How to set up burner model with only convective heat flux

[Jeremy Zhao]

Hi,

I was trying to set up a model with different burners. First is with
only convective heat flux like this:
1.&SURF ID='Burner',
COLOR='GRAY 80',
CONVECTIVE_HEAT_FLUX=54.35,
EMISSIVITY=0.00,
HRRPUA=0.00,
Another common burner is：
2.&SURF ID='Burner',
COLOR='RED',
HRRPUA=606.91,

So in 2, what amount of radiation and convection heat I will get by
setting like this? And how to consider emissivity?

Thanks,
Jeremy

[Kevin]

The burner surface will remain at ambient temperature unless you
specify material properties. See the User's Guide section entitled
"Solid Fuels that Burn at a Specified Rate".

[Jeremy Zhao]

Thanks Kevin,

What is the difference between the following two settings (with gas
burner): Are they the same?

1.

&SURF ID='Burner',
COLOR='GRAY 80',

CONVECTIVE_HEAT_FLUX=500,
EMISSIVITY=0.00,
HRRPUA=0.00,
2.

&SURF ID='Burner',
COLOR='RED',

HRRPUA=500,
EMISSIVITY=0.00,

All EMISSIVITY is zero so total HRRPUA=CONVECTIVE_HEAT_FLUX?

For a burner, the default gas is propane and surface temperature is
TMPA?

Also in my case, I know the measured total heat release rate of a gas
burner but I don't know the surface temp of the burner.
If I use HRRPUA, the radiation is calculated based on TMPA and the
emissivity, correct? then convective heat = HRRPUA - Radiation?

The following specification seems wrong but it still runs in FDS. What
the actual heat flux used in FDS?

&SURF ID='Burner',
COLOR='GRAY 80',

CONVECTIVE_HEAT_FLUX=2.0000000E003,
EMISSIVITY=0.50,
HRRPUA=1.1080000E003,
PART_ID='Tracer',
NPPC=5/

Thanks!
Jeremy

[dr_jfloyd]

Are they the same:
In one case you are specifying a temperature boundary condition and in the other case you are specifying a fuel mass flux.  The two are not the same.  I think you are confusing heat flux with heat release rate.  The first is due to heat transfer from the solid surface and the second is due to combustion in the gas.  Convective HEAT FLUX is a completely different phenomena from the convective HEAT RELEASE RATE.

If you do nothing more than HRRPUA, then yes as indicated in the Users Guide, the default fuel in FDS 5 is propane and the default surface thermal boundary condition is INERT which is a fixed TMPA surface.

Your last input runs as HRRPUA is a mass boundary condition and CONVECTIVE_HEAT_FLUX and EMISSIVITY is a thermal boundary condition.  The two inputs are for different things.