多场耦合液膜内的声空化机制及其强化二元溶液水平管降膜吸收机理研究

The mechanism and enhancement of falling-film absorption is the important research topic in absorption heat pump and refrigeration field. In this project, a novel enhancement method of horizontal tube falling-film adsorption using binary solution is studied based on the theory that the acoustic cavitation can regulate the flow characteristic of the liquid film and improve the heat and mass transfer. Using the experimental and theoretical study, the propagation characteristics and the cavitation conditions of the acoustic wave in the laminar falling-film are revealed. The mechanism of the acoustic cavitation in the liquid film with complex constraints and multi-filed coupling is mastered. The fluence of the ultrasonic field on the cavitation bubbles dynamics behavior and the liquid film flow is also revealed. The transition mechanism from the laminar flow to the wavy flow of the falling-film on the horizontal tube under the action of external incentives is discussed. It also reveals the relationship between the ultrasonic field and the heat and mass transfer in adsorption and obtains the couple rules of the heat and the mass flow under the condition of the varied interface topology and the phase transition. On the basis of the above study, a mechanism of quantitative modulation liquid film flow with acoustic cavitation is explored and built. This project is an interdisciplinary subject of ultrasonic science, thermodynamics and heat and mass transfer science. It has distinct academic value in enriching and improving the basic theory of the falling-film absorption and will provide theoretical support and experimental data for developing a new type technology of falling-film absorption and optimizing high efficiency falling-film absorber.

降膜吸收机理及强化方法是吸收式热泵/制冷领域的重要研究课题。本项目针对二元溶液水平管降膜吸收过程，研究利用声空化调制液膜流动特性强化传热传质的新方法。通过理论研究与实验相结合，揭示层流降膜内的声波传播特性及空化发生条件，掌握复杂约束、多场耦合作用下液膜内的声空化机制；揭示超声场对空泡动力学行为及液膜流态的影响规律，掌握外部激励作用下水平管降膜从层流向波动流的转捩机理；揭示超声场与吸收过程传热、传质的内在关联规律，掌握界面拓扑变化和相变条件下的热流、质量流耦合规律。在此基础上，建立声空化定量调制液膜流态强化水平管降膜吸收的方法。本项目属声学、热力学及传热传质学的交叉，对于丰富和完善降膜吸收基础理论具有鲜明科学意义，也将为发展新型降膜吸收强化技术和高效降膜吸收器提供理论支持和基础实验数据。

本项目面向吸收式热泵/制冷、海水淡化领域，以二元溶液水平管降膜流动及吸收过程为对象，通过理论分析、数值模拟结合实验，揭示超声场对降膜液膜流体动力学行为的作用机制，揭示降膜吸收过程流动特征与相间传热、传质的耦合机理，探索通过超声场调制液膜流动强化水平管降膜吸收的新方法。本项目取得的重要进展集中在三个方面：搭建超声场内水平管降膜流动可视化实验台，利用影像法获取水平管表面和管间降膜流动的演变规律，建立了超声功率、声源位置、入射角、溶液流量、溶液浓度、管径、管间距等参数与周向液膜厚度、管间流型转换雷诺数的定量关联；基于层流两相流-水平集方法，通过耦合压力声学-频域接口，建立了超声场内水平管降膜流动模型，仿真结果与实验结果吻合较好；采用VOF法建立了包含液膜流动、液相组分传递及气-液相间热质传递现象的水平管降膜吸收模型，定量分析了滴状、柱状管间流型下稳态吸收局部吸收速率的空间分布特征。本项目的研究结果将为发展新型降膜吸收强化技术和开发高效降膜吸收器提供理论支持和基础实验数据。