Studies On The Heat Feedback And Outward Radiation Characteristics Of Multiple Pool Fires

As the "blood" of industry,liquid fuel is an important driving force and guarantee for global economic development.With the rapid growth of the economy and society,the demand for liquid fuel all over the world is increasing.However,fire accidents of liquid fuels occur frequently during processing,storage and transportation.In a real fire scene,the thermal radiation from a pool fire can easily ignite other adjacent combustibles,resulting in multiple pool fires and further inducing larger-scale burning,developing into destructive regional fires.In recent years,the frequent major fire accidents caused by multiple pool fires have brought huge property losses,casualties and environmental damage to people,which is a major safety problem faced by all countries around the world including China.An in-depth understanding of the burning mechanism and the thermal hazard characteristics of multiple pool fires is of great significance for improving the prevention and control capabilities of extraordinarily major fires in the petrochemical industry.This paper combines experimental research and theoretical analysis to conduct a systematic study on the evolution law of heat feedback mechanism and external radiation characteristics of multiple pool fires.Specific work is as follows:(1)The heat feedback characteristics of multiple pool fires were experimentally studied.Multiple pool fires experiments with different fire numbers,spacings and geometrical layouts were carried out.Firstly,the burning characteristics in the steady burning stage,such as mass loss rate and flame shape,were revealed.The coupling effects of air entrainment restriction and heat feedback enhancement on burning behavior were expounded.Then,a partition measurement method for asymmetric heat feedback was proposed according to flame inclination and merging.The distribution characteristics of radiative heat flux on the fuel surface were revealed.It was found that with the reduction of the fire spacing,the flames changed from burning independently to gradually tilting and eventually merging completely.The non-uniformity of the heat feedback on the fuel surface was significantly enhanced.Finally,the evolution characteristics of radiative,conductive and convective heat feedback fractions(component proportions)with the spacing and geometric layout of multiple pool fires were further revealed based on the partition accumulation method of heat feedback and the fuel energy conservation.(2)The radiation blockage of pool fires under enhanced feedback was experimentally studied.Based on the physical mechanism abstraction of interactive heat feedback enhancement in multiple fires,experiments of evaporation and combustion of liquid fuel under the different external radiation were conducted using an external radiative heater to simulate the heat feedback enhancement.Based on the idea of decoupling,the blockage characteristics of the fuel vapor to the external radiative heat flux were studied first.It was found that with the increase of the fuel mass loss rate,the radiation absorption capacity of the vapor increased,leading to a rise in the fuel vapor effective radiation blockage coefficient.When the radiation absorption capacity of the fuel vapor tended to be saturated,the effective radiation blockage coefficient gradually tended to be constant.According to Lambert-Beer’s law,a s prediction model for the effective radiation blockage coefficient of the fuel vapor was established.Finally,the evolution of fuel vapor radiation blockage and the flame radiation blockage under external radiation was further revealed based on the prediction model and experimental data.(3)Outward radiation characteristics of multiple pool fires were experimentally studied,and the radiation prediction models were proposed.Based on the burning behaviors of single pool fires in different diameters,the moving "blackbody-infrared"measurement method was used to investigate the flame emissivity distribution.Combined with flame shape and temperature measurements,the spatial distributions of flame radiation parameters(i.e.,flame shape,temperature,emissivity)of pool fires at different scales were quantitatively characterized.A multi-layer cylindrical flame radiation model was established considering the spatial distribution of flame radiation parameters.Compared with previous models and experimental data,the proposed model was more accurate in radiation prediction.Then,the spatial distributions of the flame radiation parameters of multiple pool fires were further studied,considering the flame shape of interactive flames.Based on Boltzmann radiation law,a weight determining method using flame emissivity and the fourth power of temperature was proposed,and a weighted multi-point source radiation model was established.The model’s reliability was verified by comparing it with previous models and experimental data.