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absorption and scattering coefficient of air for DO model

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Old   June 1, 2015, 04:37
Post absorption and scattering coefficient of air for DO model
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Charlie d'hondt
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Hello,

I'm working on heat transfer problem , I simulate a test room and I put an electrical radiator.

I want to see effect of radiation heat transfer in my room.

So I use Discrete ordinate model becaus I want air medium but I don't have absorption and scattering coefficient of air.

I'm looking for this data but I don't find it anywhere.

May someone have an idea of these two properties of air ?

I want these properties for temperature between 0 and 100C and in infrared radiation.

Thank you
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Old   June 28, 2015, 11:04
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Siyang Hu
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Quote:
Originally Posted by charlie.dho View Post
Hello,

I'm working on heat transfer problem , I simulate a test room and I put an electrical radiator.

I want to see effect of radiation heat transfer in my room.

So I use Discrete ordinate model becaus I want air medium but I don't have absorption and scattering coefficient of air.

I'm looking for this data but I don't find it anywhere.

May someone have an idea of these two properties of air ?

I want these properties for temperature between 0 and 100C and in infrared radiation.

Thank you
Hi charlie.dho, I am working on a similar case with u. I've read several reference to figure out the absorption and scattering coef. of air too. But most of the papers I found can be back to 1950s-1980s. Honestly, I am less patient to read them.

You didn't give more details about your case. So, I supposed that you just use a radiator to heat up the air in the room and then figure out the warm (or buoyant flow?) air flow indoor. Am I right? If so, in my personal opinion, I would like to set these two properties to ZERO as the air (if does not contains additional greenhouse gases or particles) is almost transparent to the IR radiation. I think your case may be similar to the greenhouse process. But for a 'pure' air, its temperature is mainly increased by the thermal convection of the surface of the room but not the radiation absorption of it.

For a better interpretation, u can find the fundamental definition of greenhouse effect on Wikipedia. My solution mentioned above is based on it actually.

Good luck!

Ray
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Old   February 3, 2017, 13:27
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Quote:
Originally Posted by halfblood815 View Post
Hi charlie.dho, I am working on a similar case with u. I've read several reference to figure out the absorption and scattering coef. of air too. But most of the papers I found can be back to 1950s-1980s. Honestly, I am less patient to read them.

You didn't give more details about your case. So, I supposed that you just use a radiator to heat up the air in the room and then figure out the warm (or buoyant flow?) air flow indoor. Am I right? If so, in my personal opinion, I would like to set these two properties to ZERO as the air (if does not contains additional greenhouse gases or particles) is almost transparent to the IR radiation. I think your case may be similar to the greenhouse process. But for a 'pure' air, its temperature is mainly increased by the thermal convection of the surface of the room but not the radiation absorption of it.

For a better interpretation, u can find the fundamental definition of greenhouse effect on Wikipedia. My solution mentioned above is based on it actually.

Good luck!

Ray
Thank you so much......it's very useful
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Old   February 5, 2017, 23:38
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2 things!

1) Try looking for absorptivity instead of absorption coefficient. Absorption coefficient can then be estimated from Beer-Lambert law if you can come up with the length scale. Absorption coefficient is path dependent and includes geometry effects so it is not purely a property of the substance. Hence why is is very hard to find, because it is specific to each problem and not worth reporting, whereas absorptivity is a material property.

2) It is indeed difficult to find these properties. Try looking for properties of water vapor or wet air (not dry air). Air is primarily nitrogen and oxygen (then some trace amounts of He and Ag), which are pretty much transparent to infra-red because they're all straight molecules.

The primary participating media are the bent molecules, CO2 and H2O, which we normally don't include in the definition of dry-air!

Btw it is extremely difficult to find these properties over a range of temperatures. You will likely end up with only the properties at room temperature or something like that. Most of these properties were measured back in the old days. My undergrad heat transfer textbook (Incropera and Dewitt) has these graphs.
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Old   July 5, 2020, 07:35
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Himanshu
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Quote:
Originally Posted by halfblood815 View Post
Hi charlie.dho, I am working on a similar case with u. I've read several reference to figure out the absorption and scattering coef. of air too. But most of the papers I found can be back to 1950s-1980s. Honestly, I am less patient to read them.

You didn't give more details about your case. So, I supposed that you just use a radiator to heat up the air in the room and then figure out the warm (or buoyant flow?) air flow indoor. Am I right? If so, in my personal opinion, I would like to set these two properties to ZERO as the air (if does not contains additional greenhouse gases or particles) is almost transparent to the IR radiation. I think your case may be similar to the greenhouse process. But for a 'pure' air, its temperature is mainly increased by the thermal convection of the surface of the room but not the radiation absorption of it.

For a better interpretation, u can find the fundamental definition of greenhouse effect on Wikipedia. My solution mentioned above is based on it actually.

Good luck!

Ray
Hello Siyang,
when you are saying "(if does not contains additional greenhouse gases or particles)" ,does this mean if the air does not contain CO2 more than naturally it has?
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