Use of liquid nitrogen as wildfile suppressant

Abstract

In recent years, all kinds of fire have become one of the most severe threats to human beings and properties. Several methods are being used to extinguish the fires. Water, the most commonly used fire suppressant, has been proven to be of limited effectiveness when tackling some challenging types of fires, such as forest fires and industrial fires. Chemical foam, another popular fire extinguishment agent, causes environmental contamination after the fire is quenched. Liquid nitrogen (LN2) is a cryogenic fluid that is widely utilized in industry, and some of its characteristics such as high volatility and low temperature showcase its potential to be a novel fire suppressant. It can be produced readily from deep refrigeration of air and it is environmental-benign. In this thesis, a small-scale experiment was performed to investigate the feasibility and effectiveness of using liquid nitrogen jet as a fire suppressant. Then, a numerical simulation was carried out to determine the fate of liquid nitrogen droplets upon a jet breakup. In this calculation, the effects of the parameters such as ambient air temperature, initial droplet velocity, droplet size, droplet injection angle, and thermal radiation on the droplet flight distance and evaporation rate were studied. The experimental results demonstrate the superior performance of LN2, as compared to water, in extinguishing a fire in an enclosure. The results of numerical simulation indicate that ambient air temperature, droplet size, initial velocity, and injection angle are the main factors influencing the LN2 droplet flight distance and evaporation rate. Results reveal that coarser atomization and closer nozzle-to-fire distances of the cryogen, in comparison to water, are necessary to maximize its performance.--Author's abstract