Study On Heat Transfer And Flow Resistance Of The Plain Tube And The Twisted Tape Tube With Ultrasound

Improving the performance of heat exchangers has always been the most important project for scholars in the field of heat transfer.As a new type of active technologies,ultrasonic has attracted more and more attention.And as a traditional passive technology,the twisted tape has been widely used due to its superior capability of enhanced heat transfer.In this paper,heat transfer performance and flow resistance of the plain tube and the twisted tape tube with ultrasound has been studied by experiment and numerical simulation.And the synergy effect of the ultrasonic technology and the twisted tape on heat transfer performance and flow resistance of tube has been explored.Firstly,the experimental device for heat transfer performance and flow resistance of the plain tube and the twisted tape tube with ultrasound acting on the tube sheet is designed.And heat transfer performance and flow resistance of the plain tube and the twisted tape tube without ultrasound were tested to compared with the results of the established empirical formula,which proves the experimental results are valid.Secondly,the effects of acoustic intensity,acoustic frequency,the number of ultrasonic transducers and the position of ultrasonic transducer on the performance of the plain tube and the twisted tape tube under different Reynolds number are studied.Heat transfer performance,flow resistance and comprehensive performance of the tube are evaluated by the Nusselt number,the friction factor and the performance evaluation criterion respectively.It was found that,within the range of the research,the ultrasound applied on the tube sheet enhances the heat transfer performance of the the plain tube and the twisted tape tube with the flow resistance reduced and the overall performance improved.With an increase in the Reynolds number,the capability of enhanced heat transfer by ultrasound increases and the capability of drag reduction by ultrasound decreases.The synergy effect of ultrasound and the twisted tape on enhanced heat transfer is superior,but the synergy effect of them on drag reduction is not as good as that of ultrasound acting on the plain tube.For the parameters of ultrasound,the capability of enhanced heat transfer and the overall performance by ultrasound increase with a decrease in acoustic frequency.But the critical acoustic intensity of enhanced heat transfer and drag reduction are different at different acoustic frequency.When two ultrasonic transducers are installed on the tube sheet,the heat transfer performance of the tube is the best and the maximum increase in Nusselt number is 38.06%.When the transducer is installed horizontally on the tube sheet,the drag reduction performance of the tube is the best and the friction factor is reduced by 21.43% at most.Finally,the three-dimensional fluid-solid coupling model was established.The plain tube and the twisted tape tube under the ultrasound applied on the tube sheet with different acoustic intensity,acoustic frequency,the number of transducers and the position of transducer have been calculated by numerical simulation.The influences of the ultrasound on the field were analyzed and discussed using the results of structural amplitude,volume fraction of vapor(cavitation)and vector.The results show that the main reason of heat transfer enhancement by ultrasound is the effect of cavitation because the collapse of cavitation bubbles destroys the thermal boundary layer at the fluid-solid interface and causes the mixing of fluid near the wall.Therefore,the greater the degree of cavitation,the better enhanced heat transfer performance of ultrasound.The main reason of drag reduction by ultrasound is the effect of vibration because the vibration of high-frequency generated by the ultrasound increases the flow rate near the wall and an increase in momentum overcomes the viscous force and reduces the friction factor.Therefore,the larger the flow rate near the wall and the area of vibration caused by the vibration,the better drag reduction performance of ultrasound.