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 Jason September 23, 2004 21:06

Thermal radiation model selection and application

If I want to calculate the fire in a room, both wall surface and flame will result in radiative heat transfer, furthermore, walls will also absorb the heat it received from the flame radiation. Which model is good for this case? If I use "IMMERSOL" or "Radiosity" raidation model built in PHENICS, should I use the degree C temperature or absolute K temperature for the whole computation domain? what is the linking coefficient of TEM1 and T3 in the IMMERSOL model? thanks.

 Nuray Kayakol September 24, 2004 16:41

Re: Thermal radiation model selection and applicat

As you may find from literature, radiosity model which is equivalent to P-1 model, is inaccurate for absorption coefficient larger than 0.15 1/m. IMMERSOL may be suitable for fire simulation.

TEM1 : the fluid temperature T3 : the radiation temperature IMMERSOL solves a heat-conduction type of equation expressed in terms of T3.

Information for IMMERSOL: http://www.cham.co.uk/phoenics/d_pol...c/enc_rad3.htm

Nuray Kayakol

 Jason September 27, 2004 23:01

Re: Thermal radiation model selection and applicat

Dear Nuray Kayakol: Thanks for your message. According to an example of IMMERSOl radiation model online provided by PHOENICS, the linking coefficient of TEM1 and T3 is 1.0, what is the physical meaning of this coefficient? Should I use the aosolute temperature K for all the computation of heat transfer? thanks.

 Nuray Kayakol September 28, 2004 06:42

Re: Thermal radiation model selection and applicat

Dear Jason,

It is better to give more information about coupling of radiative heat transfer equation (RTE)to energy equation. TEM1 is obtained from the solution of energy equation. This equation has term from radiative heat transfer, divergence of heat flux, which requires the solution of RTE expressed in terms of intensity. Although recent radiation models like DOM or FVM deals with intensity, IMMERSOL simplifies the solution and express RTE in terms of new temperature dependent variable, T3 called radiation temperature. What I described until now explain how T3 and TEM1 is connected in terms of modeling. Donīt try to find an linking coefficient for your simulation.It is already well explained how to use IMMERSOL model. If you want to solve only radiative heat transfer solve T3, but if your system has convective gas medium which requires the solution of energy equation then solve either TEM1 or H1(entalpy) tohether with T3.

You may then think under what conditions TEM1 is equal to T3. In which library case they are equal or linking coeff. is 1.0?

As far as I know Kelvin is used. A RADIANT HEATER PANEL http://www.cham.co.uk/phoenics/d_pol...sol/afmpan.htm is useful to decide which unit is to be used. But it is better to check with Mike from CHAM.

Yours Nuray

 Carlos September 29, 2004 18:06

Re: Thermal radiation model selection and applicat

Hello Jason and Nuray,

Jason, I think that all information Nuray sent to you is correct. But there some extra informations:

(1) T3 has no real physical meaning except inside solid bodies, when it is equal to solid temperature.

(2) I think that the idea of T3 (T3 comes from T^3) is to use the idea of "diffusion" similar (but not the same) to Rosseland idea. And it is of great help in better connecting the radiative energy transported by fluids with the conducted energy inside the solids that are immersed in these fluids (here comes the name IMMERsed SOLids ).

(3) Do you know that reference temperature that appears in PHOENICS menu under properties (I am not sure...)? If you use tref=273, you enter celsius temperatures and receives celsius temperature back. PHOENICS converts to kelvin internally. However, if you set tref=0, you must use kelvin scale.

Hope this helps,

Carlos

 Jason September 29, 2004 22:59

Re: Thermal radiation model selection and applicat

Thanks Nuray and Carlos. As Nuray mentioned, the solution of TEM1 and T3 equations are coupled together, does the user must specify the source term of TEM1 equation that is obtained from the radiative heat transfer solution of RTE? I presume it is implemented in the IMMERSOL model for solving the gas-solid boundaries. In my case, the solid-gas boundary exchange heat energy by radiation-convection and conduction. I appreciate your comments. -Jason

 mahmood ahmadi February 19, 2005 12:52

Re: Thermal radiation model selection and applicat

 Rami February 20, 2005 03:20

Re: Thermal radiation model selection and applicat

Mahmood,

I suggest you to look in the classics:

R. Siegel and J. R. Howell, Thermal Radiation Heat Transfer, Hemisphere, 1992.

M. F. Modest, Radiative Heat Transfer, McGraw-Hill, 1993.

E.M. Sparrow and R.D. Cess, Radiation Heat Transfer, McGraw-Hill, 1978.

 ben April 16, 2005 12:32

Re: Thermal radiation model selection and applicat

if you just want to get some idea and this one is ok

M.N. Ozisik, Radiative Transfer and Interactions with Conduction and Convection

 Nuray Kayakol April 29, 2005 12:25

Re: Thermal radiation model selection and applicat

If you need futher help I can send you some documents for the comparison of gray and/or non-gray radiation models or related electronic version of basic references Nuray

 jamal September 30, 2005 09:53

Re: Thermal radiation model selection and applicat

dear sir i need a copy of Thermal radiation model selection and applicat thak u

 sourabh gandhi October 27, 2005 08:25

Re: Thermal radiation model selection and applicat *NM*

 Nuray Kayakol October 27, 2005 08:55

Re: Thermal radiation model selection and applicat

Please send me your email. Due to small tables in the text I can't post or attach it here. Are you looking for gray or non gray thermal radiation models?

Yours Nuray

 jamalgul November 18, 2005 02:23

Re: Thermal radiation model selection and applicat

thank u for responding

i am looking for gray thermal radiation model

 Nuray Kayakol November 18, 2005 06:21

Re: Thermal radiation model selection and applicat

Discrete ordinates method (DOM) is widely accepted as right choice for optically thin media like combustion space. If the geometry is complex Finite Volume Method (FVM) which is one version of DOM, is widely used. As far as I know these models are not implemented in PHOENICS yet. INFORM features of PHOENICS may help you to implement them. It would be a nice work. A few years ago I used INFORM to implement six-flux model, which is an old radiation model. Why not for DOM or FVM? If your model is computationally expensive you can use IMMERSOL which gives plausible results when walls are not black. Just define your system I can help more.

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