this will be used.

[tikker]

30 minutes ago, porina said:

I get that, been there before without the cooling part. That was too spendy for my level of interest. Still recall the fun of creating dark frames to try and subtract noise. My point remains, just how far can you get with air if the logistics of water are getting too complicated?

 

It might be easier to visualise potential solutions if we can see the physical setup where this will be used.

Ah cool. I'm curious which telescope OP is working with. If just the telescope takes up a 6 m x 6 m area it almost must be a (somewhat) known one as that's quite sizeable. If that's the entire dome area then I'm guessing it's a smaller like maybe 50-100 cm ish scope, in which case more than air may not be totally worth it as you say.

[Demonic Donut]

I'm not sure I have a solution for you, but most chillers need to be upright and level during operation, not just for the reservoir, but for the compressor.

 

Your best bet, imo, is a well engineered soft tubing solution that won't get tangled.

[ngc]

Thank you everyone for your interest!  Super nice to see some background in astronomy instrumentation too

I have attached some videos and an image to help fuel your creative minds

To answer some of the questions:
 - Liquid cooling is the only option I'm afraid for the science we want, we need the detector to get down to -60C, the camera's in built peltier stack can only do this in a stable way with liquid.  (Air cooling only gets our camera to a stable -40C at ambient temps. )
 - The telescope is 1m in diameter, but the dome is 6m in diameter, with the height more like 5m. (small-medium size in world of professional astronomy)
 - It does indeed have a limit on the rotation to prevent cable tangling. I don't know the exact value but maybe 180 degrees both ways. But even then, we worry the tubing could get stuck on something.  The power/data for the camera is internally routed through the telescope (through that black cable router in the attached videos/images), but as far as I understand, there sadly isn’t space for liquid tubing to go the same route.
 - A double pump situation could be interesting - would need to figure out how to mate that with our chiller which regulates the liquid at ~10C.

I just remembered the telescope itself will always be pointing at least 20 degrees above the horizon (any angle below that the mirror risks falling out!).
 

Do you think we could replace the tank/reservoir with one that will have the inlet/outlet in a position that will never let air go into the system, regardless of the telescope’s position (with the knowledge that it will never point below 20 degrees)? Anyone know of an existing model reservoir that could work?

[SansVarnic]

-= Topics Merged =-

[Demonic Donut]

I didn't realize you were using a peltier chiller, is the reservoir built into the chiller or do you have an external one?

 

You can do a sealed loop for the chiller if you have room for an expansion tank.

[ngc]

6 hours ago, Demonic Donut said:

I didn't realize you were using a peltier chiller, is the reservoir built into the chiller or do you have an external one?

 

You can do a sealed loop for the chiller if you have room for an expansion tank.

 

The reservoir is built in the chiller, but I am open to modification.  I'm not familiar with expansion tanks, but I'm aware some exist with a membrane to maintain pressure in the system? (say, when the telescope is upside down pointing low in the horizon).

 

 

[Demonic Donut]

2 hours ago, ngc said:

 

The reservoir is built in the chiller, but I am open to modification.  I'm not familiar with expansion tanks, but I'm aware some exist with a membrane to maintain pressure in the system? (say, when the telescope is upside down pointing low in the horizon).

 

 

Reading through the manual, I see there is an option for a sealed reservoir plug, so it may be possible to run a sealed loop.

 

You need an expansion tank to maintain consistent pressure throughout the range of operating temperature in a sealed loop. Say the loop is at ambient temp and 5psi, if the loop temp raises or drops, pressure will rise or fall as well within the loop, and depending on loop temp swing, size and material, the pressure differential can be quite extreme. The expansion tank bladder gives the loop fluid room to expand or contract but stay at a consistent pressure. You simply need a T fitting on the inlet side of the chiller, with the take off of the T going to the expansion tank. Water volume dictates the size of expansion tank needed, but I would imagine you have a very small loop and a 1 gallon expansion tank would be plenty. You'll just need to be sure to bleed any air from the system so that the pump never air locks.

 

Install a pressure gauge as well so you can monitor system pressure, especially when this is first done. This way you can adjust expansion tank pressure as needed, but generally you want to set expansion tank pressure to desired system pressure.

 

You stated -60C for operating temp, that wasn't a typo? What fluid are you using? Glycol % must be over 70% if that is the true operating temp?