Velocity measurement of sub-millimeter-scale gas flow by spark tracing method

A molecular tagging technique using the spark tracing method has been applied to measure velocity distributions in sub-millimeter-scale gas flows, which were formed as air jet flows through a sub-millimeter channel. Spark lines were generated by applying a high voltage, based on the air ionization via the discharge phenomena. The velocities using displacements of spark lines were smaller from 10% to 30% than those using the theoretical equation in a rectangular channel. In order to identify the cause of measurement errors, the relationship between the ionized air regions and the gas flow velocities was investigated by the numerical simulation. The simulation reveals that an actual spark line goes through a pathway with a minimum electric resistance, and the velocities from the theoretical equation are agreed with the velocities when the spark line width is limited to zero. The results suggest us to propose the new correction technique which estimates velocity distributions by varying the spark line widths. The velocities from the experiments with the correction were agreed well with those from the theoretical equation. Furthermore, the spark tracing method with the correction technique was applied to a mixing air flow through two channels, and the effect of the gas temperature on the velocity detection was examined.