Louis Katz on thu 9 sep 04
Burner BTU sizing is complex.
If you put a one inch gas line in a two inch tube you do not get an 8
million BTU burner. Oddly enough,( maybe not that odd) it is the air
that can be entrained in a burner that determines its maximum BTU's.
At a given gas pressure and back pressure or suction from a chimney at
the burner head, a burner' size is given for a percentage of air
entrainment through the burner.
That is how many BTU's of gas can you get through a burner and still
have the burner pull 70% of the air needed for complete combustion.
Different burners and companies list differing percentages of
entrainment in their catalogs. This means that the burner companies
when listing BTU's on unsealed burners expect that some percentage of
the air needed for complete combustion will be secondary air.
With a little negative pressure at the burner port the rating of a
burner can go way up. There is a limit for a given burner tip however
and finding a way to force more air and gas through a small burner can
cause a very unstable flame that likes to blow out at low temperatures.
Bad mixing of gas and air can also result which causes little areas of
heavy reduction in the flame. This can cause soot, even in a generally
oxidizing flame.
Quality flame retention rings (burner tips), good mixers (burner
bodies) with adjustable orifices, really make for burners that are easy
to work with that have good stable flames and can entrain the most air
for a given amount of gas. They are just so expensive. Burners with
blowers are different beasts.
Louis
image of old venture burner and safety system, in cattle marker flambe'
on board:
http://falcon.tamucc.edu/~lkatz/LK/painting/kilnpainting/pages/a.htm
Hank Murrow on thu 9 sep 04
Louis has given us a real good rundown of the importance of air
entrainment here. Look for a burner that has a machined venturi(the
inside surface), because the relation between the orifice and this
carefully machined surface is how maximum entrainment is developed.
Cheers, Hank in Eugene
murrow.biz/hank
On Sep 9, 2004, at 7:48 AM, Louis Katz wrote:
> Burner BTU sizing is complex.
> If you put a one inch gas line in a two inch tube you do not get an 8
> million BTU burner. Oddly enough,( maybe not that odd) it is the air
> that can be entrained in a burner that determines its maximum BTU's.
> At a given gas pressure and back pressure or suction from a chimney at
> the burner head, a burner' size is given for a percentage of air
> entrainment through the burner.
> That is how many BTU's of gas can you get through a burner and still
> have the burner pull 70% of the air needed for complete combustion.
> Different burners and companies list differing percentages of
> entrainment in their catalogs. This means that the burner companies
> when listing BTU's on unsealed burners expect that some percentage of
> the air needed for complete combustion will be secondary air.
>
> With a little negative pressure at the burner port the rating of a
> burner can go way up. There is a limit for a given burner tip however
> and finding a way to force more air and gas through a small burner can
> cause a very unstable flame that likes to blow out at low temperatures.
> Bad mixing of gas and air can also result which causes little areas of
> heavy reduction in the flame. This can cause soot, even in a generally
> oxidizing flame.
>
> Quality flame retention rings (burner tips), good mixers (burner
> bodies) with adjustable orifices, really make for burners that are easy
> to work with that have good stable flames and can entrain the most air
> for a given amount of gas. They are just so expensive. Burners with
> blowers are different beasts.
>
> Louis
>
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