[time-nuts] Cheap Rubidium (heatpipe cooling for)

Bob Camp lists at cq.nu
Fri Dec 25 13:26:24 UTC 2009


Hi

I'm guessing that some kapton tape will get used at the junctions to take care of that issue.

Bob


On Dec 25, 2009, at 12:04 AM, Bruce Griffiths wrote:

> Another thing to watch out for is circulating currents due to thermal emfs with the aluminium to steel contacts.
> Such thermoelectric currents will in turn generate a magnetic field.
> 
> 
> 
> Bruce
> 
> Bob Camp wrote:
>> Hi
>> 
>> The big hitters for heat outside the physics package seem to be the RF excitation and the microwave generation "stuff". The regulators will warm things up if you run high voltage into them, but I would probably not do that.
>> 
>> I don't believe that putting multiple swimming pools into the basement, mercury filled or otherwise was ever a real candidate for a solution. It is kind of interesting to see just how big the "jug of water" would have to be.
>> 
>> Right now my leading candidate is a multi layer aluminum / steel enclosure with a "point short" between each of the layers to keep the heat rise under control. Cool the "baseplate" with recirculating water and a cheap (<  $50) pump. Throw in a fan and radiator to cool the water to room temperature.  Servo the temperature with "what ever" at the point shorts. Monitor the temperature as best you can.
>> 
>> The main "what ever" still in there are TE coolers. A quick look suggests that +12 heats and -12 cools. In between the two it's not clear that much happens (maybe it does ...). Even if it does not, I haven't dug deep enough to see if something like current drive takes care of the dead band issue.
>> 
>> Some math. It's late, but I think this is about right:
>> 
>> 1) 4 layers
>> 2) Shorts at 2 C/W
>> 3) 10 W "inside"
>> 4)  80 C heat rise - not going to work
>> 
>> If I stick with 4 layers, 10 W, and a 15 C rise then the shorts need to be ~ 0.38 C/W.  A 15C rise gets me to 40C which looks reasonable based on the app notes I have read on the rubidiums.
>> 
>> If the basement moves up 5 C then I'm cold pumping 1/3 of the 10W. Same thing in reverse if the basement drops 5 C. Both are unlikely to happen as long as there isn't a catastrophic failure of the HVAC.
>> 
>> If I go to a air cooled baseplate heat sink, it's thermal resistance is going to have to come out of the budget.  My *guess* is that's going to be more involved than a simple pump and some plastic tubes.
>> 
>> Bob
>> 
>> On Dec 24, 2009, at 10:46 PM, Hal Murray wrote:
>> 
>>   
>>> lists at cq.nu said:
>>>     
>>>> The original intent was to simply take an existing "cheap" rubidium
>>>> and do simple things to it. Tearing it into pieces and redesigning
>>>> parts of it was not anything I originally contemplated. The tight
>>>> integration of the physics package to the electronics would make this
>>>> a fairly involved process.
>>>>       
>>> Sure, but if we are discussing digging a hole big enough for a ton of
>>> mercury, then taking apart a tightly integrated package seems worth
>>> considering.
>>> 
>>> I expect the packaging might be reasonable for this purpose.  After all, the
>>> designers probably wanted to keep that heat away from the electronics.
>>> 
>>> 
>>> 
>>> -- 
>>> These are my opinions, not necessarily my employer's.  I hate spam.
>>> 
>>> 
>>> 
>>> 
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>> 
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> 
> 
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