Numerical Investigation of Aerosol Generation by Laser Decontamination and Aerosol Removal by Spray Based on OpenFOAM
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摘要: 在核设施维修及退役过程中，可利用激光去污技术对安全壳内高放射性污染的构件表面进行清洗，但过程中会产生大量亚微米级放射性气溶胶颗粒。为防止放射性物质扩散至环境中，可采用安全壳喷淋系统对其进行去除。为研究激光去污产生气溶胶的物化特性以及气溶胶的喷淋去除效果，本研究进行激光去污实验以获取气溶胶生成速率、数量浓度和颗粒直径分布等数据；基于欧拉-拉格朗日方法，在OpenFOAM中开发了能够同时模拟气溶胶生成和气溶胶喷淋去除的数值模拟模型，对封闭空间内气溶胶的生成、迁移扩散以及喷淋去除特性进行了模拟和分析。模拟结果表明：喷淋区域内的气溶胶可以直接与喷淋液滴相互作用而被去除；非喷淋区域的气溶胶会随气流运动被夹带进入喷淋区域再被去除；气溶胶颗粒直径越大，喷淋去除效率也越高。本研究建立的数值模拟预测方法能够为未来优化封闭空间内激光去污及气溶胶喷淋去除技术提供模型基础和技术参考。Abstract: During the maintenance and decommissioning of nuclear facilities, laser decontamination technology can be utilized to clean the radioactively contaminated surfaces inside the primary containment vessel. However, a significant amount of sub-micron radioactive aerosol particles will be generated during the laser decontamination operations. To prevent these radioactive substances from leaking into the environment, the containment spray system can be employed to remove these submicron aerosol praticles. To investigate the physicochemical properties of the aerosols produced by laser decontamination and the efficiency of aerosol removal by spray droplets, the laser decontamination experiments were firstly conducted to measure the aerosol characteristics such as aerosol generation rates, concentrations, and particle diameter distributions. Subsequently, a CFD model was developed and implemented into OpenFOAM to simulate both the aerosol generation by laser decontamination and aerosol removal by spray droplets using Euler-Lagrange approach, and the characteristics of aerosol generation, migration and diffusion and removal by spray in an enclosed space were simulated and analyzed. The simulation results demonstrate that aerosols within the spray region can be directly removed by interacting with the spray droplets, while those in the non-spraying region need to be entrained into the spray region with the airflow movement and then removed. Furthermore, it was observed that the larger the aerosol particle size, the higher its spray removal efficiency. The numerical simulation model established in this study can be served as a foundation and technical reference for future optimizations of laser decontamination and aerosol removal by spray in enclosed space.
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Key words:
- OpenFOAM /
- Laser decontamination /
- Aerosol /
- Removal by spray
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图 1 表面激光去污及气溶胶生成测量实验装置示意图[7]
Figure 1. Schematic Diagram of Experimental Setup for Laser Decontamination and Aerosol Generation Measurement
图 4 不同功率激光照射下产生的气溶胶颗粒数量浓度
Figure 4. Quantity Concentration of Aerosol Particles Produced by Different Power Laser Irradiation
图 5 喷淋去除气溶胶颗粒CFD模型框架图
dp,n—颗粒直径；dD,m—液滴直径
Figure 5. Framework of CFD Model for Aerosol Particle Removal by Spray
图 9 喷淋液滴空间位置和气相速度
子图a中球体代表喷淋液滴，其颜色深浅代表液滴直径
Figure 9. Spatial Position of Spray Droplets and Gas Phase Velocity
图 10 无喷淋时直径为0.6 μm的气溶胶颗粒质量分数随时间的演化
Figure 10. Evolution of Aerosol (0.6 μm) Mass Fraction over Time without Spraying
图 11 喷淋时直径为0.6 μm的气溶胶颗粒质量分数随时间的演化
Figure 11. Evolution of Aerosol (0.6 μm) Mass Fraction over Time with Spraying
图 12 喷淋流场和直径为0.6 μm的气溶胶颗粒质量分数随时间的演化
Figure 12. Evolution of Spray Flow Field and Aerosol (0.6 μm) Mass Fraction with Time
图 13 不同直径气溶胶颗粒的喷淋去除效率
Figure 13. Spray Removal Efficiency of Aerosol Particles with Different Diameters
表 1 3种机械机制对单个液滴的气溶胶去除效率的经验公式[10-11]
Table 1. Empirical Formula for Aerosol Removal Efficiency of a Single Droplet by the Three Mechanical Mechanisms
机械机制种类 经验公式 惯性碰撞 $ \begin{array}{l} {\eta _{_{{\text{imp}}}}} = \left\{ \begin{array}{*{20}{l}}0{\text{ }} & S t < 0.0833 \\ {\left( {\dfrac{S t}{{S t + 0.5}}} \right)^2}{\text{ }} & 0.0833 \leqslant S t \leqslant 0.2 \\ 8.57 \cdot {\left( {\dfrac{S t}{{S t + 0.5}}} \right)^2} \cdot \left( {S t - 0.08336} \right) & S t > 0.2\end{array} \right. \\ S t = \dfrac{{{\rho _{\text{p}}}d_{\text{p}}^2\left| {{U_{\text{G}}} - {U_{\text{D}}}} \right|}}{{9{\mu _{\text{G}}}{d_{\text{D}}}}} \end{array} $ 拦截 $ \begin{array}{l}{\eta }_{\mathrm{int}}=\dfrac{1-{\alpha }_{\text{L}}}{J+\sigma \cdot K}\left[\left(\dfrac{R}{1+R}\right)+\dfrac{1}{2}{\left(\dfrac{R}{1+R}\right)}^{2} \cdot \left(3\sigma +4\right)\right] \\ \sigma =\dfrac{{\mu }_{\text{D}}}{{\mu }_{\text{G}}},R=\dfrac{{d}_{\text{p}}}{{d}_{\text{D}}}\\ J=1-\dfrac{6}{5} \cdot {\alpha }_{\text{L}}^{\tfrac{1}{3}}+\dfrac{1}{5} \cdot {\alpha }_{\text{L}}^{2},K=1-\dfrac{9}{5}{\alpha }_{\text{L}}^{\tfrac{1}{3}}+\alpha +\dfrac{1}{5} \cdot {\alpha }_{\text{L}}^{2}\end{array} $ 布朗扩散 $ \begin{gathered} {\eta _{{\text{diff}}}} = {\left( {2 \cdot Pe \cdot {d_{\text{D}}}} \right)^{ - \tfrac{1}{2}}} \\ Pe = \frac{{{d_{\text{D}}}\left| {{U_{\text{G}}} - {U_{\text{D}}}} \right|}}{{{D_{{\text{diff}}}}}},{D_{{\text{diff}}}} = \frac{{{k_{\text{B}}}TC}}{{3\pi {v_{\text{G}}}{\rho _{\text{G}}}{d_{\text{p}}}}} \\ C = \frac{{2.609\sqrt {2l} }}{{\sqrt {{d_{\text{p}}}} }}\quad 0.05{\text{ μm}} < {d_{\mathrm{p}}} < 1.0{\text{ μm}} \\ \end{gathered} $ $ {\rho _{\text{p}}} $—颗粒密度，kg/m3；$ {d_{\text{p}}} $—颗粒直径，m；$ {\mu _{\text{G}}} $—空气动力粘度，Pa·s；$ {\alpha _{\text{L}}} $—液相体积分数；J和K—经验系数；R—颗粒直径与液滴直径之比；$ \sigma $—液体动力粘度与空气动力粘度之比；Pe—贝克莱数；Ddiff—扩散系数，m2/s；kB—波尔兹曼常数；T—空气温度，K；C—坎宁安校正因子；$ {v_{\text{G}}} $—空气运动粘度，m2/s；${\rho _{\text{G}}} $—空气密度，kg/m3；l—空气平均自由程，m 
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表 2 容器内气溶胶生成速率
Table 2. Rate of Aerosol Generation in the Container
气溶胶命名 dp/μm 生成速率SG/（mg·s−1） AP2 0.198 0 AP3 0.305 0 AP4 0.407 8.26427×10−8 AP5 0.505 1.96517×10−6 AP6 0.583 1.06248×10−5 AP7 0.724 1.65405×10−5 AP8 0.778 1.82688×10−5 AP9 0.899 1.16819×10−5 AP10 1.038 3.16325×10−6
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