| With the rapid development of society and economy in China, people’s life is more and more inseparable from the application of paint. However, there are very high environmental and fire safety problems in the process of production and application of solvent paint, and the international demand for volatile organic compounds (Volatile Organic Compounds, referred to as VOC) is becoming more and more stringent. As a kind of environmental protection material, water-based paint is used more and more in the industrial production and people’s daily life. But, there are problems about improving the spraying performance and fire risk in the application of water-based paint. Therefore, the dynamic characteristics of water-based paint droplet and the fire characteristics of water-based paint are of great theoretical significance and application value.In this paper, based on the theoretical analysis, numerical simulation, and experiments, the effects of gravity, external wind field, and electrostatic field fot the motion characteristics and spreading characteristics of water-based paint droplet firstly studied. Then, the influences of external electrostatic field on the combustion characteristics of single water-based paint droplets are discussed. Finally, the effects of cross air flow, and without cross air flow for water-based paint pool fire plume characteristics are investigated, and established the prediction model of burning rate of water-based paint pool fire, flame tilt angle, flame length, and flame height.Firstly, based on the fluid mechanics and electromagnetic theory, combined with the actual process characteristics of water-based paint in car spraying, through reasonable assumption, the theoretical model of water-based paint droplets in the airflow and spreading research is established. According to the material characteristics and process parameters, by adopting simulation software Comsol to simulate the movement and spreading process, the prediction model of water-based paint droplet movement and spreading is established.Secondly, based on the numerical simulation method and combustion experiment installation for pool fire and single droplet of the water-based paint, the simulations are carried out for the single water-based paint droplet motion and spreading onto the wall and the combustion experiment researches are carried for water-based paint.The results of the single water-based paint droplet motion and spreading onto the flat wall demonstrate that the effects of gravity and wind field can be ignored for the droplet motion in the air flow. In the initial stage, the effect of electric field on the falling speed can be ignored, but with the increase of electric field the effect on the falling velocity of droplet appears. The relationship between impacting time and the electrostatic field voltage follows: timpact∝U. When the equilibrium contact angle is 100°, the relationship between the droplet eccentricity and electric field intensity is e=K×E. It is found that the relationship between the maximum deformation ratio of charged water-based paint droplet spreading onto the flat surface and We1/4 is dmax/d0∝We1/4. The maximum dimensionless spreading diameter increases with the increase of impacting velocity, and the relationship between the maximum dimensionless spreading diameter and We1/4 is Dmax∝We1/4. The deformation ratio increases with the increase of droplet size, but goes on the reverse trend with the increase of the equilibrium contact angle.The results of water-based paint pool flame combustion show that the burning rate increases with the increase of paint pool diameter without the effect of cross wind,and the relationship between the burning rate and the paint pool diameter is mcalm* = 21.62(1-e-0.036Db). The tangent of paint pool flame tilt angle increases with the increase of Fr, and the relationship between the tangent of paint pool flame tilt angle and Fr is tan θt=1.33 1Fr0.433 . The pool flame tilt angle decreases with the increase of Rm, and the relationship between the pool flame tilt angle and Rm isθt= 129.7Rm-0.125. The dimensionless flame length decrease with the increase of cross wind velocity, and the dimensionless flame length and Fr can be described as lfl*=0.631Fr-0.202. In the absence of cross wind field, the flame height of the water-based paint pool increases with the increase of the water-based paint pool, and the relationships between the dimensionless flame heights and B2/3 is Hfl,ave*=0.52·B2/3,Hfl,max*=0.78·B2/3. Under the effect of cross wind, the flame height of water-based paint pool decreases significantly, and there is a critical Fr.When Fr is less than the critical Fr, the dimensionless average flame height decreases sharply, and the relationship between the dimensionless average flame height and Fr can be expressed as Hfl,ave*=0.29 - 0.093·ln Fr at this stage.Finally, the experiment results of single water-based paint droplet combustion show that the dimensionless flame height decreases with the increase of voltage between two plates under the horizontal electrostatic field, while the dimensionless flame width increases. Under the horizontal electrostatic field, the relationship between the dimensionless maximum flame height and ε1U2/L3 is Hd,max=11.88·ε1U2/L3+13.27, and the relationship between the dimensionless maximum flame width and ε1U2/L3 can be expressed as Wd,max*=4.96·ε1U2/L3+ 2.69.In the vertical electrostatic field, the dimensionless flame height decreased with the increase of the voltage between the upper and lower plates, and the relationship between the dimensionless maximum flame height and between ε1U2/L3 can be expressed as Hd,max*=-21.21·ε1U2/L3-+10.51. With the increase of the electric field intensity, the highest internale temperature (Tmax )of a single water-based paint droplet in the electric field shows a downward trend, and the relationship between Tmax and|U| is Tmax=-11.46·|U|+1401.7. |
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