Characterization of a vapor axial deposition (VAD) flame impinging on a disk for a study o felectric field enhanced deposition

Abstract

Methane-oxygen-nitrogen flames produced in a vapor axial deposition (VAD) burner and impinging on a disk were characterized with application to the problem of increasing particle deposition (transport) rate by an electric field applied between the disk (powdered) and an inserted ring (grounded). Two-dimensional temperature and electric potential distributions in flames were measured using a B-type thermocouple and an electrostatic probe, respectively. The temperature measurements demonstrate that the concentric tube burner design is effective because it allows thermophoretic focusing of the particle distribution within the flame, thus leading to higher deposition rates. The potential measurements show that that the electrical boundary layer (Debye sheath) appears adjacent to the powered electrode and grows in thickness as the strength of the applied potential increases. For the experimental conditions studied, the probe data show that the sheath extends outside of the thermal boundary layer at a large applied potential; this is expected to increase the effective capture area for particle deposition, depending on the particle-charging mechanisms associated with the polarity of the applied potential. The probe data imply that even for a sheath of thickness smaller than the themal boundary layer thickness the additional electrophoretic effect superimposed on the thermophoresis effect also increases the particle capture area for deposition. Sample calculations of particle drift velocities were carried out based on the probe results. For an electric field of 1 kV/mm the electrophoretic drift velocity becomes higher than the thermophoretic drift velocity when the number of charge carriers attached to a particle exceeds 4.