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Fire Dynamics Simulator
https://pages.nist.gov/fds-smv/
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Replace INERT with COLDWALL? #547

Closed gforney closed 9 years ago

gforney commented 9 years ago 
Still seems to be confusion from users about what INERT means.  I think in
part that the name is easily misconstrued.  In keeping with the concept of
Science 2.0, I am opening an issue to discuss this.

Would we be be better off replacing INERT with COLDWALL (we can add a line
to change INERT to COLDWALL to maintain backwards compatibility and write a
warning message)?

Original issue reported on code.google.com by drjfloyd on 2008-12-03 20:05:15

gforney commented 9 years ago 
For the record, tell me exactly what INERT/COLDWALL does.

Original issue reported on code.google.com by gforney on 2008-12-03 20:26:48

gforney commented 9 years ago 
It is a solid surface that maintains the ambient temperature.

Original issue reported on code.google.com by mcgratta on 2008-12-03 20:38:08

gforney commented 9 years ago 
so,  heat transfer to or from this surface still occurs based upon its temperature
being at ambient?  Hence jason's suggestion to change the name to COLDWALL.

Original issue reported on code.google.com by gforney on 2008-12-03 20:49:39

gforney commented 9 years ago 
Yes.   Or maybe not COLDWALL but AMBIENT_WALL or something that more actually
reflects what the surface really is.

Original issue reported on code.google.com by drjfloyd on 2008-12-03 20:58:39

gforney commented 9 years ago 
Is not an INERT wall the same as an ISOTHERMAL wall, a wall with fixed temperature ?

Original issue reported on code.google.com by Finn.Drangsholt on 2008-12-04 14:09:43

gforney commented 9 years ago 
Yes, the wall is ISOTHERMAL, but I would rather not use that term because we use it

already on the MISC line, meaning that there are no temperature changes allowed in

the calculation.

Original issue reported on code.google.com by mcgratta on 2008-12-04 14:22:07

gforney commented 9 years ago 
in the original FDS the default condition was adiabatic.in fact it said is an 
adiabatic, inert wall. i'm sure the default has been changed for some time now. But

i need some clarification on this now as well. 
my understanding from the discussions and User manual is that the Inert boundary 
condition absorbs heat based on the temperature gradient between the gas temperature

and 20deg but doesn't heat up . how much heat does the inert surface absorb or what

it is similar to e.g. concrete, block since you've suggested replacing with 
coldwall?

Original issue reported on code.google.com by adrienne.slattery on 2009-01-19 18:10:47

gforney commented 9 years ago 
The original version assumed that there was no convective heat transfer to an INERT

wall -- that is, the wall was the same temperature as the gas. This assumption was

based on the fact that most building materials have low thermal conductivities and

are good insulators.

We kept the name INERT, even though now it refers to an ambient temperature solid.

The heat transfer to it is

q" = eps*sigma*(T_eff^4-T_amb^4) + h*(T_g-T_amb)

where T_eff is the "effective" gas temperature from the standpoint of radiation 
transport and T_g is the near wall gas temperature. T_eff is not calculated 
explicitly, but rather a detailed radiation heat transfer calculation is used to 
predict the radiative heat flux to the wall. 

Think of an INERT solid as something that never heats up, like a piece of steel that

has cold water constantly flowing across its back side. We recommend that this BC 
not be used -- it is better to assign actual material properties to everything. But

we have to have a default nonetheless.

Original issue reported on code.google.com by mcgratta on 2009-01-21 13:43:05

gforney commented 9 years ago 
before releasing 5.4.0, do we wish to take action on changing INERT to something more
meaningful?

Original issue reported on code.google.com by drjfloyd on 2009-06-09 20:32:46

gforney commented 9 years ago 
If you do, INERT should still work. Maybe just alias it somehow. I think most people

have become aware of INERT means. Changing it might confuse things more.

Original issue reported on code.google.com by mcgratta on 2009-06-09 21:17:46

gforney commented 9 years ago 
No real groundswell of support for or against the idea, so I won't take any action.

Original issue reported on code.google.com by drjfloyd on 2009-07-27 12:50:09