Papers by Keyword: Particle Deposition

Abstract: A study for uniform deposition on whole area of wafer was conducted to help check the uniformity of cleaning technology between wafer center to edge. A new method of particle deposition was devised different from the conventional studies using the center nozzle and electric field. Our deposition chamber features wafer rotating method and deposition by the principle of convection and diffusion. In this study, we focused on the effect of wafer rotation speed and rotation number to particle deposition result. After setting the optimum condition, fine results with well deposited shape on whole area of the wafer and outstanding particle size uniformity of more than 70% were obtained. Although particle size shift phenomenon occurred in the measurement result using SP5 due to the intrinsic principle, SEM analysis demonstrated that particles with 60, 80 nm sized silica particles were well deposited on wafer. We believe the standard wafer made by our particle deposition system could be utilized and helpful for performance evaluation and development of wafer cleaning technologies.

Abstract: Cold spray (CS) is a unique spraying process where the spray materials are not melted in a spray gun. Instead, the particles are kinetically deposited on the substrate at low temperature using compressed gas. This study investigates the bonding mechanism of low pressure CS (LPCS) and high pressure CS (HPCS) techniques through smoothed particle hydrodynamics (SPH) simulations, which are achieved by modeling the single and multiple particle impacts of aluminum (Al) particles on Al substrate. The impact of Al particles on the Al substrate is analyzed by evaluating the velocity, shape, temperature of the powder particles and substrate, porosity between particles, and effect of stress on the substrate. In the case of single particle impact, HPCS results in increased particle deformation. In multiple particle impact, LPCS results in low porosity. The shape of deformation, formation of pores, and residual stress of Al can be affected by the deposition process. Results indicate that LPCS is suitable for the deposition of light materials such as Al.

Abstract: The paper presents a numerical algorithm for simulating the trajectories of charged dust particles moving horizontally in the vicinity of an oppositely charged droplet. With taking the air drag, electrical and gravitational into account, the trajectories of charged dust particles are traced by solving the Newton equation. Calculation results show that the dust particles deposit in the whole surface of charged droplet by the effect of electrical force. Electrical force becomes the main factor for dust deposition at low Stokes.

Abstract: In particle deposition problems, colloidal potentials play an important role in adsorpting the colloidal particles onto the surface of the deposit wall once the colloids arrive in the vicinity of the wall. Therefore it is important to gain understanding of these potentials, in particular, how they are influenced by the problem parameters. With such an understanding, more insights into mitigating the problem can be obtained, and consequently, more effective approaches to tackle the problem can be taken. In this work, we present the effects of particle size, flow temperature and ionic strength of the solution on the colloidal potentials based on numerical analysis. The results support the conclusion that the rate of initial deposition of particles can be reduced if the particle size is smaller, the flow temperature is increased, and the ionic strength is reduced.

Abstract: Axial flow compressor is an important component, so the compressor performance is of crucial. Fouling changes blade geometry and blade surface roughness is increased, thus aerodynamic performance is affected. The flow of gas phase and gas-solid coupling phase are implemented to reveal the effect of inlet condition on particle deposition. Based on Euler-Lagrange model, this paper made numerical simulation of gas-solid two phase flow in the axial flow compressor rotor cascade. Simulation result shows that the increase of inlet temperature can result in the reduction of particle volume fraction. And particle mass concentration is affected by particle mass flow rate.

Abstract: The particle motion in fluid has attracted much attention in material engineering concerned the particle effects such as the debris in lubrication and the particles deposition in material processing. By taking the hydrodynamic effect into account, the pressure distribution around particles in fluid in confined wedge space is analyzed. The influences of the particle position, particle shape and its velocity on the pressure distribution are also investigated. Results show that in confined wedge space, the fluid pressure around the particle in the side near the upper slope plate is larger than that in another side, which may make the particle move downwards. And the pressure discrepancy between both sides of the particle increases with the particle shape, the particle velocity and the particle coordinates in both directions of x and z. These special phenomenons may be used in structured surfaces fabrication based on particle deposition by constructing special fluid field.

Abstract: Flue gas entrains a large number of ash particles which are composed of alkali substances into the heat recovery steam generator (HRSG). The deposition of particles on the tube surface of heat transfer can reduce the heat transfer efficiency significantly. In the present work, an Eulerian- Lagrangian model based on Computational Fluid Dynamics (CFD) is implemented to simulation flue gas turbulent flow, heat transfer and the particle transport in the HRSG. Several User-Defined Functions (UDFs) are developed to predict the particle deposition/ rebounding as well as the influence of physical properties and microstructure of deposits on the heat transfer process. The results show that only after one day deposition, the total heat transfer rate reduces 27.68% compared with the case no deposition. Furthermore, the total heat transfer rate reduces to only 238.74kW after 30 days of continuous operation without any slag removal manipulation. Both numerical simulation and field measurement identify that the deposits play an important role in the heat transfer in the HRSG. Especially, when the deposits can’t be removed designedly according to the actual operating conditions, the HRSG experiences a noticeable decline in heat transfer efficiency due to continuous fouling and slagging on the tube surface.

Abstract: This paper investigates numerically the motion and deposition behaviors of micro- or nano-scaled particles in fluid passing three different kinds of square pores. The three kinds of square pores represent different pore structures in porous medium. The flow fields are numerically simulated by lattice Boltzmann method (LBM). The computation procedure code was validated by comparing the results with those of the previous works for the case of particle fluid passing a square block in a two dimensional channel flow. The results show that the dispersion of particles in three different square pore structures are much different, and vary with Stokes numbers for the same square pore even the Reynolds numbers are the same. In addition, the number and the position of deposited particles are analyzed. It shows that the deposition characteristics of each wall are mainly influenced by Stokes number, Reynolds number and the pore structure.