Boundary-layer charged-particle density profiles in an atmospheric pressure plasma flow

The charged-particle density profiles inside the boundary layer formed on a flat plate or a circular cylinder located in an atmospheric-pressure plasma flow were measured with electrostatic probes. Theoretical profiles were obtained through numerical solution of momentum, species, and energy conservation equations taking account of variable transport properties. Comparison of these results leads to the following conclusions: For the flat plate boundary layer, the measured charged-particle density at the bottom of the boundary layer is higher than that calculated for the thermochemical equilibrium condition and is close to the result calculated based on 'frozen' chemistry but the state in other parts of the boundary layer deviates from the 'frozen' chemistry condition. For the cylindrical boundary layer, the measured charged-particle density is near the 'frozen' state in the neighborhood of the stagnation point, but it approaches the thermochemical equilibrium state as the angle from the stagnation point increases. Furthermore, it was found that the state in the cylindrical boundary layer changes abruptly from 'frozen' to 'thermochemical equilibrium' at the angle of 110 deg to 120 deg, which is in the neighborhood of the separation point.