| In order to meet the different functions and needs,thin materials are widely used in equipment,architectural decoration and other fields.Once the thin material has been ignited,the flame will quickly spread and ignite adjacent combustible materials,forming a large area of three-dimensional fire which is difficult to control.The occurrence and development of fire spreading affect the initial growth and scale of fire,and understanding the characteristics and mechanism of fire spreading is the important research content of fire science.Through experimental analysis,the behavior and characteristics of the thin combustible fire spreading can be used to understand the law of fire spreading scientifically,and it has important theoretical value and practical significance to guide fire protection.This paper selects the typical thin material cotton cloth as the research object,measuring the fire response characteristics of thin cotton cloth,and using the different tilt angle of the design,the flame spreading test bench is measured,and by means of measuring the shape of flames.On the surface temperature field,fire spreading speed and other fire spreading characteristic parameters,and the reason and intrinsic mechanism of accelerating mutation phenomena are discussed,and the critical criterion is proposed for the qualitative and quantitative analysis of the accelerating phenomena of fire spreading.Through the study of hot weight and radiative ignition of cotton cloth,the starting temperature Ti,the maximum weightlessness temperature Tm and the termination temperature Tf are 294 ?,respectively 355 ?,389 ?,and calculate the cotton cloth activation Energy E as 125.3 k J/mol;with the increase of external radiant heat flux,the ignition time of cotton specimen is shortened obviously,the external radiation intensity meets the linear relationship between the countdown and the ignition time and calculates 0.255 mm of thin cotton light critical heat flux CHF is 12.6 kW/m2.In this paper,the experimental study of fire spreading characteristics under 9 angles of working condition is carried out.When the specimen tilt angle,the fire spreads to present a stable state;when the specimen tilt angle,the fire spreading early stage presents different degrees of acceleration phenomena,fire spreading to a certain stage,fire spread gradually stabilized,the fire spreading acceleration tends to 0.The critical angle of a thin cotton fire spreading accelerated mutation is 15°.According to the experimental phenomena and results,the fire spreading process of different tilt angles is divided into 3 regions,which are stable spreading zone,slow acceleration zone and fast acceleration zone respectively.At that time,the fire spread early stage acceleration,the pyrolysis striker height over time showed exponential growth,the phenomenon of slow acceleration.At the time,the Pyrolysis striker was high in time to show power function growth,which appeared fast acceleration phenomenon.The spreading velocity of fire increases with the increase of the inclination angle of specimen,and the empirical formula of fire spreading velocity under different inclination angles is obtained by fitting the fire spreading velocity and sin theta.The paper adopts the angle between the pyrolysis zone length and the flame body and the inclined specimen surface as the characteristic parameter to judge the accelerating mutation of fire spreading.With the increase of tilt angle,with the increase,while decreasing,when the specimen angle exceeds 15°,and the apparent jump,the fire spread the acceleration phenomenon.The dimensionless number of the accelerating critical criterion for the fire spreading of thin combustible material under different inclination angles is deduced by theory,and the surface fire spreading of inclined specimens will accelerate when dimensionless number is not possible. |
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