Recent content by Carlos de Meo

Hi Guys I´m studying the heat exchange problem in furnaces and, to begin with, i started with Incropera´s book. One thing is actually driving me crazy On the last part of this exercise´s solution (part 3), the physical principle involved is not very clear to me. To calculate the absorptivity of...

Now that makes sense. Thank you very much Bystander

I was thinking about the solid structure and the interaction with . When a photon is absorbed promoting a system to a quantum excited state, it might emit a photon, undergo a nonradiative relaxation or a combination of both. For a selective surface, the key is to enhance the nonradiative...

So the main idea behind of this kind of material is to control the nonradiative relaxation and preventing it to achieve thermal equilibrium?

Hi Guys I was reading about selective surfaces for solar thermal conversion and, according to the literature, an ideal material for that would have high absorptance in the 0.2-2.5 μm (due to the Planck distribution for a 5000 K black body, i guess) and also low emittance to suppress the losses...

Sorry for not being specific enough. I wanted to say a problem like this. Imagine i have a solid body and i know that there is a vibrational mode that responds to a specific photon frequency (let´s say this photon is in the Infra red range). Now assuming that all the radiation described is...

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Hi Guys Studying thermal radiation here and I am kinda stuck at one point Kirchhoff law states that at thermodynamical equilibrium, the amount of energy absorbed must be reemited. But before the system reaches equilibrium, is there a model to predict how much energy of these photons absorbed...

Oh, now that makes sense. Thank you very much @Charles Link

But doing the calculations and adding now the second reflection at the second interface, i still don´t get how Callister made the (1-R)2. Now i get a value of (1-R)/(1+R) instead of the value above

Hi Guys Studying some optical properties of materials and found this equation on Callister T = I0*(1-R)2*(exp(-βx) Where T is transmission, R reflection, β the absorption coefficient and x the lenght. In the same chapter, the author says that this equation´s derivation is homework I tried to...

Oh sure, sorry about that. If we think an enclosure containing a gas inside. This system is already at thermodynamic equilibrium. The walls are reflecting, absorbing and emitting photons,the gas is absorbing and emitting (lets not talk about scattering at the moment). So if i apply the Kirchhoff...

Hi Guys I´m studying the absorption and emission phenomena of a gas and, according to Kirchhoff "extended" law, for a body at thermodynamic equilibrium, the following statement is true. ελ(T,θ,φ) = Aλ(T, θ,φ). So, if i understood correctly the meaning of this equation, The amount of absorbed...

Hi Guys I was studying the thermal properties of SiC at high temperatures and now i have a few questions Usually, at high temperatures, the photons effect are much more intense than phonons at high temperature, correct? According to Rosseland heat diffusion equation Krad = 16σT3 /3β, β= 4πK/λ, σ...

And the complex part of these models comes from the absorption due to the high free electrons density?