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Author Topic: Fire Suppression of Burner with specified HRRPUA  (Read 934 times)

Stefan Löffel

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Fire Suppression of Burner with specified HRRPUA
« on: July 23, 2019, 04:02:35 am »

Hello everyone

I am new to FDS/PyroSim modelling and I am attempting to model fire suppression of post-flashover compartment fires. The goal is to produce numerical models which replicate full-scale experiments conducted a while ago. I have successfully modeled the fire development and am now looking at the suppression phase.

For my current model I have a 2.4 x 3.6 x 2.4m compartment in which I placed a burner with a specified HRRPUA of 601.4 kW/m2. The fuel that I am using is pine with an auto-ignition temperature of 427 degrees. I have implemented a single nozzle which is set to activate once an average ceiling temperature of 840 degrees has been recorded. I understand that it is possible to suppress burner fires using the extinguishing coefficient However I have simulated various scenarios where the extinguishing coefficient ranges from 16-250. Furthermore, the flow rate of the nozzle is set to 300LPM for an infinite duration, however, the temperature only decreases to approximately 700 degrees before reaching a plateau which is also indicated by the HRR which remains at 3850 kW throughout the simulation which does not correlate with the experiment in which a flow of 115LPM was used for a duration of 45 seconds to fully extinguish the fire.

This makes me think that either I am misinterpreting:
  • The Reaction. Under the "Edit Reactions" tab I enabled fire suppression and have set the autoignition temperature equal to 427 degrees (autoignition temperature of the pine). However, I have read up about the critical flame temperature in the FDS manual and am uncertain as to whether or not I should leave it at the default value of 1427 degrees
  • The Burner.
As i mentioned I set the HRRPUA to 601.4 kW/m2. The reaction is governed by the reaction properties assigned to the fuel i.e. pine. Since the pine has an autoignition temperature of 427 degrees it is first necessary for the burner to heat up to that value before a reaction takes place or not? Therefore do I need to adjusted the thermal boundary condition under the thermal tab of the burner to a fixed temperature with lets say a surface temp of 650 degrees to ensure that the reaction takes place or should I keep it at ambient temperature and use an ignitor to initiate the reaction? I think this may be my issue.

I understand that the explanation of my issue may be confusing but like I said I am new to FDS/PyroSim modelling. I have attached the psm.file to make things clearer.

Thank you in advance.
« Last Edit: July 23, 2019, 07:35:54 am by Stefan Löffel »