Study on the coupling mechanism of acoustic streaming and temperature outside an elliptical heat exchanger tube

The coupling model of acoustic waves, velocity, and temperature fields is applied to the global computation of thermoacoustic streaming outside the elliptical tube. The traveling wave field constructed by single-sided velocity excitation more closely resembles the actual working conditions of elliptical heat exchanger tubes in the boiler, making the conclusions more practically relevant. A multi-parameter analysis based on angle of attack (AOA), pulsating Reynolds number (Re0), and pulsating Strouhal number (St0) has deeply revealed the coupling mechanism between the external acoustic streaming and temperature. The introduction of the relative Nusselt number (NU) and the relative shear rate (SH) quantifies the effects of acoustic streaming on enhancing heat transfer and removing ash deposits. The acoustic streaming structure is primarily determined by frequency f. At low frequencies, as AOA increases, the inner and outer vortices sequentially undergo separation, merger, and then re-separation, while at high frequencies, the inner vortices gradually become invisible, and the temperature contour lines exhibit significant shifts along with the outer vortices. The magnitude of this shift is positively correlated with the acoustic streaming intensity. The maximum acoustic streaming velocity u2max* and the maximum temperature Tmax* exhibit an inverse correlation. In both the radial and circumferential directions, temperature is not sensitive to velocity fluctuations. Through Nusselt number analysis, flexible control of acoustic parameters can effectively improve local heat transfer. Additionally, inner vortices i = 1, 2 exhibit extremum values of SH around the circumferential angle α = 35°, providing important guidance for selecting the optimal AOA.