10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
The Experimental Research on the Effect of Humidity on Fly-ash Collision Behaviour with Planar Surface
XUE LI, Ming Dong, Sufen Li, Dalian University of Technology
Abstract Number: 606 Working Group: Combustion-Generated Aerosols: the Desirable and Undesirable
Abstract Particle dynamic processes are widely used in various industries, such as electrostatics precipitators (ESPs), fluidized beds, chemical and food. Especially agglomeration processes, particles interact with each other, deposition in low temperature ESPs. The discrete element modelling (DEM) is becoming a more commonly used tool for simulating dynamic processes involving solid particles. DEM traces the movement of all particles in a system and can provide particle-level information, which is often difficult to achieve by experiments. One of the required input parameters for DEM simulations is the coefficient of restitution, which can describe the energy losses during particle collisions and is important for proper modelling of particle dynamics.
In this present paper, a detailed research of particle-wall collision mechanics is proposed to determine the normal coefficient of restitution by using high-speed camera in different humidity conditions. Experiments were performed to measure the incident and rebound velocities of different kind of fly ash particles driven by gas flow onto a flat surface. The experimental system is designed for an aerosol inlet particle velocity range of 1 – 7 m/s. The coal used are bituminous coal from Fushun, Liaoning Province (LN), meager coal from Zhundong, Xinjiang Province (XJ), and anthracite coal from XinlinGol, Neimeng Province (NM) which are turned into fly-ash particles with a diameter of approximately 7 μm by using muffle furnace. The determination of the coefficient of restitution for single component particles is relatively straightforward process, however, when considering multicomponent particles like fly-ash and humidity environment, the unpredictable property of particles after impact makes the analysis of the coefficient of restitution more involved. In addition, a dynamic model is developed to calculate the damping coefficient, contact time, critical impact velocity, and contact displacement under both dry and humid conditions during impact. The modified Stokes number and elasticity parameter are proposed to further explore the relationship between the normal restitution coefficients under dry and humidity conditions. The main results can be summarized as follows.
Firstly, the results show that the normal coefficient of restitution decrease with increasing density, Young's modulus, and humid condition. The particles with humidity 65% seems much easier to be captured than other cases. These results demonstrate that the process of capture of micro-particle is more likely to happen for higher humidity.
Secondly, based on the dynamic model calculation, the damping coefficient and contact time are obtained with different impact velocities in a collision. The values of the damping coefficient and contact time are larger under humid conditions due to the effect of capillary force. The critical capture velocity increases with increasing humidity, because viscous damping by humidity increases.
Finally, the maximum contact displacement increases with normal incident velocity, and decreases with the humidity. The total force is a monotropic function of the contact displacement for the same kind of particle that is increasing with the contact displacement.
Keywords: Normal coefficient of restitution; Fly-ash; Humidity; Critical capture velocity