Visualization of flow fields and numerical calculation of collection efficiency in low pressure impactor

Flow fields of nitrogen (N2) and argon (Ar) gases in a low pressure impactor are visualized by using a Laser Induced Fluorescence (LIF) technique of iodine molecules under typical MLIS (Molecular Laser Isotope Separation) operating conditions for uranium hexafluoride (UF6). The flow fields with different pressure ratios (downstream pressure/upstream pressure) and nozzle-to-plate distance are examined. It is shown that various shock waves exist in the low pressure impactor. The axisymmetric Euler equation is solved by using the Harten-Yee TVD method. The calculated shapes and locations of shock agree well with experimental data obtained by LIF. The calculated solutions compared with those previously calculated, however, a remarkable difference is observed between these two calculated results. With the aid of calculated flow fields, the collection efficiency is determined by tracking the particle trajectories. The diameter of 50% collection is found to be dependent on the pressure ratios and nozzle-to-plate distance. It is shown that the dependency of diameter of 50% collection on these parameters is different between this study and previously calculated one. (author)