Does a gas flame emit less radiant heat than a coal flame?

[Green Xenon]

Hi:

 

I have some questions regarding flames.

 

A dicyanoacetylene-ozone flame reaches a temperature of 5516 K. This causes it to emit EM radiation mostly in the UV spectrum. A wooden log flame reaches only 1170 K, as a result it emits most of its EM radiation in the IR spectrum. Since IR generates more heat on human skin than UV of the same intensity, does this mean that a wood log flame will be perceived to be emitting more radiant heat than a dicyanoacetylene-ozone flame?

 

Also, does a yellow bituminous coal flame give off more infrared radiant heat than a blue methane flame? My guess is yes, because the former gives off light due to incandescence [about 90% of which is emitted in the infrared spectrum] while the latter gives of higher-energy EM radiation due to quantum jumps [i.e. the blue spectrum].

 

So even though a blue flame is hotter than a yellow flame, the latter will emit more radiant heat while the former will emit more convective heat. Do I guess right?

 

 

Thanks,

 

Green Xenon

Edited September 14, 2009 by Green Xenon

[insane_alien]

Since IR generates more heat on human skin than UV of the same intensity,

 

err... no if the intensity is the same then you will get the same amount of heating.

 

UV is actually better at heating than IR as you can deliver the same energy with less photons.

[CaptainPanic]

IR radiation isn't my expertise, but isn't it true that different materials emit at different wavelengths (which are also a function of the temperature)?

 

In addition, the human skin, or your clothing reflect different wavelengths with different efficiency. So, certain wavelengths will hardly heat you at all, while others are absorbed almost entirely and will heat you efficiently.

 

I can't think of how to write it down, but I would evaluate this with a proper heat balance (on one side the wavelength and flux of the radiation, and the other side the selectivity of the type of wavelength are the main factors).