Quiz 9 Flashcards
What does the back side condition INSULATED mean in FDS?
That a virtual layer is applied to the back of the wall with 100% insulating capability. Therefore no heatloss through the wall.
What does the back side condition VOID mean in FDS?
That the back side of the wall connects to ambient properties. Heat loss is present and lost from the simulation to the void.
What does the back side condition EXPOSED mean in FDS?
Heat is transported to the back side of the wall and able to do heat exchange with the surrounding fluid.
What criteria have to be met for FDS to accept the EXPOSED back side condition?
The wall can be a maximum of 1 cell thick and some computational domain must be present on the other side.
Are there any practical problems in FDS with walls that are not symmetrical (as in same composition regardless of viewpoint)? If so, how do you solve it?
o Yes, FDS uses a left-to-right standard when telling it what layers are present. Therefore an innermost layer will be facing the outside if heat returns through the layers.
o To deal with this one must create two SURF:s with layers in correct order from where heat is transferred.
By default in FDS, how many dimensions does the solid phase heat transfer model use? Can you name a few pros and cons of this approach?
o 1D
o fast calculations, good approximation when homogenous boundary conditions
o No distribution of heat within the material to the “neighbouring sides”/lateral heat transfer. Not good when inhomogeneous boundary condition present (e.g. flame against wall)
Does FDS allow for temperature dependent material properties? If so, how is it implemented?
Yes, through the ramp function one can apply dependent properties at points that FDS then interpolates between.
What is the difference between THICKNESS defined on a SURF line and the thickness you define on an OBST line? Which one does FDS use for heat transfer in the solid using the standard heat transfer model?
SURF thickness is used for conduction heat transfer. OBST thickness obstructs the fluid flow.
Do you see any practical limitations (besides computational cost) with using the 3D heat transfer model in FDS?
o Thin and multi-layered walls are a problem since the thermal properties must be uniform within each cell. Hence one must use many cells to get the resolution needed or try to mix with the thermal properties.
o Needs very fine cells to properly model heat wave
