Louis Katz on fri 10 apr 98
Most Venturi burners are designed to entrain less than the amount of air
needed to bring about complete combustion. The rest of the air is intended to
be brought in as secondary air. The amount that is entrained by these burners
is controled by many factors. Here is a list.
1. The energy transmitted to the air by the gas flowing from the orifice under
pressure. Higher pressure gas coming out of a small orifice will entrain more
air than the same amount of low pressure gas coming from a larger orifice, all
else being equal of course.
2. The efficiency of the mixing tube (Venturi). Better made mixing tubes will
entrain air more efficiently than poorly designed and cast tubes.
3. The quality of the (Flame Retention Ring). These rings serve many purposes,
but one is to control turbulence. Turbulence can have a negative impact on air e
4. Negative pressure (relative to air pressure) at the burner ports. If the
kiln is busy sucking air through the burners, they will entrain more air.
5. The design of the burner ports. Although my ports are square, round burner
ports should provide less turbulence in the stream of gases entering the kiln
and increase the entrained air.
6. Burners mounted under a kiln or facing up are probably more able to entrain
air than those aimed at a bagwall. The airstream would be straighter; less turbu
I have used Eclipse and Pyronics mixer tubes and retention rings at near Sea
Level and in Montana at above five thouseand feet. These atmospheric burners
have worked fine. The higher you get the more the factors mention above become
important. If your orifices are too big you will need a huge chimney to try
and make up the difference.
I like burners, especially at elevation, with adjustable orifices. Then I can
set the orifice size as small as possible and still get enough gas. This means
that the gas will be under more pressure and will have greater ability to
entrain air. You will need bigger chimneys than you do at sea level, but most
(IMHO) chimneys are too big to begin with.
Louis
The information contained above is gleaned from catalogs, discussions, high
school physics, and firings. I hope it is accurate and helpful. I have written
plenty in the past that I find flawed today. This post might be the
embaressment of tommorrow.
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