[time-nuts] Cheap Rubidium
lists at cq.nu
Wed Dec 23 22:33:42 UTC 2009
The idea of locating the fan far removed from the heat sink and then using some kind of a duct might work pretty well.
On Dec 23, 2009, at 3:31 PM, Joe Gwinn wrote:
>> Date: Thu, 24 Dec 2009 08:57:42 +1300
>> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
>> Subject: Re: [time-nuts] Cheap Rubidium
>> To: Discussion of precise time and frequency measurement
>> <time-nuts at febo.com>
>> Bob Camp wrote:
>>> So if I want to set up 4 uncorrelated systems, that would require 20 tons of
>>> water split into 4 tubs. Each tub would be roughly 3' x 4' x 15'. Of course
>> > if they are all in the same basement, I still have a correlation problem. My
>>> guess is that no matter what I do, any system that controls all the systems
>>> the same way will run into correlation.
>>> Oils, silicon fluids, and the like mostly hold less heat than water so the
>>> tubs would get bigger. Maybe a few tons of mercury...
>> Try about 145 tons of mercury per rubidium source as the specific heat
>> of mercury is about 1/29 that of water.
>> The redeeeming feature is that it will only occupy about 2.14x the volume.
>> The specific of some oils may be as large as 1/2 that of water however
>> the density is around 10-20% lower.
>>> Active heat control and a rational heat sink is sounding like a better
>> Distributed heating using wire wound or printed heaters perhaps, but to
>> reduce the associated magnetic field bifilar winding should be considered.
> Non-inductive power resistors, which are commercially available, have very low magnetic fields.
> The low-inductance resistors have Ayrton-Perry windings, which are bifilar.
>> The major limitation is that the 25W or so dissipated by the rubidium
>> source has to be transferred to ambient without raising the rubidium
>> temperature too much.
>> This limits the maximum thermal resistance between the baseplate and
>> ambient that can be safely used.
> I would be tempted to regulate temperature by actively controlling the speed of the fan (or pump) driving air (or oil) through the heat sink, as has been suggested.
> Joe Gwinn
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