Simulation Study On Pyrolysis And Combustion Process Of Typical Non-charring Polymer Materials Under High Radiation Heat Flow Conditions

The building and decoration sectors both make extensive use of non-charring polymers.Most charcoal-free polymers are susceptible to pyrolytic ignition,which can lead to fire.In fires,melting and blistering can also occur.This makes studying fire dynamics difficult,and the diffusion of pyrolysis gases into unburned areas can lead to further fire spread.This paper uses the typical non-charring polymer PMMA as the research object,based on the experimental conditions of the cone calorimeter,using Fluent software,the VOF model,component transport FR/ED model,and other models.By simulating the process,many phenomena related to PMMA melting and the material’s characteristics during pyrolytic combustion are investigated.Simultaneously,a cone calorimeter,thermogravimetric analyzer and other instruments verified the simulated data experimentally.The results obtained are as follows:（1）Simulation study on the melting process of non-charring polymer PMMA.The research shows that in the early stage of the melting process,the melting trend of the material is a constant decline in the level.In contrast,in the middle and late stages,the changing trend of the material shape shows a horizontal concave line,and the curvature of the material surface becomes more evident as time increases.The melting of the material causes the formation of bubbles on the surface of the molten layer,and the phenomenon of volume expansion,and the formed molten layer will hinder the heat transfer inside the material.In the early melting stage,the thermal conductivity has little effect on the material’s phase transition process and temperature.Later,as the melting process intensifies,the greater the thermal conductivity of the material,the stronger the heat transfer capability,and the faster the temperature rises,putting the material in the solid phase.The melting rate is significantly accelerated.（2）Simulation study on pyrolysis and combustion process of non-charring polymer PMMA.The changes of multiple fields in the computational domain during the reaction process are analyzed through simulation.Under the radiant power of 50 k W/m²,the maximum outflow rate of pyrolysis gas is 0.015 g/s;the maximum temperature in the gas phase calculation domain occurs 2.5 cm above the sample surface,and the maximum temperature is 634 K.The combustion reaction occurs in the mixed layer area where the gaseous monomer and air are in contact.The mass fraction of oxygen near the surface of the monomer gas flow gradually decreases as the reaction progresses.Through the analysis of the flow field,it is found that the combustion will accelerate the expansion of the gas so that the gas diffusion speed will be accelerated.The maximum velocity value will appear at the boundary condition of the velocity outlet of the model,and the peak value can reach 6 m/s.（3）The pyrolysis and combustion process of materials under different thermal radiation powers was studied experimentally using a cone calorimeter,and numerical simulations were carried out under the same conditions.Comparing the obtained mass loss rate,CO₂ production rate,and other data,it is found that the overall change trend of the simulated value and the experimental value is consistent,and the combustion model reasonably captures the peak value of the material mass loss rate and CO₂ production rate in the experiment.Temperature measurement experiment measured the material’s surface and internal temperature,and the temperature distribution was predicted.Research shows that the change in internal temperature mainly experienced three stages:slow rise,accelerated rise,and flattening.The peak temperature mainly appeared in the middle and late stages of combustion.