Theory of stagnation-point heat transfer in a partially ionized diatomic gas

Abstract

Abstract : Stagnation-point heat transfer in a partially ionized diatomic gas is considered. The concept of frozen thermal conductivity is used, and a simplified binary diffusion model of the gas is proposed. In this model the charge-exchange cross-section for atom-ion collisions is taken to be infinite so there is no relative diffusion of the atoms and the ion-electron pairs. This permits the diffusion effects to be dealt with as if there were only two components, molecules and atom-ion-electron particles, and thus greatly simplifies the calculations. However, the thermodynamic and transport properties are evaluated using all four components, molecules, atoms, ions, and electrons. With this model, calculations are made for both frozen and equilibrium boundary layers in nitrogen up to about 60,000 ft/sec, and arguments are presented for applying the results to air. The results show the equilibrium heat transfer rate to be progressively smaller than the frozen rate as the velocity increases above 30,000 ft/sec, the ratio reaching 2/3 at 50,000 ft/sec. Simple correlation formulas for the results are given.