Setting Initial Thermocouple Temperature

[MScFire Student]

Scenario:

- Ambient temperature is 5C.

- Initial fire compartment temperature is 18C.

Objective:

- Compare compartment FDS temperatures to experimental data recorded via thermocouples. 

Model:

- Set ambient temperature                                                                           - MISC TMPA=5 /

- Set fire compartment initial local temperature                                           - &INIT XB=X,X,Y,Y,Z,Z, TEMPERATURE=18 /

- Set fire compartment initial surface temperature                                       - &SURF TMP_INNER=18 /

- Provide thermocouple device to mimic experiment                                   - &DEVC ID='TC', QUANTITY='THERMOCOUPLE', XYZ=X,Y,Z /

- Provide device in same location to record gas temperature as a backup - &DEVC ID='TEMP', QUANTITY='TEMPERATURE', XYZ=X,Y,Z/

Prediction:

- Thermocouple temperature is initially recorded as 5C, rises slowly, then reacts as expected.

- Gas temperature is initially recorded as 18C and then reacts as expected.

Issue:

I haven't been able to find a thermocouple device parameter which allows the setting of the thermocouple initial temperature to 20C and not the defaulted TMPA.

If there is no way of doing this, will using a temperature device impact greatly on comparing FDS temperatures with the experimental?

[Kevin]

Why would the TC temperature be different from the air temperature surrounding it? I know that there may be radiation effects at higher temps, but why a difference near ambient?

[MScFire Student]

 Kevin,

That's what through me. I initially thought that I incorrectly setup the local initial temperature device so I changed the TMPA a few times and each time the thermocouple device output temperatures started off at TMPA not the local temperature.

It wasn't until I put in a temperature device that I realised that the local temperature was being correctly set but that the thermocouple device was initially defaulting to the TMPA.

Is there a way of setting the thermocouple devices to the initial local temperatures and not to the TMPA, like with the sprinkler device parameter (INITIAL_TEMPERATURE)?

If not, will a temperature device suffice for comparison with experimental results?

[Randy McDermott]

In the code, the initial temperature of the thermocouple is actually set with (line 10703 in read.f90)

DV%TMP_L = PROPERTY(DV%PROP_INDEX)%INITIAL_TEMPERATURE

So, I would think you could add a PROP line with INTITIAL_TEMPERATURE = 18 and tie this to your DEVC via PROP_ID

&PROP ID='p1', INTITIAL_TEMPERATURE = 18 /

&DEVC ID='TC', QUANTITY='THERMOCOUPLE', XYZ=X,Y,Z, PROP_ID='p1' /

Does this work?

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[Randy McDermott]

You can also use the PROP line to set details about the thermocouple like BEAD_DIAMETER, BEAD_EMISSIVITY, etc., that can have an effect on the results.  See the input files at

FDS-SMV/Validation/UMD_Gas_Burner/FDS_Input_Files/*.fds

for an example.

[MScFire Student]

Randy,

Setting the local thermocouple temperature using the &PROP line worked.

I can now set local compartment gas and thermocouple devices temperatures different from the ambient. Cheers!