Meaning of surface temperature in the formula for 'RADIATIVE HEAT FLUX GAS'

[GGfire]

Hi,

In Paragraph  22.10.12 "Heat Flux", the User Guide for the device  ’RADIATIVE HEAT FLUX GAS' states  "This output quantity is the same as ’RADIATIVE HEAT FLUX'". The quantity ’RADIATIVE HEAT FLUX' is the difference between the incident heat flux and sigma*Ts^4. I don't understand which is the surface temperature (Ts)  when I use the 'RADIATIVE HEAT FLUX GAS'. Is it the temperature of the gas in that point? Does the particle has properties as an objects?

Thank you

[Kevin McGrattan]

Ambient temperature

[GGfire]

Ok, so the temperature of everything at the start of the simulation. Just another quick question: having one device ( such as 'RADIATIVE HEAT FLUX GAS') in the exactly same location as another device can affect the results?

[Kevin McGrattan]

No, these devices are not "seen" by the flow.

[D D]

Kevin, when saying ambient temperature, shouldn't it be the calculated at any given time? In other words, I expect the Ts in the following equation changes during runtime even for ’RADIATIVE HEAT FLUX GAS' . Correct?

[Kevin McGrattan]

If you want T_s to change, then use 'RADIATIVE HEAT FLUX' and attach the device to a solid surface or solid particle. 'RADIATIVE HEAT FLUX GAS' is meant to be placed at some arbitrary location away from a solid, in which case there is no "surface" to heat up. The assumption that T_s=T_ambient is the same as assuming that your gauge is at ambient temperature. 

[D D]

Kevin, I understand what you say. However, the temperature of the gas cell where the RADIATIVE HEAT FLUX GAS' DEVC is placed, will increase by convection of hot gases traveling. So, shouldn't then Ts be equal to the cell temperature? From the other hand, if at this point there is no mass to collect heat, then why the above equation isn't just q"r=es x q"-inc ?

[dr_jfloyd]

When you use RADIATIVE HEAT FLUX GAS, FDS creates a virtual particle whose surface ORIENTATION is used to determine the flux. This calculation uses the existing machinery in FDS for determining the heat flux to a solid surface. The particle has a surface temperature that is set to TAMB.