----- Original Message -----
Sent: Saturday, August 31, 2002 10:48
AM
Subject: [GBlist] sodium sulfate
dekahydrate or dexahydrate
Hi all,
I have been having another of my dangerous
conversations with my brother the chemist......Okay you're probably tired of
hearing about these, but he brought up something he learned about the salt
called sodium sulfate dexahydrate, I think, aka glauber's
salt. Apparently glauber's salt (which I used to use for doing dye
work on fabric) is highly efficient at capturing heat and releasing the heat
later. My bro read something to me from one of his chemistry books about
a woman in Mass (I believe he said she is a prof at MIT) who built a house
using a glauber's salt heating system. In that climate it was necessary
to build with a back up heating system, but the article he read to me said
that it took 11 consecutive cloudy days to deplete the glauber's salt
system. Anybody heard about this? If anyone knows of any good
links to check into, I'd appreciate it.
Thanks,
Elizabeth
Dr. Maria Telkes from MIT build a solar heated
house back in the 40s, called the Dover House, that used the heat of fusion of
Glauber'salt to store energy. There was a fair amount of discussion
about using Glauber's salt for solar storage back in the seventies. I have
always been a little surprised that more was not done with it, because it is
incredibly effective. The best information I have found online suggests
that it can be used either to provide heating or cooling, by modifying the
ingredients. Apparently there can be some loss of
performance over time, but it is cheap and non-toxic. In earthquake
country we get a little nervous around big tanks of water, but it is certainly
fireproof. You can put the stuff into lots of small plastic
containers. It does need to be contained.
I plan to incorporate ferrocement benches and
planter box stands filled with Glauber's Salt in a solarium. After
reading this study, I am thinking about adding other salts to modify the melting
point from 90.5 degrees F to about 80 degrees F. Essentially, the phase
shift that happens at 80 degrees will tend to keep the temperature around 80,
especially if the amount of phase shift material/thermal mass is
large.
Anyone who knows anything about using PSMs for
cooling, please let us know.
Richard
Here is an excerpt from:
However, Glauber’s salt melts incongruously and the salt tends to
separate into a saturated solution
with insoluble anhydrous sodium sulphate
crystals. Since these crystals are more dense than the
saturated solution
they tend to settle out of solution due to gravity. When the PCM is next
frozen
these crystals are unable to recombine with the saturated solution,
resulting in a loss in TES capacity
of the system (6) .
This occurs during each freeze/melt cycle, and if unchecked leads to a gradual
but
continual loss of performance.
A wide variety of thickening agents
have been applied in the past (7). The most widely used
material
was a clay-like substance but the recent work has concentrated on
using other thickening agents, in
particular synthetic polymer
gels.
A number of suitable
polymers have been identified which can function satisfactorily in the
harsh
environment of the PCM mixture (8). New ways of producing
stable, efficient, and easily applicable
PCMs are being developed which will
help raise the profile of PCM thermal energy storage.
Following extensive research, the author has identified a number
of satisfactory PCMs which melt and
freeze between + 4 ° C ( 39.2 °F) and +
117 ° C (242.6 °F) and therefore suit the majority of the air
conditioning
and refrigeration applications. A number of these PlusICE solutions (8) are
incorporated
in Table 2.3.3.
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