Gas-phase DEVC probe point set in solid that can burn out

[DOGzym]

Hi all,
In PMMA combustion model (BURN_AWAY = .TRUE.) I set up a series of gas phase probes inside the solid. When the THICKNESS probe set on the solid surface indicates that the interior is burned out, the output of the solid internal probe point remains unchanged.
I wonder if the solid-phase grid will not be replaced by a gas-phase grid after it is burned out. Therefore, the gas phase probe point in the solid can never identify the data. Is there any way to output the gas phase data at the same position after the solid phase is burned out?

[mcgratta]

I would need to see a simple input file demonstrating the problem. I would expect a gas phase quantity probe would begin to register meaningful results when the solid cell disappears.

[DOGzym]

Thank you for your patient reply.
I've attached the simplified input file and the DEVC output file below. At x=0.01750, I set a series of gas-phase property probes in the vertical direction (ranging from 15mm inside the solid to 6mm above the solid surface), expecting to output the temperature distribution and CO2, O2, and MMA mass fraction distribution within this range. The surface is set with THICKNESS probes to detect detect the solid-phase burnout position.
However, when the THICKNESS probes show considerable burnout, the output results of the DEVC that should be converted from the solid-phase grid burnout to the gas-phase grid remain unchanged. It is obviously impossible that no solid burnout occurred there. Is it because the gas-phase probes inside the solid cannot identify the grid at the burnout point?

fds_file.txt
THICKPMMA_30_25_A_devc.xlsx

[drjfloyd]

Solid cells are not removed untill they are completely burned away. If you have a non-zero thickness, then the cell is still solid and the gas phase device will not change.

[DOGzym]

Does this mean that unless all solid grids in the thickness direction are burned out (the THICKNESS probe output result is 0), a series of gas-phase probes in the solid (even the probe closest to the solid surface) can simultaneously identify the gas-phase grids and output meaningful data?

[drjfloyd]

correct.

[mcgratta]

Let me preemptorially (I coined a new word) answer your next question. That is, the solid grid cell will not necessarily disappear exactly when the THICKNESS recedes the width, or depth, of the grid cell. You might have a grid cell that is burning on more than one side, which is why we generally use the cell's mass is the trigger for its removal. All this being said, I would discourage the use of the BURN_AWAY feature if you are doing a detailed study of material pyrolysis. There are too many approximations and assumptions built into it such that eventually you will encounter physical impossibilities. We generally use BURN_AWAY to make large boxes of miscellaneous combustibles disappear when there is nothing left to burn. In these cases, there is usually a simple HRRPUA applied at the surface.