Theoretical And Experimental Study Of Compartment Fire Suppressed By Water Mists

Study of heat and mass transfers between droplet and high temperature environment, study of critical extinguishments model of compartment fire and theoretical critical water application rate, as well as study of dominant extinguishments mechanisms of water mist and the confecting of compound additive were conducted by means of combination of theoretical research, numerical analysis and simulation experiments in the dissertation. The research content and main achievements are as follows.1. The differential equations for a single water droplet's trajectory were deduced by analyzing the forces exerted on the droplet. Numerical calculations for motions of droplets with typical diameters and different initial velocities were carried out, and some basic laws of droplet's motion were found. 80μm is a dividing diameter to which terminal velocity are in different proportions of square and liner relations.2. Equations of heat and mass transfers for a single droplet in static environment and high temperature environment were established, and some basic laws of heat and mass transfers between droplet and high temperature were gained. It was put forward that droplet accomplish heat and mass transfers with high temperature environment mainly by evaporation. Coupling interactions between heat and mass transfers, diameter variation and velocity variation in the forced convective environment were taken into account in the first time, and it was concluded that the lifetime of droplet is not proportional to square of initial diameter of droplet any more. From the thermal distances, it was suggested that for class 1 and class 2 water mists, the dominant extinguishments mechanisms of them are gasification.3. The critical extinguishments model of compartment fire was deduced using zone model and thermal extinguishments theory. Main influencing factors of critical conditions were discussed. The critical conditions do not depend upon the initial temperature of the upper layer. The critical condition curve was determined. An example of a compartment fire was given to show the efficiency of the critical extinguishments model.4. Analytical models were developed to model extinguishments of compartment fire under water mist suppression condition. Determinative method of critical water application rates to suppress compartment fire under conditions of two limits of regimes of purely convective heating up and complete evaporation and general case including two regimes of heat transfer were developed.5. Experimental apparatus were setup, and experiments of extinguishing kerosene pool fire in confined space were conducted. Some factors affecting extinguishments time were investigated. It was clear that there are core reaction region, ventilation-controlled region and fuel-controlled region in the pool fire flame and the predominant extinguishments mechanisms of water mist are possibly gas cooling and flame cooling. The exactness of hypothesis on which the critical extinguishments condition model and water application rate model are based was verified.6. Based on preliminary choice of suppression additive, high efficiency compound fire suppression additive was made up by orthogonal experiments and effects analysis. Comparing with pure water mists, water mists containing compound additive extinguished pool fire with very short time, low flame temperature, low oxygen consumption and low production of CO and CO₂. According to the formula and experimental results, the predominant extinguishing mechanism of water mist containing additive was brought forward. That the chemical suppression effect of compound fire suppression additive was primary one, i.e. inhibition and extinguishments of fire is achieved due to radical depletion and reaction termination by metallic ion.