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DIFFUSIVE SEPARATION OF A GAS MIXTURE APPROACHING A SAMPLING PROBE
CALIFORNIA UNIV BERKELEY INST OF ENGINEERING RESEARCH
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The effect of inserting a probe into a flow field of a flowing gas mixture to obtain localized concentration measurements is considered. The diffusion mechanisms, due to the baro-diffusion and the thermal diffusion effects that cause the concentration variations in the original flow field, cause further changes in the mixture composition during the sampling process. The corrections in the measured composition due to the presence of the probe are calculated for a specific experiment using air as the gas mixture. The corrections are presented as curves for Mach numbers of the approaching stream between 0.1 and 0.4, and Reynolds numbers of the probe between 0.4 and 40. The corrections are based upon the numerical integration of the diffusion equation derived in the ChapmanEnskog Kinetic Theory. The fluid dynamic effects due to the composition change are ignored by using existing pure flow solutions in the flow model. Baro-diffusion is retained as the primary component-separating mechanism in the sampling region. The variation in the composition of the mixture along the stagnation streamline of the approaching flow is found. The total change in composition found here is taken as the correction desired for the probe presence. Author
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