| At present,polystyrene(PS)foam has a wide range of applications in the fields of construction,transportation,and chemical engineering.Because its advantages of small thermal conductivity,light weight,low cost,moisture resistance,etc.,it has been widely used as an insulation material in building exterior walls.Insulation,movable board room sandwich panel.At the same time,in recent years,the state has attached great importance to building energy conservation.In the plateau environment,EPS wall insulation has gradually developed into a trend,and will be the primary task of building energy conservation in high altitude areas in the western China.However,PS is poor in fire resistance and can easily be ignited.It easily emits a lot of heat and flammable,explosive,and irritating harmful gases.Once a fire accident occurs,the fire is particularly harmful.Therefore,it is of great practical significance to carry out research on the combustion characteristics of insulation material PS in different areas.At the same time,it also has far-reaching significance to provide reference for formulating thermal insulation material design specifications with regional environmental characteristics in China,and to enriche theoretical characteristics of thermal insulation materials under low pressure and low oxygen environment.This article takes the typical EPS and XPS materials as research objects,and conducts small-scale experimental research on pyrolysis,combustion,flame spread,and extinction of materials,and studies parameters such as activation energy and pre-exponential factors in the pyrolysis process of materials;The regional environment,that is,the characteristics of PS combustion and flame spread at different altitudes,focuses on the analysis of parameters such as the flame spread speed,flame configuration,and mass loss rate.At the same time,the influence of the density,thickness and angle on the flame spread and extinction of EPS was discussed under low density conditions.Finally,combined with numerical simulation methods,the combustion of PS materials and the spread of flame at different altitudes are studied,and the regularity and phenomena appearing in the experiment process are well verified.Furthermore,it provides reference and reference for the development of thermal insulation material PS fire characteristics inquiring system with the characteristics of China's regional environment.First,the ignition temperature and oxygen index in the PS combustion were measured by an experimental apparatus to evaluate the combustion grade of the material.Then micro-scale thermal analysis experiments were used to explore the effects of different heating rates(10-50°C/min)and different atmospheres(nitrogen and air)on the thermal decomposition characteristics of PS,and analyzed the pyrolysis characteristics.It was found that the initial pyrolysis weight loss temperature,the pyrolysis maximum rate temperature,and the pyrolysis termination temperature of the PS material all increase with increasing heating rate.There is only one stage of thermal decomposition in both nitrogen and air.The pyrolysis activation energy in the nitrogen atmosphere is calculated to be about 300 kJ/mol,and only 175kJ/mol in air,making it easier to pyrolysis in air.Secondly,through the establishment of a small-scale experimental platform,the vertical combustion and flame spread characteristics of PS materials at different altitudes were experimentally studied.Characteristics of flame structure,flame spread speed,mass loss rate,and temperature of smoke plume were analyzed.It was found that in the process of vertical flame spread of the PS material,the combustion zone includes a surface combustion zone,a wall fire zone,and a pool fire zone formed by the molten dripping down.In the plain area as Hefei,higher atmospheric pressure and sufficient oxygen concentration allow the PS material to maintain a good vertical burning and spread of flame;the flame spread process includes the development stage and the acceleration stage.As the spread of flame progresses,the fire spreads faster and faster,and the pool fire zone formed by molten dripping increases in quality.In the plateau area as Lhasa,the lower atmospheric pressure and oxygen concentration can only maintain the vertical combustion and flame spread of the PS material for a short period of time,and finally cause the flame extinguishing phenomenon in the surface flame area during the spread process.The entire fire spread includes development stages and stagnation stages.This is mainly due to Lhasa environment,the pressure and oxygen concentration is small,while the smoke plume and the air surrounding the sample in the process of vertical spread of the winding suction,so that the oxygen concentration of the PS sample surface of the combustion zone is further reduced,eventually causing extinction occurs.Then,a serious of small-scale experiments was carried out to reveal the effects of density,thickness and incline angle et al.comprehensive factors on EPS flame spread and extinction.It was found that,for EPS with a density of 6 kg/m~3,as the density is very small,the effects of thickness of the material and the incline angle are restrained by the influence of the density.Therefore,EPS could not be ignited by the fire source and go on flame spread.While,for the density of 10kg/m~3 of EPS,with the increase of thickness and incline angle,the sample goes from non ignition,“S”type extinction,normal flame spread to shrinkage extinguishment.It was also found that,for the density of 10kg/m~3 and the thickness of 4cm of EPS,when the incline angles are 0°,10°,20°and 30°,the flame spreads normally.With the incline angle increasing to 40°and 50°,the shrinkage extinguishment is formed,which can be attributed to the competitive mechanism between flame spread speed and preheating length,by setting up shrinkage extinguishment model.Finally,numerical simulations of PS vertical and horizontal flame spread characteristics at different altitudes were performed.For the combustion process,the parameters of flame spread speed,mass loss rate,heat release rate and temperature distribution were studied numerically.The numerical simulation results and the experimental results are very testable.The study found that in the vertical vertical flame spread,in Hefei,the thermal insulation material PS accelerated during the spread process,while in Lhasa,the extinction occurred during flame spread process,which is consistent with the experimental results.The simulation found that in Hefei,the flame temperature of the PS material was nearly 900°C,while the Lhasa environment was only 700°C.In the simulation of horizontal flame spread,it was found that PS material can perform spread well in Lhasa,and no extinguishing phenomenon occurs.This is mainly due to the influence of lower atmospheric pressure and oxygen concentration on flame temperature,flame spread speed,and heat release rate during PS combustion and flame spread. |
PDF Full Text Request