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CN-122017118-A - Water-formed film foam extinguishing agent performance characterization method based on molecular dynamics simulation

CN122017118ACN 122017118 ACN122017118 ACN 122017118ACN-122017118-A

Abstract

The invention discloses a molecular dynamics simulation-based performance characterization method of an aqueous film-forming foam extinguishing agent. According to the method, through establishing an air-AFFF-combustor three-phase model and an air-AFFF-enhancement component-combustor four-phase model, and carrying out molecular dynamics simulation under different temperature conditions, microscopic indexes such as combustor molecular diffusion, interface structure, water film/hydration layer and the like are extracted, and the barrier effect of AFFF and a compound system thereof on fuel molecular diffusion is represented and evaluated.

Inventors

  • ZHOU XIA
  • HA HONGJIE
  • PAN RENMING
  • LIU ZIHENG
  • LI QUANWEI

Assignees

  • 南京理工大学

Dates

Publication Date
20260512
Application Date
20260312

Claims (10)

  1. 1. The method for characterizing the performance of the water-formed film foam extinguishing agent based on molecular dynamics simulation is characterized by comprising the following steps of: S1, respectively establishing an air box, an AFFF box and a burner box by utilizing a Amorphous Cell module in MATERIALS STUDIO software, and combining the three boxes into an air-AFFF-burner model by using Build Layers; s2, performing structural optimization on the air-AFFF-combustor model based on a COMPASSII molecular force field by using a Forcite module in MATERIALS STUDIO, and performing geometric optimization by using a Smart algorithm of the Forcite module after each step of the optimization process to obtain an air-AFFF-combustor optimized structural model with the lowest energy; S3, performing three groups of temperature variable simulation by using a dynamic task under a Forcite module of MATERIALS STUDIO software, placing an air-AFFF-combustor optimization structure model in a regular ensemble to perform molecular Dynamics simulation, wherein the convergence standard of the system is that the temperature and the energy curve of the system fluctuate within 5%, and after the system is simulated to be balanced, taking a balanced track file for result confirmation and discussion analysis; s4, analyzing tasks under a MATERIALS STUDIO software Forcite module are used for the balanced track file to obtain a mean square displacement curve of the molecules of the combustion products, and a diffusion coefficient D, a component density distribution diagram, a radial distribution function diagram of water molecules, a water film thickness and a surfactant molecular tail chain inclination angle are obtained through calculation; S5, constructing an enhancement component box by utilizing a Amorphous Cell module in MATERIALS STUDIO, and adding an enhancement component layer through a Build Layers module on the basis of an air-AFFF-combustor model to ensure that the enhancement component layer is positioned between the AFFF layer and the combustor layer so as to form the air-AFFF-enhancement component-combustor model; S6, performing structural optimization on the air-AFFF-enhanced component-combustor model based on a COMPASSII molecular force field by using a Forcite module in MATERIALS STUDIO, and performing geometric optimization by using a Smart algorithm of a Forcite module after each step of the optimization process to obtain an air-AFFF-enhanced component-combustor optimized structural model with the lowest energy; S7, performing three groups of temperature variable simulation by using a dynamic task under a Forcite module of MATERIALS STUDIO software, placing an air-AFFF-reinforced component-combustor optimization structure model in a regular ensemble to perform molecular Dynamics simulation, wherein the system convergence standard is that the temperature and energy curve of the system fluctuate within 5%, and after the system is simulated to be balanced, taking a balanced track file for result confirmation and discussion analysis; S8, using MATERIALS STUDIO an Analysis task under a software Forcite module to the balanced track file obtained in the S7 to obtain a molecular mean square displacement curve and a diffusion coefficient D of the combustion object, a component density distribution diagram, a radial distribution function diagram of water molecules, a water film thickness and a surfactant molecular tail chain inclination angle; S9, changing the concentration or molecular type of the enhancement component, repeating S5-S8, and obtaining a mean square displacement curve and a diffusion coefficient D of the burner molecules of different air-AFFF-enhancement component-burner models, a component density distribution diagram, a radial distribution function diagram of water molecules, a water film thickness and a tail chain inclination angle of the surfactant molecules; s10, analyzing and comparing the influence of the concentration of the enhancement component or the molecular type on the AFFF fire extinguishing effect.
  2. 2. The method for characterizing the performance of an aqueous film-forming foam fire extinguishing agent according to claim 1, wherein in S1, an air box comprises 100 air molecules, an AFFF box comprises 82 organic molecules and 700 water molecules, a combustion box comprises 100 combustion molecules, the length and width dimensions of the box are 30a×30a, and a 2 a vacuum layer is arranged between each two layers.
  3. 3. The method for characterizing the performance of an aqueous film-forming foam extinguishing agent according to claim 1, wherein in S1, air molecules in an air box consist of 21 oxygen molecules and 79 nitrogen molecules, 82 organic molecules in an AFFF box consist of 10 sodium benzoate molecules, 30 sodium sulfate molecules of C10 fatty alcohols, 30 glycerol molecules, two alkyl glycoside molecules and 10 FC-1157C molecules, and a combustor box consists of 100 n-hexane molecules.
  4. 4. The method for characterizing the performance of an aqueous film forming foam extinguishing agent according to claim 1, wherein in S2, the energy difference is set to 0.0001kcal/mol, the RMS force standard is 0.005kcal/mol·a, and the number of iterations is 30000.
  5. 5. The characterization method of the water-based film-forming foam extinguishing agent according to claim 1, wherein in S3, three groups of simulation temperatures are respectively set to 303K, 323K and 342K, the total duration of molecular dynamics simulation is 500ps, and the simulation step size is set to 1fs.
  6. 6. The method for characterizing the performance of an aqueous film forming foam extinguishing agent according to claim 1, wherein in S4 and S8, the calculation formula of the radial distribution function is: (1), Wherein: (r) is the probability of other particles occurring at a position from the center particle r, dN is the number of other particles in the spherical region at a position from the center particle r, ρ is the system density composed of various surfactant molecular models, dr is the thickness of the spherical region, and r is the distance from the center particle.
  7. 7. The method for characterizing the performance of an aqueous film-forming foam extinguishing agent according to claim 1, wherein in S4 and S8, the calculation formulas of the molecular root mean square displacement MSD and the diffusion coefficient D are respectively: (2), (3), Wherein N is the total number of diffusion molecules in the simulation system, r i (t) is the position of the particle i at the time t, r i (0) is the position of the particle i at the initial time, D is the diffusion coefficient of the microscopic particle, and a is the linear slope of the root mean square displacement and time.
  8. 8. The method of characterizing the performance of an aqueous film forming foam fire extinguishing agent according to claim 1, wherein in S4 and S8, the water film thickness is defined as the water film thickness of water between 10% and 90% of the bulk water density.
  9. 9. The method for characterizing the performance of an aqueous film-forming foam extinguishing agent according to claim 1, wherein in S5, the reinforcing component boxes comprise different numbers of reinforcing component molecules, the length and width dimensions of the reinforcing component boxes are 30A multiplied by 30A, the reinforcing component molecules are one of perfluoropropyl polyacrylamide, ammonium polyphosphate and SiO 2 nano particles, and the polymerization degree is set to be 20.
  10. 10. The method for characterizing the performance of a water-forming film foam fire extinguishing agent according to claim 1, wherein in S10, MSD curves and diffusion coefficients D of fuel molecules are used for characterizing migration capacity of the fuel molecules near an AFFF interface film, lower MSD growth rate and diffusion coefficient D mean that the fuel molecules are limited in transmission across the interface, so that the AFFF has stronger shielding and sealing capacity on fuel vapor, component density distribution is used for revealing enrichment degree of water molecules of a system and blocking degree of diffusion of the fuel molecules, if the fuel molecules are mainly limited on the fuel side, water phase and surface active agent form a continuous enrichment layer at an interface, the interface film has stronger blocking effect on diffusion of the fuel molecules so as to correspond to better steam sealing capacity, if the water molecules F reflect local ordering and molecular aggregation characteristics of the interface water phase, the AFFF system is considered to form an aqueous phase barrier more favorable for inhibiting penetration of the fuel molecules, the water film thickness directly reflects the liquid phase formed on the fuel surface, the film thickness is larger in the inclination angle and the film thickness is more stable, the interface film thickness is more favorable for inhibiting the absorption and concentration of the water molecules form a better phase, and the absorption and better phase is more stable than the interface film is more favorable, the interface film is more concentrated in the interface film is more stable, and has better absorption resistance to the interface film absorption resistance is more favorable to the interface surface film absorption resistance, thereby improving the vapor sealing capability of the AFFF.

Description

Water-formed film foam extinguishing agent performance characterization method based on molecular dynamics simulation Technical Field The invention belongs to the technical field of fire extinguishing agent performance calculation simulation, and relates to a water film forming foam fire extinguishing agent performance characterization method based on molecular dynamics simulation. Background Aqueous film-forming foam extinguishing Agents (AFFF) are widely used in liquid fuel fires, where the mechanism of fire extinguishment involves the formation of a water film/foam film on the fuel surface, lowering interfacial tension, inhibiting fuel vapor escape, insulating heat and oxygen, and the like. In practical application, in order to further improve film forming property, liquid separation resistance and foam stability of the AFFF, a compounding thought of a surfactant and an additional component is often adopted for formula optimization, but a foam system is in a thermodynamically metastable state and is obviously influenced by liquid film drainage, interface disturbance and the like, and certain additional components can also have adverse effects on the foam under improper conditions, so that effective screening and evaluation means are needed. Literature 1（Schaefer T, Dlugogorski B Z, Kennedy E M. Vapour Suppression of n-Heptane With Fire Fighting Foams Using Laboratory Flux Chamber[C]//AOFST 7. 2007.） sets up a laboratory flux chamber (flux chamber), places n-heptane 10mm deep over different types of foam layers, measures the n-heptane concentration in the outlet gas stream with a gas chromatograph-hydrogen flame ionization detector (GC-FID), and calculates therefrom the mass flux of n-heptane through the foam layers, by comparing the steam breakthrough times of different types of foam layers for n-heptane (sampling time when the flux exceeds 1x10 -6kg·m-2·s-1), it is found that the steam breakthrough time of the fluorosurfactant-free AFFF is lower than the fluorosurfactant-free AFFF, and therefore its sealing ability against n-heptane steam is the strongest. However, the existing macroscopic experiments (for example, measuring the steam breakthrough time) can reflect the sealing capability of foam to fuel steam, but generally have the problems of high experiment cost, strong variable coupling, difficulty in revealing mechanisms on a molecular scale, low formula screening efficiency and the like. Molecular dynamics simulation is a computational method for performing numerical solution on atomic and molecular motion processes based on classical mechanics. The method can obtain the structural evolution and dynamic behavior information of the system on a microscopic scale by constructing a molecular system model, selecting a proper force field and solving the integral of a particle motion equation. Compared with a macroscopic experiment method, the molecular dynamics simulation can reveal adsorption, arrangement and interaction mechanisms of the surfactant at the interface from the molecular level, so that the method has unique advantages in the aspects of researching the stability of a foam liquid film, the transmission of fuel molecules across the interface, a steam sealing mechanism and the like. Disclosure of Invention The invention aims to provide a molecular dynamics simulation-based water-formed film foam extinguishing agent performance characterization method, which is characterized in that an air-AFFF-combustion three-phase model and an air-AFFF-enhancement component-combustion four-phase model are established, molecular dynamics simulation is carried out under different temperature conditions, indexes such as a molecular diffusion coefficient, component density distribution, a radial distribution function, a water film thickness, a surfactant tail chain inclination angle and the like of the combustion are extracted, and the blocking effect of AFFF and a compound system thereof on fuel molecular diffusion is characterized, so that the closed loop of model construction, structure optimization, dynamics simulation, result analysis and formula optimization is realized, and the formula research and development efficiency and the mechanism interpretation capability are improved. In order to achieve the above purpose, the invention adopts the following technical scheme: The method for characterizing the performance of the water-formed film foam extinguishing agent based on molecular dynamics simulation comprises the following steps: S1, respectively establishing an air box, an AFFF box and a burner box by utilizing a Amorphous Cell module in MATERIALS STUDIO software, and combining the three boxes into an air-AFFF-burner model by using Build Layers; s2, performing structural optimization on the air-AFFF-combustor model based on a COMPASSII molecular force field by using a Forcite module in MATERIALS STUDIO, and performing geometric optimization by using a Smart algorithm of the Forcite module after each st