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Computational Model for Fire Growth and Spread On Thermoplastic Objects. Final Report.

pdf icon 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.


National Institute of Standards and Technology, Gaithersburg, MD


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


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.