Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Petrochemicals on 18/05/2018 18:17:38

Title: Is the maximum temperature achievable limited by combustion flame temperature?
Post by: Petrochemicals on 18/05/2018 18:17:38
As in such things as a kiln or furnace, is the maximum achievable temperature within limited by the flame temperature, or is it possible to to exceed this temperature by heat storage?

Cutting and welding torches are fuelled with acetylene, oxyacetylene and other non-oxygen bearing fuels as oxygen can limit flame temperature. Temperature is after all the energy in molecules and they can surely build up  energy, but the thought is that due to the molecules having only the same energy as the flame, this temperature cannot be exeeded.

Nuclear can develop great temperatures as it releases great energy per particle, so can if given enough reactions develop high near temperatures, and can give serious burns from its radiation, these being destructive forms of radiation too.

So, any thoughts?
Title: Re: Is the maximum temperature achievable limited by combustion flame temperature?
Post by: Bored chemist on 18/05/2018 18:42:04
https://en.wikipedia.org/wiki/Electric_arc_furnace
Title: Re: Is the maximum temperature achievable limited by combustion flame temperature?
Post by: evan_au on 18/05/2018 23:50:01
The maximum temperature achievable by a furnace is often not limited by the reactants, but by the containment.

In rocket engines, they intentionally don't burn the fuel at its optimum ratio to obtain the highest possible temperature, as the flame would burn through the rocket cone.

Plus, they use tricks like injecting a layer of unburnt fuel along the inside of the cone, to keep the burning fuel away from the cone, and pipe cryogenic fuel around the cone to keep it cool.

An oxyacetylene torch (=acetylene fuel + oxygen oxidiser) achieves temperatures as high as 3500C - just hot enough to melt tungsten (the metallic element with the highest melting point); but the fuel & oxidiser is combined in metal pipes. This is possible because the hottest part of the flame occurs outside the metal pipes, in free air, so it doesn't need solid containment.

Many nuclear fusion experiments produce a very hot plasma (ITER is planned to reach 150 million C). They use strong magnetic fields to keep the plasma away from the walls of the reactor; as soon as the plasma touches the walls, it cools down, and it also vaporises the wall material, which loses heat much more effectively than the plasma itself.

But the hottest of all manmade temperatures is in subatomic particle accelerators; the LHC produces an effective temperature of 5 trillion C - all contained in an extreme vacuum, and isolated by strong magnetic fields.
Title: Re: Is the maximum temperature achievable limited by combustion flame temperature?
Post by: Petrochemicals on 19/05/2018 02:02:34
Yes that is true evan, lazers heating things are limited by the ammount of radiation absorbed versus emission, nuclear fires by radiation and energy releases onto surroundings , particle accelerators as you say achieve high temperatures, and as you say limited by the containment. I know heat pumps are capable of raising temperatures to  higher than the source temperature through refrigerants\ pressure etc.

As an example with a flame source, is it possible to raise the temperature of propane conbustion to say 3500 degrees in a brick kiln, this i believe is above the threshhold of heat pumps.