Fire Smoke Movement Rules And Optimization Of Ventilation In Utility Tunnel

Fire smoke movement law and smoke control are classic problems in disaster research.A large number of scholars' research results have strengthened related fire disaster prevention and control capabilities.However,the developing structures such as utility tunnel pose new challenges to fire smoke research.Compared with the research on fire smoke in narrow tunnels,the fire smoke movement laws in utility tunnel are special due to the different functional positioning,building structure and fire protection concept.In this paper,the fire smoke in a utility tunnel is taken as the research object.A two-dimensional vector field measurement method for fire based on optical flow conservation is proposed to reveal the smoke layer under the closed and ventilated state of the utlility tunnel.The study summarizes the influence of the vertical smoke temperature decay law under the smoke screen,reveals the unique smoke field filling law of the utility tunnel fire,and establishes the prediction method of the self-extinguishing time in utility tunnel fire.The research optimizes the minimum combustion gain in the ventilation of the utility tunnel,and propose the scientific basis of the smoke control and firefighting design in the utility tunnel.The specific work includes the following four aspects:In view of the fact that the fire experiment is a severe environment with high temperature,high heat and limited,it is difficult to achieve the velocity field measurement by conventional measurement methods.This paper introduces the optical flow conservation theory to improve the capture ability of the smoke particle movement,mainly including pre-processing image enhancement and optical flow calculation.The method and post-processing image filtering break through the dependence of the traditional PIV device on the addition of tracer particles.The study solves the problem of non-uniform distribution of smoke particles.A variety of dense optical flow calculation methods were compared to explore the optimal method,the pre-processing,optical flow calculation and post-processing modes was checked to establish the two-dimensional vector field measurement,in which are suit for the fire scenes without the additional tracer particles.The difference between the thermal stratification and the visible stratification of the smoke was analyzed,and the phenomenon of stratified thickening of the smoke caused by the shear motion was found.Based on visual processing methods and theoretical analysis methods,a definition method of smoke layer based on the combined effect of thermal buoyancy and shear force is proposed,and it is help to reveal the special law of the smoke layer of the utility tunnel under the closed and ventilated state.Meanwhile,the study considers the temperature characteristics of the smoke layer at different heights under the condition.The smoke screen and the obstacles are set inside the structure in experiments,it is found that the temperature change in the boundary layer of the ceiling is the key to characterizing the influence of smoke screen and obstacles.Based on the theory of thermal boundary layer,through the small-scale experiments and numerical simulation,the sudden effect of smoke screen on longitudinal temperature attenuation is revealed,and the distribution of smoke thermal boundary layer under the ceiling is quantitatively determined.Finally,a predictable longitudinal temperature decay model under the smoke screen is found.Compared with the general closed building fire,the narrow and long closed utility tunnel has obvious characteristics.The remote air cannot be supplied to the combustion in time due to the blockage of smoke in utility tunnel.A multi-scale experiment of a fully closed underground comprehensive corridor fire is carried out to explore the process of smoke filling and its temperature and velocity characteristics,flame shape,ceiling jet layer distribution and the law of its entrainment velocity.The attenuation of the combustion under the pressure of the smoke of the closed utility tunnel fire were explored,and the law of self-extinguishing fires in utility tunnel was found,in which was caused by the smoke and air entrainment.Finally,the paper establishes a prediction model of the self-extinguishing time of the fire under the pressure of the smoke in the closed utility tunnel.Meanwhile,the safety of the design of the enclosed section of the utility tunnel is discussed.According to the situation of the longitudinal distribution of combustibles in the utility tunnel,the ventilation of the utility tunnel in fire accident is different from the general building or tunnel fire.The axial ventilation in the accident may cause the rapid spread of the fire.This paper focuses on whether the corridor can be ventilated and exhausted in fire accident.The morphological characteristics of smoke plume under different ventilation environments was analyszed.The study reveals the fire field movement rules under ventilation.Combining the Thomas' critical velocity theory and the plume Constraints such as the concave-convex characteristics,stability and balance of the morphology,an optimized ventilation strategy was found that effectively prevents smoke backflow and minimizes flame combustion gain.