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.

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

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.

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. Don´t 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.

Please don´t hesitate ask more.

Yours Nuray

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

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

hi I am looking for some references about radiation modeling,about history of radiation modeling and etc? please help me?

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.

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

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

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

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

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

thank u for responding

i am looking for gray thermal radiation model

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.