Influence of Rheological Property and Surface Tension on the Micro Breakup of Coal Water Slurry
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摘要: 以神华煤和华电煤为原料制备了质量分数为58%~62%的水煤浆，使用旋转流变仪、静/动态表面张力仪、高速摄像机和图像处理软件等研究了水煤浆理化参数对其微观破裂过程的影响。水煤浆属于剪切变稀的非牛顿流体，采用Herschel-Bulkley模型建立了水煤浆流变关系式；与静态表面张力不同，水煤浆的动态表面张力随着特征气泡时间的增加先减小后增加，表面张力最小值出现在200 ms附近；获得了基于水煤浆流变性和动态表面张力函数的水煤浆微观破裂特征直径与时间的关系式。Abstract: In the process of the slurry breakup, the throat of the liquid bridge keeps shrinking. When the minimum characteristic diameter of the liquid bridge is close to the size of the solid particle, the slurry will exhibit the complex variation characteristics in the process of time, which is significantly different from pure liquid. Therefore, the study of the micro breakup characteristics of the slurry is helpful to reveal the atomization mechanism and improve the simulation model of slurry. Here Shenhua coal and Huadian coal are used as the raw materials to prepare coal water slurry with a mass concentration range of 58% -62 %(mass fraction). The influence of the physical and chemical parameters of coal water slurry on its microscopic breakup process has been studied by the rotary rheometer, the static surface tension meter, the dynamic surface tension meter, the high-speed camera, the image processing software, and so on. Coal water slurry is a shear thinning non-Newtonian fluid. So in this paper the Herschel-Bulkley model is used to establish the rheological relationship of coal water slurry. Unlike the static surface tension, the dynamic surface tension of coal water slurry decreases with the increase of the characteristic bubble time. After increasing, the minimum surface tension appears around about 200 ms. Finally based on the rheological properties and the dynamic surface tension of coal water slurry, the relationship between the change of the characteristic diameter of coal water slurry micro-breakup and the time of breakup is obtained.
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Key words:
- coal water slurry /
- micro breakup /
- surface tension /
- viscosity /
- rheology
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图 1 煤粉的粗、细颗粒粒度分布
Figure 1. Size distribution of coarse and fine particles of pulverized coal
图 2 浆体微观破裂实验示意图
Figure 2. Schematic of slurry micro breakup experimental equipment
1—Coal water slurry and nozzle；2—High speed camera；3—Computer
图 3 水煤浆黏度随剪切速率的变化
Figure 3. Variation of viscosity of coal water slurry with shear rate
图 4 不同质量分数水煤浆的表面张力变化情况(其中水平线为静态表面张力)
Figure 4. Surface tension of coal water slurry (Where the horizontal line is the static surface tension)
图 5 水煤浆动态表面张力实验值与拟合值对比
Figure 5. Comparison of experimental value with fitted value of dynamic surface tension of coal water slurry
图 6 水煤浆喉部直径（Dm）示意图
Figure 6. Schematic diagram of the diameter (Dm) of the coal water slurry throat
图 7 典型水煤浆破裂实验照片
Figure 7. Photograph of typical breakup experiment of coal water slurry (w=60%, Huadian coal)
图 8 水煤浆喉部直径随时间变化关系（不同颜色表示为3次实验结果）
Figure 8. Relationship between the diameter of the coal water slurry throat and time (Different colors represent the results of three experiments)
图 9 不同煤种和浓度条件下水煤浆喉部直径实验值与拟合值（式（5））对比
Figure 9. Comparison of experimental and fitted values (Eq. 5) of the diameter of coal water slurry
表 1 煤粉颗粒粒度及水煤浆质量分数
Table 1. Particle size of pulverized coal and mass fraction of coal water slurry
Sample D32 /μm D43 /μm w(Slurry)/% Coarse particle size Fine particle size Coarse particle size Fine particle size Shenhua coal 90.1 10.1 265 39.4 60 62 Huadian coal 22.8 8.55 129 31.0 58 60 
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表 2 水煤浆的Herschel-Bulkley模型参数
Table 2. Model parameters of Herschel-Bulkley model for coal water slurry
Sample w(Slurry)/% $ {\tau _{\rm{o}}} $/Pa K/(Pa·sn) n Shenhua coal 60 0.024 0.79 0.88 62 0.036 1.10 0.76 Huadian coal 58 0.019 0.76 0.94 60 0.077 0.94 0.93
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