Questions about heat conduction and INTERNAL_HEAT_SOURCE

[ESett5555]

Hi everyone,

I have a few questions concerning heat conduction in solids in FDS, mainly about the parameter INTERNAL_HEAT_SOURCE. I am trying to better understand how this parameter is implemented in FDS, and how it behaves towards other namelists and parameters such as SURF, OBST and GEOM namelists

1. In the FDS Technical Guide, equation (7.2) explains how FDS use each parameter specified by the user in the solid phase. What is INTERNAL_HEAT_SOURCE in this equation? Is INTERNAL_HEAT_SOURCE equal to the source term qsm? It is written that this source term qsm is equal to the heat production rate given by the pyrolysis model plus the radiative absorption in depth, and I don’t find any mention of an user specified INTERNAL_HEAT_SOURCE in paragraph 7.1.

2. If I want to use the GEOM namelist, I understand that I should use the 1D conduction algorithm, and not the 3D algorithm. Is the computing of solid conduction done on each one of the faces of a GEOM obstruction? What should one specify about the THICKNESS? Can one use VARIABLE_THICKNESS=T with a GEOM obstruction?

Thank you very much for your help an have a great day.

[drjfloyd]

1. INTERNAL_HEAT_SOURCE is a source term which means it is a part of q'''_s in Eq 7-1. That bit of the Tech Ref was written before that input existed and good catch that we should say something in that Chapter. I'll add.
2. Yes each face has its own 1D conduction solution. THICKNESS should represent the through thickness of the face. VARIABLE_THICKNESS is for HT3D which cannot be used with GEOM.

[ESett5555]

Thank you for your answer !

I have a few more questions about INTERNAL_HEAT_SOURCE:

1. It seems to me that INTERNAL_HEAT_SOURCE should be specified in the SURF line unless one is trying to use 3-D Heat Conduction, where it should be specified in the OBST line. If I understand it correctly, if I want to use it with a GEOM obstruction, I should specify INTERNAL_HEAT_SOURCE in the SURF line and then apply my SURF to some of the surfaces defined with the GEOM line. Am I correct or should I specify INTERNAL_HEAT_SOURCE in the OBST line?

2. How does it behave with a GEOM obstruction? I want to create a vertical 1 cubic meter cylinder that releases 1 kW of heat. Should I write these lines ? :

&SURF ID=’TOP-BOTTOM’, MATL_ID=’STEEL’, THICKNESS=1.0, BACKING=’EXPOSED’, INTERNAL_HEAT_SOURCE=1.0/
&SURF ID=’SIDE’, MATL_ID=’STEEL’, THICKNESS=1.12, BACKING=’EXPOSED’, INTERNAL_HEAT_SOURCE=1.0, GEOMETRY=’CYLINDRICAL’/

&GEOM ID='cylinder', 
SURF_IDS='TOP-BOTTOM', ’SIDE’, ’TOP-BOTTOM’,
CYLINDER_LENGTH=1.,
CYLINDER_RADIUS=0.56,
CYLINDER_ORIGIN=0.,0.,0.5,
CYLINDER_AXIS=0.,0.,1.,
CYLINDER_NSEG_AXIS=6,
CYLINDER_NSEG_THETA=48 /

3. Would it be possible to specify a vertical 1 cubic meter cylinder (regarding the solid conduction algorithm, not the gaseous flow) that releases 1 kW of heat without using the GEOM namelist ? Will these lines release 1kW or around 1.25 kW (as I specify a cartesian OBST with l x L x h=0.56 x 0.56 x 1, which makes a volume of 1.25m^3) :

&SURF ID=’TOP-BOTTOM’, MATL_ID=’STEEL’, THICKNESS=1.0, BACKING=’EXPOSED’, INTERNAL_HEAT_SOURCE=1.0/
&SURF ID=’SIDE’, MATL_ID=’STEEL’, THICKNESS=1.12, BACKING=’EXPOSED’, INTERNAL_HEAT_SOURCE=1.0, GEOMETRY=’CYLINDRICAL’/

&OBST XB=0.0,0.56,0.0,0.56,0.0,1.0, SURF_IDS='TOP-BOTTOM', ’SIDE’, ’TOP-BOTTOM’/

Just for an information, I am currently working with version FDS-6.10.1-0-g12efa16-release

Again, thanks a lot for your answers !