CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > FLUENT

absorption and scattering coefficient of air for DO model

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By LuckyTran

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 1, 2015, 05:37
Post absorption and scattering coefficient of air for DO model
  #1
New Member
 
Charlie d'hondt
Join Date: Jun 2015
Posts: 1
Rep Power: 0
charlie.dho is on a distinguished road
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 100°C and in infrared radiation.

Thank you
charlie.dho is offline   Reply With Quote

Old   June 28, 2015, 12:04
Default
  #2
New Member
 
Siyang Hu
Join Date: Jun 2015
Posts: 1
Rep Power: 0
halfblood815 is on a distinguished road
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 100°C 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
halfblood815 is offline   Reply With Quote

Old   February 3, 2017, 14:27
Default
  #3
New Member
 
ss
Join Date: May 2016
Posts: 4
Rep Power: 9
sanket9921 is on a distinguished road
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
sanket9921 is offline   Reply With Quote

Old   February 6, 2017, 00:38
Default
  #4
Senior Member
 
Lucky
Join Date: Apr 2011
Location: Orlando, FL USA
Posts: 5,654
Rep Power: 65
LuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura aboutLuckyTran has a spectacular aura about
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.
fredericgaillard likes this.
LuckyTran is offline   Reply With Quote

Old   July 5, 2020, 08:35
Default
  #5
Member
 
Himanshu
Join Date: Jan 2017
Posts: 33
Rep Power: 9
Himanshu_Shrivastava is on a distinguished road
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?
Himanshu_Shrivastava is offline   Reply With Quote

Reply

Tags
absorption coefficient, air, do model, scattering coefficient

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
mass flow in is not equal to mass flow out saii CFX 12 March 19, 2018 06:21
Simulation of a single bubble with a VOF-method Suzzn CFX 21 January 29, 2018 01:58
Constant velocity of the material Sas CFX 15 July 13, 2010 09:56
air bubble is disappear increasing time using vof xujjun CFX 9 June 9, 2009 08:59
Two-Phase Buoyant Flow Issue Miguel Baritto CFX 4 August 31, 2006 13:02


All times are GMT -4. The time now is 05:28.