Simulations Of Influences Of In-Depth Radiation Absorption And Fluid Motion On The Heat Transfer And Ignition Behavior Of Polymers

The melting phenomenon occurs in many polymeric materials during combustion,and this phenomenon often has great impact on the combustion behavior.The influence mechanism may lie in the radiation absorption of melt which affects the temperature distribution and mechanical properties of melt which triggers the fluid motion to change the heat transfer mode and efficiency.Therefore,it is important to study the influence of radiation absorption on the ignition of polymers and the effect of melt motion on heat transfer under radiation absorption for fire prevention and control.In this paper,the radiation absorption coefficients of two polyethylene waxes were measured by conical calorimeter test,and then Fluent software was used and the DO radiation model was selected to simulate the influence of radiation absorption coefficient and other parameters on polymer ignition time under thermal radiation.Finally,on the basis of DO radiation model,Mixture model and VOF model were chosen to simulate and study the effect of melt motion on heat transfer process under the action of airflow shear force,thermal capillary force,buoyancy force and viscous force.The main findings are as follows:（1）The radiation absorption coefficients of PE wax DH-96 and PE wax AC-6 are between 166m^-1 and 204m^-1.（2）The smaller radiation absorption coefficient leads to the inverse temperature gradient from the inside to the surface of polymer specimen and longer ignition time.The ignition time is a logarithmic function of the radiation absorption coefficient.（3）As the gradient of surface tension coefficient increases with temperature or the viscosity decreases,the thermal capillary effect is enhanced,resulting in the accelerated motion of molten surface layer,the more uniform temperature distribution and the enhanced heat transfer.（4）When the radiation absorption coefficient is 966m^-1,the buoyancy effect counters the thermal capillary effect.Compared with the case where the buoyancy effect is not considered,the buoyant force decreases the motion of molten surface layer,leading to the less uniform temperature distribution and the weakened heat transfer.（5）When the radiation absorption coefficient is 200m^-1 there is an inverse temperature gradient from the inside to the surface.If the buoyancy effect is not considered,compared with the radiation absorption coefficient of 966m^-1,the thermal capillary effect at the bottom is enhanced and the overall heat transfer is strengthened.If the buoyancy effect is considered,the overall heat transfer is weakened,but the heat transfer in the local field with inverse temperature gradient is enhanced.Compared with the radiation absorption coefficient of 966m^-1,the thermal capillary effect and the heat transfer are enhanced.