The effect of acoustic vibration on forced convective heat transfer

In an effort to study the effect of acoustic vibration on forced convective heat transfer, sound at resonant frequencies of 198, 256, and 322 c./sec., as well as sound at nonresonant frequencies, was imposed on air flowing at Reynolds numbers of 560 to 5,900 in the core of a horizontal, double pipe, steam to air, heat exchanger. Increases in Nusselt number of up to 51% in the nominally laminar region and up to 27% in the nominally turbulent region were obtained. The improvement peaked sharply at resonance and increased with both amplitude and resonant frequency. A qualitative dual mechanism is suggested, and correlations for the experimental results are presented.