Thermal camera Hairdyer gap paradox
The IR 'hairdryer paradox'.
This is a thermogram of an operating hairdryer, taken using the same technology by which we understand the greenhouse gases - thermoelectrics.
Why is there a gap after the hairdryer outlet?
Is the air not hot? Yes, it is; it is blowing onto a surface, so it must be hot.
Is the air not radiating infrared (heat)? Everything with a temperature radiates IR; but, from this image, it appears 'air' (mostly nitrogen and oxygen) doesn't - hence they are termed non-greenhouse gases. But this is wrong. It is that the instruments thermoelectric detector do not transduce electricity from the heat of nitrogen and oxygen.
How did the 'air' get hot in the first place - and so quickly - if it does not absorb IR radiation? Air is an extremely poor thermal conductor of heat (0.026 W/(m K) ), and convection must imply radiation and/or conduction.
It has to be from radiation. Nitrogen and Oxygen both have emission spectra lines in the IR range of the EMS; this is where they absorb their heat from the glowing hot radiating elements in the dryer.
What would it look like if we put carbon dioxide through it? Would there be a gap then?
No, CO2 is thermoelectric and will flow out.
I aim to try this as soon as I can.