Burnout Time Calculator for Fire Dynamics Simulator (FDS)

Burnout time is a required parameter for the combustion sub-model in an LES solution using NIST's Fire Dynamics Simulator (FDS). The burnout time is based on McCaffrey's fire plume model. In an LES solution the combustion model generates heat release rate particles that release energy for a specified time. The basic idea is that the particles burnout out within the flame based on McCaffrey's model. Therefore, the upper and lower bounds of the burnout time correspond to intermittant and persistent flaming regions, respectively. The default value for burnout time is 0.25, however, this calculator can be used to define a value more appropriate to the problem at hand. This calculation requires the ambient temperature and total heat release rate and provides the upper and lower bounds as well as the mean value for the burnout time based on McCaffrey's fire plume model.

Theory

A more complete treatment of this topic can be found in the FDS Technical Reference.
Q: kW
Tamb: C
TBO(min): s
TBO(mean): s
TBO(max): s

Instructions

  1. Enter values for total heat release rate and ambient temperature.
  2. Click on the "GO" button.
TBO(min) = 1.05(D*/g)1/2
TBO(max) = 1.86(D*/g)1/2
where:
D* = Q/(cprambTamb(g1/2))
D* - nondimensional diameter
g - acceleration due to gravity (m/s2)
Q - total heat release rate of fire (kW)
cp - specific heat of ambient air at constant pressure (kJ/kgC)
ramb - density of ambient air (kg/m3)
Tamb - ambient air temperature (oC)
TBO - particle burnout time (s)

Equations used are from:
McGrattan, K.B., H.R. Baum, R.G. Rehm, A. Hamins, and G.P. Forney, "Fire Dynamics Simulator - Technical Reference Guide," Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6467 (2000) pp.7-8.
Send e-mail to: ierardi@wpi.edu

Last Modified: Fri 7 July 2000.

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