盐溶液闪蒸过程两相流动与传热传质机理研究

Flash evaporation of saline solutions is widely used in industry such as sea water desalination, food processing industry, chemical industry and so on, due to its ability for solution condensation and components separation. Saline solutions may contain different salts, as a result, they have different properties to pure water and one of the differences is the boiling-point elevation of saline solutions. In order to obtain fundamental understanding of the flash evaporation of saline solutions, the studies of the nucleation, two phase flow and heat and mass transfer phenomena during the flash evaporation process are very important. Moreover, these studies are useful to develop new engineering technologies in many flash evaporation industries mentioned above. In this proposal, both experimental and numerical studies will be conducted to study the flash evaporation of saline solutions. In the experimental study, the phase-change phenomenon accompanied with two-phase flow in flash boiling will be observed for several different saline solutions. In the simulation study, a new lattice Boltzmann method, which can simulate saline solution phase-change by taking into account the boiling-point elevation, will be developed. Using this model, the effects of the solution properties on flash evaporation are examined and the detailed information of two-phase flow, as well as the component and temperature distributions during the flash evaporation of saline solutions are obtained. Based on these studies, the effects of the properties of saline solutions on bubble nucleation and growth, phase-change and two-phase flow during their flash evaporation processes will be further analyzed, and the mechanism of heat and mass transfer in these processes will also be discussed. The results from this program will provide theoretical basis and guidance for the development of solution condensation and components separation industries by using flash evaporation technology.

运用闪蒸实现盐溶液浓缩和组分分离的技术在海水淡化、食品加工及化工等领域中广泛存在。盐溶液具有不同于纯水的热物性，且存在沸点升高现象，开展盐溶液闪蒸过程汽泡成核、两相流动和传热传质机理的研究，对认识多组分盐溶液相变传递现象和发展相关新技术有重要价值。本项目采用实验和模拟相结合的研究策略，实验观测多种盐溶液闪蒸时汽泡的成核生长过程以及沸腾阶段汽液两相的流动相变过程，并通过拓展介观的格子Boltzmann模拟方法，建立适用于盐溶液闪蒸模拟的多相格子Boltzmann模型，模拟盐溶液物性和沸点升高对闪蒸汽液相变过程的影响规律，获得盐溶液闪蒸过程汽液流动以及组分和温度分布的详细信息。本项目深入分析盐溶液物性对盐溶液闪蒸汽泡成核条件、汽泡生长规律及汽液相变流动规律的影响，揭示盐溶液闪蒸在汽泡成核和沸腾阶段传热传质现象的物理机理，为有关盐溶液闪蒸浓缩和组分分离技术的发展提供理论依据和技术支持。

闪蒸是一种常见的沸腾现象，液体闪蒸具有很强的热量和质量交换能力，因此广泛应用于物质分离和快速冷却等领域。运用闪蒸实现盐溶液浓缩和组分分离的技术在海水淡化、食品加工及化工领域中广泛存在。盐溶液具有不同于纯水的热物性，且存在沸点升高现象，开展盐溶液闪蒸过程汽泡成核、两相流动和传热传质机理的研究，对认识盐溶液相变传递现象和发展相关新技术有重要意义。本项目采用实验和理论相结合的研究策略，实验观测了盐溶液闪蒸时汽泡的成核生长过程以及沸腾阶段汽液两相的流动相变过程，研究了盐溶液物性和沸点升高对气泡成核和闪蒸汽液相变过程的影响规律。项目获得了不同溶液过热度、真空腔初始压力和不同降压速率条件下纯水和盐溶液闪蒸过程的温度、压力、不平衡温差、不平衡分数等参数的变化规律，拟合出了考虑盐溶液浓度的闪蒸不平衡温差的实验关联式，并提出了较为精确的溶液闪蒸过程热/质传递物理模型，模拟结果与实验结果吻合很好。另外，项目对闪蒸过程气泡的成核和生长规律开展了细致的研究，尤其是利用两参数关联式（TCPC）提出了耦合盐溶液浓度的气泡生长模型，获得了气泡生长速率、气泡形变与气泡运动速率之间的相互耦合关系，并考虑了闪蒸过程降压速率的影响因素。所提出的模型可以准确的预测不同盐度以及工况下气泡的生长与运动规律。通过将盐度引入状态方程，建立了适用于盐溶液相变的多相格子玻尔兹曼模型，较为准确的预测了盐溶液的饱和蒸汽压以及表面张力随溶液盐度的变化规律。此外，项目还实验观测了过热度、降压速率和盐度对盐溶液闪蒸过程中闪蒸面演化过程的影响。该项目深入分析了盐溶液物性对盐溶液闪蒸汽泡成核条件、汽泡生长规律及汽液相变规律的影响，揭示了盐溶液闪蒸在汽泡成核和沸腾阶段传热传质现象的物理机理，为有关盐溶液闪蒸浓缩和组分分离技术的发展提供理论和技术支持。