【作者】 夏再忠；

【导师】 过增元； 李志信；

【作者基本信息】 清华大学 ， 工程热物理， 2001， 博士

【摘要】 建立在整体性能的描述和评判基础上的传热强化的目标是适应和促进高热流。传热强化的途径是依靠各种强化技术来改变热量在空间内的输运过程，通常是通过设计热过程的局部行为而实现整体性能的强化。当考虑局部设计的约束条件时，传热强化则表现出从整体到局部的过程优化的特征。也就是说，为使传热整体性能达到最优如何去设计过程的局部行为。本文以导热和对流换热的过程为研究对象，借助变分原理解决传热强化理论研究的基本问题，并为具体强化技术的选择和实施提供理论指导。对于导热强化，提出并理论证明了温度梯度全场均匀化是控制导热系数空间最优分布的基本原则。基于这一原则，提出并采用了仿生方法来寻找一定量的高导热材料在导热空间内的构造形式，以使给定温差下的传热量达到最大。对于对流换热强化，提出并理论证明了场协同方程是控制着流动阻力一定下传热整体性能达到最优时的速度场。对于翅片强化对流换热，提出用填充率、扩展量和伸展方向这三个物理量在空间内的分布来描述翅片系统的一般结构，并建立了相应的热量输运模型。在此基础上，提出并理论证明了低阻力高传热的翅片结构的优化设计应遵循的三个基本原则。为了用数值方法研究传热过程的优化，发展了一种基于同位网格的流场计算的双速度算法以及描述各优化原则的迭代过程。针对具体模型的计算结果表明过程优化可带来显著的传热强化效果，对强化技术研究具有理论指导意义。在仿生优化中，通过数值模拟复现了一个确定性的简单原则控制下的纷繁复杂的高导热材料几何形状的演变过程。在速度场优化中，数值模拟结果明确地指出设计具体强化方式时该如何去“掺混”流体以使传热强化效果达到最大。随着对流换热空间的几何形状、边界特征和流动总阻力的变化，最优速度场表现出的流态结构由量变到质变的过程充分证明了速度场与热流场之间的相互协同关系，从而进一步丰富和发展了对流换热的场协同理论。在翅片结构优化中，数值模拟结果提供了应在何处去扩展翅片面积以及扩展多少等详细的局部构造信息。基于理论分析的结果，设计加工了两种带有纤毛状翅片结构的强化换热管，实验测试结果表明，它们具有高传热和低阻力的优越特性，支持了翅片结构优化的结论。更多还原

【Abstract】 The goal of heat transfer augmentation established on the description and judge of the whole heat transfer performances can be stated as the desire to encourage or accommodate high heat fluxes. Almost all the augmentation techniques are used to vary the local behavior of heat transfer so as to improve the whole performance. Considering the constraint conditions, heat transfer augmentation appears the feature of optimizations from whole to local, namely, in order to realize the best whole heat transfer performances, how to design the local behavior of the heat transfer process? Taking heat conduction and convection optimizations as the research objects, this dissertation is to solve the above foundational problems by means of variation principle in the field of heat transfer augmentation, and explore some theoretical conclusions to direct the selection and actualization of augmentation techniques. For the augmentation of heat conduction, the principle of temperature-gradient uniformity governing the optimal distribution of the thermal conductivity is presented and proved theoretically. Based on this principle, bionic optimization technique is introduced to search the optimal spatial distribution of the high-conductivity material in pursuit of the maximum heat transfer at a given temperature difference. For connective heat transfer augmentation, the field-coordination equations are given and theoretically proved to achieve the optimal heat transfer performance at a constant flow resistance. For fin system, the spatial distributions of three defined physical quantities, filling ratio, extend measure and stretch direction, are described for general fin structures. Based on which the heat transfer between fin system and fluid is modeled mathematically. Finally, three foundational principles are presented for the optimal design of the fin system with lower flow resistance and higher heat transfer rate.To perform the optimization analysis, a new numerical simulation method, named as dual-velocity algorithm for flow calculation on collocated grids，is developed and the iterative formulas of the optimization principles are presented. Numerical simulations on specific heat transfer problems are performed to show the<WP=10>remarkable augmented effects resulting from process optimization, and to recognize the theoretical significances of process optimization to the study of heat transfer augmentation. Dominated by the deterministic simple principle, numerical simulations of bionic optimization show picturesquely the evolution procedure of numerous and complicated shapes of high-conductivity material. In the velocity field optimization, the optimal velocity fields are able to direct augmentation techniques how to blend or to mix fluid so as to realize the maximum effect of heat transfer augmentation. With the variations of the configurations, boundary conditions or flow resistance, the trend from quantitative variation to qualitative variation of the optimal flow state is full proof of the coordination between the velocity and heat flux fields, which enriches and develops further the field-coordination theory. In the fin-structure optimization, numerical results can offer detailed constructional information about the optimal fin system, for example, where fin needs to extend its surface, and how much area fin extends, etc. Furthermore, two kinds of heat transfer enhancement tubes with fiber fins are designed and tested. The results show that the two enhancement tubes developed by means of the fin system augmentation principle are of superior performances of lower flow resistance and higher heat transfer, which is coincident with the prediction in fin-structure optimization.更多还原