Concentration measurements of jets utilizing Rayleigh scattering

Concentration measurements of CO2 and He jets utilizing Rayleigh scattering are reported. In the experiment, an Ar ion laser (488 nm, 200 mW) was used as a light source and the scattered light intensity was analyzed by a double monochromator and a photon counting system. It is demonstrated that time averaged concentration profiles are determined with sufficient spatial resolution. The concentration profiles obtained are compared with the analytical solutions for velocity profiles by Schlichting and Tollmien. The normalized concentration profile in laminar region shows an excellent fit to the normalized velocity profile by Schlichting. On the other hand, the comparison in turbulent region, however, results in some deviation from both the Schlichting's and Tollmien's profiles, particularly outside the turbulent core region. It was found that the turbulent Schmidt number Sct is 0.6-0.8, showing that, in turbulent region, mass transfer is more diffusive than momentum transfer.