My understanding is that it doesn’t really depend on the metal much. It’s just the blackbody radiation associated with that temperature. So basically anything glowing red from heat is probably over 500°C.
“As the object increases in temperature to about 500 °C (773 K; 932 °F), the emission spectrum gets stronger and extends into the human visual range, and the object appears dull red.”
But less than you’d think, given the extreme coefficient, as human perception of brightness is nonlinear. An object twice as bright as another looks pretty similar to the eye.
Thanks for the correction. I’m absolutely not gonna pretend I fully understand this, but isn’t it still the case that anything glowing red from heat pretty much has to be over 500°C? I.e. https://en.wikipedia.org/wiki/Draper_point ?
So when you say “Autoignition”, then ignition of what? For natural gas to “ignite”, as in burn or in other words oxidize, there need to be an oxidizer present.
Autoignition here is referring to the temperature at which it will ignite immediately upon mixing with oxygen. Below that temperature, they can mix and not burn (like what happens with a gas leak).
Autoignition temperature of natural gas is above 500c. Need a spark, or enough heat, there could even be a leak and this not be enough heat to ignite.
I’m pretty sure if it’s red hot it’s close to if not over 500°C but I guess it depends on the metal.
At least according to this Wikipedia article. https://en.wikipedia.org/wiki/Red_heat
My understanding is that it doesn’t really depend on the metal much. It’s just the blackbody radiation associated with that temperature. So basically anything glowing red from heat is probably over 500°C.
“As the object increases in temperature to about 500 °C (773 K; 932 °F), the emission spectrum gets stronger and extends into the human visual range, and the object appears dull red.”
https://en.wikipedia.org/wiki/Black-body_radiation
The intensity does depend on the emissivity of the material, and emissivity is a bit counterintuitive:
https://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html
But less than you’d think, given the extreme coefficient, as human perception of brightness is nonlinear. An object twice as bright as another looks pretty similar to the eye.
Thanks for the correction. I’m absolutely not gonna pretend I fully understand this, but isn’t it still the case that anything glowing red from heat pretty much has to be over 500°C? I.e. https://en.wikipedia.org/wiki/Draper_point ?
Oh yeah, for sure. That pipe is hot.
Thanks!
So when you say “Autoignition”, then ignition of what? For natural gas to “ignite”, as in burn or in other words oxidize, there need to be an oxidizer present.
Autoignition here is referring to the temperature at which it will ignite immediately upon mixing with oxygen. Below that temperature, they can mix and not burn (like what happens with a gas leak).