| Fire is one of the main threats to public safety and social development.Fires can bring great harm to individuals,families,and society,including casualties,property damage,and environmental damage.With the development of society and the improvement of urbanization rate,the probability and harm of fires are constantly increasing,especially Class B,C,and D fires involving flammable substances such as liquids,gases,and metals,which have gradually become the main types of fires.Ultra fine dry powder fire extinguishing agent has the advantages of versatility,high fire extinguishing efficiency,high permeability,non conductivity,non corrosiveness,and environmental friendliness,making it a widely used fire extinguishing agent.This article mainly focuses on the following aspects of research:A numerical simulation method for a vehicle mounted ultrafine dry powder injection system has been proposed.The basic theory of computational fluid dynamics is analyzed,and factors such as the applicable scope,calculation accuracy and calculation speed of the calculation model are comprehensively considered;Euler multiphase flow model and Realizable k-ε The turbulence model simplifies the structural characteristics of the vehicle mounted ultra-fine dry powder injection system,reduces the computational complexity of the model,and divides the system into three parts: air charging fluidization of the dry powder tank,gas-solid two-phase flow transportation,and two-phase flow injection dispersion.The distribution characteristics of the flow field inside the vehicle mounted ultrafine dry powder tank were studied.Expanding the diameter of the pipeline during the inflation process and reducing the inflation time to within the specified range;The flow field distribution of nitrogen in a dry powder tank was studied,and different fluidized gas cap states were compared.It was found that the mushroom head type gas cap had good performance in the process of aeration and fluidization.A two-phase flow conveying pipeline model for a vehicle mounted ultrafine dry powder injection system has been established.Analyzed the flow characteristics of gas-solid two-phase flow in three characteristic models: straight pipe,curved pipe,and telescopic pipe.Compared the pressure distribution,cross-sectional velocity changes,and solid particle concentration changes of ultrafine dry powder gas-solid two-phase flow in the pipeline under different flow rates,it was found that the gassolid two-phase flow in the cross-sectional area of the pipeline showed a distribution of fast in the middle and slow in the surrounding areas,and the influence of solid particle volume fraction on the flow rate can be ignored.The results of numerical simulation experiments show that the different velocity distributions on the cross section lead to the annular distribution of the ultra-fine dry powder concentration,and the gas phase drag force is related to the initial velocity,and is independent of the dry powder concentration.After adding rubber gaskets at the connection of the expansion pipe,the resistance can be reduced when the inlet flow rate is less than 12m/s,but increased when it is greater than 12m/s;When the flow rate exceeds 75m/s and the volume fraction exceeds 10%,the resistance no longer increases with the increase of the volume fraction.The dispersion characteristics of gas-solid two-phase flow injected into the pipe gallery of a vehicle mounted ultrafine dry powder injection system were studied.The spray dispersion characteristics of gas-solid two-phase flow at different positions were compared.Through numerical simulation and experimental verification,it was found that the fastest dispersion velocity can be obtained by spraying horizontally from the middle roof of the pipe gallery to the surrounding areas. |
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