Thursday, July 24, 2014

Mohr Non-Sense: Adiabatic Flame Temperature

Every now and then I get an email about the latest non-sense that is being passed around on certain forums where the so-called "debunkers" get together to talk trash. These days, this sort of forum chit-chat has become so obviously sad and wrong that people don´t bother mentioning it most of the time, but sometimes the BS is covered with enough sophistry to hide the worst of the stench.

For example, Rev. Chris Mohr posted a comment on the JREF forum on July 11, 2014, where he actually cites authentic scientific papers! He does believe they back-up his faith in the fairy-tale that says office fires melted rust-flakes in the Twin-Towers on 9/11, and formed iron-rich spheres.

Part One: Macroscale temperature vs the microscale.

 Rev. Mohr has up until now refused to accept the concept of the "melting-point" and refused to believe that metals (iron for example) do not melt until they reach the designated temperature point at which they begin to melt. This concept has messed with his faith because the melting-point of iron is around 1500C, while the maximum temperature of a building fire is about 1000C, and the realistic temperature to be expected is less than 650C, which means an office fire cannot melt iron.

Rev. Mohr has finally implicitly admitted that the "melting-point" of a metal means exactly what you would expect it to, but he has managed to use his imagination to find a way around it:
"...a typical office fire might burn at, say, 1100-1800F bulk temperature. But, the adiabatic flame temperature, the theoretical upper limit of burning materials starting at room temperature, is much higher. For hydrocarbon fuels it is 3600-4500F, for wood it is almost 3500F. If you use laser to focus in on the flame temperature as they did in these published papers (below), observable local instantaneous temperatures can actually approach the adiabatic temperature. Any tiny flake of rust exposed to such micro near-adiabatic temperatures could easily hit the melting point of iron."
He essentially claims that although the temperature of the "bulk" of a fire might be less than 1000C, you can find microscopic spots at double that temperature, if you have equipment sophisticated enough to detect those spots. You might want to ask how microscopic those spots are and for how long they remain so hot, but you would get no answers because the cited papers in support of this phenomenon do not actually feature, describe, or mention it at all, and are therefore utterly irrelevant (more on that below). Rev. Mohr may not be intentionally lying; he just does not understand technical papers or know what he is talking about.

The other problem with this theory is that even if true, it would have no relevance to the "real world" or the potential of an office fire to melt iron or rust flakes. If you research things on a small enough scale, you can start to feel like Alice in Wonderland, but careless researchers can really humiliate themselves by making silly assumptions based on the nano-world.

Part Two: You may be wondering what Rev. Mohr´s cited papers actually talk about? 

Before we go into that, let´s quickly review the topic at hand: the adiabatic temperature of a carbon-fueled fire vs the actual temperature of an open-air fire, as explained by Dr. Thomas Eagar in 2001.

The adiabatic (the theoretical maximum) temperature from a carbon fuel (like jet fuel) is about 3000C, but that requires the fuel to be premixed to contain pure oxygen in the perfect ratio. Normal fires, however, rely on the same external air supply that we breathe, not pure oxygen mixed into the fuel, so the actual maximum temperature of an open-air fire is about 1000C, even with jet-fuel. In-between those two extremes, there are jet-engines and various other burner/furnace/torch designs that involve multiplying the supply of air with turbines etc, or adding a stream of pure oxygen. Using various techniques, blast-furnaces, burners, jet-engines, and torches can achieve temperatures way above 1500C, and torches with premixed pure oxygen can achieve over 2500C. This is old news, but normal fires in open air are still limited to the 1000C, and the only thing any researcher has to remember is to not confuse open-air fires with jet-burners and torches etc.

You can probably guess now what mistake Rev. Chris Mohr made? His first source is a paper on "piloted methane-air jet flames stabilized on a burner" which is basically a pressurized gas burner that yields a blue-hot flame. This burner also happens to be a hybrid design that burns air and the fuel is also partially pre-mixed with oxygen: the jet fluid is 3/4 air for "a more robust flame." Again, this is a known technique to increase the temperature, and one should not confuse gas-burners and torches with open-air flames.

Rev. Mohr goes on to say that "You can also use as a reference showing temperatures in the vicinity of 2000C a paper out of Purdue" and this is another paper on a gas burner. This burner can indeed achieve close to 2000C at the optimal distance from the nozzle, and even close to 2500C when run on pure oxygen.

- Note that these are the actual temperatures of the "bulk" of the flames at the optimal distances from the jets or the nozzles, not some microscopic points in the flame - these burners really are this hot. This is impressive, but again utterly irrelevant to a normal open-air fire, which is still limited to about 1000C.

Part Three: Flatulence along with the stinker.

Mohr´s forum buddies did not notice that his cited papers do not support his premise in any way, or even touch the subject for that matter. The premise that his cited papers show normal fires achieving adiabatic temperatures is completely bogus, and the papers are not about temperatures at the micro level at all either. Mohr´s theory is all non-sense, but this does not stop the flatulent and rambling comments from people who seemingly never verify "information" purported to support their faith:
"Only that we need to remind ourselves that behavior on the macro level is not necessarily reflective of behavior on the micro level. And that's a mistake I think we all commonly make - myself so very included - even outside this issue. This post helps remind us of that"
"Thanks, Chris. I fully expect the Trust hers to focus on "Sandia National Labs" instead of the truth of what is being said."

"In other words...AE Truth is full of it!"

"Thanks Chris, let's hope MM forwards this information to his super hero Neils Harrit ? although I expect the peer reviewed article will be ignored due to it not being presented in a court of law"
Part Four: Rev Mohr also talks about iron reduction at low temperatures, trying to tell himself that the fires at the WTC could have melted iron and reduced it:
"There are several oxides of iron, and each has a different melting point. The lowest of these is FeO (also called wüstite) at ~ 1377 C, i.e. lower than the melting point of Fe (~ 1535 C). Rust (Fe2O3, or hematite) decomposes/reduces around 1566 C in air, but under partially reducing atmosphere this can shift to much lower temperature. For instance, in an incompletely-burned fuel fire with hydrocarbons and CO, reduction of iron oxides to metallic iron can occur << 1000 C (I’ve seen it at 600 C under a dilute hydrogen stream). Stating from hematite the reduction sequence would be as follows: Fe2O3 – Fe3O4 – FeO – Fe, thus as rust is reduced it reaches FeO (lowest melting phase) before Fe.Could it be that the “iron rich” microspheres are FeO, or a mixture of Fe and Fe3O4 from the disproportionation reaction of FeO (4FeO = Fe + Fe3O4)?"
No, the iron-spheres featured in Harrit et al are not FeO as even the "typical" ones have a 2:1 Fe-O ratio (see figure 21), meaning if you want to assume the one part oxygen is bound as FeO, the other part Fe is still oxygen free; you began with two parts iron and are still left with the other half of the Fe without any oxygen to bind with, meaning at least half the iron is pure iron. Harrit et al also observe that their iron spheres have Fe-O ratios "up to 4:1" so the conclusion that there is substantial amount of pure iron in the observed spheres is quite solid. Not all of the iron is pure iron and that is to be expected in thermite reactions: some of the iron will be bound with oxygen, perhaps as Fe3O4 or FeO, or as inter-metallic aluminum-iron-oxygen compounds (see Harrit et al figures 24 to 26).

Partial carbon-reduction of iron-oxides can take place well below 1000C but full reduction to pure iron requires about 1200C. Again, it may be possible to do this at lower temperatures in controlled lab conditions in the presence of special elements and specific conditions such as "under a dilute hydrogen stream" but such findings have no relevance to an open-air building fire.