• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.22 no.1
• /
• pp.61-69
• /
• 1998

Vapor Axial Deposition (VAD), one of optical fiber preform fabrication processes, is performed by deposition of submicron-size silica particles that are synthesized by combustion of raw chemical materials. In this study, flow field is assumed to be a forced uniform flow perpendicularly impinging on a rotating disk. Similarity solutions obtained in our previous study are utilized to solve the particle transport equation. The particles are approximated to be in a polydisperse state that satisfies a lognormal size distribution. A moment model is used in order to predict distributions of particle number density and size simultaneously. Deposition of the particles on the disk is examined considering convection, Brownian diffusion, thermophoresis, and coagulation with variations of the forced flow velocity and the disk rotating velocity. The deposition rate and the efficiency directly increase as the flow velocity increases, resulting from that the increase of the forced flow velocity causes thinner thermal and diffusion boundary layer thicknesses and thus causes the increase of thermophoretic drift and Brownian diffusion of the particles toward the disk. However, the increase of the disk rotating speed does not result in the direct increase of the deposition rate and the deposition efficiency. Slower flow velocity causes extension of the time scale for coagulation and thus yields larger mean particle size and its geometric standard deviation at the deposition surface. In the case of coagulation starting farther from the deposition surface, coagulation effects increases, resulting in the increase of the particle size and the decrease of the deposition rate at the surface.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.11
• /
• pp.3063-3071
• /
• 1995

An experimental study has been carried out for the heat transfer and particle deposition during the Outside Vapor Deposition process. The surface temperatures of deposited layers, and the rates, efficiencies and porosities of particle deposition were measured. It is shown that the axial variation of the surface temperature can be assumed to be quasi-steady and that as the traversing speed of burner is increased, the deposition rate, efficiency and porosity increase due to the decreased surface temperature. As the flow rate of the chemicals is increased, both the thickness of deposition layers and the surface temperature increase. Deposition rate also increases, however, deposition efficiency decreases for tests done. Later passes in early deposition stage result in higher surface temperatures due to increased thickness of porous deposited layers, which cause the deposition rate, efficiency, and porosity to decrease.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.11
• /
• pp.3057-3065
• /
• 1994

An experimental study has been made for heat transfer and particle deposition during the Modified Chemical Vapor Deposition process which is currently utilized to manufacture high quality optical waveguides. The distributions of tube wall temperatures, rates and efficiencies of particle deposition were measured. Results indicate that the temperature distributions of the tube wall in the axial direction yield the quasi-steady form in which temperature distributions fit in one curve if the relative distance from the moving torch is used as an axial coordinate. Due to the repeated heatings from the traversing torch, the wall temperatures are shown to reach the minimum ahead of torch and it is shown that the two torch formulation suggested by Park and Choi is valid to predict this minimum temperature. Measured wall temperatures, particle deposition efficiencies and tapered entry length are compared with the previous modelling results and shown to be in agreement.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.1
• /
• pp.193-202
• /
• 1994

A study of heat transfer and particle deposition has been made numerically for outside vapor deposition process. Heat conduction through the two layer cylinder which consists of the target and the deposited layer is included together with heat transfer and gas jet flow onto the cylinder from the torch. Temperature and flow fields have been obtained by an iterative method and thermophoretic particle deposition has been studied. Of particlar interests are effects of the thickness of the deposited layer, the torch speed and the rotation speed of the cylinder on particle deposition flux and efficiency. Effects of buoyancy, variable properties and tube rotation are included.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.4
• /
• pp.239-248
• /
• 2017

It is important to understand the dispersion and deposition characteristics of particles in the flow around a circular cylinder. The rotation of a cylinder is considered as a means to modify the particle deposition in this study. We numerically investigate the effects of the rotational speed of a cylinder and the particle Stokes number on particle dispersion and deposition as well as flow characteristics. Results show that the deposition efficiency of small particles (with the Stokes number smaller than 4) decreases significantly as the rotational speed increases. However, when the Stokes number is larger than 4, the deposition efficiency increases slightly with the rotational speed of the cylinder. Meanwhile, for a given rotational speed, the increase in the Stokes number leads to an increase in deposition efficiency and deposited area.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.2
• /
• pp.641-648
• /
• 1996

Thermophoretic particle deposition on a circular cylinder in a uniform laminar air flow was numerically investigated using a control volume method based on the generalized non-orthogonal coordinate system. Variation of air properties due to the change of temperature was taken into account. Effects of variable property on the distribution of heat transfer and deposition rates of particle were discussed. A new correlation of thermophoretic particle deposition on a circular cylinder was proposed in the present study.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.5
• /
• pp.424-432
• /
• 2002

Numerical analysis has been conducted to characterize deposition rates of aerosol particles onto a heated, rotating disk with electrostatic effect under the laminar flow field. The particle transport mechanisms considered were convection, Brownian diffusion, gravitational settling, thermophoresis and electrophoresis. The aerosol particles were assumed to have a Boltzmann charge distribution. The electric potential distribution needed to calculate local electric fields around the disk was calculated from the Laplace equation. The Coulomb, the image, the dielectrophoretic and the dipole-dipole forces acting on a charged particle near the conducting rotating disk were included in the analysis. The averaged particle deposition vetocities and their radial distributions on the upper surface of the disk were calculated from the particle concentration equation in a Eulerian frame of reference, along with a rotation speed of 0∼1,000rpm, a temperature difference of 0∼5K and a charged disk voltage of 0∼1000V.Finally, an approximate deposition velocity model for the rotating disk was suggested. The present numerical results showed relatively good agreement with the results of the present approximate model and the available experimental data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.5 no.2
• /
• pp.130-140
• /
• 1993

Average particle deposition velocity toward a horizontal semiconductor wafer in vertical airflow is measured by a wafer surface scanner(PMS SAS-3600). Use of wafer surface scanner requires very short exposure time normally ranging from 10 to 30 minutes, and hence makes repetition of experiment much easier. Polystyrene latex (PSL) spheres of diameter between 0.2 and $1.0{\mu}m$ are used. The present range of particle sizes is very important in controlling particle deposition on a wafer surface in industrial applications. For the present experiment, convection, diffusion, and sedimentation comprise important agents for deposition mechanisms. To investigate confidence interval of experimental data, mean and standard deviation of average deposition velocities are obtained from more than ten data set for each PSL sphere size. It is found that the distribution of mean of average deposition velocities from the measurement agrees well with the predictions of Liu and Ahn(1987) and Emi et al.(1989).

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.5
• /
• pp.1624-1638
• /
• 1996

A study of thermophoretic particle deposition has been carried out for a particle laden stagnation flow considering the effect of radiative heat transfer. Energy, concentration and radiative transfer equations are all coupled and have been solved iteratively assuming that absorption and scattering coefficients were proportional to the local concentration of particles. Radiative heat transfer was shown to strongly affect the profiles of temperature and particle concentration. e. g., radiation increases the thickness of thermal boundary layer and wall temperature gradients significantly. As the wall temperature gradients increase, the particle concentration at the wall decreases due to thermophoretic particle transport. The deposition rate that is thermophoretic velocity times particle concentration at the wall decreases as the effects of radiation increases. The effects of optical thickness, conduction to radiation parameter and wall emissivity have been determined. The effects of anisotropic scattering are shown as insignificant.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.10a
• /
• pp.571-572
• /
• 2012