[time-nuts] temperature stability basics
phk at phk.freebsd.dk
Fri Nov 26 23:34:24 UTC 2010
In message <20101126223543.7151480003B at ip-64-139-1-69.sjc.megapath.net>, Hal Mu
>How about aluminized Mylar?
Reflective insulation only works if you have significantly different
Look up Stefan-Bolzmanns law, and notice the T^4 term, but pay attention
to T being absolute temperature (ie: Kelvin above abs zero).
As a rule of thumb, and at humane temperatures, reflective isolation
will do nothing for you until you have 20K temperature difference
and only really kick in once you get above 40K temperature difference.
>If the many-reflective-layers idea really works, I'd expect somebody to sell
>foam built that way. Why don't they?
They do, search for "airflex" for instance.
If you live in the south, this is a great material to insulate your
roof with: On one side 100C hot roof, on the other side 20C hot living
room. In that case, a 6mm reflective insulation does as good or better
than 200mm mineral wool.
Now add somebody who doesn't understand physics and starts selling
product in Denmark as "equivalent to 200m mineral wool" totally
disregarding the temperature difference being 10K most of the time
and 30K worst case, and you have ...
...what happened a couple of years ago :-(
So unless you put your electronics in arctic areas or near furnaces,
you can forget reflective insulation. If you do either of those
things, you would be stupid to forget it, but it may be as simple
as using a unpainted alu-enclosure, rather than a painted one.
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.
More information about the time-nuts