The Optimization Of Inner Flow Field Of A Curved Tube Based On Entransy Extreme Principle

Curved tube is one of the most ordinary heat transfer elements in engineering applications. Entransy dissipation extreme principle is employed to numerically calculate the flow fields of laminar convective heat transfer when the Entransy dissipation of the heat transfer process reaches extreme value. The calculated flow fields are named as optimized flow fields. The result indicate that within the research conditions, the PEC of the optimized flow fields increase by 70% to 150% compared to original flow fields of the same curved tube. The mechanism of heat transfer characteristics of the optimized flow field is analyzed based on Filed synergy principle. Driven by the additional forces deduced from the Entransy Extreme Principle, tangential velocity is generated at the central part of the flow field. With the help of fluid viscosity tangential velocity is passed to the fluid near the boundary. The optimized flow fields of the curved tube then present a significant difference from the original flow fields. The motion mode of the fluid of the optimized flow fields is axial and helical rotation which does not appear in the original ones. The unification of temperature gradient of the optimized flow field is increased by the change of motion and the temperature difference and cosine of field synergy angle of the fluid near by the boundary elevate. On the spots of the optimized flow field where the heat transfer coefficient increase, the radius velocity or the tangential velocity and the density of temperature contour is larger than the one in the original flow fields.Guided by the optimized flow fields, the structure of the curved tube is optimized. Looped-ribs are adopted as the method to optimize the flow field. Inner looped ribs could induce tangential or radius velocity and increase the similarity of the flow field to the optimized one. Three kinds of i curved tubes with inner ribs were devised and named as positive lean inner looped ribs curved tube (SXL), radial inner looped ribs curved tube (ZL) and negative lean inner looped ribs curved tube (NXL). Numerical simulations under the same working conditions of the original one were employed to evaluate the heat transfer characteristics of the three newly devised curved tubes. The result indicated that tangential velocity could be induced by the Negative-lean Looped-ribs and radial velocity could be induced by radial looped-ribs. Compared to two ribs mentioned above, the positive-lean looped-ribs have a limited effect on inducing velocity and optimize flow field. With the help of the viscous effect, the tangential velocity near the boundary induced by the negative-lean looped-ribs could drive the fluid in the central part to have tangential velocity. At the tangential velocity' effort, the density of temperature contours and cosine of field synergy angle both increase. The flow field as well as the heat transfer characteristics is optimized in this way. Radial velocity induced by radial looped-ribs has a significant effect on heat transfer coefficient improvement. But it always goes hand in hand with a measurable pressure drop. Eventually the PEC increase of the ZL under every research working condition is not as high as that of NXL which could reach to over 70%. The SXL has the worst effect on heat transfer enhancement of all.Further structure optimization of NXL is conducted. The inner part of the negative-lean looped-ribs which has no obvious effect on tangential velocity inducing is incised to reduce the pressure loss and increase the PEC. The sizes of the cut-off part are set as 60°and 90°of central angle. The numerical simulation results indicate that the 60°has a PEC increase of 10%-30% over the ordinary NXL and the PEC increase of 90°is less than 10% which means the 60°performs better in heat transfer augmentation.