基于超声技术的沉浸式换热器强化传热研究

Aiming at the problem of heat transfer enhancement outside the tube of immersed coil heat exchangers, the ultrasound is imposed into the heat exchanger by means of vibration surface, and the influence of ultrasonic field on the flow pattern, cavitation phenomenon and heat transfer enhancement outside the tube of immersed coil heat exchanger is studied. The cavitation and ultrasound propagation phenomenon are generated by ultrasonic technology. The cavitation phenomenon induces liquid-vapor phase transition near the vibration surface, while the expansion of tiny bubbles occurs away from the vibration surface. The average vapor volume fraction of the heat exchanger without the ultrasound is 0.01302, which increases to 0.01359 with the ultrasound. The ultrasound propagation makes the flow velocity of the fluid outside the tube have the same pulsating change characteristics as that of the ultrasonic wave, by which the fluid flows towards both sides of the heat exchanger with high-low velocity interval distribution. The fluid has the lowest velocity near 0, and the highest velocity of 4.93 m·s^-1, the average velocity of the whole heat exchanger increases from 0.0248 to 0.102 m·s^-1 under the significant influence of the ultrasound. Under the dual effects of cavitation and acoustic flow, the average value of turbulent kinetic energy on the outer surface of the heat exchange tube increased from 2.090×10^-4 to 0.01847 m²·s^-2, indicating that the fluid on the outer surface of the heat exchange tube was disturbed and enhanced, the convective heat transfer coefficient of the outer surface of the heat exchange tube increased from 1634.533 to 2031.069 W·m^-2·K^-1, and the heat transfer enhancement ratio reached 24.26%. This research is of great significance to the application of ultrasonic technology in immersed coil heat exchanger.