Study On Enhanced Heat Transfer Characteristics Of Convex Tube And Its Optimization Design

With the increasing shortage of energy,high-efficient energy-saving heat exchanger to improve energy efficiency has become a hot topic at home and abroad.Passive reinforcement technology in convective heat transfer strengthening technology is widely used in heat exchange equipment for it does not need additional power supply.In this paper,a convex cell heat transfer tube was proposed to improve the heat transfer efficiency on the basis of convex cell pit plate heat exchanger.It is formed by stamping a certain depth on the surface of circular smooth tube.Firstly,the enhanced heat transfer mechanism of convex cell tube was analyzed on the basis of verifying the correct calculation model.Then the influence of structure parameters and arrangement on the heat transfer and flow resistance of the convex cell tube was studied and optimized.Finally,the performance of the convex cell tube was compared with that of the spiral groove tube and the transverse groove tube.The main findings are as follows:(1)The simulation results were compared with the experimental data and empirical formulas in the literature to verify the correctness of the calculation model.The enhanced heat transfer mechanism of the convex cell tube was analyzed from the velocity field,turbulent kinetic energy and field cooperation theory.Compared with the smooth tube,the heat transfer performance of the convex cell tube increased by 14.93～25.87%,and the flow resistance increased by 18.17%on average.It can be seen from the analysis of heat transfer mechanism that the secondary flow perpendicular to the mainstream direction can be produced when the fluid passes through the convex cell,which reduces the field coordination angle and thus improves the heat transfer efficiency.(2)The change rules of convex cell structure parameters and flow parameters on heat transfer and flow resistance performance were studied respectively from single factor and multi-factor,and the influence degree of each parameter was analyzed.The Nu、f criterion correlation formula was fitted by linear regression analysis of 69 groups data obtained by MATLAB simulation.The structural parameters and flow parameters were optimized with Nu、f、PEC as the objective function.The optimization results obtained from the ANSYS Workbench and the fmincon functions were compared.It was found that the enhanced heat transfer effect of convex cell tube was the best when h=2.4mm,r=2mm,p=20mm.(3)The three ways of convex cell staggered,opposite row and spiral arrangement were compared.And the heat transfer performance and anti-fouling performance of convex cell tube were compared with that of transverse groove tube and spiral groove tube.The results showed that Nu of the opposite row was not much different from the staggered row.Thef of opposite row was slightly larger than the staggered row,and the PEC was weaker than that of the staggered row.The heat transfer performance was optimal when the convex cell spiral arrangement angle was 120 degrees,and the flow resistance also reached the maximum.The Nu、△P of the convex cell tubes was the smallest,the field coordination angle was the largest,and the PEC was optimal under the specific structure studied.The fouling deposition of convex cell tube in three heat transfer pipes was the smallest,and the fouling resistance was the best.(4)The App of convex cell tube heat exchanger was designed using App Designer tools in MATLAB.Accurate reliability of App was verified by examples.Compared with the convex cell tube heat exchanger and smooth tube heat exchanger designed under the same working conditions,the advantages of the convex cell tube heat exchanger were highlighted.The results achieved in this paper provided a certain theoretical basis for the application of the new convex cell heat exchange tube in practical engineering,and provided new ideas for strengthening the heat exchange technology.