CONDENSATION OF SF6 IN SEEDED SUPERSONIC JETS

Fractional condensation in seeded supersonic free jets of SF6 has been determined at different locations along the jet axis and at different stagnation pressures using a diode laser absorption technique. Rotati onal temperature and relative number densities of SF6 have been determ ined from Q-branch absorption of the nu3 band. The fractional condensa tion increases with increased stagnation pressure as well as with incr eased dilution. The onset pressure for condensation of SF6 in pure SF6 jets is above 2000 torr, whereas in seeded jets, it is much lower (90 0-1200 torr). Calculated dimer mole fractions do not account for the o bserved degree of condensation. Experimentally observed local onset nu mber density can be reasonably correlated with the trimer critical mod el of Fisher.