Hi The idea of locating the fan far removed from the heat sink and then using some kind of a duct might work pretty well.
Bob On Dec 23, 2009, at 3:31 PM, Joe Gwinn wrote: >> Date: Thu, 24 Dec 2009 08:57:42 +1300 >> From: Bruce Griffiths <[email protected]> >> Subject: Re: [time-nuts] Cheap Rubidium >> To: Discussion of precise time and frequency measurement >> <[email protected]> >> >> Bob Camp wrote: >>> Hi >>> >>> 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 >>> approach... >>> >>> >> 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. > > <http://www.token.com.tw/resistor-pd/power-resistor-ah.htm> > > >> 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 > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
