HEAT TRANSFER THRESHOLD VALUES FOR RESONANT ACOUSTIC VIBRATIONS IN A HORIZONTAL ISOTHERMAL TUBE

Abstract : Data are reported for experiments conducted to study the effects of a resonant acoustic vibration on the heat transfer coefficient for air flowing through an isothermal tube for Reynolds numbers between 16,000 and 200,000. The local heat transfer coefficient varies periodically between the nodes and loops of the resonant sound wave. For Reynolds numbers below approximately 20,000 the maximum local Nusselt numbers occur at the velocity loops of the standing wave. AboveA Reynolds number of 40,000 the maximum values of the Nusselt numbers shift to the velocity nodes. This shift appears to take place gradually between Reynolds numbers of 20,000 and 40,000. Above a Reynolds number of approximately 40,000 resonant acoustic vibrations tend to suppress the over-all heat transfer rate. Threshold sound pressure level values for a resonant frequency of 222 cps were obtained for various Reynolds numbers from 16,000 to 80,000. These critical sound pressure level values fell into two distinct regimes when plotted versus the corresponding Reynolds number. In each regime the critical value was directly proportional to the Reynolds number. (Author)