The Influence Mechanism Of Solid-Liquid-Gas Interface Interaction On Water-Based Extinguishing Agents Seepage In Granular Material Stacks

Stacks of self-heating materials takes huge risk of smoldering fire due to the internal exothermic reactions when exposed to the air environment for a long time,such as pulverized coal,wood chips,straw dust,etc.It is the key step to improve the efficiency of extinguishing smoldering fires to quickly transport water-based extinguishing agents to the fire point inside such stacks.Based on the structural characteristics of typical self-heating granular materials and the physical properities of water-based extinguishing agents,the liquid seepage process in such granular material stacks and the influencing factors were studied with the combination of experimental method and numerical simulation.In response to the needs of modeling the internal structure of large-size stacks,a modeling method of granular-type material stacks was proposed based on Matlab Code.Based on above basis,the transient simulation of the dynamic changes of the solid-liquid-gas interface in capillary pores was carried out from a microscopic view,and the mechanism of the solid-liquid-gas interface interaction such as contant angle,additional pressure and other parameters on the liquid seepage process in such stacks was studied.Taking pulverized coal as a typical self-heating material,the study on liquid seepage in granular material stacks was carried out.There was a critical permeating pressure,which was related to the stack porosity,the stacking height and the cross-section size.Liquid can permeate through the granular material stacks only when the hydrostatic pressure above the stack exccedes the critical permeating pressure.According to the packing properties of pulverized coal stacks,the influences of the porosity,the height,and the section size of pulverized coal stacks on the critical permeating pressure were studied.The results showed that the smaller the stacking porosity and the higher the stacking height,the greater the critical permeating pressure.The cross-section size has little effec.The method of combining ultra-depth-of-field microscope shooting and advanced image processing technology was used to construct the flow field model of real pulverized coal particle stacks.The flow field model was verified by the seepage experiments with the maximum error of 6.15 %and 6.53 %,respectively for hydraulic conductivity K and permeability k.The effects of driving hydrostatic pressure,liquid viscosity and pore size were studied.It was observed that the pressure drop along the seepage direction and the seepage mass flow rate increased linearly with the driving hydrostatic pressure.The more the pore size changed,the more drastically the liquid flow state changed and the greater the seepage flow rate dropped.To avoid the disadvantages of traditional large-size stack modeling method being affected by the size of the equipmengt and the sampling method may damaging its internal structure,this study proposed a new modeling method of granular material stacks based on Matlab Code.This modeling method controlled the solid particle size with the particle size distribution curve,determined the particles position based on the random packing theory of Andreasen,and finally correctted the granular material stakcs model by porosity,which method was not limited by the sampling size and can maintain the spatial pore structure without destroying the force state.Verified by seepage experiments,this modeling method had a good applicability for different porosity and hydrostatic pressure conditions,providing reference methods for the related research of liquid permeating in granular material stacks.The essence of liquid seepage in granular material stacks is the process of the liquid phase displacing the gas phase in capillaries,which is influenced much by the solid-liquid-gas interface interaction.This study focused on the detailed liquid dynamic flowing process in capillary pores,and the influence mechanism of the solid-liquid-gas interface interaction such as the contact angle,additional pressure and other parameters.A series of liquid dynamic moving simulation in capillaries under different diameter and contact angle conditions were carried out to study the oscillating characteristics of the liquid,obtaining an oscillation attenuation equation of the three-phase line.The transient simulation of liquid seepage in real pulverized coal stacks was carried out,and the influences of the pore size changing on the liquid front movement was analyzed.It was observed that the liquid flowed further distance with higher velocity in the case of more pore size reduction.The flowing distance and velocity in the four research paths varied by 1.68 to 6.25 times due to the pore size reducing.This paper provides a theoretical basis for promoting liquid seepage process in granular material stacks,present important guiding significance for the modeling of granular material stacks,and reveal the interaction of solid-liquid-gas interface affects the liquid in the pores.The influence mechanism of the liquid seepage process has important theoretical value and practical significance for the rapid disposal of smoldering fires of particle stacks.