Rotational Relaxation in Nitrogen Freejets in the Transition Regime

Abstract

The aim of the present paper is the experimental study of rotational-translational relaxation in a nitrogen freejet and the definition of a region where relaxation but not condensation is important. Studies were performed in a low-density wind tunnel using electron and molecular beam diagnostics. At low local gas temperatures «80 K)> rotational population kinetics are complicated by condensation. Also, under some flow conditions, the Maxwell-Boltzmann distribution of molecular velocities is distorted. Data on perpendicular and parallel temperatures are measured in this case. Then, data are generalized in the coordinates suggested by G. A. Bird. Rotational population temperatures (TK) are also measured,and generalized using Bird's parameter Pg m u l t i p l i e d by a function of the rotational quantum number k. The obtained empirical generalization permits estimation of the distribution of rotational level populations in the region ranging from continuum to near free-molecular flows.