Computational Model for Fire Growth and Spread On Thermoplastic Objects. Final Report.
Computational Model for Fire Growth and Spread On
Thermoplastic Objects. Final Report.
(4759 K)
Bockelie, M.; Tang, Q.
NIST GCR 07-914; REI Project 4716; 419 p. November
2007.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Keywords:
thermoplastics; computer models; fire growth;
computational fluid dynamics; melting; gasification;
heat flux; computers; algorithms; simulation; resins;
heat transfer; sensitivity; velocity fields; mass loss;
loss rate; time
Abstract:
In this report is described the work effort by Reaction
Engineering International (REI) to develop, demonstrate
and deliver to the National Institute of Standards and
Technology (NIST) a condensed phase computational fluid
dynamics (CFD) based tool to model the processes of
melting, flow and gasification of thermoplastic
materials exposed to a high heat flux. Potential
applications of the tool include investigating the
behavior of polymer materials commonly used in personal
computers and computer monitors if exposed to an intense
heat flux, such as occurs during a fire. The model
delivered to NIST is based on a time dependent (time
varying) grid CFD method. (*) The model is written in
FORTRAN 90 in an object-oriented form. A 3D, finite
volume, multi-block body-fitted time dependent (time
varying) grid formulation is used to solve the unsteady
Navier Stokes equations. The time integration, spatial
discretization and overall solution procedure are based
on standard CFD methods from the literature. A
multi-grid method is used to accelerate convergence at
each time step. (*) Sub-models are included to describe
the temperature dependent viscosity relationship and
in-depth gasification and absorption of thermoplastic
materials, free surface flows and surface tension. NIST
data is used for key material properties of the
thermoplastic materials of interest. (*) A variety of
boundary conditions can be used for the velocity field
(no-slip, free-slip) and heat transfer to the object
(adiabatic, heat loss, specified heat flux). (*) Model
outputs include the time dependent velocity, temperature
and position (displacement) at points in the
thermoplastic body which can be imported to standard CFD
visualization packages. Additional outputs include the
time history of the mass loss rate and heat fluxes. (*)
The accuracy and capabilities of the modeling tool are
demonstrated on a series of test cases of increasing
complexity. The test cases include grid sensitivity
studies, adding heat loss boundary conditions,
simulations for two thermoplastic materials (PP702N,
PP6523), different heat flux scenarios and test problem
configurations.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899