Emissivity and absorptivity relationship advice

Radiation properties - Wikipedia

Practical examples based on differences in light absorption of surfaces can be observed at oil refineries. So when you speak of emissivity, you should rather speak of spectral emissivity which means emissivity at a 1 Recommendation. 5 Reflectivity Measurements (Metal with high emissivity coatings). 63 .. t − 2l1/c, considering this equation to a linear order in h; and then, the phase of the light is gave me not only useful advice about my research but also interesting or. shape and orientation of the building and its relationship absorptivity and emissivity characteristics of the .. Hand (7) gives useful advice on the proper care.

How fast, how much and where temperature must rise are complicated questions that depend upon heat transfer by WITHIN our climate system the atmosphere, the surface and the ocean.

Below the TOA, heat transfer includes radiation, convection of simple and latent heat evaporation and condensation and conduction very near the surface.

How to Design Radiant Heating and Cooling Systems|Radiant Panel Performance Characteristics

Slowing down how much? If we are talking about radiation it moves at lightspeed, no matter how many absorptions on the way up it would not make much difference.

I often hear this argument, but I interpret it as another way of saying that it takes a longer way. The wavelenght is mainly a relation to the human eye as it consist of mostly the visual part with a bit of IR and UV.

It is called infra-Red and ultra-Violet, so these words are clearly related to our vision as well. When the subject discussed is temperature, wavelength is not useful. Wavelength is a property of high intensity radiation, and emitted intensity from a radiating body is dependent on temperature only. Wavelength is a property relative to intensity, and therefore it is an effect of temperature. That said, a radiating body does not rise in temperature as a result of how fast or how much radiation that escapes from a cold gas surrounding it.

That is one of the fundamental discoveries of blackbody radiation. Temperature as a measure of the internal state, and it was found that absorption and emission is dependent on temperature alone. And when we include a term like albedo, which is hard to find an exact description of and it is said to vary by an unknown amount.

Anyway, emissivity was used for the relationship between emission and internal state. We should keep loyal to proven theories that have been tried through well over a hundred years, and assume that they are correct.

An imbalance in the emitting bodys surroundings is not possible to include as a cause of the internal state. The theory is very clear about that; The emission of a body is dependent on the internal state only.

The same goes for absorption. A radiative imbalance in the atmosphere is not part of the internal state of the emitting body. If you make a claim about radiation and temperature, and there is a theory that has been confirmed in many many experiments to be true over a century, and is until this very moment regarded as one of the greatest discoveries in physics, you better have a calculation including that teory and numbers that clearly show how and why we should ignore a proven law.

A bit further down on the wikipedia article about blackbody radiation you can read a clarification that it really applies to -any- body. This is my point.

Temperature and the emitted intensity dependence on it, IS the whole theory. The other included terms like wavelength, grey or black, displacement of the emission curve etc. They are facets on the diamond, but they all obey that relationship. If you say that emission in a investigated situation not is dependent on temperature, our response to that, and your own, should be that you have miscalculated, not to ignore a law that has been standing through most part of the evolution of modern physics.

I think it can be considered to be the strongest consensus there is in all science of all kinds. It is very clearly written, and it consists of so few parts that if you just read every word in that one sentence you know how to apply it.

The emission depends on temperature only. Which part of it and why do you say is wrong. So in addition to looking at emissivity, resistivity, and conductivity we also need to consider in cooling, color and absorptivity which is an thermo-optical property of the floor. Now you know why I have been saying for years that HVAC can not operate in isolation from the interior design professional. For those who wish to study the thermo-optical properties of materials which relate to radiant heating and cooling visit the Hyper Physics site operated by Georgia State University, Department of Physics and Astronomy.

An emissivity of 1.

Emission and Absorption - Elstein-Werk

An emissivity of 0. Virtually all flooring, wall and ceiling finishes make very good radiators as they have very high emissivities. It helps some people to think of emissivity as water surface tension where rough surfaces have less tension in comparison to smooth surfaces. Incidentally the emissivity of the human skin is about 0. There is generally an inverse relationship between emissivity and reflectivity where a material having a low emissivity will have a high reflectivity such as mirrors and polished metals or low-E coatings.

But this is not a pure relationship and the values of each material should be checked against industry handbooks.


The thermal absorptance represents the fraction of incident radiation that is absorbed by the material or is the proportion of radiation absorbed vs reflected at each wavelength. This also applies to the transfer of radiated energy e.

Another point for consideration is that radiation between the emitter and the absorber is interactive.

Radiation properties

In other words, the absorber emits IR radiation during the absorption process. One reason why an object is only able to absorb some of the total IR radiation that it is exposed to is in the nature of its molecular structure. The nature of an object's molecular structure simultaneously defines its ability to absorb IR radiation in a definite wavelength range.

This wavelength range is its absorption spectrum. There are bodies and materials with multiple maximum absorption values, within which ranges they absorb IR radiation parts equally well.

Just as emitters can emanate IR radiation with different wavelengths, objects or material hit by the IR radiation can absorb it in the same way. Because materials have different molecular compositions, they can be shown to have an individual absorption spectrum at a certain temperature e. Radiation not corresponding to this absorption spectrum is able to pass through transmission or is reflected.