Transfer of gas-ion momentum and energy to an electrically conductive surface partially coated by a thin dielectric layer

Abstract

Thedynamic interaction of bodies with a rarefied gas flow is characterized to a significant extent by exchange of momentum and energy, or the corresponding accommodation coefficients. The momentum and energy accommodation coefficients are used to determine aerodynamic characteristics and heat exchange of bodies in a rarefied medium and are an important element of the computation relationships no matter what pattern of gas-atom interaction with the surface is chosen. The present study will examine interaction of gas atoms with purely crystalline structures. There are available a significant numberof studies which have performed numerical simulations of atomic particle collisions with a solid surface and offered approximate analytical solutions characterizing the mechanism of gas-atom momentum and energy transfer to ideal crystalline surfaces [i, 2]. In practical targets with an ideal single-crystal structure are rarely found. In the majority of cases the surface flowed over a polycrystalline structure with individual crystallites randomly oriented. In numerical study of collision of atomic particles with an atomically smooth polycrystalline surface it is necessary to average the interaction characteristics, which significantly complicates the problem [3]. The situation becomes even more complicated for technological materials such as alloys with complex structure and surface relief. The literature provides an insufficient volume of data on calculated and experimental values of gas particle accommodation coefficients for the velocity range u~ ~ i0 km/sec which is of practical interest in aerodynamics. Experimental values of the accommodation coefficients are few in number, and refer to varied experimental conditions. Calculations of aerodynamic characteristics and heat exchange of bodies moving in a rarefied medium require knowledge of a complex of parameters characterizing the dynamic interaction of the body with the incident flow. In connection with this it becomes necessary to perform general studies to determine the gas-particle momentum and energy accommodation coefficients on the surface flowed over. The present study will experimentally investigate the effects of a number of factors characterizing interaction of a gas with a surface upon the values of the momentum and energy accommodation coefficients of gas ions with atomic masses from 4 to 131 on the surface of an aluminized polymer film with a conductive face surface coated by a glass screen (dielectric grid with transparency coefficient of %0.12), the outer surface of vacuumscreen thermal insulation [4]. i. The force action of a flow of partially ionized gas of low density on a surface being flowed over having a "floating" potential is determined by bombardment of electrons, ions, rapid and slow neutral particles produced by ion charge exchange with the residual gas, metastable particles, etc.: