The Unofficial Mamod and Other Steam Forum

RocDoc · Posted: Wed Nov 04, 2009 10:32 pm Post subject: Burner to Boiler distance

I've always wondered about this ... is there a certain distance a burner tube should be from a boiler for optimal heating?

I'm thinking meths burners like the Bowman, Mamod ones etc. I guess it all depends upon the size of the burner - boiler etc etc.

Just wondering ...

Pete

Roly Williams · Posted: Wed Nov 04, 2009 11:07 pm Post subject:

The flame should just touch the bottom of the boiler. The tip of the flame is the hottest part. The same applies to blow torches etc.
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Roly Williams

"God is not dead - he is alive and well and working on a much less ambitious project" (MRFS)

Atticman · Posted: Thu Nov 05, 2009 1:19 am Post subject:

I always thought the blue bit was the hottest on a blow torch- just about in the middle -thats what the chemistry teacher used to say about his bunsen burners

I suppose it depends then if the flame has that "blue" middle bit- cant think of that happening with my meths burners.

Some of my engines have the top of the flame above the top of the SV though

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metalhead100 · Posted: Thu Nov 05, 2009 2:30 am Post subject:

It gets deeper than that......

Dr. McCaffrey, who made extensive measurements of temperatures in turbulent diffusion flames. He used gas burners in a "pool fire" mode (i.e., non-premixed) and studied various characteristics of such fire plumes. He described three different regimes in such a fire plume:

1. Slightly above the base of the fire begins the continuous flame region. Here the temperatures are constant and are slightly below 900°C.

2. Above the solid flame region is the intermittent flame region. Here the temperatures are continuously dropping as one moves up the plume. The visible flame tips correspond to a temperature of about 320°C.

3. Finally, beyond the flame tips is the thermal plume region, where no more flames are visible and temperature continually drop with height.

French researchers at the University of Poitiers recently made the same types of measurements and reported numerical values indistinguishable from McCaffrey's. Cox and Chitty measured similar plumes and obtained very similar results: a temperature of 900°C in the continuous flame region, and a temperature of around 340°C at the flame tips. The latter value does not appear to be a universal constant. Cox and Chitty later measured slightly higher heat release rate fires, and found a flame tip temperature of around 550°C. In a later paper , researchers from the same laboratory examined turbulent diffusion flames under slightly different conditions, and found peak values of 1150-1250°C for natural gas flames, which is rather higher than 900°C. The above results were from fires of circular or square fuel shape. Yuan and Cox measured line-source type fires. They found a temperature of 898°C in the continuous flame region, and a flame tip temperature of around 340°C. This suggests that such results are not dependent on the shape of the fuel source.

In studying fires in a warehouse storage rack geometry, Ingason found an average solid-flame temperature of 870°C. At the visible flame tips, the average temperature was 450°C, but the range was large, covering 300~600°C. In a related study, Ingason and de Ris found typical flame tip temperatures of 400°C for burner flames of propane, propylene, and carbon monoxide fuels.

http://www.doctorfire.com/flametmp.html

Is where i stole this

Jim
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Roly Williams · Posted: Thu Nov 05, 2009 1:30 pm Post subject:

There's a fundamental difference between a bunsen burner and a meths burner. In a bunsen burner, the air is mixed with the gas before it burns. In a meths burner, the air comes from outside of the flame. However, I think, in both cases, it's only the outside edge of the flame that is actually burning. The middle of the flame is, I guess, quite cool (in comparison). I seem to remember, from my school days, if there's a luminous (yellow or white) part and a blue part, then the hottest point is the tip of the blue part. If there's no blue part then I'm not sure where the hottest point is. My school days were quite a long time ago

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Roly Williams

"God is not dead - he is alive and well and working on a much less ambitious project" (MRFS)

Caprice · Posted: Fri Nov 06, 2009 9:21 am Post subject:

Interesting thread!
A little more about flames temperature: