Numerical Simulation And Experimental Study On Heat Transfer Enhancement Characteristics Of Heat Transfer Tubes With Twisted Tape Insert

As a widely used equipment in the industrial field,heat exchangers does a great significance for the efficient use of energy and energy saving.Being a simple and practical tube insert element,twisted tape is suitable for technical transformation of existing equipment with its dual performance in heat-exchanging and anti-scaling.Numerical simulation and experimental research are combined in this paper.Besides,Two numerical models of plain tube and tube with twisted tape insert are established according to the experimental requirements.In the case of turbulent flow(Re=5000~30000),numerical simulation of the plain tube and twisted tape insert in the way of characteristics of heat transfer and resistance is carried out firstly with the help of FLUENT 17.0.Then,the calculation results of the two are compared under the same working conditions.Finally,the enhanced heat transfer performance,resistance characteristics and comprehensive heat transfer performance PEC of the tube with twisted tape insert are analyzed.The conclusions are as follows:Under the same Reynolds number Re,the tube with twisted tape insert Nusselt number is 33%~60% higher than the l plain tube,and the tube with twisted tape insert is obviously superior to the plain tube in heat transfer performance;the drag coefficient 1),the tube with twisted tape insert is 167%-205% higher than the plain tube,and the fluid resistance in the tube with twisted tape insert is obviously larger than that of the light pipe;in the simulated Reynolds number,the tube with twisted tape insert PEC decreases with the Reynolds number.The comprehensive heat transfer performance is better on condition that the Reynolds number varies from 5000 to 20000 and the PEC value lies between 1.0 and 1.1.In order to optimize the structural parameters of the twisted tape,the numerical simulation of the tube with twisted tape insert under three different torsion ratios(Y=1,2,3)is carried out.The result shows that the overall heat transfer performance of the helical ties is better when the twist rate is Y=2.A comprehensive performance experimental platform for heat exchangers is built,and a self-rotating twisted tape device is used as a heat-exchange element.The heat exchanger is designed for medium-temperature water-water heat exchange.The experimental parameters are set to refer to the hot water heat exchange system of a mining enterprise employee.Firstly,the rotation condition of the twisted tape device is tested under cold experimental conditions.It shows that when the heat exchange tube with only one twisted tape device was allowed to pass the water flow.When the twisted tape can achieve rotation,the flow rate was 0.4 m/s,while the larger the flow rate,the faster the rotation speed of the twisted tape;All the twisted tapes in the unit can achieve continuous rotation when the seven heat exchange tubes in the heat exchanger are equipped with the twisted tape and the flow rate of heat transfer is 1.11 m/s.This test provides a reference for the practical application of the rotating spiral ties.The experiment focuses on the determination of the heat transfer coefficient k and the pressure drop value ?P of the plain tube heat exchanger and the self-rotating twisted tape heat exchanger.According to the experimental results,the heat transfer coefficient k and pressure drop ?P of the two devices is plotted under the same working conditions.With the change of the flow rate v,the experimental results are obtained through comparative analysis of the data: the heat transfer performance of the heat exchanger equipped with the twisted tape device is greatly improved under the turbulence of the twisted tapes.And the heat transfer coefficient of the contrast tube heat exchanger can be nearly doubled at experimental flow rate of 1.5 m/s.The addition of the twisted tape device increases the flow resistance in the heat exchanger while enhancing heat transfer.In a certain range of experimental velocity,the pressure drop of the tube with twisted tape insert heat exchanger is nearly twice as high as that of the light tube heat exchanger.