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RADIATIVELY DRIVEN ACOUSTIC WAVES IN A GAS IN A CYLINDRICAL TUBE - THEORY AND EXPERIMENT AT RESONANCE.
STANFORD UNIV CALIF DEPT OF AERONAUTICS AND ASTRONAUTICS
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Analysis and measurements have been made for the acoustic pressure generated by the absorption of radiation in an infrared-active gas. This is a relatively simple and fundamental problem with coupling between radiative transfer and acoustic motion, and one in which the experiment can be analyzed on the basis of a reasonably complete theory. The gas is contained in a cylindrical wave tube, 10-cm I.D., 75-cm long, closed at one end with an opaque wall and at the other end with a window. Time-modulated 175 to 1100 Hz infrared radiation from an external source enters through the window and is absorbed by the gas, raising its temperature and pressure and generating acoustic waves. The pressure in these waves is measured with a microphone, and the input radiant energy with an infrared radiometer. The present work is confined primarily to the resonant condition in which the radiation is modulated at a natural acoustic frequency of the gas in the tube. The measurements are compared with a theoretical model that predicts the pressure response for a gas in molecular equilibrium. The analysis requires neither the grey-gas assumption, nor the substitute-kernel approximation. Closed-form solutions are developed for a monochromatic pressure response and the spectral integration is then performed numerically. Comparisons have been made for CO2 and CO. Author
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