[Clayart] Kiln Flue question

[Jeff D. Walker via Clayart]

I am going to have to work on the 82 cuft kiln we have as the flue opening is starting to collapse. My question is out of curiosity on using two kiln shelves (for 2" thick Lintel) to cross the opening (cut to size of course) and hard brick on the flue opening. Any draw backs to this thought. The original opening is 8.5" tall by 14" wide.

Jeff Walker | Lead Potter HillCreek Pottery
Silver Dollar City


c: 816-808-2680 o: 417-338-8168
e: jdwa...@silverdollarcity.com<mailto:jdwa...@silverdollarcity.com>



399 Silver Dollar City Pkwy
Branson, MO 65616




[Logo]<https://www.silverdollarcity.com/>



-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.clayartforum.com/pipermail/clayart/attachments/20240514/f496eb8a/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 16285 bytes
Desc: image001.png
URL: <https://lists.clayartforum.com/pipermail/clayart/attachments/20240514/f496eb8a/attachment.png>

[David Woof via Clayart]

Hi Jeff,
To give you a more considered answer to your actual question, more information re. your kiln's construction, i.e. if sprung arch, catenary, hard brick, or IFB, could help us. But be as that may, a 14-inch lintel span supported only by kiln shelves to stabilize the weight of the kiln wall gives me pause.
The type of kiln wall regarding the angle of the wall, also dictates and indicates the direction and amount of angular thrust against whatever you attempt to construct to support the collapsing wall.
As I'm sure you know, kiln shelves are prone to sag and or crack under weighted heat stress.
Depending on shelf material composition some are stronger than others. Please do your own research.

It appears that you have ample space to set a stacked 4.5" hard brick support pillar under the mid-point of that kiln shelving lintel bridge you are suggesting. And you will likely still have more than adequate cubic inches for an efficient flue opening.

Mel mentioned placing removable loose bricks to block excessive flue openings, and to fine tune the flue. This is an easy go to if you build for access during firing when changing conditions warrant.
Overbuilding flue, and stack or chimney is good sense if you understand the "why" to have a reserve for when the atmospheric and barometric conditions are causing a stall or conversely as Mel says, the kiln is a acting like a "runaway train" and one is heating the sky.

Please let us know how it all works out. Clayart is dedicated to mutual learning as well as Q&A.

Misneach,

David Woof......................................................................................................................................
****************************************************************************************
________________________________
From: Clayart <clayart...@lists.clayartforum.com> on behalf of Jeff D. Walker via Clayart <cla...@lists.clayartforum.com>
Sent: Tuesday, May 14, 2024 1:53 PM
To: cla...@lists.clayartforum.com <cla...@lists.clayartforum.com>
Cc: Jeff D. Walker <jdwa...@silverdollarcity.com>
Subject: [Clayart] Kiln Flue question

URL: <https://lists.clayartforum.com/pipermail/clayart/attachments/20240520/dd601994/attachment.htm>

[David Woof via Clayart]

Hi Jeff,
Have you considered corbeling the main IFB wall just around and above where you need your exit flue opening and then building a hard brick catenary arch for the flue? One could then "chink up" and use the castable to fill in the gap spaces between the IFB and exit flue arch.

I use term "exit flue" to avoid confusion and attempt clarification regarding the "stack" or "chimney" as some refer also as flue.

Also often overlooked is that building the size of exit flue openings and chimney volume, and propensity for "stalling" are influenced and dependent on geographic altitude as well as other physical or human caused landscape features and sudden weather and barometric changes during a firing. One size does not fit all under all conditions.
Some may get their panties skid marked, or in a bunch over my saying this, but the proof lies in the solutions.............

Misneach,

David Woof...........................................................................................................................................................
*****************************************************************************************************
________________________________

-------------- next part --------------
An HTML attachment was scrubbed...

URL: <https://lists.clayartforum.com/pipermail/clayart/attachments/20240528/1bafb30c/attachment.htm>

[ronroy--- via Clayart]

An oversized flue opening can always be made smaller - or maybe just
close your damper more. Care should be taken to make sure dampers
close properly to control cooling.

Getting cracking during bisque cooling? Look to see if your damper is
closing completely.

RR

Ron Roy
ron...@ca.inter.net
Web page ronroy.net

[joel joelfink.net via Clayart]

This is a curiosity to me.

I can't do Bernoulli's math, so there is that. But, I do conceptually understand the dynamics of fluid flow to some usable degree.

If we remove turbulence from the equation, just to look at other variables unimpeded, can someone tell me what the difference is between a wide flu and an open damper, and then of a small flu and an equally closed damper?

In my imagination, speaking specifically of a pressurized system (gas-fired) the venturi effect of a gradual narrowing of the orifice is negated by the damper opening dimensions, if they are less than the upper point of the final diameter of the venturi. In other words; In a gas kiln, the flu only needs to be as large as the widest the damper will be open. After that, the pressure differential is set by the interior pressure and the damper aperture, and not by the flu itself.

Isn't the pressure differential the actual number in this equation?

Jeff is speaking about a Guil kiln with the damper being roughly the height of the kiln and not a venturi, so my comments go to that example.

Note: I'm asking in curiosity. I would very much like to hear anyone's knowledge as to what happens in a gas-fired kiln's flu, if the flu size is greater than the maximum damper aperture.

As to turbulence, in my mind this will create myriad minor eddy currents along the imperfections in the wall, such that a slightly larger flu would compensate for any backpressure.

Joel Fink
Ficklefink Pottery.
________________________________
From: Clayart <clayart...@lists.clayartforum.com> on behalf of ronroy--- via Clayart <cla...@lists.clayartforum.com>
Sent: Wednesday, May 29, 2024 11:12 AM
To: Clayart international pottery discussion forum <cla...@lists.clayartforum.com>
Cc: ron...@ca.inter.net <ron...@ca.inter.net>; Jeff D. Walker <jdwa...@silverdollarcity.com>
Subject: Re: [Clayart] Kiln Flue question

URL: <https://lists.clayartforum.com/pipermail/clayart/attachments/20240602/b818f849/attachment.htm>

[David Finkelnburg via Clayart]

Joel,
As you know, the goal of a well-designed fuel-fired kiln flue with
damper is to provide smooth control of the flow of combustion air into the
kiln (and simultaneously the flow of kiln gases out through the flue) over
a wide temperature range and a wide range of damper positions. The trouble
with very oversized flues is that a small change in damper position
produces a large change in combustion air flow.
If you look at Euler's derivation of what's commonly called Bernoulli's
equation, the velocity of the flowing fluid is typically the significant
factor in controlling pressure loss through a flue system. The elevation
and density factors are important, of course, but the shape of the entrance
to the flue and the dimensions of the dampered section determine the flow
rate and velocity of the kiln gases to the flue exit.
You are right in saying, "the flu only needs to be as large as the
widest the damper will be open." Ideally, maximum air flow and fuel
efficiency occurs with the damper wide open.
The turbulence is very important in a heavily dampered, oversized
flue. Wall turbulence in the stack is usually a minor influence on flow up
the flue.
Regards,
Dave Finkelnburg

URL: <https://lists.clayartforum.com/pipermail/clayart/attachments/20240601/8c2fde4c/attachment.htm>