Statistical Lagrangian particle tracking approach to investigate the effect of thermophoresis on particle deposition onto a face-up flat surface in a parallel airflow

Thermophoresis can affect the particulate contamination of wafers and photomasks. Thermophoretic effect on particle deposition velocity in the cleanroom environment has been intensively investigated for the free-standing wafer situated perpendicular to the top-down airflow, but it has been examined by few studies for the wafers or photomasks in the parallel airflow. In this study, the particle deposition velocity onto a face-up flat surface under the influence of thermophoresis was numerically investigated, when the face-up flat surface was exposed to the parallel airflow. Statistical Lagrangian Particle Tracking (SLPT) model with the aid of commercial codes, i.e. FLUENT and DPM, was employed. The SLPT model was validated by comparing the numerically obtained particle deposition velocities with the theoretically predicted data, with and without considering the thermophoresis, and found to produce correct results. The effects of temperature difference (between the face-up flat surface and the ambient air), parallel airflow velocity, and particle density on the particle deposition velocity onto the face-up flat surface in the parallel airflow were investigated using the SLPT model, when the temperature of the face-up flat surface was either higher or lower than the ambient temperature.