Hi If I can keep the "inside can" reasonably gradient free, then I don't need as many layers. Fewer layers probably means less temperature rise. That should stretch out the lifetime of the already "used up" rubidium.
Bob On Dec 23, 2009, at 6:31 PM, Bruce Griffiths wrote: > You shouldn't need to try to keep the gradients within the box low as long as > they are stable despite changes in ambient temperature, pressure, humidity > etc. > The mulitlayer technique just ensures that the distribution of heat flow to > ambient is invariant thereby ensuring that the inevitable gradients within > the rubidium package are relatively invariant. > > Bruce > > Bob Camp wrote: >> 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<bruce.griffi...@xtra.co.nz> >>>>>> Subject: Re: [time-nuts] Cheap Rubidium >>>>>> To: Discussion of precise time and frequency measurement >>>>>> <time-nuts@febo.com> >>>>>> >>>>>> 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 -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
