微尺度气液两相传递强化及分散体系调控Boltzmann研究

The microscopic physical mechanisms in microscale fluid flow and heat transfer are researched by using the Boltzmann equation, and the principles of the relationship between momentum and energy transport are presented. Based on the continuum assumption, the effects of slip boundary condition, the viscous dissipation and compressibility in the motion continuity equation are concerned, to get the revised fluid mechanics equations and boundary conditions. Based on which, the specific scope of microscale fluid flow and heat transfer problems can be studied. the relationship between the macro and micro fluid flow is be explored. The heat exchangers with silicon parallel microchannel array are designed and manufactured by using directional etching process. The experiment of micro fluid flow and convective heat transfer will be done with deionized water as the working fluid. Micro-PIV experiment will be done on the microstructure of fluid flow field. So, the characteristic correlations of micro fluid flow and heat transfer within wide scope are summarized. It is going to reveal the association mechanism of momentum and energy transport in microstructure. In another case, heat transfer enhancement mechanism in microscale heat exchangers are studied, as well as to study microchannel geometry parameters impact on micro fluid flow and heat transfer. Numerical equations would be established according with the physical model, as well as taking into account of variety of special micro fluid flow and heat transfer factors. In a word, system academic solution and simulation for microscale heat exchangers are trying to be achieved.

对微尺度气液两相流体流动与传热传质的复杂机理建立数值模型，利用格子Boltzmann 方程对动量及能量输运的微观物理机制进行研究，揭示微结构中气液流体流动与传热、传质规律；格子Boltzmann方法是介于微观分子动力学和基于连续介质假设的宏观方法之间的一种桥梁；从连续介质假设出发，将滑移边界条件、黏性耗散及可压缩性与运动的连续方程结合起来，对传统的流体力学方程及边界条件做适度修正，研究特定范围内的微尺度气液两相流体流动问题，试图寻求宏观与微观之间的桥梁；拟采用定向蚀刻工艺，设计并加工硅制平行阵列微通道换热器，进行以去离子水、超临界CO2为工质的微通道换热器、微反应器内流体流动与对流换热及化学反应实验，改造项目组现有的LDV及PIV使之适应微尺度观察，对微结构内流场状况进行可视化测量，以期总结出适用范围较宽的微通道气液流体流动特性和传热、传质特性关联式；揭示微结构内动量及能量输运机制。

研究项目构造了适合多孔介质的LBGK模型和非正交MRT-LB模型，并进一步对非正交MRT-LB模型中温度的宏观方程进行恢复。利用非正交MRT-LB模型对通道中的强制对流，方腔中的自然对流进行数值模拟，对比分析了非正交MRT-LB模型、正交MRT-LB模型以及LBGK模型，研究了非正交MRT-LB模型的精度和计算效率。利用非正交MRT-LB模型对方腔内多孔介质纳米流体进行模拟，总结了速度、温度、压力的分布情况，分析了不同体积分数的纳米流体、Ra数、Da数、孔隙率、纳米流体粒径以及腔体的宽高比等因素对流动和换热的影响，通过壁面的Nu数等指标来评价换热情况。考察了不同吸收剂在弹状流内吸收CO2的传质行为，得到了弹状流内速度场和浓度场分布，考察了吸收CO2物理和化学过程的液相体积传质系数、CO2吸收率和增强因子，分析了接触时间和气泡速度对流动和传质变化的影响，分别提出了在物理吸收和化学吸收情况下预测液相体积传质系数的经验关系式。采用二维耦合双分布函数(DDF)热格子Boltzmann模型，研究了封闭腔充满空气时，在双壁驱动下，差热方腔内无等温热源和有等温热源时的混合对流换热。在Shan-Chen模型的基础上添加了温度场，构造了一个全新的模型。利用该模型研究了在温度场下的两相分离及其流体流动与传热特性。详细分析了液滴形成所经历的碰撞、界面打开、融合三个过程的表现。. 以上研究侧重于微通道或多孔介质内流体流动特性和传热、传质特性，研究结果能够为微尺度换热器、微反应器的开发与应用提供技术支持；能够为多孔介质内多相流流动（比如，石油开采）提供技术参考。