31
votes
How does fire heat air?
Fire is a reaction that includes the air. To be precise, it includes a part of the air, oxygen. It releases the results of the reaction as a new part of the air. Those reaction results are hot and mix ...
- 2,001
19
votes
Accepted
How does fire heat air?
Heat conductivity is not the same as the ability to absorb heat, only to pass the absorbed heat through the material. Air within the flame can absorb heat, but the air cannot quickly pass the heat to ...
- 1,252
10
votes
How does fire heat air?
That is the reason fire is hot.
While others have pointed out the role of the exhaust products, the main takeaway is that yes, air is not easily heated by fire.
What happens is that the excess energy ...
6
votes
How does fire heat air?
The fire is a sustained combustion process resulting from the combination of oxygen from the air, fuel and heat sustaining an exothermic chemical reaction that produces various gases (CO2, CO, etc.) ...
- 75.6k
5
votes
Challenge: How can this meta-material be in thermal equilibrium?
Interesting question! I always enjoying trying to see where the second law is hiding.
Rather than considering the details of the CPCs, I'm going to steel man the concept and consider a perfect optical ...
- 3,299
4
votes
How does fire heat air?
Molecular collisions
Fire generates heat in several ways: mostly as radiation, but also as the kinetic energy of the products of the chemical reactions (which are mostly the products of oxidation of ...
- 61.8k
4
votes
How does fire heat air?
The air is part of the chemical reaction which produces the "heat" and the gaseous products of combustion have more kinetic energy than the air had originally.
The products of combustion ...
- 98.6k
4
votes
Accepted
Is thermal conduction really radiation?
The important distinction between thermal conduction and thermal radiation is that the heat exchange is driven by the difference in temperature for thermal conduction and the heat exchange is driven ...
- 105k
3
votes
Accepted
Stationary equation of radiation transfer: Which one is correct?
I believe the first version of the equation is correct (although it ignores the intrinsic emission coefficient of the material, $j_\nu$, which should appear as an additive term on the RHS. However, it ...
- 135k
3
votes
Accepted
How can I determine how much energy a sensor pixel can withstand before exploding?
This isn't trivial. Silicon sensors can generally handle power well above saturation without damage. Usually, the limit is temperature. So, what you need to do is a heat transfer calculation involving ...
- 21.8k
3
votes
Challenge: How can this meta-material be in thermal equilibrium?
In other words, there are three choices here.
There is a fourth choice; your analysis is incorrect. We know this because it violates the Second Law, which has extraordinarily credibility—far higher ...
- 27k
2
votes
Melting plastic with radiant heat?
Yes it is perfectly possible - I used to get into trouble doing things like this as a kid. When I grew up powder-coated steel, made in exactly this way, was common for industrial furniture.
If you ...
- 7,478
2
votes
What would be a beginner's book on radiative transfer?
In my opinion, one suitable book for beginners is the S. Chandrasekhar's books called Radiative Transfer (1960). Basic concepts and derivations are very well explained. Again, this is my opinion :).
1
vote
How radiative heating of a gas should scale with gas density
That would depend on whether it was optically thick (absorbs all radiation incident upon it) or optically thin (allows almost all radiation through), or somewhere in between.
If the gas is thin and ...
- 135k
1
vote
What is the ideal amount of shade for a house with air conditioning and solar cells on the roof?
I would expect that the ideal situation would be to shade all of the house except the solar panels (which are presumably on the roof). These would actually shade the house themselves, and would ...
- 10.1k
1
vote
How does radiation heating work at the fundamental level?
How does radiation heating work at the fundamental level?
In the question for
1.You forget that in matter the relaxation photon can interact further with atoms in the gas, there are $~10^{23}$ atoms ...
- 235k
1
vote
Accepted
What would be a beginner's book on radiative transfer?
Chandrasekhar's book is anything but suitable for beginners.
Rob Rutten's course on radiative transfer is classic in the field of stellar atmospheres. It is available here:
https://robrutten.nl/rrweb/...
1
vote
Is thermal conduction really radiation?
You are correct that virtual photons are not photons; what we refer to as radiative heat transfer is mediated by the latter. Conductive heat transfer occurs through physical contact and is not ...
- 27k
1
vote
Kirchhoff's Law of Thermal Radiation - When is a (radiative) process in thermodynamic equilibrium?
This post pretty much answers the question that I had.
To reiterate, the emissivity in the Stefan-Boltzmann law is a spectral-averaged emissivity, that is
\begin{gather}
\varepsilon = \int_0^\infty \...
- 195
1
vote
Accepted
Change of intensity along path element - plane-parallel geometry
The full radiative transfer equation is,
$$
\frac{1}{c}\frac{\partial}{\partial t}I_\nu + \hat{\Omega} \cdot \nabla I_\nu + (k_{\nu, s}+k_{\nu, a}) I_\nu = j_\nu + \frac{1}{4\pi}k_{\nu, s} \int_\Omega ...
- 3,299
1
vote
Accepted
Radiative transfer equation for a three-level system
The derivation is easy but a bit long, so I'm going to link a clear resource and just say the steps.
Step 1: Write the total Hamiltonian of the system
Step 2: perform rotating wave approximation and ...
- 2,233
1
vote
Accepted
Calculating pressure and flux tensors in radiative astrophysics
First I start with the component formulation of the (monochromatic) radiative flux tensor $\mathbf{F_\nu}$, i.e. $\left( \mathbf{F_\nu} \right)^{i} \equiv F_\nu^{\;i}$,
$$
F_\nu^{\;i} := \oint_\Omega ...
- 301
1
vote
Temperature rise due to thermal radiation?
Given the emissivity of the rod and the plate and the geometry of their configuration, you could probably determine the power flux between the two.
But it's a big step to go from that to the ...
- 41.9k
1
vote
Shouldn't $CO_2$ forcing depend on the surface temperature?
This is more of an observation than an answer. The term "radiative forcing" is a linear, one-dimensional way of describing the effect of CO2 in the atmosphere. There are MANY effects going on that ...
- 12.3k
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