Experimental Investigation And Numerical Simulation Of Heat Exchange Tube With Trefoil Insert

As basic heat conversion equipment,the heat exchanger plays a vital role in industrial production.Improving its efficiency is of great significance to energy conservation and emission reduction.In this paper,the advantages of wing vortex generators,three-blade tubes,and twisted tapes to enhance heat transfer are combined.Developing new trefoil inserts and trefoil-twist inserts to improve the heat transfer efficiency of the heat exchanger is developed.It is studied using an enhanced heat transfer experiment and computational fluid dynamics numerical simulation.Firstly,when the Reynolds number Re is in the range of 12 787～21 629,the heat transfer enhancement experiments of five kinds of trefoil inserts with different wing structures are carried out with water as fluid.The results show that the nonporous trefoil insert does not enhance heat transfer.In contrast,the installation of downstream,countercurrent,staggered downstream,and staggered countercurrent trefoil insert can improve the heat transfer effect of the heat exchanger to varying degrees.Among them,the best comprehensive performance is the staggered downstream trefoil insert.Compared with the plain tube,when Re is 21 629,the increase of Nusselt number Nu is 129.5%,the increase of friction resistance coefficient f is 530.9%,and the performance evaluation criteria PEC is 1.33.Secondly,twisted tapes with different torsion rates T are added to the four structures of trefoil inserts that can enhance heat transfer,forming trefoil-twist inserts,and the heat transfer enhancement experiment is carried out under the same conditions.The results show that the twisted tape structure can further improve the comprehensive heat transfer performance of the four trefoil inserts.The smaller the torsion ratio T of the twisted tape,the greater the resistance loss will be caused,but a better heat transfer effect can be obtained,which further improves the comprehensive heat transfer efficiency.Among them,the best comprehensive performance is the countercurrent trefoil-twist insert with the torsion ratio T of 3.Compared with the plain tube,when Re is 21 629,the increase of Nu is191.8%,the increase of f is 663.4%,and the PEC is 1.56.The experimental prediction correlations of Nu and f are fitted for downstream,countercurrent,staggered downstream and staggered countercurrent trefoil inserts with different torsion rates T.The deviation between the predicted value and the experimental results is within 10%.Finally,the physical models of staggered downstream,countercurrent trefoil inserts and staggered downstream,countercurrent trefoil-twist inserts with torsion T of 3 are established.The mechanism of heat transfer enhancement is discussed by numerical simulation of computational fluid dynamics.The results show that the structure of the forward flow wing of the staggered downstream trefoil insert acting on the central part of the fluid is better than that of the counter flow wing of the countercurrent trefoil insert.The fluid flow and mixing mode formed are more reasonable and more conducive to heat transfer.The addition of the twisted tape structure can improve the convective heat transfer rate of staggered downstream,countercurrent trefoil inserts,to further enhance the effect of enhanced heat transfer.