Mixing Process of Two Different Gases by a Pulsed Jet with a Periodic Reverse Flow (A Case Issued Carbon Dioxide Gas into Still Air)

Abstract

A strongly pulsed jet is considered as a method for rapid mixing of two different gases. Carbon dioxide gas with a pulsation was discharged from a convergent and round nozzle into still air. An oscillatory and reversed flow at the nozzle exit was produced by the pulsation with high intensity. The spatial and temporal variations of concentration and velocity were measured in the mixing region of the pulsed jet. The mixing rate of the gases is dramatically enhanced near the nozzle exit. Neither the mean concentration nor the mean velocity monotonically decays in the stream-wise direction, because the ambient air is drawn inside the nozzle periodically by the reversed flow. The direction of the velocity changes periodically at a certain boundary, which is the position where the mean concentration becomes the minimal value. When the mixing gas is aspirated inside the nozzle, the fluid lump of any concentration is separated to two fluid lumps because of the direction change in the velocity. The issuing mean velocity becomes larger than the velocity determined by flow rate of supplied carbon dioxide gas. The axial distribution of the mean velocity increases near the nozzle exit. There is also a phase difference between the concentration and velocity oscillations.