Shock tube determination of the heat conductivity of non-ionized and partially ionized argon

A procedure to determine the heat conductivity of a monatomic gas, from measurements of the structure of the unsteady thermal boundary layer at the end-wall of a shock tube, is proposed. In the non-ionized case the structure of the boundary layer determined by means of laser schlieren measurements appears to be self-similar. Improved analysis of the schlieren data and accurate pressure measurements yielded conductivity data with an accuracy of 4% for temperatures up to 7000 K. In the ionized case a model for the development of the thermal boundary layer was proposed to consider the processes of ionization and thermal relaxation. Data on electron and atom density profiles from laser schlieren measurements agree within 10% with theory for a moderate degree of ionization (3%). Quantitative information on radiative cooling was obtained from absorption and pressure measurements outside the boundary layer. Experimental information on the influence of ionization relaxation on the structure of the boundary layer and data on the ionization rate of hydrogen by collisions with argon atoms is also presented.