Resonant acoustic measurements in a half-inch tube, in the neighbourhood of 2000 Hz, were carried out in argon, nitrogen and air when the mean gas pressure was varied from 30 mm Hg up to atmospheric. The variation of the sound pressure levels (SPL) with mean gas pressure can be expressed as SPL=58 lg (p(M/Mair)12/), where p is the mean gas pressure and M is the molecular weight of the gas. The sound field was traversed by a 2 mm damped probe whose attenuation was found to be dependent on the type of gas, the mean gas pressure and the strength of the sound field.
The problem of simultaneous convection and radiation in the laminar boundary layer on a flat plate is formulated and solved. The plate surface is assumed black and the fluid medium is a perfect gas for which the mass absorption coefficient for radiation is considered to be independent of frequency and temperature. The solution is of the iterative type and includes effects of viscous dissipation, secondary emission and absorption, and incident external radiative fluxes. Illustrative examples of temperature profiles and local and average heat transfer rates are presented.
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