/pdf/fire-dynamics-simulator-version-5-user-s-guide-5058kzb0fm.pdf

Fire Dynamics Simulator (Version 5): User's Guide

/pdf/fire-dynamics-simulator-technical-reference-guide-volume-1-15a6kbrhbq.pdf

Fire dynamics simulator technical reference guide volume 1 :: mathematical model

Data for estimating the burning rate and heat output of large pool fires (diameter ≳ 0.2 m) are compiled and computational equations presented. Since a large scatter in the reported data is noted, attention is also focused on areas where further research is most needed in order to improve predictability.

Estimating large pool fire burning rates

Study of critical velocity and backlayering length in longitudinally ventilated tunnel fires

Thermal radiation hazards from hydrocarbon pool fires

Two-dimensional upward flame spread and subsequent steady turbulent burning of a thermally thick vertical fuel surface is examined theoretically and experimentally. The upward spread rate for vertical PMM slabs is observed to increase exponentially with time. This result is predicted in terms of measured fuel thermophysical properties, flame heights and heat feedback to the fuel surface. The local steady burning rates established after completion of upward spread exhibit a minimum at a height of 18 cm from the bottom edge and increase continuously beyond this height, becoming 70% larger at a height of 140 cm. This increase is shown to be entirely attributable to increasing flame radiation. Individual measurements of the various energy transfer components during steady burning of the PMM slabs are obtained from radiant intensity measurements of (1) the surface alone and (2) flame plus surface. Above 76 cm flame radiation ranges from 75 to 80% of the total (radiation plus convection) heat transfer from the flames to the fuel surface. Surface heat transfer by convection decreases slightly with height.

Upward turbulent fire spread and burning of fuel surface

We present an algorithm for the burning of moderate-scale (0.1–0.7 m dia.) pool fires in terms of the pool scale and fuel properties. Previously one could not solve the energy balance at the fuel surface due to lack of information on the feedback radiation. In general this feedback radiation depends on the flame radiation temperature and absorption-emission coefficient, as well as the flame size and shape. through the use of scanning radiometer measurements on gaseous burner fires it is shown that the flame size and shape are independent of fuel chemistry for a given overall rate of combustion heat release, as suggested by Froude modeling. The average absorption-emission coefficient at an assumed global flame temperature is related to the radiant fraction of combustion heat release. An analytic flame shape expression is developed which provides the mean beam length required for predicting the radiative feedback. The remaining terms of the energy balance are solved using established procedures.

Froude modeling of pool fires

A large-scale gas-supplied sintered-metal burner was used to study radiation and spatial orientation effects on steady turbulent fires over a range of mass transfer driving forces, B . Three principal burning modes are evident: (1) turbulent pool fires from θ =0° to θ =15°; (2) upward turbulent burning from θ ∼15° to θ ∼168°; and (3) cellular ceiling fires from θ ∼168° to θ =180°. Steady burning rates decrease rapidly with inclination from the horizontal within the pool regime, followed by a more gradual decreases with inclimation within the upward turbulent burning regime being minimum θ ∼168°, i.e., 12° from the horizontal ceiling orientation. This trend is ascribed to the decreasing direct gravitational generation of turbulent kinetic energy, causing a reduction in the turbulent flame thicknesses with their reduced radiant fluxes. Previous laminar burning studies showed opposite trends, with minimum burning rates in the “pool” orientation. Increased cellular flow mixing is accompanied by a sharp increase in burning rate as the fuel surface rotates from 168° to the horizontal ceiling fire. Radiometer comparison of outward and surface directed radiant flux for a vertical burning surface indicate at least 7% absorption by combustion products and intermediates near the surface. Radiation is found to exceed convective heat transfer to the fuel surface for B >1.0. At large B numbers the burning is increasingly radiation-dominated as convection decreases due to heat blockage.

The role of buoyancy direction and radiation in turbulent diffusion flames on surfaces

A dimensionless correlation of pool burning data

The relationship between the radiant fraction, X R, of the total heat release rate from buoyant turbulent diffusion flames and a fuel's laminar flame smoke point is refined and extended to include: additional hydrocarbon fuels, fuel dilution with nitrogen and a range of oxygen/nitrogen ambient environments. Correlation of the data allows one to predict X R in terms of the: (1) fuel smoke-point laminar flame height, l 3, (or corresponding heat release rate Q SP ), (2) adiabatic stoichiometric flame temperature, T ad of the supplied reactants, and (3) stoichiometric oxidant to fuel mixture mass ratio S. The existence of such a general correlation for S ≥ 12 suggests that the buoyant flame radiation is effectively controlled by only these three reactant properties. The present correlation does not apply for S < 12 because of the increased importance of gaseous radiation for reduced 5. The above correlation of turbulent flame ;XR with the laminar-flame smoke point is achieved by consistently referrin...

L. Orloff

Papers

Upward turbulent fire spread and burning of fuel surface

Froude modeling of pool fires

The role of buoyancy direction and radiation in turbulent diffusion flames on surfaces

A dimensionless correlation of pool burning data

Radiation from Buoyant Turbulent Diffusion Flames