“Relay-mode”promoting permeation of water-based fire extinguishing agent in granular materials porous media stacks

Water-based fire extinguishing agent is the main means to deal with smoldering fires.However,due to the hydrophobic properties of the particle surface,the porous medium channel provide resistance and slow down the extinguishing agent flow during the downward permeation process.To promote the liquid permeation process in such porous media,this work studied liquid imbibition process and analyzed the oscillating and attenuating process of liquid level in capillary channel by theoretical,experimental,and numerical methods.An empirical mathematical equation was proposed to describe the oscillating process,and the effects of the capillary diameter and contact angle parameters on the transportation process were analyzed.Based on this,the“relay-mode”was proposed to promote the liquid transportation forward.Finally,the transient simulation results of liquid permeation in coal stacks showed when the liquid flowed through the channel with changed diameter from large to small ones,the transportation distance was several times longer than that through the unidiameter ones.The trend of liquid“relay-mode”in capillaries can be used to promote the permeation in granular materials porous media stacks.The relevant results also provide new thoughts to develop the water-based fire extinguishing agents and then improve the firefighting efficiency of deep-seated fire in porous media stacks.

Investigation on the characteristics and mechanism of AZ80A magnesium alloy corrosion by Halon 1301 and CF_(3)I

In order to study the application of gas fire extinguishing agents in civil aircraft fire extinguishing systems,the corrosion characteristics and mechanisms of Halon 1301 and CF_(3)I on AZ80A magnesium alloy were comparatively analyzed.The experimental methods combined with density functional theory were applied to explore the corrosion mechanism.The results indicate that Halon 1301 and CF_(3)I exhibit good compatibility with AZ80A magnesium alloy through physical adsorption at room temperature and pressure,where Halon 1301 has a more stable adsorption configuration.However,with increasing temperature,pyrolysis reactions occur leading to the formation of fluorine containing corrosive substances which can react with magnesium alloy to generate the corrosion production of MgF_(2) and coke.Although MgF_(2) and coke can partically reduce reaction rates and protect against corrosion,the presence of MgF_(2) promotes further pyrolysis,generating more corrosion products.Consequently,the accumulation of corrosion products leads to a loss of metallic luster and a decline in mechanical properties of magnesium alloy along with interfacial cracking due to mutual extrusion between MgF_(2) and carbon deposition layers.These studies offer theoretical guidance for utilizing CF_(3)I in civil aircraft fire extinguishing systems while facilitating rapid screening for efficient clean gas extinguishing agents.