弯管论文：弯管 (火积)耗散 场协同

弯管论文：弯管 (火积)耗散 场协同 弯管论文:弯管 (火积)耗散 场协同 【中文摘要】弯管是工程中常用的换热元件之一。本文将火积耗散极值原理应用于弯管管内层流对流换热,建立数学模型,数值计算得到弯管管内层流对流换热火积耗散取得极值时的流场,称为优化流场。数值模拟结果表明,优化流场在各研究工况下,PEC提高幅度普遍高于70%,最高高于150%。应用场协同原理优化流场径向截面强化传热机理。对比优化流场与原型流场截面速度场可发现,在附加体积力作用下,优化流场在流体中心区域产生较大的切向速度,通过流体粘性带动边界附近流体产生切向速度,使整个流域内流体做轴向螺旋流动。运动方式的改变使得优化流场截面温度梯度场均匀性增加,换热表面附近温度梯度加大,边界层附近协同角余弦值提高。在优化流场截面表面传热系数高的区域通常具有较大的径向速度或切向速度以及等温线密度。以优化流场为依据,对弯管管内流道进行结构优化。优化思路为在壁面处添加环肋,通过肋片的导流作用诱导流体产生径向速度或切向速度,以取得与优化流场相似的流场形态。依照以上优化原则设计出顺向环肋弯管、径向环肋弯管、逆向环肋弯管三种内环肋弯管,数值模拟其换热性能。对比三种内肋弯管在径向截面速度场发现,三种环肋具有不同的导流效果:逆向环肋能诱导边界处流体产生较大切向速度,径向环肋弯管能诱导流体边界处产生较大径向速度,顺向环肋弯管导流效果较差。逆向环肋弯管在边界处诱导流体产生较大切向速度后利用流体粘性带动中心区域流体产生切向速度,流动方式的变化提高了截面温度梯度场均匀性、加大边界处等 温线密度以及边界层附近协同角余弦值。径向环肋能诱导流体产生较 大的径向速度,径向速度的存在同样可以增大边界附近等温线密度, 改善边界层附近流场与温度场的协同性,提高流场换热性能,但同时 造成较大的压力降,使得PEC提高幅度低于逆向环肋弯管。对比三种 内肋弯管各工况下PEC可知,逆向环肋弯管PEC最高,较之原型弯管提 高幅度普遍高于50%,最高可达70%。其余两种内肋弯管提高幅度在 20%左右。逆向环肋弯管PEC与优化流场存在一定差距,作者认为原因 在于切向速度产生的位置不同。优化流场切向速度产生于流场中心位 置,对整个流场的优化效果好于切向速度产生与边界处的逆向环肋弯 管。逆向环肋弯管PEC高于其余两种内肋弯管表明诱导流体产生切向 速度对流场优化作用好于径向速度。进一步优化逆向环肋弯管结构, 优化途径为在环肋与玩管内侧接触位置切口。切口大小分别为60? 圆心角和90?圆心角。对切口后逆向环肋弯管的换热特性进行数值 模拟研究,结果表明60?切口逆向环肋弯管较之未切口逆向环肋弯管 PEC提高10%-30%,90切口逆向环肋弯管PEC提高幅度小于10%。60? 切口逆向环肋弯管换热效果最好。 【英文摘要】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. 【关键词】弯管 (火积)耗散 场协同 【英文关键词】entransy dissipation extreme principle curved tube field synergy 【目录】基于火积耗散极值原理的弯管管内流场优化研究 摘 要 8-10 Abstract 10-11 符号对照表 12-14 第一 章 前言 14-23 1.1 概述 14 1.2 强化传热技术的研究 现状 14-16 1.3 强化传热技术的研究 16 1.4 场协 同理论概述 16-17 1.5 强化传热效果的评价方法 17 1.6 火积与火积耗散理论概述 17-21 1.6.1 耗散的度量 18 1.6.2 传热系统优化过程 18-21 1.7 弯管传热特性研究现状 21-23 第二章 弯管内原型流场与优化流场的数值计算 23-40 2.1 数值计算控制方程及方法 23-28 2.2 原型流场与优化流场PEC对比分析 28-30 2.3 原型流场与优化流场截面流场对比分析 30-39 2.4 本章小结 39-40 第三章 内环肋弯管管内流场分析 40-74 3.1 优化策略 40-41 3.2 顺环肋弯管的流场分析 41-52 3.2.1 数值模拟模型 41 3.2.2 数值模拟结果分析 41-52 3.3 径向环肋弯管流场分析 52-61 3.3.1 数值模拟模型 52 3.3.2 数值模拟结果分析 52-61 3.4 逆向环肋弯管流场分析 61-71 3.4.1 数值模拟模型 61 3.4.2 数值模拟结果分析 61-71 3.5 本章小结 71-74 第四章 切口逆向环肋弯管的数值模拟 74-94 4.1 缺口顺向环肋弯管的结构及数值模拟方法 74-75 4.2 60?切口逆向环肋弯管层流对流换热数性能分析 75-84 4.2.1 数值模拟模型 75 4.2.2 数值模拟结果分析 75-84 4.3 90?切口逆向环肋弯管层流对流换热数性能分析 84-93 4.3.1 数值模拟模型 84-85 4.3.2 数值模拟结果分析 85-93 4.4 本章小结 93-94 第五章 全文 94-96 5.1 主要工作和结论 94-95 5.2 主要创新 95 5.3 主要不足 95-96 参考文献 96-98 硕士期间发表的论文 98-99 致谢 99-100 学位论文评阅及答辩情况表 100 【采买全文】 1.3.9.9.38.8.4.8 1.3.8.1.13.7.2.1 同时提供论文写作一对一辅导和论文发表服务.保过包发 【说明】本文仅为中国学术文献总库合作提供，无涉版权。作者如有异议请与总库或学校联系。