Attenuation of Infrared Radiation Emitted from Hot Surface by Transpiration of an Absorbing Gas
Final rept. 3 Sep 1968-31 Aug 1970
PURDUE UNIV LAFAYETTE IN HEAT TRANSFERLAB
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Analyses and measurements of attenuation of thermal radiation leaving a heated plate caused by a layer of absorbing gas are discussed. Both a near stagnant fluid and flow over a flat plate were investigated by analysis and experiment. An apparatus in which various porous plates were heated electrically was designed and constructed so that it could be adopted to either the stagnant or flow systems. Radiant energy fluxes in specified wavelength bands leaving the plate were measured with an infrared radiometer developed and built for this purpose. Specifically, radiometric measurements for the 4.3 micron band of carbon dioxide were made for various plate surface temperatures, injection rates, thicknesses of the absorbing gas layer and viewing angles. In addition to the above parameters the Reynolds number was varied and the effect of the starting length investigated for flow over a flat plate. It was found that the gas is capable of attenuating a significant fraction of the radiation leaving the hot plate. Increases in the plate temperature and gas layer thickness increased the attenuation. For a given mass injection rate of an absorbing gas the attenuation increased with an increase with the Reynolds number. The analyses and experiments show that in order to obtain significant attenuation over large spectral regions a mixture of selected gases or gas-particulate mixtures would have to be injected.