Regarding HRR prediction of FDS for lower external heat flux

[pavithra]

Hi all,

             I am simulating the cone calorimeter scenario in FDS by inputting the the HRR of the experiment obtained from cone calorimeter for the external heat flux of 35 kW/m^2 as a RAMP function.

            I found the thermal inertia and ignition temperature (by following the procedures in the literature) of the material by testing the material at different heat fluxes in cone calorimeter. However I found the the experimental curve and the the HRR curve predicted by FDS do not match (FDS predicted HRR curve has a shift in ignition time). I calibrated the ignition temperature and thermal inertia to match the experimental HRR curve. But these calibrated ignition temperature and the thermal inertia is far less than what has been reported in literature for that particular material.

           I want to know why there is this shift in the curve (the curves match only when I use ignition temperature/thermal inertia which is far less than what has been reported in the literature for the material so far). What is the reason behind this?.  Please find attached the curves and the snippets of the code. TIA

[Kevin McGrattan]

The RAMP in this case should start at t=0, not t=32. The time when the surface temperature reaches 367 C is t=0.

[pavithra ct 19250009]

       The attached curve shows the heat release rate for another material (experiment and FDS for external heat flux 35 kW/m^2). There is a shift in the curve even if the ramp starts at t=0. 

        The experimental curve and  the HRR curve predicted by FDS do not match (FDS predicted HRR curve has a shift in ignition time). The calibrated ignition temperature and the thermal inertia is far less than what has been reported in literature for this material also in order to match the experimental curve .TIA.

On Tue, Jan 26, 2021 at 8:04 PM Kevin McGrattan <mcgr...@gmail.com> wrote:

The RAMP in this case should start at t=0, not t=32. The time when the surface temperature reaches 367 C is t=0.

--
You received this message because you are subscribed to the Google Groups "FDS and Smokeview Discussions" group.
To unsubscribe from this group and stop receiving emails from it, send an email to fds-smv+u...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/fds-smv/CAAJimDF82KFuF_O8qEts%2BKW7-0jZNs9mLnn7b-Rb465OYQ7WeA%40mail.gmail.com.

[Kevin McGrattan]

Does FDS start ramping up the HRRPUA when the surface temperature reaches IGNITION_TEMPERATURE? If yes, then FDS is working properly and the question to be asked is why is the surface temperature profile different in FDS and the experiment.

[pavithra ct 19250009]

Yes, FDS is ramping up the HRRPUA once the surface reaches the ignition temperature. What could have been the reason for the difference in the surface temperature of experimental and FDS. TIA.

On Tue, Jan 26, 2021, 10:06 PM Kevin McGrattan <mcgr...@gmail.com> wrote:

Does FDS start ramping up the HRRPUA when the surface temperature reaches IGNITION_TEMPERATURE? If yes, then FDS is working properly and the question to be asked is why is the surface temperature profile different in FDS and the experiment.

--

You received this message because you are subscribed to the Google Groups "FDS and Smokeview Discussions" group.
To unsubscribe from this group and stop receiving emails from it, send an email to fds-smv+u...@googlegroups.com.

To view this discussion on the web visit https://groups.google.com/d/msgid/fds-smv/CAAJimDFDg8vyLXhjTwsM4PWeLe5AieP_LMMYz_xW3PZ9i02tVA%40mail.gmail.com.

[Kevin McGrattan]

The thermal properties like the conductivity, density, specific heat. Emissivity? Compare the measured and predicted surface temperature, and back surface temperature.

[pavithra]

In one of the simulations of the above two materials, I found that the HRR starts to ramp up 50 seconds after the surface has reached the ignition temperature. What could be the reason for this?

[Kevin]

Does the RAMP function start to ramp up at T=0?

[pavithra]

Dear Kevin,

                Yes the ramp did start at T=0. Does IGNITION_TEMPERATURE on SURF_ID have any relation to piloted ignition and auto ignition? In my experiments in cone calorimeter, the materials are  ignited by piloted ignition. 

[Kevin]

When the surface temperature reaches IGN_TEMP, the material burns following the ramp. It is assumed the RAMP T(ime)=0 corresponds to the time of ignition.