The Theory And Numerical Simulation Study Of Ultrasonic Enhanced Heat Transfer Tube With Staggered Rows

Owing to the development of heat transfer enhancement technology,ultrasonic enhanced heat transfer technology has attracted widespread attention as a new type of heat transfer technology.In this study,a series of numerical simulation and theoretical analysis have been employed to research the ultrasonic heat transfer enhancement mechanism and heat transfer effect.The main conclusions of this paper are as follows:(1)In terms of theoretical analysis,we have carefully considered the main dominating factors of ultrasonic enhanced heat transfer,which combined the Cavitation Effect and Vibration Effect.Furthermore,two factors that influence the cavitation effect are analyzed: sound intensity and frequency.Then,according to the ultrasonic “cavitation chain reaction”,we analyzed the ultrasonic enhanced heat transfer: Ultrasound leads to the collapse of cavitation bubbles,which leads to vibrating and releasing energy at the same time.Moreover,this energy will activates the surrounding nucleation nucleus in a dormant state and forms new cavitation bubbles under the action of ultrasonic waves,which promotes the cavitation effect and ultimately improves the heat transfer effect.We proposed the concept of calculating the effective value that based on the periodic results that we simulated in this process.(2)It was found by numerical simulation that the local velocity of fluid was non-uniformly changed after applying ultrasonic wave,However,the overall velocity,pressure,and temperature all showed periodic changes.And the outlet area of the flow channels,the pressure is distributed evenly.The smaller the ultrasonic frequency applied,the greater the fluctuation of the outlet temperature and the maximum velocity of the fluid were achieved.And the different frequencies of ultrasonic waves result in the same fluctuations about pressure drop generated in the fluid.Within the limited condition,as the ultrasonic frequency increasing,the effect of enhanced heat transfer is worse.Finally when the ultrasonic frequency was stabled in 20 kHz,the effect of enhanced heat transfer was the best,and the outlet temperature was increased by 12.57 K.The larger amplitude of ultrasonic sound pressure applied,the greater outlet temperature,maximum fluid velocity,and pressure drop fluctuation were achieved.Within the limited condition,as the ultrasonic sound pressure amplitude increasing,the enhanced heat transfer effect was better.Finally,when the amplitude of ultrasonic pressure was 9000 Pa,the outlet temperature increased by 18.03 K.Within the scope of the study,as the inlet velocity increasing,the heat transfer effect was better.However the pressure drop gradually increased.At a speed of 5 m/s,the outlet temperature increased by 24.51 K.(3)We applied ultrasonic waves in the two tube walls at the same time,which had a better heat transfer effect than a single row(front or rear)tube wall,and ultrasonic waves generated at the same time in the two tubes at the same time,which obtained the least flow resistance.As the diameter of the pipe increasing,the heat transfer effect increased firstly,and while weaken finally.When the pipe diameter was 10μm,the heat transfer effect was best,and the exit temperature increased by 14.14 K.Nevertheless,as the size of pipe expanding,the resulting flow resistance gradually increased.