Investigation On The Particle Motion And Distribution Characteristics In Rotational Flow Field

Liquid(gas)-solid two-phase flow has been widely existed in the electric power, chemical industry, pharmaceutical, food and other traditional areas as well as emerging industrial fields such as biology and material. The particle motion in rotational flow field is an important subject in the research of liquid(gas)-solid two phase flow. In the real process, due to the complex fluid-particle and particle-particle interactions, the particle motion in rotational flow field usually shows the complexity and polytrope. Until now, the physical mechanism and inherent law of the particle motion in rotational flow field is still less understood. In this context, the theory and experimental researches on particle motion and distribution behaviors in rotational flow field not only has the important scientific significance in exploring mechanism of interaction between particles and liquid (gas) and among particles, but also has important engineering application for the guidance of design and optimization of granular flow.At present, the quantitative experimental research on particle motion in flow field still have the disadvantages of the great difficulties and high expense, so the numerical simulation has gradually become an important method to study the particle motion in flow field. Until now, the particle collison, motion and distribution in rotational flow field resulting from excitation of two equal coaxial impinging jets are not completely known. In addition, the particle motion and distribution behaviors in rotational flow field with gas-liquid two-phase coexistence and in self-excited rotational flow field inside twisted duct flow are still waiting to be explored. Therefore, the thesis introduces the Direct Simulation Monte Carlo (DSMC) method to characterize the inter-particle collisions in dense particle flow inside rotational flow field resulting from excitation of two equal coaxial impinging jets. Taking into consideration of particle collision and rotation, a theoretical model of dense particle flow in rotational flow field resulting from excitation of two equal coaxial impinging jets is developed and numerically analyzed to investigate the particle motion and distribution in rotational flow field. Visualization observation on particle motion and collision behaviors in rotational flow field resulting from excitation of two equal coaxial impinging jets inside the cylinder was performed. Based on VOF(Volume of Fluid) and DEM (Discrete Element Method)method, a theoretical model of particle flow in a partially filled rotating cylindrical tank is established and numerically analyzed to investigate the particle motion, dispersion and collision. The process of particle motion, flow mode and distribution characteristics in a partially filled rotating cylindrical tank is visualized by experimental method. CFD-DEM method is used to numerically simulate particle movement and distribution characteristics in rotational flow field within twisted duct with square cross section. The main contents and conclusions are as follows:1. With consideration of particle collision and rotation, DSMC method is used to study particle behaviors in rotational flow field resulting from excitation of two equal coaxial impinging jets inside the cylinder. The effects of the inlet gas velocity and particle rotation on particle behaviors in rotational flow field are examined and analyzed. In addition, the particles behaviors in rotational flow field are visually observed by the experiment. The results indicate that the particle collision, permeation and rotation motion are existed in rotational flow field inside the cylinder resulting from excitation of two equal coaxial impinging jets. The particle collision could make particles directly leave collision area and also could make the back and forth movement in collision area. Increases in inlet gas velocity strengthen the particle dispersion from collision area to other zones. Particle rotation prompts the particle more quickly departure from collision area, which leads to a smaller particle concentration in the centre of collision area.2. The visualization experiment is conducted to study the motion and distribution characteristics of particle in a partially filled rotating cylindrical tank. The effects of liquid height and rotational velocity on particle distribution in liquid is examined and analyzed. The results indicate that three modes of transverse particle motion are observed in a partially filled rotating cylindrical tank, including the slipping, slumping, attracting. The mode of particle centrifuging motion is shown as cylindrical tank is completely filled with liquid. A vortex forms in liquid flow field within a rotating cylindrical tank. Almost no particle movement to the region where the container rotates into liquid phase as rotational speed is lower. When the rotational speed increases to a certain value, the particle movement to the region where the container rotates into liquid phase. And the particle number increases with increasing of rotational speed. If the liquid height is relatively low, the particle mainly accumulated at the region where the container rotates out the liquid phase. For a higher liquid height, the particle motion in the region where the container rotates out liquid phase, and the distribution of the particles tends to be scattered. With further increase of liquid height, the scope of particle distribution extends the region where the container rotates into liquid phase, and the annular distribution of particles appears.3. The VOF-DEM method is used to study motion and distribution characteristics of particle swarm in a partially filled rotating cylindrical tank. The effects of particle-density-to-liquid-density ratio, liquid viscosity, liquid height and rotational speed of the tank on particle behavior characteristics in liquid are analyzed. The results indicate that the vortex formation occurs in liquid flow field within a rotating container. The particle swarms move following the vortex and gradually disperse into the whole region of the liquid phase. The increase in liquid viscosity could improve dispersion performance of particle swarms in the liquid phase. The increase in particle density suppressed the driving force for particle dispersion and hence leaded to a decline in dispersion performance of particle swarms in the liquid phase. With lower and higher liquid height in rotating cylindrical tank, the particles accumulated at the region where the container rotates out liquid phase or gas-liquid interfacial area and contact region between liquid phase and wall. The particles accumulated at the region where the container rotates out liquid phase as the angular velocity of cylinder rotation is small. The partially particles could move to the region where the container rotates into liquid phase as the angular velocity of cylinder rotation increased, and particle dispersion performance could be certainly improved.4. The Euler-Lagrange method is applied to study particle motion and solid-liquid flow within twisted duct with square cross-section. The effects of geometric construction, inlet liquid velocity and particle density on solid-liquid flow, particle motion and particle distribution in twisted ducts are examined and analyzed. The results indicate that there exist a appreciable global clockwise swirling flow at cross section of twisted duct, of which the secondary flows in the four corners constitute the major part. The most particles have spiral motion in twisted duct. Comparing with straight duct, the swirling flow induced by twisted duct improves the consistency of the particle velocity. With smaller inlet liquid velocity and twist ratio, the inlet liquid velocity has less influence on the particle dispersion, while the inlet liquid velocity have significant influence on particle dispersion for larger inlet liquid velocity and twist ratio. The role of particle density on particle dispersion is tiny in tube with smaller twist ratio while the particle density plays a significant role in particle dispersion in a tube larger twist ratio.