【作者】 陈群；

【导师】 过增元；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2008， 博士

【摘要】 热量、质量和动量传递是能源利用中的重要环节,传递过程性能的提高对节能减排意义重大。基于这些传递现象的类比性,本文引入了质量积和动量积的概念,分别代表介质中质量扩散和动量扩散的能力;定义了质量积和动量积的耗散函数;举例说明了积(热量积、质量积和动量积)的耗散而并非熵产是不涉及热功转换的传递过程不可逆性的量度;提出了最小积耗散原理就是传递过程的最小作用量原理的观点,并导出了输运系数为常数的牛顿粘性定律、傅立叶导热定律和菲克扩散定律,表明这些定律本身反映的就是最优的传递过程。为了揭示对流换热的热力学优化与传递过程优化的差别,用积耗散极值原理和熵产最小原理分别导出了对流换热性能最佳时流体速度场所需满足的相应欧拉方程。对圆管层流换热优化的结果表明,积耗散极值原理更适合于与热功转换无关的对流换热过程的优化。通过定义了湍流换热中的热量积及其耗散函数,以及采用零方程湍流模型导得了泵功给定时湍流换热性能最优的速度场需满足的欧拉方程,从而把层流换热中的热量积耗散极值原理推广至湍流换热。对平行平板通道内湍流换热的优化结果表明了微肋管能有效强化湍流换热,指出了不同Re下微肋的最佳高度。将对流换热的场协同理论推广到对流传质过程,导得了对流传质的场(速度场与组分浓度梯度场)协同方程,即为质量积耗散取极值时需满足的用于对流传质优化的欧拉方程。利用空气与水的对流传质实验验证了对流传质场协同理论,并将其用于空间站实验舱内通风排污过程和光催化反应器内对流传质过程的优化。结果表明,采用集中进风代替均匀进风,舱内污染物浓度最大值从0.47%降为0.22%;双斜内肋板式反应器比平板反应器的排污效率高22%。将对流换热的场协同理论也推广到流动过程,导得了流动过程的场(速度场和速度梯度场)协同方程,即为动量积耗散取极值时需满足的用于流动过程优化的欧拉方程。将其用于并联通道流和稠油输运过程的优化结果表明,设置适当的导流片使流动阻力减小了5%;管内形成多纵向涡的流动结构使稠油保温输运过程中的粘性耗散降低了19%。更多还原

【Abstract】 Heat, mass and momentum transport processes are the three important parts in energy utilization. Transport performance improvement is of great significance to the energy conservation and emission reduction. In terms of the analogy among the heat, mass and momentum transport phenomena, the concepts of mass entransy and momentum entransy have been introduced, they represent mass and momentum transfer ability of a system. The mass entransy dissipation function and the momentum entransy dissipation function have also been defined, and it is the entransy dissipation rather than entropy generation that measures the irreversibility of a transfer process, that is unrelated with the heat-work conversion in a thermodynamic cycle. Further, the minimum entransy dissipation principle is pointed out to be the least action principle in transport processes. For constant transport coefficient, the Newton’s law of viscosity, Fourier’s law of heat conduction and Fick’s law of diffusion have been deduced from this least action principle, suggesting that these laws themselves reflect the optimal transport processes.In order to illuminate the differences between the thermodynamic optimization and the transport optimization for convective heat transfer, two different Euler’s equations have been deduced from the extremum principle of entransy dissipation and the entropy generation minimum principle, respectively, which lead to two different fluid velocity fields with the best heat transfer performance. The optimization results of the convective heat transfer of laminar flow in a tube show that the extremum principle of entransy dissipation is more suitable for the convective heat transfer optimization than the entropy generation minimum principle.By defining the concepts of heat entransy and the heat entransy dissipation function for the convective heat transfer of turbulent flow and utilizing a zero equation turbulence flow model, an Euler’s equation, which leads to a velocity field with the best turbulent heat transfer performance, has been developed for a given pumping power. The extremum principle of entransy dissipation for laminar heat transfer optimization has then been extended to the turbulent heat transfer optimization. As an example, the field synergy analysis for turbulent heat transfer between parallel plates is presented. The results support that the tubes with micro fins effectively enhance heat transfer, and have clarified the best heights of the fins for different Reynolds numbers.The field synergy principle for convective heat transfer has been extended to the convective mass transfer. The concept of field synergy between the velocity vectors and concentration gradients is introduced, and then the convective mass transfer field synergy equation is deduced, it is just the Euler’s equation for convective mass transfer optimization with the extremum value of the mass entransy dissipation. This principle has been validated experimentally through a convective mass transfer process between air and liquid water, and then been used to optimize the decontamination ventilation designs in space station cabins and the geometric structure designs of photocatalytic oxidation reactors. The results show that by utilizing the concentrated air supply system to substitute the uniform air supply system, the maximum contaminant concentration in the cabin is decreased from 0.47% to 0.22%, and the contaminant removal effectiveness for the discrete double-inclined ribs plate reactor is increased by 22 % compared to the smooth plate reactor.The field synergy principle for convective heat transfer has also been extended to the fluid flow. The concept of field synergy between the velocity vectors and velocity gradients is introduced, and then the fluid flow field synergy equation is deduced, it is just the Euler’s equation for fluid flow optimization with the extremum value of the momentum entransy dissipation. As an example, the field synergy analyses for duct flow with two parallel branches and insulated transport process of thick oil are presented. The results show that by adding a flow divider nearby the fork may reduce the flow drag of duct flow by 5%, and the resulting multi-longitudinal vortex flow reduces the flow drag by 19% during the insulated transport process of the thick oil.更多还原