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

Mon Dec 28 15:52:41 UTC 2009

Hi
With all the dialog on controlling temperature of the Rb unit I decided to  
take my Frequency Electronics Inc. 5062B apart since the Oven Controlled  
Oscillator and Rb Physics Package are separate and I may want to replace the  
oscillator with a HP 10811 that Corby has tested to be better than 1 E 12 
from 1  to 100 sec.
In order to proceed it would help if any one out there has any information  
on the circuitry, the unit has two modules and two PC boards. The boards 
are  power supply and synthesizer and the modules are Rb unit and oscillator. 
I have  opened the Rb unit and I am convinced that it can be a candidate for 
heat pipe  cooling. Since it can be operated separate from the rest of the 
unit it will be  possible to measure heat rise. 
The published  plot of a 5600 shows a temp performance of +- 3 E -11  from 
-5 to +45 C. I am not sure if there is room for improvement. 
Any help would be greatly appreciated.  

Bert Kehren    WB5MZJ    Miami

In a message dated 12/27/2009 2:18:14 P.M. Eastern Standard Time,  
lists at cq.nu writes:

Hi

The tip it and listen to it slam test is a standard way  of checking out a 
triple point of water cell for basically the same reason  (you check the 
vacuum. Of course since a TWP cell is thin glass and not a nice  metal pipe, 
you *may* break the seal by testing it  ....

Bob

On Dec 27, 2009, at 9:33 AM, Joe Gwinn  wrote:

> At 12:00 PM +0000 12/27/09, time-nuts-request at febo.com  wrote:
>> 
>> Date: Sat, 26 Dec 2009 17:04:46  -0700
>> From: Robert Darlington  <rdarlington at gmail.com>
>> Subject: Re: [time-nuts] Cheap  Rubidium (heatpipe cooling for)
>> To: Discussion of precise time and  frequency measurement
>>      <time-nuts at febo.com>
>> 
>> My comments are in-line,  below....
>> 
>> On Fri, Dec 25, 2009 at 4:38 PM, Joe Gwinn  <joegwinn at comcast.net> wrote:
>> 
>>> At 12:45 AM  +0000 12/25/09, time-nuts-request at febo.com wrote:
>>>  
>>>> 
>>>> Date: Thu, 24 Dec 2009 17:14:38  -0700
>>>> From: Robert Darlington  <rdarlington at gmail.com>
>>>> Subject: Re: [time-nuts]  Cheap Rubidium (heatpipe cooling for)
>>>> To: Discussion of  precise time and frequency measurement
>>>>       <time-nuts at febo.com>
>>>> 
>>>>  
>>>> On Thu, Dec 24, 2009 at 1:32 PM, Bob Camp  <lists at cq.nu> wrote:
>>>>  
>>>>   Hi
>>>>>  
>>>>>  A heat pipe might work if the fluid had a  sufficiently low boiling
>>>>>  point.
>>>>> 
>>>> 
>>>>  
>>>> The working fluid in a heat pipe will boil at every  temperature above 
its
>>>> melting point.
>>>>  
>>> 
>>> Well, I've been thinking about this, and I  used the term "heat pipe" 
too
>>> loosely.  Both the one- and  two-pipe systems mentioned here have no 
wicks,
>>> and so  technically are two-phase thermosyphons, which depend on 
gravity  to
>>> circulate vapor and condensate.  A true heat pipe has  a wick, and will 
work
>> > in zero gravity.
>>>  
>>> One gets significant heat transfer by phase change so long as  the vapor
>>> pressure in the heat input end is high enough to  generate enough vapor 
to
>>> carry the thermal power flow, and  this makes the pipe isothermal.  
However
>>> the temperature  (although constant along the pipe) varies with the 
thermal
>>>  power flow (in thermal watts) being carried.
>>> 
>>>  What I'm looking for is related but different:  A device where the  
heat
>>> transfer capacity varies sharply with temperature, so  that there is a 
range
>>> of heat transfer rates over which the  input-end temperature will be
>>> substantially constant.   This is why I envision the fluid boiling 
(versus
>>> evaporating),  which is actually out of the operating regime of a true 
heat
>>>  pipe.
>>> 
>> >
>>>> I tend to use  water because it's cheap, but have made them
>> >> with 3M  "engineered fluids", Fluorinert, and denatured alcohol.
>>  >
>>> Fluorinert.  I think that's what the expensive  commercial CPU-cooling
>>> heatpipes use.
>>>  
>> $1000 a gallon!  Or $5 a drum when you buy it at a salvage  auction.
> 
> That explains why low-end heatpipes use alcohol or  acetone.
> 
> Actually, one ought to be able to use the freon  intended for automobile 
air conditioners, for a whole lot less money, even  new.
> 
> 
>> >>  I've  found
>>>> that ordinary solder works just fine.  A trick  to make these things 
easy
>>>> to build is to use a ball valve  at the top (I'm assuming there is a 
top and
>>>> we're going  with gravity return because it's simple).  I've got a few 
 that
>>>> are still under vacuum for several years now in this  configuration.  
My
>>>> giant heat pipe of doom is a 10  foot stick of 1/2" copper with a ball 
valve
>>>> at one end and  an end cap at the other.  There is perhaps 100ml water 
 in
>>>> there total, and no air.  You can either boil the  liquid until it 
builds up
>>>> a nice head of steam, or go the  easy way and pull a vacuum with a 
pump and
>> >> just close the  valve.
>> >
>>> I wouldn't have thought that an  ordinary ball valve would be tight 
enough,
>>> allowing the water  to escape and the air enter, slowly, although I 
suppose
>> > one  can replace the water if it comes to that.
>> >
>> Mine  have been running for a few years with no sign of needing to be  
pumped
>> down again.  They just work.
>> 
>>  > But I think people want to build this exactly once, so I  followed
>>> refrigeration practice.  A properly made  hermetically sealed 
refrigeration
>>> system keeps its working  fluid essentially forever.  I suppose one can 
use a
>>>  refrigeration fill valve, say from an automobile air conditioning  
system,
>>> but these all leak to some degree.
>>>  
>>> Is the ball valve anything special?
>>  >
>> Nope, just whatever was on the shelf at the local hardware  store.
>> Stainless ball with brass valve body.  Teflon bearing  surface.
> 
> Ahh.  A quarter-turn ball valve, used as a  cutoff.  The term "ball 
valve" isn't quite precise in plumbing  parlance.
> 
> These are very good, but still they are not  hermetic, and will over 
decades (if not a few years) lose their working  fluid.  I bet that while water 
will be contained, freon will diffuse  right through the teflon seal of the 
ball valve.  So, there's the  tradeoff.
> 
> 
>> >>  These things are  incredible.  If you pack snow around
>>>> the end of this  thing, the other end that is ten feet away gets cold  
almost
>>>> immediately.  They want to stay isothermal and  the heat transfer is 
at the
>>>> speed of sound through the  working fluid.  Delays are introduced 
because
>>>> you're  dealing with a thermal mass of copper pipe that needs to change
>>  >> temperature along with the working fluid so it's not quite instant,  
but
>>>> still about 10,000 times faster heat transfer than  copper by itself.  
They
>>>> are certainly handy for  getting heat out of confined spaces.
>> >>
>>>  
>> > What is the purpose of the heatpipe of doom?   Education?
>> >
>> Education, fun, and then later a  demonstration piece.  It's fun to 
rapidly
>> move the thing  along its axis, upward and then stop.  The slug of water
>>  moves up and then slams back down to the bottom and sounds like a steel 
 ball
>> in the pipe.  It makes a satisfying clang  sound.   A couple of years 
back
>> when I did a demo,  people were convinced I had a metal part in there 
that
>> was  loose.  I opened the valve and out came a 100ml water and  nothing
>> else.   Too cool, and you can make them at home  for next to nothing.
> 
> This definitely sounds like a good  physics demo for school use.
> 
> 
>> Before
>>  I started using vacuum pumps to pump them down, I'd use a blowtorch to  
boil
>> the water and use the valve to throttle the steam coming  out.  Once the
>> steam is coming out really fast you basically  just quickly close the 
valve
>> and remove from the heat  source.   That's it!  For smaller diameter 
pipes I
>>  use other methods and other working fluids because heating tends to  
just
>> eject the sometimes very expensive fluid.
> 
>  What sizes, what fluids, what purposes?
> 
> 
> Joe
>  
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