THE EFFECTS OF RESONANT ACOUSTIC VIBRATIONS ON HEAT TRANSFER TO AIR IN HORIZONTAL TUBES

摘要

Results are presented of a series of experiments conducted for the purpose of studying the effects of acoustic vibrations on convection heat transfer in horizontal tubes. The experimental apparatus was calibrated without sound to determine the relationships between local average Nusselt numbers and Graetz numbers in the test section with no sound influences. The results of the calibration tests were reproducible within +5$ and were correlated within a range of Graetz numbers from 60 to 1300 by an analytical equation. Experimental tests were then conducted using sound levels up to 151 decibels in the test section. Experimental evidence is given that a threshold sound pressure level exists below which little or no effect is produced. Above this value, signif?icant increases of up to 75% in the local average Nusselt numbers are produced. This threshold sound pressure level value is approximately l4l decibels. Experimental sound studies were conducted at frequencies of 217 cps, 325 cps, and 500 cps, and at sound pressure levels between 140 db and 151 db, for each frequency. The complexity of the phenomena has prevented either a qualitative analysis or an analytical expression for the acoustic effects on heat transfer with the present data. Further studies producing 'considerably more data are necessary before the analytical phase of this investigation can be accomplished.