Study On Flow Behavior, Mixing Mechanism And Enhancing Means Of Mini Opposed Jets Reactors

Impinging jets is one of technologies for enhancing mixing performance, which has been applied successfully for increasing industrial processes, e.g. gasification, polymer injection molding, cell disruption. Understanding the flow regimes and mixing mechanism of opposed jets is crucial for the development, design and operation of impinging jets reactors.Based on opposed jets reactors, the flow behavior and mixing mechanism in a mini confined impinging jets reactor have been studied by using a Particle Image Velocimetry, Planar Laser Induced Fluorescence, High Speed Camera, Hot-Wire Anemometer and image processing method, and the influence of excitation on the flow and mixing was investigated. The main contents are as follows:1. Dynamic behaviors in the confined impinging jets reactor were experimentally studied by a flow visualization technique at 100≤Re≤2000. Results show that with the increase of the Reynolds number, a segregated flow regime, a radial deflective oscillation, an axial oscillation and a vortex shedding regime emerge in turns in the confined impinging jets reactor. The transition of the flow regime between the radial deflective oscillation and the axial oscillation is Re≈300. The onset and the evolution of the natural instability of the jets and the impinging instability in the impingement region are the origins of the radial deflective oscillation, while it is self-sustained by the interaction between the impingement plane and the confined chamber wall in the reactor. And the onset of the natural instability and the confined chamber wall are the main reasons for the cause of the axial oscillation.2. The influence of the excitation on the oscillation characteristic of the impinging plane was studied by a flow visualization technique. Results show that the periodic oscillation of the impinging plane is induced by the excitation, whose oscillation frequency is equal to the excitation frequency, and the amplitude of the impinging plane decreases with the increase of the excitation frequency. The excitation can induce different scales of vortices in the impinging plane at Re≤100, and the scale of the vortex decreases with the increase of the excitation frequency.3. The influence of the excitation on the mixing performance of the fluids in the confined impinging jets reactor was investigated by the mean of Planar Laser Induced Fluorescence. Results show that the mixing effect of two fluids is significantly improved when flow transitions from the segregated steady flow to the radial deflective oscillation in the confined impinging jets reactor. The excitation affects the mixing process in the confined impinging jets reactor, and the mixing performance under excitation is enhanced in the case of the segregated flow regime. However, the excitation has no significant influence on the mixing performance for the flow with the oscillation regime.