[time-nuts] Re: MHM-A1 maser temperature stabilization

[djl]

sooo, rigid connected foam that will hold the water...

On 2023-01-17 13:01, Bob Camp via time-nuts wrote:
> Hi
> 
> Yes, a big swimming pool of mercury or water is going to do a lot of 
> things that
> make it really fun to analyze. Folks seem to run circulation pumps to
> reduce the
> impact. Not on my list right now ….
> 
> Water is attractive because it holds a lot of heat per unit mass. One
> KG of concrete
> soaks up 880 J/(Kg-K). One L of water comes in at  4,181. More fun 
> numbers at:
> 
> https://www.omnicalculator.com/physics/specific-heat
> Specific Heat Calculator
> omnicalculator.com
> 
> 
> Solid concrete weighs about 3X what water does by volume, but water 
> still wins
> the race. If the concrete has air spaces in it, it falls further
> behind on a volume basis.
> 
> In terms of a practical answer for a fluid, put it in small(er)
> containers (or baffle it).
> Then you don’t have it doing weird flow stuff. Yes, another rabbit
> hole to wander down.
> Right now a bunch of 2 L glass jars are sitting over there on the shelf 
> …..
> 
> Coming back to the basic question:
> 
> 	Concrete *or* water, how much do I need?
> 
> Not looking for anything past a rough order of magnitude to see if my 
> magic
> math number of  > 250 liters of water is anywhere close. ( In concrete 
> numbers,
> is > 400 liters close? )
> 
> Just trying to get an idea of the scope of the project. If the answer
> is 25 and not 250,
> it’s trivial to do. If it’s 250 … gulp … If its 2,500 … yikes ….. As
> you might guess from
> the reference to the glass jars, empirical data suggests that 25L is
> not the answer.
> 
> At some point adding this or that makes the enclosure bigger and the
> insulation needs
> to get thicker to stay at the same net loss value. There’s only so
> much room over there :)
> 
> Bob
> 
>> On Jan 17, 2023, at 2:03 PM, Poul-Henning Kamp <phk at phk.freebsd.dk> 
>> wrote:
>> 
>> --------
>> Bob Camp writes:
>> 
>>> As I do this in my usual hand waving fashion, I come up with hundreds 
>>> of liters of water for
>>> the thermal mass. It just goes up if I move from 1C and get closer to 
>>> 0.1C.
>> 
>> Liquids and gasses are trouble in this context, because you easily
>> end up with stationary or oscillating circulations which, if nothing
>> else, really ruins the predictability.
>> 
>> So let us stick to solids for the moment:
>> 
>> A thermal resistance is an insulating material with low thermal
>> mass: Sheep's wool, mineral wool, foam-boards, extruded foam and
>> ultimately aerogel.
>> 
>> A thermal capacitance, is a material with high thermal mass and
>> high thermal conductivity:  Ideally silver and copper, but in general
>> any metal.
>> 
>> We know of no materials which act as pure thermal inductances:  It
>> would be a material which conducts heat well, but resists change
>> to the heat-flow.  Certain crystaline semiconductors behave a little
>> bit like a thermal inductance under certain circumstances, but it
>> is not useful in practice.
>> 
>> So we are more or less limited to RC filters.
>> 
>> We can make a "lumped" RC with foamboard insulation and
>> a lot of metal inside.
>> 
>> This is what metrology-labs do for their resistance standards:
>> 
>> Typically a slap of aluminium roughly 1'x2'x2' with holes for the
>> individual resistors (+oil) insulated with 4" of foam/mineral wool
>> or similar.
>> 
>> But that concept, as your own calculation also showed you, scales
>> up badly:  A big box of foam-board and lots of metal (or water),
>> is both expensive and unpractical in so many ways.
>> 
>> Fortunately almost all geology is a distributed RC thermal filter:
>> Limited heat conductivity combined with some thermal mass.
>> 
>> A "box" built from 2" aerated concrete, cinderblocks or pretty much
>> any geology you might have at hand, is cheaper, much more practical,
>> and almost certain to give better results.
>> 
>> I mention 2" aerated concrete specifically, because if you cut the
>> slabs to size and paint them to bind the dust, they are very
>> handy building blocks:  You can stack them around your equipment
>> when you want to, and remove again when you need to access it.
>> 
>> --
>> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>> phk at FreeBSD.ORG         | TCP/IP since RFC 956
>> FreeBSD committer       | BSD since 4.3-tahoe
>> Never attribute to malice what can adequately be explained by 
>> incompetence.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe send an email to time-nuts-leave at lists.febo.com

------------
"If you don't know what it is, don't poke it."
Ghost in the Shell
----------------------
Dr. Don Latham  AJ7LL
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304