Nonequilibrium in high enthalpy carbon dioxide flows

Abstract

A study of high enthalpy nonequilibrium flows of carbon dioxide is presented. Chemical and thermodynamic models are obtained for nozzle and model flows. A numerical survey of high enthalpy carbon dioxide nozzle expansions shows that the assumption of vibrational equilibrium is a good one, and that ionization is energetically insignificant up to a reservoir specific enthalpy of 3.3 x 10¹¹ cm² s⁻². It also shows that the reservoir entropy correlation observed to hold for air by Warren and Harris (1964) applies to carbon dioxide expansions. A numerical survey of wedge flows shows that over a large range of conditions vibrational relaxation of C0₂ and CO is slow enough to be an important nonequilibrium process in flows or laboratory scale. The effect of translational nonequilibrium between the electrons and heavy particles is significant in blunt body flows at high enthalpies. Experimentally, the importance of various nonequilibrium processes is examined under different flow situations. The measurements of nozzle flow variables show good agreement with predictions. Single wavelength interferometry is used to observe the complete flow fields of wedges and blunt bodies. The channelled spectra technique is used to measure the electron and heavy particle densities in the shock layer of a blunt body. Estimates of electron densities are consistent with predictions. The hook method is used to estimate the impurity levels. It is shown that these impurities have a negligible effect on the electron densities measured. The dissociation rate of undiluted carbon dioxide is measured in the temperature range 2500-7000 K and compared with those by other workers. An activation energy of 104 Kcal/mole from these measurements is in agreement with some recently reported measurements. Studies of normal shock waves in the velocity range 3 to 17.3 Km/s show that above a velocity of 11 Km/s, the thermodynamic model of carbon dioxide used in equilibrium calculations is inadequate and that above 13 Km/s, significant radiation losses can be expected. Instabilities are observed in the shock heated gas slug behind a normal shock wave, for various shock tube and driver conditions, and an empirical stability correlation is obtained from these conditions. Show more