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Author: Subject: High-temperature flames.
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[*] posted on 14-4-2010 at 12:28


Quote: Originally posted by hissingnoise  
Oh yeah, liquid ozone vs. gaseous ozone. . .
The liquid ozone will react faster than gaseous ozone.
The faster reaction will produce the higher temperature.



[Edited on 14-4-2010 by hissingnoise]



You dobe assuming liquid O3 @ -113o will react at all!
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[*] posted on 14-4-2010 at 13:47


Well yes, certainly - with the right conditions; it isn't, after all, noted for its stability. . .

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[*] posted on 14-4-2010 at 14:07


Quote: Originally posted by hissingnoise  
Well yes, certainly - with the right conditions; it isn't, after all, noted for its stability. . .



I have not great faith in generalities. That said I would note
that the temperature of detonation is usually greater than
that of combustion for the same chemical. The difference is attributed to ....
different reaction products/reaction product ratio's between combustion
and detonation. I, however, am not sure this applies to chemical mixtures vs.
explosive chemical compounds where the heat is the result or the rearrangement
of the explosives elements as opposed to redox reactions.
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[*] posted on 14-4-2010 at 14:58


A dispersion, in gaseous ozone, of finely divided carbon can be expected to explode on ignition.
If, that is, such a mixture isn't hypergolic to start with?
But the explosion produced by LOZ/carbon will have a considerably higher velocity and temperature.



[Edited on 14-4-2010 by hissingnoise]
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[*] posted on 14-4-2010 at 21:58


You still have not said where the extra energy comes from.
You just keep repeating the "mantra" that it's faster so it will be hotter.
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[*] posted on 14-4-2010 at 22:50


With rapidly occurring exothermic reactions the energy liberated can not dissipate, this results in an increase in temperature and reaction velocity. This is a fundamental difference between combustion and detonation.
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[*] posted on 15-4-2010 at 10:04


"With rapidly occurring exothermic reactions the energy liberated can not dissipate,"
Now look up the meaning of adiabatic.
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[*] posted on 15-4-2010 at 11:22


Are you sure you're not the one having difficulty with 'adiabatic processes'?

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[*] posted on 15-4-2010 at 13:05


from
http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/adiab.html

"An adiabatic process is one in which no heat is gained or lost by the system."


It's the whole reason why flame temperatures are calculated for the adiabatic condition- it saves having to estimate how much energy is lost because that depends on the experimental design.

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[*] posted on 16-4-2010 at 13:25


Quote: Originally posted by unionised  
Now look up the meaning of adiabatic.


Yeah, and? Adiabatic flame temeprature isn't even the highest flame temperature. That is the theoretical flame temperature. An example is stoichiometric combustion of methane in oxygen, which has a theoretical flame temperature several thousand degrees higher than the adiabatic flame temperature. The difference between those two is dissociation. This is also why burning combustibles in oxygen gets hotter than burning in air even with the same amount of oxygen, which latter dilutes with nitrogen.
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[*] posted on 17-4-2010 at 08:24


I'd still like to know where the extra energy comes from.

Also, since it is never possible in practice to ensure that no heat is lost from a reaction all adiabatic temperatures are theoretical. You are therefore saying that the theoretical temperature is higher than the theoretical temperature. That seems odd.

The adiabatic temperature is what you calculate id you share out the energy released from the reaction among all the products of that reaction. Obviously that means finding (or calculating) the heat capacity of those products as a function of temperature. In doing that you have to take account of dissociation and other effects like electronic excitation. It's tot a trivial exercise but, if you say it doesn't give the highest temperature possibel then you are saying, in effect, that letting the heat out (i.e. not running the reaction adiabatically) makes it get hotter.
Again, that seems odd.

[Edited on 17-4-10 by unionised]
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[*] posted on 17-4-2010 at 10:26


The explanation earlier was one that I saw it was from an inorganic chemistry book by Erwin Riedel. Even in a closed container, if we burn something the energy release is much more gradual, but in a detonation this energy release is abrupt and rapid. Since temperature is due to kinetic energy movement in a material, and detonations are much more kinetic in nature than combustions, it seemed to make sense.

Dissociaton in the products could play a role. Detonations develop very high pressure. And it is known high pressure reduces dissociation in combustions (flame temperatures are known to be higher under high pressure). This could account for thousands of degrees in difference.

After looking around a little, it turns out even for the flame temperature, adiabatic is not the theoretical limit. Described in Fuels and Combustion by Samir Sarkar. According to him, there are four categories of flame temperatures:

Theoretical flame temperature: maximum value of fuel and oxidant at stoichiometric amounts. Not enough oxidant dilutes and incomplete combustion results. Too large of an amount dilutes the products and takes away heat. Those both lower flame temperature. Degree of dissociation reactions increase with temperature and an endothermic effect results (e.g. CO2 = CO + 0.5 O2 + 67,636 kcal). Example: CH4 with O2: 5050 C.
Adiabatic flame temperature: flame temperature at adiabatic conditions. Example: CH4 with O2: 2740 C.
Actual flame temperature: This is practical combustion under regular conditions (non-adiabatic).
Maximum adiabatic flame temperature (also called maximum flame temperature): realized when the fuel is in slight excess of stoichiometric amounts. Examples: H2 in 78.0% oxygen: 2660 C. C2H2 in 44.0% oxygen: 3137 C. C2N2-oxygen (CO, N2 as products): 4580 C. Hydrogen-fluorine flame: 4300 C.
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[*] posted on 17-4-2010 at 11:14


That theoretical maximum is a weird flame temperature; it's how hot you have to get the mixture before the forward and reverse reactions are equally fast.

As has been mentioned, if you pre heat the starting materials you get a higher temperature but, even then there is a limit- if you heated the fuel and oxygen to over 5050C then mixed them, they wouldn't react much because the reaction products would decompose back into the starting materials.
OK, that's a maximum temperature- but it's never going to have a meaningful realisation.

In particular, it's not going to be obtained by cooling the starting materials.

The adiabatic temperature is the highest temperature you can reach from any given starting temperature (usually STP). Of course, it depends on the fuel: oxidant ratio but, for any given pair there will be a limit.
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[*] posted on 17-4-2010 at 14:27


What exactly constitutes flame ?

If ultra high temperature is desired it is acheived by a thermic lance.
http://www.wisegeek.com/what-is-a-thermal-lance.htm

Heat generated at the burning end of the steel clad magnesium tube
into which oxygen is fed , can be enhanced by providing an electric
current from an arc welding tranformer.

Something close to 11000 ºF has been attained.

_ _ _ _ _ _ _ _ _

Tempeartures acheived by particle collision in accelerators made
for the purpose generate transient peaks of billions of degrees.

.
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[*] posted on 17-4-2010 at 20:13


Quote: Originally posted by unionised  
That theoretical maximum is a weird flame temperature; it's how hot you have to get the mixture before the forward and reverse reactions are equally fast.

As has been mentioned, if you pre heat the starting materials you get a higher temperature but, even then there is a limit- if you heated the fuel and oxygen to over 5050C then mixed them, they wouldn't react much because the reaction products would decompose back into the starting materials.
OK, that's a maximum temperature- but it's never going to have a meaningful realisation.

In particular, it's not going to be obtained by cooling the starting materials.

The adiabatic temperature is the highest temperature you can reach from any given starting temperature (usually STP). Of course, it depends on the fuel: oxidant ratio but, for any given pair there will be a limit.


Sakir attributes the whole difference between theoretical and adiabatic flame temperature in methane and oxygen to dissociation. I take it then that the adiabatic flame temperature is a calibration of the theoretical flame temperature. Resistance of reaction products to dissociation (and high reaction enthalpy) is the reason e.g. hydrogen and fluorine flames reach such high temperatures.

While it's true pre-temperature has a role in flame temperature, in a detonation (which can be thousands of degrees higher) this effect doesn't seem appreciable as a mixture of charcoal and liquid oxygen (23/73) has an estimated detonation temperature of about 6600 K.
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[*] posted on 18-4-2010 at 05:02


Franklyn, could you translate that temperature into Rankine please?


Anyway, I'd still like to know where the energy comes from to give hotter products if you start with something colder. I have an idea of what it might be, but I'm not sure.

[Edited on 18-4-10 by unionised]
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[*] posted on 19-4-2010 at 11:07


What is your idea?
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[*] posted on 20-4-2010 at 10:30


@ unionised

Rankine is degrees Farenheit minus ~ 460 ( approximately , actual absolute zero is very slightly less )

Kelvin is degrees Celsius minus ~ 273 ( again approximately , actual value is very slightly more )

See => http://en.wikipedia.org/wiki/Rankine_scale

____________________


The incandescent plasma being electrically conductive can be heated to higher temperature than
from the combustion of the metal by the supplemental current from an arc welder. The energy
provided is additive.


Attachment: phpzm0BMi (12kB)
This file has been downloaded 218 times

[Edited on 20-4-2010 by franklyn]
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[*] posted on 20-4-2010 at 10:30


Imagine I dispersed a cloud of charcoal in some ozone and lit it, the product would be a a much larger volume of very hot gas.
Now imaging that I took that gas and adiabatically squashed it to the volume of a lump of charcoal soaked in liquid ozone.
Doing so would need me to do a lot of work and (like the air in a diesel engine) heat the gas mixture.
I'm not sure if that would get it to 6600K or whatever, but I can see it getting rather hot.
At least it's a possible answer- it's the energy not lost pushing back the atmosphere.
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[*] posted on 20-4-2010 at 10:34


Well yes free expansion of a gas does not reduce it's temperature unless it has done work ( pushing something ).

True of the individual particles ( molecules , atoms , ions )
The average apparent temperature factors in the volume.
The solar wind is a very high temperature rarified gas the
apparent temperature of a volume of space is near
absolute zero.

.

[Edited on 20-4-2010 by franklyn]
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[*] posted on 26-6-2010 at 05:57


Quote: Originally posted by franklyn  
@ unionised

Rankine is degrees Farenheit minus ~ 460 ( approximately , actual absolute zero is very slightly less )

Kelvin is degrees Celsius minus ~ 273 ( again approximately , actual value is very slightly more )

Degrees Kelvin is Celsius PLUS 273 since 0 kelvin is absolute zero




[Edited on 20-4-2010 by franklyn]


[Edited on 6/26/2010 by Justin]

[Edited on 6/26/2010 by Justin]
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[*] posted on 26-6-2010 at 16:21


Probably F2 burning with B(CN)3 would be super hot.
By the way, B(CN)3 probably polymerizes under heat and pressure to make a superstrong ceraminc armor.

Or SF6 burning with magnesium
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[*] posted on 3-8-2011 at 07:37


A simple hydrogen flame can be brought up to temperatures exceeding 5000C if an electric arc is maintained between two tungsten electrodes. The energy from the arc is absorbed by diatomic hydrogen and then released again when the hydrogen radicals strike a cold metal surface. This is the theory behind AHW or atomic hydrogen welding.
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[*] posted on 3-8-2011 at 09:36
Can you top this?


Can you top 6500o K?

The experimental combustion phase was aimed at producing the highest, possible temperature
by varying the metal, the oxidizer ant he pressure of the reaction. It was found, both theoretically
and experimentally that higher temperatures, were achieved with higher pressures. Two techniques,
were used to achieve higher pressures: (a) Dynamic pressurizing of metal powder and solid, oxidizer:
and (b) pre -pressurizing metal wool with gaseous oxygen The results achieved with these two
techniques are shown graphically in Figure 1. This snows that the pressurized oxygen system
produces brightness temperatures equivalent to those of dynamic pressurization, but at, lower
pressures. The highest brightness temperature 6500o K, was obtained by the, reaction of hafnium
powder and potassium perchlorate under a pressure of approximately 40,000 psi. However, it can,
be seen from Figure 1 that temperatures -greater than, 6000o K are achieved at the much lover
pressure of 1450 psi by pressurized oxygen.



Accession Number : AD0443158
Title : SPECTRAL EMISSIVITY OF FLASH COMBUSTION REACTION STUDY PROGRAM
Descriptive Note : Final technical rept. 1 Jun 1963-31 May 1964
Corporate Author : NORTH AMERICAN AVIATION INC LOS ANGELES CA
Personal Author(s) : Gerhauser, J. M.
Handle / proxy Url : http://handle.dtic.mil/100.2/AD443158
Report Date : 06 JUL 1964
Pagination or Media Count : 178

Abstract : This study was initiated to provide the additional data required on maximum intensity,
spectral distribution, duration, and efficiency of radiation emitted by high energy metal-oxygen
reactions and the degree of control that might be achieved over these characteristics. In brief, the
study has shown: (1) several reactions produce brightness temperatures above the approximate
threshold temperatures for neodymium (3500 to 5000 K) and ruby (5200 K) with a maximum of 600 K
achieved; (2) the brightness temperatures are a strong function of pressure with highest temperatures
achieved between 2000 and 50,000 psi; (3) except in the early stages of unpressurized reactions
where line and band emission are present, the spectral distribution is a continium, but not necessarily
a black body distribution; (4) the time duration of the flash can be controlled to within 1/2 to
3 milliseconds; and (5) that these reactions can be effectively used to pump high energy density
laser systems.

Descriptors : *LIGHT, *LASERS, *COMBUSTION, *PYROTECHNICS, LASER PUMPING, MAGNESIUM,
BRIGHTNESS, ALUMINUM, CHEMICAL REACTIONS, ZIRCONIUM, PERCHLORATES, CHLORATES,
LINE SPECTRA, POTASSIUM COMPOUNDS, EMISSIVITY, TRANSFORMATIONS, BAND SPECTRA,
NEODYMIUM, ABSORPTION SPECTRA, RUBY, SODIUM COMPOUNDS, THORIUM, PRESSURE,
LIGHT PULSES, PUMPING(ELECTRONICS), HAFNIUM, HIGH TEMPERATURE, ENERGY, INTENSITY
Subject Categories : PYROTECHNICS

----------
Actually - the Analogue Guy has found a ref
to higher temp's if'n I can relocate it I'll
post it.


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[*] posted on 3-8-2011 at 10:07


Extracted from
High-Temperature Research
By means of "liquid containers," liquid metals can be studied at
much higher temperatures than heretofore.
Aristid V. Grosse
Science Volume 140 781-789.
17 May 1963

because La PDF is a bit over
3 meg thus toooo large to post here.



Methods were developed at our institute to
burn many metals at atmospheric pressure.
The metals were burned in the solid state (as rods, pipes,
balls, sheets, and powders), in the liquid
state, and in the vapor state. The
expected adiabatic temperatures in the
range of 3000o to 5000°K were reached
(2). The highest temperature, close to
5000oK, was attained (3) through
burning zirconium powder in a torchtype
apparatus. Beryllium, at pressure
of 1 atmosphere, in oxygen produces a
temperature of 4300oK, and aluminum
and magnesium, temperatures of 3800o
and 3350oK, respectively.

Fluorine is the most electronegative element
known, and thus many fluorine compounds
are more stable than the corresponding
oxides, because of the
greater strength of the fluorine bond.
A good example is hydrogen fluoride.
When it is formed from hydrogen and
fluorine a flame temperature of 4000°K
is reached (6, 7). At a total pressure
of 5 atmospheres the temperature is
raised to 4200oK (6). In contrast, the
maximum temperature of the hydrogenoxygen
flame is only 2930°K at atmospheric
pressure.

When a mixture of cyanogen and
oxygen was burned according to the
equation (CN)2 + 02 > 2CO + N2,
one of the highest flame temperatures
so far attained, 4800°K (at atmospheric
pressure), was produced (8). By burning
the same mixture under a total
pressure of 100 pounds per square
inch, a temperature of 5050°K was attained
(9).

It was found that the unstable colorless
liquid, carbon subnitride, C4N2-
the first member of the dicyanoacetylene
series-can be burned with oxygen
(J0) in either a diffusion flame or a
flame of premixed type, according to
the equation C4N2 + 202 - > 4CO
+ N2. The calculated flame temperature
is 5260°K at atmospheric pressure.

Since the flame temperature calculated
for the cyanogen-oxygen flame
has been checked experimentally (8),
the enthalpy data for CO and N2 may
be used with confidence. The accuracy
of the calculated flame temperatures is
+2°. In all these combustion studies
ordinary oxygen, 02, was used. It was
recognized that significantly higher
temperatures could be obtained if ozone,
03, were substituted for 02. The heat
of formation of ozone from oxygen
is +33.98 kilocalories per mole of
ozone; thus, the amount of heat liberated
is increased, and, provided the
stoichiometry of the combustion is adjusted
to produce the same reaction
products as with oxygen, the flame
temperature is also increased.
However, pure ozone in either gaseous,
liquid, or solid form may detonate
with great violence to molecular oxygen,
although with proper handling it
can be made to burn in a regular, but
faint and nonluminous, blue flame (11)
to oxygen, according to the equation
203 >- 302. Because of the experience
we had gained in handling and
burning 100-percent ozone we were
able to premix and burn various mixtures
of hydrogen (12) and cyanogen
(13) with ozone. The mixture 3(CN)2
+ 203 burns uniformly, noiselessly, as
brightly as an electric arc, and with a
pink-violet color: 3 (CN)2 + 203 -*
6CO + 3N2. At pressures of 1 and 10
atmospheres, its calculated temperatures
are 52080 and 55060K (±20), respectively.
The temperatures of the corresponding
oxygen flame, 3 (CN)2 +
302 -- 6CO + 3N2, are 48560 and
5025 OK, respectively.
The cyanogen-ozone and the carbon
subnitride-oxygen flames, with temperatures
of 52080 and 5260°K, respectively,
produce the highest chemicalflame
temperatures achieved to date at
pressure of 1 atmosphere. Calculations
indicate (10) that substitution of ozone
for oxygen in the carbon subnitrideoxygen
flame, provided explosions and
detonations could be avoided, particularly
under pressure, would produce a
temperature higher than 6000°K (see
Table' 2). These flame temperatures
represent the ultimate goals with chemical
reactions.

Use of the noble gases helium and
argon makes it possible to produce a
chemically inert "flame" of temperature
up to 25,000oK.

The first ionization potential of
argon is 15.68 volts, equivalent to 362
kilocalories per gram atom; that of
helium is 24.46 volts or 565 kilocalories
per gram atom. Helium begins to
ionize appreciably only in the 20,000o
to 25,000oK range, and therefore its
heat content is lower than that of argon.
Up to 10,000o Another problem relates to the nature
of chemical substances that can be
heated to extremely high temperatures.
As I have said, the highest temperature
attainable through ordinary chemical
reaction is in the range 5000° to
6000°K. This is the limit of existence
of chemical compounds. At these temperatures
all chemical bonds break and
all molecules are dissociated into transient
radicals or atoms. Thus, flame
temperatures higher than these cannot
be produced through chemical reaction.
The temperature above which no
known solid can exist has been reached.
The metal with the highest melting
point is tungsten, which melts at
36430K, and the oxide with the highest
melting point is thorium dioxide,
which melts at 3300°K. Tantalum
carbide, which melts at 4200°K, has
the highest melting point of any known
substance. For purposes of containment,
in practice at our laboratories,
these maxima are attained and used
only rarely, because of (i) chemical
reaction between the high-melting substance
and any other substance being investigated; (ii) the occurrence of
eutectic mixtures, which lower the melting
point; and (iii) thermal shock.

And it is not likely that substances
will be found with melting points many
hundreds of degrees higher. Thus, we
are compelled to find, if possible, thermally
stable liquids if we want to contain
higher temperatures in some useful
way.

Fortunately for the future development
of high-temperature research and
technology there are substances which
will exist as liquids up to very high
temperatures-much higher than any
at which we had thought liquids could
exist. These substances are the refractory
metals, which will eventually be
useful in our rocket and space technology.
Some of them remain as rather
dense liquids even up to temperatures
of 20,000°K. Since they are
elementary monatomic liquids they cannot
undergo any chemical change (except
for ionization), even at extremely
high temperatures.

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