Hi If I could figure out a way to put the rubidium and a fan inside a box, that would keep the gradients down to a pretty low level. Then do the layer thing around that box. I could make it work with a set of fan blades on a plastic shaft, but that could get a little crazy.
Bob On Dec 23, 2009, at 5:46 PM, Bruce Griffiths wrote: > The stability of the temperature distribution within the baseplate can be > improved with respect to changes in the speed of the cooling fluid (gas, or > liquid) by connecting the heat exchanger (finned heatsink or equivalent) to > the rubidium base using alternating layers of good thermal conductor and poor > thermal conductor). > As the number of layers increases the inner high thermal conductivity layers > will tend to become isothermal even if the heat exchanger or the base of the > rubidium source is not. > This stabilises the temperature gradients seen at the base of the rubidium > source. > > Bob Camp wrote: >> 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. >> >> > > > > _______________________________________________ > 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.
