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PhD dissertation on fire behaviour of polymeric materials

2020-03-05

On March 20th at 09.15, Abhishek Bhargava will defend his PhD-thesis "Fire behavior of selected polymeric materials - Numerical modelling and validation using microscale and bench scale test methods".

The act will take place in lecture hall V:B (at John Ericssons väg 1 in Lund) and will start with a 30 minutes presentation followed by a short break before the defence starts. The entire dissertation normally takes 2-3 hours. The entire session will be performed in English.

After the seminar, lunch will be served and if you want to participate, please send an e-mail to johanna.kruse@risk.lth.se no later than March 10th. No notification is needed to only attend the defence act.

The thesis (excluding papers) can be found here.

Abstract:

Computational  fluid  dynamics  (CFD)  based  fire  models  are  used  for  the prediction of heat and smoke spread in building spaces. Such models use some form of Navier-Stokes equations representative of different transport processes (physical and chemical) occurring in the considered spatial domain during the course of fire. Typically, these equations consist of mass, energy and momentum conservation along with applicable boundary conditions, which are solved using appropriate numerical methods for different field variables (typically, pressure, density, temperature and velocity). With increasing computational power, such calculations can be applied to numerous fire scenarios and completed in time bound manner to provide improved fire safe building design solutions to architects, fire engineers and regulatory bodies. However, CFD based simulations face several challenges related to prediction accuracy and computational costs. To improve upon the speed and prediction ability of CFD based fire models, it is necessary to upgrade not only the computational infrastructure, but also invest enough resources to explore new and accurate sub models and acquire better experimental devices to provide material input parameters for simulating a given fire scenario. Unless the material fire behaviour cannot be predicted accurately in microscale and bench scale studies, it is likely there will be large deviations in the prediction accuracy of field models also.  A large number of polymers are used in building and construction sector, whose fire performance is of particular interest from safety point of view.  In this industrial PhD work, the main research objective was to improve prediction of fire performance of common polymer materials using numerical modelling and simulation tools. To achieve that aim a novel one-dimensional computational pyrolysis model was developed and validated for the solid phase. The method followed a combination of deterministic and stochastic means following a multiscale approach. The material property input parameters were acquired using experiments performed in microscale analytical devices while validation was performed on bench scale device. Another focus of the work was to explore stand-alone chemical reaction sub-models that can describe multiple reactions in polymeric materials of common and industrial relevance. A sensitivity analysis framework for standalone chemical kinetic models was also presented.

The overall results show the model is capable of predicting key fire technical properties of interest obtained in a standard cone calorimeter device such as mass loss rate (MLR), heat release rate (HRR) total heat released (THR).  The developed model could be incorporated it into a bigger CFD code and can be used for estimation of fire propagation rate on successively incremental scale. The performance of novel pyrolysis model considers several physicochemical transformation complexities occurring in the material and renders a satisfactory performance of the investigated materials on microscale and bench scale level simulations.  A discussion section is also presented on how to incorporate higher degree of complexity for gas diffusion and in-depth radiation absorption for improving the prediction ability of the current form of the model. In conclusion, the material presented in this thesis contributes to better understanding of burning behaviour of selected polymers. These findings can be used as a foundation for expanding the current level of understanding for flame spread calculations. It is envisaged that the work shall be useful for practicing engineers and researchers involved in the field of fire development and CFD based fire risk assessment.