Study On The Flow And Heat Transfer Characteristics Of Staggered Twisted Tube Bundles

With the progress of human society and the rapid development of economy,human’s demand for energy continues to increase,and the development of efficient and energy-saving heat exchange equipment has attracted the attention of all countries in the world.As a common heat exchange equipment,tube bundle heat exchanger is widely used in industrial manufacturing with simple structure and low cost.Changing the tube shape of the heat exchanger helps to enhance the flow disturbance,promote the heat exchange of fluids in the heat exchanger channel and improve the comprehensive heat transfer performance of the heat exchanger.Therefore,it is of great significance to study the flow and heat transfer characteristics of cross-flow twisted tube bundle to improve the heat transfer performance of heat exchanger.In this paper,the effects of different structural parameters on the temperature field,flow field,heat transfer performance and flow resistance of the tube bundle heat exchanger are studied and analyzed by changing the twist pitch,aspect ratio and torsional direction of the twisted flat tube.The comprehensive heat transfer influence coefficients under different parameters are compared,and the heat exchanger model with the best overall heat transfer performance is obtained.Based on the optimal arrangement of twisted flat tube bundle,the same number of twisted flat tube and straight flat tube were combined,and the flow heat transfer performance of the combined tube bundle was compared.The results show that the combined tube bundle can improve the comprehensive heat transfer of the heat exchanger.The specific results are as follows:(1)As the twist pitch S of the twisted flat tube bundle increases,the Nu,Eu and PEC all decrease.When Re is 15000,the twisted flat tube bundle with a twist pitch of 100 mm has the best overall heat transfer performance,and the Nu reaches a maximum of 98.32,which is10.15% higher than that of the circular tube bundle.The Eu increases by a maximum of9.53%,and the PEC increases by a maximum of 6.86%.However,when the twist pitch is220 mm,the Nu and PEC of the twisted flat tube bundle are the smallest.(2)While keeping the twist pitch constant,as the aspect ratio A/B of the twisted flat tube bundle increases,the Nu,Eu and PEC all increase.When Re is 15000,the twisted flat tube bundle with an aspect ratio of 2.85 has the best overall heat transfer performance,and the Nu reaches a maximum of 103.70,which is 16.18% higher than that of the circular tube bundle.The Eu increases by a maximum of 18.86%,and the PEC can be increased by a maximum of 9.68%.When the aspect ratio is 1.73,the Nu and PEC of the twisted flat tube bundle are at their minimum.(3)When the twisted flat tube bundles are arranged in the same direction,the comprehensive heat transfer performance is the best,with a maximum increase of 9.68%compared with the PEC of circular tube bundles.However,when the twisted flat tubes are arranged in different directions,the heat transfer capacity of the twisted flat tube bundles can be increased,but at the same time,the resistance in the heat transfer channel is increased,leading to a decrease in comprehensive heat transfer performance.When Re is 15000,the Nu of the twisted flat tube bundles can be increased by a maximum of 21.62% compared with the circular tube bundles,the Eu can be increased by a maximum of 47.74%,and the maximum increase in PEC is 7.25%.(4)When the twisted flat tubes are combined with straight flat tubes,the Nu of the combined tube bundles is smaller than that of the twisted flat tube bundles,indicating weaker heat transfer performance than the twisted flat tube bundles.Moreover,the resistance of the combined tube bundles is relatively small,with Eu is smaller than that of the circular tube bundles and twisted flat tube bundles.With the increase of Re,the Nu and PEC of the combined tube bundles also increase.When Re is 15000,the Nu of the combined tube bundles can be increased by a maximum of 12.77% compared with circular tube bundles,and the maximum increase in PEC is 16.52% compared with the circular tube bundles.