Numerical simulation on circulation and absorption
of sulfur dioxide inside droplet
1. School of Energy and Power Engineering, Jiangsu University, Zhenjiang, Jiangsu 212013, China; 2. School of Mechanical and Aerospace Engineering, Gyeongsang National University, Gyeongnam Jinjusi 660701, Korea
摘要 喷雾烟气脱硫过程中液滴在流场中运动时,在表面剪切力的作用下形成内部循环流动,影响液滴内部传质特性,进而影响雾滴吸收SO2的过程.以单个悬浮液滴为研究对象,采用VOF(volume of fluid)方法计算了不同雷诺数下雾滴内部流动特性和SO2气体在水雾雾滴内部的扩散,探讨了不同雷诺数下雾滴表面的速度分布以及雾滴内部循环流动对雾滴内部SO2浓度分布的影响.数值计算结果表明:气流流场中的液滴与气流存在相对运动时,在表面剪切力的作用下液滴内部会产生2个相互对称的涡流,涡心距离液滴中心的距离为23Rd,涡流速度随着雷诺数的增加而增大.雾滴对SO2的吸收过程受到2种机理的控制:一种是在浓度梯度推动下向雾滴内部的径向扩散;另一种是雾滴内部循环流动诱发的扩散传质.通过SO2在雾滴中径向扩散时间与涡流形成的特征时间、内部循环流动诱发SO2传质的特征时间的对比,表明在雾滴内部,循环涡流流动对吸附传质过程具有重要的影响,随着雷诺数的不断增加,雾滴内部循环流动对SO2传质影响逐渐增大.
Abstract：When the droplets move in flow field in processes of spray flue gas desulfurization, the internal recirculation flow is formed inside droplet due to surface tangent stress to influence the internal mass transfer of droplet greatly and improve the SO2 absorption by spray droplet. The volume of fluid (VOF) method was employed to simulate the internal circulation flow and diffusion inside water droplet. The distribution of tangential velocity at interface and the effect of internal circulation on sulfur dioxide transfer were analyzed for different Reynolds numbers. The numerical results indicate that there are two symmetrical vortexes inside droplets when there is relative motion between gas phase and liquid phase. The distance between vortex core and droplet center is 23Rd, and the vortex velocity is raised with the increasing of Reynolds number. The absorption of sulfur dioxide by droplet is controlled by two mechanisms of radial diffusion by concentration gradient and diffusion by internal circulation. The comparison of characteristic times for radial diffusion inside droplet and vortex formation and sulfur dioxide mass transfer by circulation flow shows that the internal circulation flow has remarked effect on the sulfur dioxide mass transfer of water droplet. The effect of internal circulation is gradually enhanced with the increasing of Reynolds number.
2017, Vol. 38 
