Visualization of Influence of Preferential Diffusion in Jets

Abstract

Preferential diffusion in nonreacting jets was visualized by a Rayleigh scattering method. The jets initially consist of a mixture of CO₂ and He with volume fractions 39.9 and 60.1, the effective Rayleigh scattering cross-section of which is the same as that of air. A pulsed Nd : YAG laser and a CCD camera were used as a light source and a detector to measure Rayleigh scattering images instantaneously. The Rayleigh scattering images show that the scattering intensity is different from that of the surrounding air at the boundary of the laminar jets, which implies that preferential diffusion occurs in the jet. The high CO₂ region tends to increase when a laminar jet has a convex curve with respect to the surrounding air. On the other hand, the region tends to decrease when the jet has a concave curve with respect to the surrounding air. For a turbulent jet (Re=4000), there is also an intensity difference in the images compared to that of the surrounding air, which implies that preferential diffusion occurs in turbulent jets.