SCATTERING OF THERMAL ENERGY GAS BEAMS BY METALLIC SURFACES.
UNITED AIRCRAFT CORP EAST HARTFORD CONN RESEARCH LABS
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Modulated molecular beam techniques have been employed to measure the spatial distribution of rare gases and atmospheric gases scattered from surfaces of polycrystalline platinum, tantalum, nickel and tungsten. In some cases, molecular velocity changes which occured during collisions between the beam and surface were determined through observations of shifts in the phase of the detector signals. Diffuse scattering of the gases was observed from contaminates surfaces. Collision induced molecular velocity changes of rare gases scattered from platinum were determined and used to calculate energy accommodation coefficients the results were correlated with changes in scattering distributions. Accommodation coefficients for helium and neon obtained with a clean platinum surface agree with literature values for clean metallic surfaces as determined by a hot filament technique. Calculations were made of the influence of diffuse and lobular scattering on the lift and drag coefficients of flat plates in free-molecular flow. For more dense flows, the dependence of the extent of the slip flow region on the tangential momentum accomodation coefficient was evaluated. Author