Radiation between two vertical side

Numerical methods and mathematical models of Elmer
Post Reply
coni
Posts: 5
Joined: 22 Jan 2015, 12:54
Antispam: Yes

Radiation between two vertical side

Post by coni »

Hi,

I try a simple test (see geometry in attachement) on a square to test radiation between two vertical side (bc1 and bc2).

Below are the parameters, with heat equation actived :

boundary condition 1 :
temperature (dirichlet condition)=800
radiation=diffuse gray
emissivity=0.8
radiation target body = 1

boundary condition 2 :
temperature (dirichlet condition)=1200
radiation=diffuse gray
emissivity=0.9
radiation target body = 1

material body 1:
density=0
heat capacity=0
heat conductivity=0

The result is a file with list of viewfactor who seem to be >0, but the flux over Bc1 or Bc2 are nul ?
Is there an error on the method ?

Thanks
Attachments
carre.jpg
carre.jpg (40.79 KiB) Viewed 2655 times
raback
Site Admin
Posts: 4812
Joined: 22 Aug 2009, 11:57
Antispam: Yes
Location: Espoo, Finland
Contact:

Re: Radiation between two vertical side

Post by raback »

Hi

Your case does not make sense to Elmer as all the material parameters are zero. So you're basically solving for equation 0*x=0 and as a solution you get the BCs you put in.

Even further the radiation boundary should be complete (2PI) or be decleared Open. Otherwise Elmer tries no normalize the view factors to full angle.

-Peter
coni
Posts: 5
Joined: 22 Jan 2015, 12:54
Antispam: Yes

Re: Radiation between two vertical side

Post by coni »

Hi the Forum,

I come back on this old subject.
I'm trying to obtain boundary total heatflux (conduction + radiation) and net radiative heat flux alone, without success.

The cavity (body1) is a square 0,2m*0,2m.

Actived equations are :
- Heat equation (with calculate_loads actived)
- flux&gradient (calculate flux and grad actived)
- result_output
- savescalar (wich save [diffusive flux: temperature over bc] and [boundary sum: temperature loads over bc])

Body1 material is density=1, heat capacity=1, reference temperature=293, heat conductivity=0.5

Left and right sides are cold wall (287,5 K) and warm wall (297,5 K).
Up and bottom sides are linear temperature imposed from 287,5 K to 297,5 K.
All boundary conditions have diffuse_gray_radiation activated with epsilon=0.8 and radiation_target_body=1.

After simulation, the left or right Boundary heatflux in Savescalars or Resultoutput is equal to pure conduction heatflux (5 W/m or 25 W/m²).
The same simulation with adiabatic condition instead of linear temperature on the top and bottom sides shows an influence of radiation on the distribution of temperature on the top and bottom sides and inside the cavity.
I deduce that radiation is active in the two cases but it seems that the calculated boundary heat flux is only the conductive one.

I would like to obtain boundary total heatflux (conduction + radiation) and net radiative heat flux alone. How can I obtain that ?

Thanks for helping me
Attachments
Forum_Elmer_dT=10 et HB_Tlin.zip
(276.79 KiB) Downloaded 225 times
Post Reply