Suppression of Particle Deposition to Surfaces by the Thermophoretic Force

Product contamination by particles is of major concern in the electronics industry. It has become increasingly important because of the decreasing size of the product elements. In a study of the feasibility of using the thermophoretic effect to reduce particle contamination of surfaces, a simple asymptotic formula has been derived for the thickness of the dust-free space in the boundary layer over a flat plate with a flow normal to the surface. This simple formula compares well with the results of a numerical solution. For a temperature difference between the surface and the surrounding gas of 10–30° K and face velocities between 0.3 and 1.0 m/s, the thickness of the dust-free space is between 0.1 and 0.4 mm, much larger than the particle size (0.1 μm ≥ Dp < 0.5 μm). The results indicate that, under conditions representative of clean-room applications, thermophoresis can be effective in protecting surfaces against particle deposition.