含纤维状颗粒的液固两相流动的模拟和实验研究
文献类型：学位论文
| 作者 | 范茏 |
| 学位类别 | 博士 |
| 答辩日期 | 2004 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 中国科学院过程工程研究所 |
| 导师 | 毛在砂 |
| 关键词 | 搅拌槽 细长颗粒 取向 固液两相流 数值模拟 曳力系数 虚拟质量力 层流 湍流 |
| 其他题名 | Numerical simulation and experiment of solid-liquid two-phase flow |
| 学位专业 | 化学工艺 |
| 中文摘要 | 细长颗粒因其特殊的形状一直是过程工程研究中的难点，但对造纸、合成纤维素、催化剂等行业，纤维状颗粒的分散、流体力学特性等都是重要影响因素，因此有必要深入研究纤维状颗粒在液相中的流体力学特性。固液体系是搅拌槽中极常见的多相流，由于颗粒尺寸相差很大，流型不均匀，颗粒与颗粒的聚集及颗粒间作用力等影响因素，在混合设备内很难达到均匀的分布。为此，有必要对搅拌槽中固体颗粒的运动情况进行研究。本论文主要研究搅拌槽中固相为大长径比细长颗粒时的液固两相流动。论文采用CCD等技术实验测量了单个细长颗粒在沉降过程中的曳力系数，将颗粒的曳力系数与其下降过程中的取向联系起来，得出了以雷诺数（以颗粒柱端直径为特征尺寸）、取向和阿基米德数表达的经验关联式。发现长径比、周围流体速度等均对颗粒在层流区的曳力系数没有影响。在单个细长颗粒实验基础上，对细长颗粒群的曳力系数进行了实验研究。实验范围内，颗粒群的曳力系数与单颗粒服从同一规律，颗粒的浓度、长径比等对颗粒群曳力系数没有影响。利用DPIV技术实验研究了搅拌槽中含细长颗粒的液固两相流，在得到固相为细长颗粒的固液两相湍流流场和细长颗粒取向的同时，测得了搅拌槽中单相湍流流场和固相为球形颗粒的固液两相湍流流场。对有挡板的标准Rushton桨搅拌槽中的单相、固液两相层流流场进行了较系统的实验研究，获得了单相、固相为球形颗粒和固相为细长颗粒的固液两相层流流场较完整的实验数据，和三维层流流场中细长颗粒的取向分布。对层流和湍流流场中，搅拌转速、颗粒长径比和固相浓度对流场、颗粒取向的影响分别作了讨论，比较了球形颗粒与细长颗粒的速度场。发现湍流和层流流场中，颗粒的长径比、浓度对流场的影响不大，实验范围内，速度均与单相时的速度较接近，说明固体颗粒的加入对流场影响不大。随着搅拌转速的增大，径向和轴向速度均增大；随着离槽中心距离的增大，轴向速度增大趋势减小。颗粒的取向随着一长径比、搅拌转速的变化均会发生改变；随着搅拌转速的增大，在搅拌桨附近，颗粒长轴与水平面间的夹角减小。数值模拟方面，采用改进的内外迭代法模拟了有挡板的标准Rushton桨搅拌槽中的单相层流流场，计算了流动准数、功率准数，计算值与文献值吻合良好。将此方法扩展到固相为球形颗粒的层流流场的模拟中，模拟结果与实验结果差别不大，证明本模拟方法是可靠的。讨论了搅拌桨位置对流场的影响，径向速度和轴向速度随着搅拌桨位置的下移而减小。在固相为细长颗粒的层流流场模拟中，采用直接求解刚性颗粒转动方程的方法，通过数值模拟得出颗粒的取向。分析了搅拌转速、颗粒长径比、虚拟质量力等因素对流场、颗粒取向的影响，比较了细长颗粒与等体积球形颗粒的速度场。层流流场中，细长颗粒的径向速度与等体积球形颗粒的径向速度有着明显差别，而轴向和切向速度差别较小。采用两流体模型、改进的内外迭代法模拟了有挡板的标准Rushton桨搅拌槽中含细长颗粒的液固两相湍流流场，并利用刚性颗粒的转动方程，得出三维湍流流场中颗粒的取向分布。比较了细长颗粒与等体积球形颗粒的速度场，在湍流流场中颗粒的形状对流场影响不大，球形颗粒与细长颗粒的速度很接近。讨论了搅拌转速、颗粒长径比、虚拟质量力等对流场、颗粒取向的影响。虚拟质量力和颗粒长径比对流场影响不大，而取向发生了较大变化，二者对取向的影响随着径向位置和轴向位置的不同而不同。将湍流流场中各影响因素与层流流场中的影响比较，流场不同，各因素的作用也不同。 |
| 英文摘要 | Slender particle displays quite different behavior for its special shape. The dispersion and fluid dynamic characteristics of slender particles are important to many process industries, such as papermaking, synthetic fiber, catalyst, etc. It is necessary to study the hydrodynamic features of slender particles in fluids. Solid-liquid two-phase flow is very common in stirred tanks. Because of large variation in particle dimensions, complexity of flow field and particle interaction with one another, uniform dispersion is difficult to obtain. Therefore, the behavior of solid particles in stirred tanks is worthy of investigation. The aim of this thesis is to study solid-liquid two-phase flow involved with slender particles in stirred tanks. The drag coefficient of a single slender particle in sedimentation is measured with the CCD technique. The drag coefficient is correlated with the orientation of a particle in sedimentation and an empirical correlation is given in terms of the Reynolds number (based on the cylinder diameter), orientation and the Archimedes number. It is found that the aspect ratio and fluid velocity have no effect on the drag coefficient. On the basis of experiments of a single slender particle, the drag coefficient of slender particle swarm is also determined. In the range of parameters investigated, drag coefficient of multiparticle systems follows the same law as that of single slender particle. Concentration and aspect ratio of solid particles exert little influence on drag coefiicient of slender particles in a swarm. Solid-liquid turbulent two-phase flow involved with slender particles and orientation of slender particles in a stirred tank are measured with the digital particle image velocimetry (DPIV). Furthermore, turbulent flow fields of single-phase liquid flow and solid-liquid two-phase flow with spherical particles are experimented respectively. In the baffled tank stirred by a standard Rushton turbine, a systematic experimental investigation is done on single-phase and solid-liquid two-phase laminar flow with spherical and slender particles respectively. Orientations of slender particles in three-dimensional laminar flow are also determined. The influences of agitation speed, aspect ratio and solid concentration on flow field and orientation are discussed in both laminar and turbulent flow. Flow fields involving with spherical and slender particles are compared with each other. It is found that solid concentration has little influence on flow field in both laminar and turbulent flow. In the range of solid concentration investigated, velocity of two-phase flow is very close to that of single-phase flow. It gives a good indication that the inclusion of dilute solid phase exerts little impact on flow field. The aspect ratio shows also little influence on the flow field. As far as orientation is concerned, the orientation of slender particles changes with the variation of aspect ratio and stirred speed. With the increase of stirred speed, the angle of slender particles with respect to the horizontal plane decreases. The single-phase laminar flow in a baffled tank stirred by standard Rushton turbine is simulated with the improved inner-outer iterative method. Flow number and power number are calculated and compared with the literature. The simulation method is extended to the simulation of solid-liquid two-phase laminar flow with spherical particles. The discrepancy between simulation and data is small and gives good evidence for the reliability of the present numerical method. The effects of impeller location on flow field are discussed. The lower the impeller, the smaller the radial and axial velocities below the impeller. In the simulation of slender particles, the orientation is obtained directly from the rotational motion equation of a rigid particle. The influences of impeller speed, aspect ratio and virtual mass force on flow field and orientation are modeled. Both aspect ratio and virtual mass force have little effect on velocity field, while showing significant effects on orientation. In the region near the impeller, with the increase of radial distance, the influences increase too. By comparison of velocity profiles between spherical and slender particles, small difference between them is discerned. Solid-liquid two-phase turbulent flow involved with slender particles is numerically simulated with two-iluid model and improved inner-outer iterative method. The orientation of slender particles in three dimensional turbulent flow is obtained using the evolution equation of rigid particles instead of the Jeffery equation. In comparison with velocity profiles of spherical particles, it is found that the shape of particles has little influence on flow field in turbulent flow. The effects of agitation speed, aspect ratio and virtual mass force on flow field and orientation are discussed, and compared with their effects in laminar flow field. Both the virtual mass force and aspect ratio have little effects on flow field, but with significant effects on orientation. The effects on orientation vary with radial and axial locations. The effects of aspect ratio and virtual mass force are compared between laminar and turbulent flow fields, and their effects differ in different flow fields. |
| 语种 | 中文 |
| 公开日期 | 2013-09-16 |
| 页码 | 183 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1420]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 范茏. 含纤维状颗粒的液固两相流动的模拟和实验研究[D]. 中国科学院过程工程研究所. 中国科学院过程工程研究所. 2004. |
入库方式： OAI收割
来源：过程工程研究所
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