Rick Hintze on wed 26 jan 00
I would sure appreciate some information on how one calculates the external
surface temperatures of a kiln wall and chimney for given internal
temperatures. I am dealing with building inspectors who are not familiar with
kilns and I need to prove, as accurately as possible, preferably with
documentation, what sort of temperatures these surfaces will reach. I have
had a little trouble getting more than thermal conductivity numbers for the
materials I will be using. Alas, a math or physics wizz I am not, so I need
help!
I will be using G-26 IFB (9 inch walls and arch) in the kiln and plan to use
molded kaowool fiber sleeves inside of galvanized pipe for the chimney. The
sleeves are rated at 2300 F and are 3/4" thick with a density of 22 Pcf.
They are made from a much less dense fiber but end up at this figure. I also
plan to build a passive damper into the chimney to introduce cooler air to
lower the temperature of the gases in the higher parts of the chimney. Here
again, I could use some advice on how to calculate the temperature lowering
effects of introducing this air.
I am trying to avoid using a "metalbestos" type pipe, primarily because of
the cost, but also because my ceramics intuition tells me that the kaowool
sleeves are superior to stainless steel in this sort of application. Since I
don't know how to calculate these temperatures, I am not sure. I am putting
this chimney through a wooden roof and want to be sure that I have the
optimum protection.
Are there any books with figures on this sort of information?
You may send replies to me at rickhintze@aol.com
Thanks a bunch in advance,
Rick Hintze
Dave Finkelnburg on thu 27 jan 00
Rick,
On the stack, I need some additional information. I need to know the
inside diameter of the pipe, inside the insulation. Also, it would be handy
to have a rough idea of the thickness of the galvanized steel.
It's really hard to calculate this without knowing just what sort of
blanket insulation you have. Can you be any more specific? Have you
compressed it quite a bit?
I was able to make an old Thermal Ceramics heat flow program work on my
PC, and I have
used it to calculate the outside temperature for your kiln. I didn't know
your
firing temperature, so I calculated the skin temperature twice for 2,600
degree F insulating firebrick.
According to the program, at cone 5, on a windless, 80 degree F day, the
outside of your kiln will be about 280 degrees F, plus or minus 20 degrees.
This is the maximum skin temperature for the kiln, assuming the heat can
escape from the skin and is not held in by another surface over it. This
also assumes the kiln has been at 2,185 degrees F long enough that the heat
leaving the surface is equal to the heat coming from the inside. In truth,
you'll probably see the cones bend and start cooling down before the outside
skin gets this hot, unless you use an hour or two soak at the peak
temperature, which would put you up around cone 6 anyway.
Because of the excellent insulating value of your brick, at cone 10, for
the conditions above, the outside of your kiln will only be about 20 degrees
F hotter than at cone 5 according to the program.
I'm going to guess that your stack will be around 600 degrees F on the
outside if the inside is 2,000 degrees. I think that's kind of the worst
case analysis.
Later.
Dave
dfinkeln@cyberhighway.net
-----Original Message-----
From: Rick Hintze
To: CLAYART@LSV.UKY.EDU
Date: Wednesday, January 26, 2000 1:51 PM
Subject: external kiln and chimney temps
>----------------------------Original message----------------------------
>I would sure appreciate some information on how one calculates the external
>surface temperatures of a kiln wall and chimney for given internal
>temperatures. I am dealing with building inspectors who are not familiar
with
>kilns and I need to prove, as accurately as possible, preferably with
>documentation, what sort of temperatures these surfaces will reach. I have
>had a little trouble getting more than thermal conductivity numbers for the
>materials I will be using. Alas, a math or physics wizz I am not, so I
need
>help!
>
>I will be using G-26 IFB (9 inch walls and arch) in the kiln and plan to
use
>molded kaowool fiber sleeves inside of galvanized pipe for the chimney. The
>sleeves are rated at 2300 F and are 3/4" thick with a density of 22 Pcf.
>They are made from a much less dense fiber but end up at this figure. I
also
>plan to build a passive damper into the chimney to introduce cooler air to
>lower the temperature of the gases in the higher parts of the chimney. Here
>again, I could use some advice on how to calculate the temperature lowering
>effects of introducing this air.
>
>I am trying to avoid using a "metalbestos" type pipe, primarily because of
>the cost, but also because my ceramics intuition tells me that the kaowool
>sleeves are superior to stainless steel in this sort of application. Since
I
>don't know how to calculate these temperatures, I am not sure. I am putting
>this chimney through a wooden roof and want to be sure that I have the
>optimum protection.
>
>Are there any books with figures on this sort of information?
>
>You may send replies to me at rickhintze@aol.com
>
>Thanks a bunch in advance,
>Rick Hintze
>
ferenc jakab on fri 28 jan 00
I'm no expert on designing kilns, I've only built two. My gas kiln is built
with a single layer of insulating fire brick ( I think thats what you call
soft bricks) with a very high alumina content. Over this I placed a layer of
Ceramic fibre about 1.5 inches thick. At 1150 deg C. (2102 deg F.) my
outside temp is about 80 - 90 deg C tested with a low temp probe.
Feri.
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