this post was submitted on 04 Dec 2023
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How does heat get from the water radiator to the air?
Radiation.
Atoms don't physically touch. The electrostatic force that both binds atoms into molecules and keeps molecules separated is mediated by photon exchange.
The fan blowing on the radiator: Excuse me?
This. And what heat exchange mechanisms are in play when you have a moving fluid? That's right! Convection!
(And a bit of conduction at the boundary layer, but I already shut off a different fork of this thread by limiting pedantry)
The fan blows air on the radiator. Those air molecules can't physically touch the radiator. The electostatic forces of atoms keep everything separated. When you touch something, you are feeling the electrostatic force of your finger's atoms pushing against the electrostatic force of the object's atoms.
The electrostatic force (that is the electro magnetic force that electrons radiate) is actually photons. The particle of electromagnetism is the photon. When you touch something you are feeling the photons exchanging between the electrons in the atoms of your fingers and the object.
The definition of radiation is photon emission/absorption.
and in convection, at what point are photons being exchanged?
How about in conduction?
I'm pretty sure both of those are just ripples of heat in atoms & molecules spreading to nearby atoms & molecules via more nano-mechanical means, with the former case having that amplified by the fact the atoms & molecules are in motion at a larger scale.
Loosely couple two identical oscillators and excite one, and the second will move as well, no photons needed. At a nano scale, that is how conduction works. And again, convection adds to that the fact that the oscillators can freely move around each other
At the atomic level, nothing physically touches. Electrons do not physically touch each other to transfer momentum. When two atoms get close, the electromagnetic field pushes the electrons away from each other before the electrons touch.
The electromagnetic field is made of photons.
https://en.m.wikipedia.org/wiki/Photon
Counterpoint: at the boundary layers, right where the air touches the fins, the main mechanism for heat exchange is conduction. Ultimately, convection is just conduction, where the medium undergoing heat conduction is a moving fluid, which massively amplifies the rate of heat exchange.
Air is kinda shit at taking in heat through radiation, but fine at doing so via conduction and convection.
The metal atoms in the fins don't move into the air. They stay on the fins. The fins' atoms have to transfer their kinetic energy via photon exchange to the atoms in the air.
So conduction is radiation at atomic distances.
Ah, I see we're getting to the point where it's hard to tell if we're being philosophical or pedantic.