Investigations of the effect of acoustic vibrations on convective heat transfer

Abstract : The experimental and analytical results obtained for the heat transfer coefficients in an isothermal tube which had an unheated starting length are presented. Data on heat transfer coefficients for Reynolds numbers from approximately 10,000 to 65,000 are presented for conditions of no-sound (without resonant acoustic vibrations) and for conditions of a resonant frequency in the tube of approximately 90 cps. For turbulent flow the effect of the resonant sound field is to reduce the heat transfer coefficients. A half-wave length periodic effect on the local heat transfer coefficient was noted. The local values of the turbulent heat transfer coefficients are correlated in relation to the no-sound values as a function of U sq/Vc, where U is the maximum sound particle velocity, V is the mean through flow velocity and c is the speed of sound. The parameter U sq/Vc was determined to have a theoretical basis from the solution of the energy equation for the laminar flow situation with sound. The analytical solution for the local heat transfer coefficient for laminar flow in a channel is given and compared to the results obtained in the heat transfer tube. A preliminary determination of velocity profiles by means of a hot wire anemometer for both no-sound and sound conditions, indicated that the sound tends to alter the profile. (Author)