| Shell and tube heat exchangers are widely used in many fields, such as chemicalengineering, power engineering, petroleum and metallurgy industries. The engineering fieldsabove involve various types of the working medium. Among these，there is low viscousworking medium, such as gas, water, etc., there is also high viscosity of working medium,such as polystyrene, etc. Different medium requires for different heat transfer technology.However, traditional plain tube used in many heat exchangers has the shortage of low heattransfer. It is difficult to meet the requirements of all aspects of heat transfer process. Thetechniques of heat transfer enhancement is an important means of advocating high efficiencyand energy saving. The techniques for heat transfer enhancement can be divided into twocategories. One is the active strengthening technique and the other is the passive one. Due toits easier operation and higher reliability, the passive strengthening techniques are morecommonly used in the engineering. Among these passive strengthening techniques, tubeinserts are practical and popular, especially in the working medium with high viscosity fluidin heat transfer. Tube inserts can improve heat transfer by mixing fluid between the near wallzone and mainstream zone, and change the distribution of velocity field and temperature fieldinside to improve the synergy between them, so as to acquire low resistance and high efficientheat transfer performance.Firstly, this paper expounds tube inserts strengthen heat transfer mechanism andadvantages,tube inserts research status at home and abroad are introduced. At the sametime,field synergy theory and CFD numerical simulation of heat transfer enhancement inapplication are summarized. A brief introduction to the heat transfer enhancement and theevaluation method is presented.Numerical simulation and analysis of the flow field structure for a kind of organicthermal oil as viscous medium in the tube, which is inserted into the Kenics static mixer, hascompleted by FLUENT to investigate the different twist ratio (y=1.5,2.0,2.5) influence onheat transfer and flow characteristics. The results are compared with the smooth tube, and theresults show that due to the segmentation and vortex effect of the Kenics ’s mixing element, which leading to the velocity gradient and temperature gradient of the mainstream are reduced,the heat transfer performance is promoted. At the same time, the increase of pressure drop isvery large. Thus, the comprehensive heat transfer performance factor don’t improve too much.Comprehensive comparison find that when twist rate y=2.0, the comprehensive heat transfereffect is the best.A tube in which inserted with spaced cross semi-elliptical tapes and water as workingfluid is investigated by FLUENT. The investigation of the angle (φ=30°,60°,90°) and thecross semi-elliptical tapes numbers (N=3,4,5) which affecting the performance of heattransfer and fluid resistance. It shows that within the scope of the Re is300~2000, the PECvalue is1.1~1.95. Demonstrating the convective heat transfer of laminar flow fieldcooperative relation, the smaller the synergy Angle θm, the better collaborative betweenvelocity field and temperature field, and the temperature distribution of the fluid in tubes ismore uniform and get better heat exchange efficiency. In the tube which inserted spacingmultiple cross semi-elliptical tapes, when the tube is fixed with four cross semi-ellipticaltapes, the heat exchange comprehensive performance is the best for the angle of60°,followed by90°’s, the minimum is30°’s. When the angle of the cross semi-elliptical tapes is60°, the comprehensive evaluation factor, that is,the PEC value can reach1.95. Along withthe increasing the number of cross semi-elliptical tapes number, the comprehensive evaluationfactor, i.e, the PEC is greater. |
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