Experimental Investigation On Extinguishing Feasibility Of Liquid Nitrogen In Urban Utility Tunnel

As the main channel of urban material and energy supply,urban utility tunnel undertakes urban water,electricity,transportation and communication,which is worthy of the name of urban lifeline.In recent years,with the rapid development of the utility tunnel,the safety risk of utility tunnel began to expose.The fire of utility tunnel has a wide range of influence and a long recovery time,which affects the normal functioning of the city.Its fire tackling capacity is an important aspect of urban disaster resistance engineering.As an efficient and environmentally friendly cryogenic extinguishing agent,liquid nitrogen is highly promising for fire extinguishing in utility tunnel.In order to study the feasibility and effectiveness of liquid nitrogen fire extinguishing in utility tunnel,an experimental platform of liquid nitrogen fire extinguishing was designed to observe the interaction between liquid nitrogen and fire source,and to analyze the extinguishing mechanism.At the same time,by changing the injection direction of liquid nitrogen,liquid nitrogen release distance,the extinguishing effect of liquid nitrogen under different power fire sources were studied.The results show that:After liquid nitrogen is injected into the closed utility tunnel,the interaction with fire source and fire smoke mainly includes: the impact of high-speed air flow on fire source and the smoke make the flame size increase briefly.The evaporation of liquid nitrogen cools the fire smoke,which makes the combustion rate of fire source decrease.The diffusion of cryogen nitrogen cloud makes the oxygen concentration in the combustion area decrease.The oxygen concentration is quickly reduced to the limit oxygen concentration,and the fire source is suffocated.Finally,the fire was extinguished under the combined effect of cooling and inerting.The fire source with higher power is easier to be extinguished.Under the condition of lower power fire source,the phenomenon of fire enhancement is maintained for a longer time at the initial stage of injection.With the increase of liquid nitrogen release distance,the fire extinguishing time becomes longer and the effect of nitrogen injection is weakened.In addition,the effect of injection in the vertical direction is always better than that in the horizontal direction,but as the release distance of liquid nitrogen increases,the gap between the effects gradually decreases.