Discussion in 'Fettling Forum' started by ColinG, Dec 7, 2019.
Does anyone know the approximate temperature that a mantle burning kero reaches?
I have a type k thermocouple somewhere in the shop, sounds like an great beer fueled experiment for the weekend.
I remember reading a while ago that the temperature inside an Aladdin mantle is about 2000F.
About the temperature of lava.
I wondered because I used aluminium for a support rod that is close to the mantle on my Superb and I'd rather it didn't melt!!! I might replace it with steel if I can find some.
Aluminum melts at around 1250F and loses strength rapidly over 600F, I'm quite sure that in close proximity to the mantle it would melt.
Perhaps head to a hardware store and check their supply of bolts.
There is something called the 'adiabatic' flame temperatures of different fuels in air. They are theoretical calculated max. values, not the actual temperatures. That puts kerosene-air mix at a temperature slightly in excess of 2000 deg C!
But in actual, the flames are never adiabatic. Therefore, they'll be considerably lower in temperature.
I'd say, the actual temperature within the mantle in a kero lantern would fall somewhere between 900-1100 deg C. But as the combustion gases leave the mantle or the flame front, they'll expand and the temperature would drastically fall below anything that would melt brass.
If you replace the Thorium mantle with an asbestos or metal mesh, the colour of the glow should roughly indicate the temperature as would be radiated from a "blackbody'. You could refer to a colour temperature chart for that.
Note: the 'colour temperature' of a typical Thorium mantle is well above 2000K, say 2300-2500K, which is approximately indicative of a glowing tungsten filament in an incandescent electric light bulb. But Thorium oxide behaves rather differently from most solid materials when heated. They glow with higher colour temperatures than the actual temperature they're at.
Just a thought .... the MilSpec lamp, and including the Colman 252A lantern version has an aluminium tube generator. Mine runs very well with no sign of any aluminium heat degradation to the aluminium generator.
Ahhh, interesting! I decided to make a steel support anyway as I found a length of rod more or less the right diameter. I have never heard of an aluminium generator before. The heat transfer would be excellent being aluminium and it must be able to withstand the temperatures because... well, it does!
The aluminum generator would be cooled by the fuel evaporating in it, same as the water in a boiler tube prevents it from melting down.
Good point, that would indeed be the case ...... still it was just a thought.
Those aluminium vapourisers have been known to crack.
Finally got around to measuring the mantle temp. Used a Petromax 829 that was warmed up for 20 minutes and the temp according to the thermocouple was 1988F.
So Thomas, exactly how much beer was used in this alchemic experiment, exactly???
Great result! ..and great pics! ... and considerably higher than the melting point of Mild Steel
What is the function of the copper tube in the preheat cup?
How many °C would that be?
About 1085 C according to an online converter
1086 deg C is definitely hot enough to have melted the aluminium rod I originally used on the rebuilt Veritas Superb so it's a good job i asked!
That is the pre heater !
It makes a nice flame which is the last part of the pre heating. The flame then ignites the light.
You can even just see the small pipe recevoir the make the realy the last flame. The pipe is hollow and ha a hole just above the bottom of the cup, so it fills up.
Whoops! didn't notice it was Fahrenheit! ...Silly me!
just did a bit of research( made sure the glasses were on this time) and that is pretty much the melting point of Copper! I think most brasses are lower than that than that?
The obvious question therefore, is how do the mantle holding bits (spigots?) not melt if the mantle burns at a temperature that melts brass?
I'm probably just being dim!
I wonder if it is a little under estimated. The thermocouple is a considerable size and will have lost heat by conduction/radiation.
White hot is 1300C, 1080C is just in the orange range.
I’m thinking that the unburnt fuel/air mix keeps the brass bits cooler. The flame is below the burner head (that holds the mantle) consequently the heat is in the mantle, not in the burner manifold.
Nice experiment. I'd guess that's fairly accurate. If you leave a brass tube inside the mantle, the zinc would vaporize first, leaving the copper to oxidize black. It might not melt the copper if its a large enough to conduct the heat away soon enough.
A measured temperature is not sufficient do describe the energy conditions to bring a mantle to light.
The reason is simple: The temperature of a substance is a measure for the average kinetic energy of its molecules. The mantle doesn't care about an "average" energy, it needs a minimum energy to produce photons (approx. 160 KJ/mol for red, 300 KJ/mol for violet light).
In systems which are in (or near) a thermodynmic equilibrum, e.g. the tea in your teacup, the energy distribution of the molecules meets a Maxwell–Boltzmann distribution.
A flame is far away from a thermodynamic equilibrum, but in a steady state. Molecules of fuel and oxygen enter the flame, react with each other, hit the mantle, and the reaction products escape through the hood. In a flame, the energy distribution is significantly broader, and the Cerium atoms in the mantle can convert some of the high energy states to light.
Years ago, I tried to explain that here (sorry, German):
That was an interesting article, @ludwig .
You must be a physicist to dwell into such in depth theory.
I'd need to translate the German into English to grasp the essence of the article.
Yes, you indeed have a detailed explanation on the molar energies required for photonic emissions of the different wavelenghts of visible light. I've always been curious about the characteristics of Thorium dioxide in relation to the somewhat shorter wavelengths(less reds, more green/blue/violet) when its heated to incandescence compared to other substances. And about the supposedly 'candoluminescent' phenomena, if that's proven in any way. Understanding the exact physics behind it is probably beyond me. Its also interesting to note the synergistic effect of the small percentage of cerium oxide has in thoriated mantles in the way that it would significantly increase the visible light output. I've noted that its somewhat different from the oxy-hydrogen flame on calcium oxide in the case of 'limelights'.
Very informative, Ludwig.
Not surprisingly there are a few scientists collecting pressure lamps and posting messages on this forum! I’m a research chemist with a background in thermochemistry and combustion. Hence the fascination with old lamps! Nice experiments.
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