Most building insulation foam sold here in UK has an Alu foil cladding on
both sides ...
Dave
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Predrag Dukic wrote:
How well depleted it really is?
DU has about 1/3 the U235 of natural U, of which less than 1% is U235.
All the isotopes are radioactive, but I don't recall what the relative
activities are. I think U238 has a half live of 4E9 years or more, so
not very many atoms
Hi Bob:
How about just wrapping the aluminum block in aluminum foil with the
shiny side out. Then wrap the Styrofoam cube with the shiny side in
before putting it in the aluminum box?
Have Fun,
Brooke Clarke
http://www.PRC68.com
Bob Camp wrote:
Hi
Since styrofoam is being rated as a
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Thermal time constant
Hi Bob:
How about just wrapping the aluminum block in aluminum foil with the
shiny side out. Then wrap the Styrofoam cube with the shiny side in
before putting it in the aluminum box?
Have Fun
: [time-nuts] Thermal time constant
Most building insulation foam sold here in UK has an Alu foil cladding on
both sides ...
Dave
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Jack Smith at Clifton Laboratories built a replacement for the 1502
chart recorders. An early prototype can be seen here:
http://www.cliftonlaboratories.com/mar_2007.htm
On Thu, 11 Mar 2010 04:51:00 +, Mark Sims hol...@hotmail.com
wrote:
Gawd, tell me about it... I just got through
That's the 1502/1503 chart recorder that uses a hot stylus and paper roll with
a punched timing track. Paper is available at $25-$36 a roll (min purchase 10
rolls). I have a mod that lets you use $1-$2 a roll ECG paper.
The 1502B/1503B/1502C/1503C are a different animal. Their chart
Hi Mathew:
There are a bunch of them, but I like the DS3231 because it has a
software frequency tweak and I2C interface.
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4627/t/al
http://datasheets.maxim-ic.com/en/ds/DS3231.pdf
Hi Bruce:
Do you have a value for the thermal resistance of
Hi Bruce:
What does m2K/W mean? See:
http://building.dow.com/europe/uk/proddata/styrofoam/thermal.htm
50 mm it's about 1.5 and for 100 mm it's about 3.
Have Fun,
Brooke Clarke
http://www.PRC68.com
Bruce Griffiths wrote:
Bruce Griffiths wrote:
Brooke Clarke wrote:
Hi:
For some time I've
~3.3E-2 W/mK.
If, as I suspect, its transparent to 10-20um infrared then adding
intermediate aluminium foil radiation shields may be useful.
Some styrofoam insulating panels include carbon black to inhibit
infrared transmission:
Thermal resistance is measured in degrees (C or K or ..) per watt.
Its inversely proportional to area and proportional to thickness.
I think the clueless clown who created that table means that for a 1
square meter panel of the specified thickness the thermal resistance is
the tabulated value
Hi Bruce:
If a square meter of Styrofoam is 1.5 deg C/W then a cubic inch would be
39.37 * 39.37 * 1.5 or 2,325 deg C/W
The DS3231 dissipates about 1 mw when running. I'm not sure how to come
up with an allowable temp increase, but suspect it's based on not
exceeding the max allowed
-nuts-boun...@febo.com] On
Behalf Of Brooke Clarke
Sent: Wednesday, March 10, 2010 4:28 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Thermal Time Constant
Hi Bruce:
If a square meter of Styrofoam is 1.5 deg C/W then a cubic inch would be
39.37 * 39.37 * 1.5
Surely you meant 1 square inch of styrofoam with the specified thickness??
For a 100 hour (3.6E5 seconds) time constant and 1000 deg C/W thermal
resistance you need a thermal capacitance of 3.6E5/1E3 = 360 J/C
or 360/0.8371 = 430 gm of Aluminium which has a volume of 430/2.7 = 159 cc.
You
Looking at the specific heat of metals:
http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html
Wouldn't Beryllium be better instead of aluminium?
I could foresee a few problems though eg machining holes at home,
never mind where to get a block from.
Phil
Hi
The gotcha is that you are interested in the amount of heat per cubic foot
rather than the amount of heat per pound. You need to take the standard heat
per weight numbers and convert them to heat per volume numbers.
Of the things you can easily get, copper is good. Steel is not as good as
A better metric may be stored heat for a dollar's worth of material. Scrap
iron is pretty cheap.
From:
Bob Camp li...@rtty.us
To:
Discussion of precise time and frequency measurement time-nuts@febo.com
Date:
03/10/2010 06:03 PM
Subject:
Re: [time-nuts] Thermal time constant
Sent by:
time-nuts
p...@pseng.org.uk wrote:
Looking at the specific heat of metals:
http://www.engineeringtoolbox.com/specific-heat-metals-d_152.html
Wouldn't Beryllium be better instead of aluminium?
I could foresee a few problems though eg machining holes at home,
never mind where to get a block from.
Phil
Just in case anyone finds a beryllium brick somewhere and tries to
use it:
Beryllium is very very poisonous.
cheers,
Neville Michie
On 11/03/2010, at 10:08 AM, Bruce Griffiths wrote:
p...@pseng.org.uk wrote:
Looking at the specific heat of metals:
There's at least one known case where someone attempted to grind a
beryllium mirror substrate using conventional methods without proper
control of dust resulting in his death.
Bruce
Neville Michie wrote:
Just in case anyone finds a beryllium brick somewhere and tries to use
it:
Beryllium is
Hi
The same caution applies to the beryllium in beryllium oxide heat spreaders.
You find them in old RF transistors and some RF tubes.
Bob
On Mar 10, 2010, at 6:45 PM, Bruce Griffiths wrote:
There's at least one known case where someone attempted to grind a beryllium
mirror substrate using
Beryllium copper parts are also an issue although the beryllium content
is only 0.3%-0.5% by weight.
Bruce
Bob Camp wrote:
Hi
The same caution applies to the beryllium in beryllium oxide heat spreaders.
You find them in old RF transistors and some RF tubes.
Bob
On Mar 10, 2010, at 6:45
Hi
So getting back to the original idea.
Taking the other extreme - if you go for ~20 C / W on the insulation:
The mass of the block will be ~50X what it was before.
1.6 on a side goes to ~5 on a side.
Surface area goes up ~10X.
200 C/W with 2 foam goes to 20 C/W
Outer surface area goes
The suggestion of beryllium was somewhat tongue-in-cheek ie not to be
taken seriously, I did mention there would be a few problems, death
being somewhat a terminal one.
I agree with Bruce that specific heat*density is what is really
required (I'd forgotten how light beryllium is. I don't
Hi Bob:
I like the idea of a six inch on a side cube. An outer aluminum box,
styrofoam insulation, and a block of (copper, Aluminum, etc.) in the
center. A DS3231 or similar RTC and a PIC with a DB-9 connector on one face.
Have Fun,
Brooke Clarke
http://www.PRC68.com
Bob Camp wrote:
Hi
I have been wondering about achieving the rated thermal resistance
from plastic foam,
the problem being that radiant transmission may be very strong
through the foam.
What happens if you interleave concentric sheets of foam plastic with
aluminium foil? (taking care to keep the foil
on
Hi
That raises the interesting question of weather radiant transfer is already
included in the rated thermal resistance. My guess is that the 8 of foam is
enough to cover any radiation issues and still get you above 20 C / W.
Since you are probably starting with 1 or 2 slabs, including the
Radiative heat transfer (for a surface with an emissivity of 1) is
around 150uW/square cm /degreeC at 300K.
That's equivalent to about 10cm of styrofoam.
It seems unlikely that the radiative heat transfer component is included
in the thermal resistance rating for Styrofoam.
The radiative
Oops forgot a factor of 4
Radiative heat transfer for surface with an emissivity of 1 at 300K is
about 612uW/square cm/degree C
which is equivalent to about 25mm of styrofoam.
Which raises the question what's the emissivity of the isothermal
surface used when measuring the thermal resistance
Hi
Since styrofoam is being rated as a building insulation, it's reasonable to
believe that the material on both sides is up around 1. I highly doubt that
somebody tossing styrofoam in walls is going to add a radiation factor ...
In our application we're talking about a metal block inside a
There's a small problem with my calculation and the published figures
for the thermal resistance of styrofoam.
If the measurements include radiative transfers the thermal resistance
per unit area of a styrofoam slab should reach a limiting value (when
the radiative transfer component dominates)
Hi
Low density (1 or 2 lb / cu ft) urethane foam is going to be a better insulator
than styrofoam. I believe it's reasonably opaque at IR.
Bob
On Mar 10, 2010, at 8:23 PM, Bruce Griffiths wrote:
There's a small problem with my calculation and the published figures for the
thermal
Depends on the duration of the experiment.
Urethanes arent well known for stability.
The low thermal resistance of close cell urethanes is largely due to
their better retention of the blowing agent which has lower thermal
conductivity than air.
Closed cell foam glass (however the sulphur
Brooke Clarke wrote:
Hi Bruce:
What does m2K/W mean? See:
http://building.dow.com/europe/uk/proddata/styrofoam/thermal.htm
50 mm it's about 1.5 and for 100 mm it's about 3.
thermal resistance (you can tell because it's degrees/watt, as opposed
to watts/degree which would be conductivity)
Brooke Clarke wrote:
Hi Bruce:
If a square meter of Styrofoam is 1.5 deg C/W then a cubic inch would be
39.37 * 39.37 * 1.5 or 2,325 deg C/W
The DS3231 dissipates about 1 mw when running. I'm not sure how to come
up with an allowable temp increase, but suspect it's based on not
exceeding
Bob Camp wrote:
Hi
The gotcha is that you are interested in the amount of heat per cubic foot rather than the amount of heat per pound. You need to take the standard heat per weight numbers and convert them to heat per volume numbers.
Of the things you can easily get, copper is good. Steel is
Gawd, tell me about it... I just got through rebuilding the drive roller in
half a dozen Tektronix YT-1 and YT-1S chart recorders for the
1502B/1520C/1503B/1503C TDR's. The recorders were built by AstroMed and the
roller was made of a black urethane that reverts back to its primordial
water is pretty good, too and cheap. Coupling to it is easy as well.
Don
- Original Message -
From: jimlux jim...@earthlink.net
To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Sent: Wednesday, March 10, 2010 9:35 PM
Subject: Re: [time-nuts] Thermal time
How well depleted it really is? Uranium separation is not perfect.
Some radioactivity is still left.
I don't think it is healthy to have it beside You for a long time.
Certainly not 8 pounds :))
At 05:35 11.3.2010, you wrote:
Bob Camp wrote:
Hi
The gotcha is that you are
Hi:
For some time I've considered surrounding a free running 32678 Hz
oscillator (like a Dallas 32khz, or one of the newer Maxim units) with
thermal mass and insulation in order to get the time constant into the
range of some days. To get a feel for it a simple experiment shows that
a half
Quoth Brooke Clarke at 10/03/10 10:22...
...like a Dallas 32khz, or one of the newer Maxim units...
There's a Maxim part to supersede the DS32kHz? I know that my regular
vendors [Farnell, Soanar, Futurlec] in Australia don't stock the
DS32kHz, which makes them mega-expensive to acquire.
Brooke Clarke wrote:
Hi:
For some time I've considered surrounding a free running 32678 Hz
oscillator (like a Dallas 32khz, or one of the newer Maxim units) with
thermal mass and insulation in order to get the time constant into the
range of some days. To get a feel for it a simple
Bruce Griffiths wrote:
Brooke Clarke wrote:
Hi:
For some time I've considered surrounding a free running 32678 Hz
oscillator (like a Dallas 32khz, or one of the newer Maxim units)
with thermal mass and insulation in order to get the time constant
into the range of some days. To get a feel
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