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FLOW VISUALIZATION AND QUANTITATIVE GAS DENSITY MEASUREMENTS IN RAREFIELD GAS FLOWS
AERONAUTICAL SYSTEMS DIV WRIGHT-PATTERSON AFB OH
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The use of an electron beam to stimulate emission from a gas with the resultant beam intensity providing a measure of point-by-point gas density has been investigated. The tests have been conducted in the 1 to 200 micron pressure range, at standard temperature, employing a 5 to 20 kev electron beam. Analysis was performed by photographing the beam at conditions of varying density, and examining the film by means of a microdensitometer. A low-cost electron gun capable of projecting a 20 kev, Soomicroampere beam across a 24-inch test charnber was successfully developed. The results of the program indicate that at the beam voltages employed. scattering of the electrons by the atoms of the gas severely limits the particular technique used. The analytical and experimental results of the program indicate that gas density measurement and flow visualization may be possible by employing a more energetic electron beam. By observation of the beam-excited emission spectra, it is possible to measure the rotational and vibrational temperature of the nitrogen molecules as well as the number density of nitrogen molecules in the gas. Further investigation of this latter electron beam technique as a diagnostic technique in hypervelocity flows is recommended.
APPROVED FOR PUBLIC RELEASE