Talbott on mon 13 jan 97
As a matter of practice I usually wrap the outside, side walls of
our gas kiln in heavy duty aluminum foil. The kiln is located outside under
a covered shed. ... Would any of you engineer types care to comment on how
much advantage that I gain from this practice... Since my previous post
was on R-values (as in insulating ability), I thought this would be a good
time to ask this question... ...Best Wishes..Marshall
------------------------------------------------------------------------------
1ST ANNUAL CLAYARTERS' GALLERY - NAPLES, MAINE (Summmer 1997)
{contact me directly for more information}
Celia & Marshall Talbott
Pottery By Celia
Route 114
P.O. Box 4116
Naples, Maine 04055-4116
(207)693-6100 voice and fax
clupus@ime.net
Gavin Stairs on tue 14 jan 97
> As a matter of practice I usually wrap the outside, side walls of
>our gas kiln in heavy duty aluminum foil. The kiln is located outside under
>a covered shed. ... Would any of you engineer types care to comment on how
>much advantage that I gain from this practice... Since my previous post
>was on R-values (as in insulating ability), I thought this would be a good
>time to ask this question... ...Best Wishes..Marshall
Depends on the temperature of the outside of the kiln. The aluminum skin
insulates by changing the emittance of the heat radiating surface. The
value for Aluminum is a lot less than that of, say, a dark clay. However, a
titanium dioxide white paint is almost as good. Here's how to tell is it's
doing any good: measure the outside wall temperature of the kiln without
the foil when the kiln is at your maturation temperature (Tmaturation)(T1),
and then on the next firing, put on the foil and measure it again in just
the same way (T2). Measure the temperature at the brick or clay sparging,
not the foil. If you know the (approximate) insulating value of the brick
wall (R), you can then calculate the change in heat flow through the wall:
Difference in heat loss per unit area =
(Tmaturation2 - T2)/R - (Tmaturation1 - T1)/R
Iff Tmaturation1 = Tmaturation2, then:
Difference in heat loss per unit area =
(T1 - T2)/R
R has units of ft^2*hr*oF/BTU. So you get BTU/(ft^2*hr) from the above if
you use oF for the temperature. You multiply by the area of the kiln wall
in ft^2 to get the heat loss difference in BTU/hr through the wall at that
temperature.
Then you need to estimate the effect of this throughout your firing cycle.
It will be significant only at high temperatures. You could get a better
estimate by measuring the temperatures at timed intervals throughout the
firing, multiply by the time interval in hours, and add it all up. You
would need a pyrometer to do this. By the way, the result of this
calculation is negative, which means that you are losing less heat with the
foil. After all this effort, you will get the savings in heat, in BTU,
which you can translate into cost of gas equivalent. Of course, if your
firing goes faster, you need to take this into account as well.
Watch out for water condensation behind the foil, which may damage the outer
coating of the kiln.
Hope this helps.
Bye, Gavin
Marcia Selsor on tue 14 jan 97
Dear Marshall,
When I was in grad school at SIU Carbondale, Rob Levin (fellow grad)
had built a wood fired salt kiln in an old corn crib. At the end of the
firng, and salting, a tornado came by and the stack fell on all those
who were in the corn crib. Lo and behold, it had disintegrated
to the point of being ashen flakes.No injuries.
I mention this because when I was rebuilding a kiln which had been lined
with aluminum foil between the two courses of arch brick,
I discovered a similar ashen flakes which had the insulating property
of tracing paper.
I think aluminum foil usage on a kiln is a myth.I use wax paper to line
arch forms while casting only because the form will slide out easier.
Marcia in Montana
--
Marcia Selsor
http://www.imt.net/~mjbmls/
mjbmls@imt.net
| |
|
