潜热型液-固两相介质熔盐泵输送机理研究

A molten salt pump is a crucial piece of equipment used for high temperature heat transfer and storage of molten salt in the solar energy industry. Research on the influences of phase change and microscale effect of molten salt on the two-phase flow in a molten salt pump is an entirely new task. Visualization measurement of internal flow in the molten salt pump, which transports high temperature medium, is extremely difficult. Firstly, the internal flow in the molten salt pump is chosen as the main research object. In consideration of phase change and microscale effect, the acting forces between the two phases are analyzed. Flow mechanism of latent heat type liquid-solid two-phase coupling in the molten salt pump is explored, and the corresponding CFD model is established. Secondly, Based on the established model above, the influences of flow passage structure, media properties and operating conditions on the characteristics of the molten salt pump are investigated. A characteristic prediction model of the molten salt pump is built regarding the latent heat type liquid-solid two-phase coupling. Then, a high efficient intelligent optimization algorithm is investigated, and a multiobjective optimal method is put forward considering steady and unsteady hydraulic performances and wear performance of the molten salt pump. Finally, the visualization measurement of internal flow in the molten salt pump is investigated. A series of tests on the molten salt pump are performed to verify the validity of the latent heat type liquid-solid two-phase coupling CFD model, the characteristic prediction model and multiobjective optimal method. The results in this project will benefit the development of two phase flow mechanics and provide the theoretical reference for the design of high-performance molten salt pumps.

熔盐泵是太阳能高温传热蓄热中输送熔盐的关键装备。熔盐的相变和微小尺度效应对熔盐泵内两相流动的影响是一个全新的课题，输送高温介质的熔盐泵内部流动可视化测量有相当难度。首先，本项目以熔盐泵的内部流动为研究对象，分析存在相变和微小尺度效应的两相介质相间作用力，阐明熔盐泵内潜热型液-固两相耦合的流动机理，建立潜热型液-固两相耦合的计算流体动力学模型。其次，以此为基础，探索流道结构、介质属性和工作条件对熔盐泵外特性的影响规律，建立基于潜热型液-固两相耦合的熔盐泵外特性预测模型。然后，研究高效智能优化算法，提出同时考虑熔盐泵定常、非定常水力性能和磨损性能的多目标优化方法。最后，研究熔盐泵内部流动可视化测量方法，进行熔盐泵性能试验，验证所建立的潜热型液-固两相耦合CFD模型、外特性预测模型和多目标优化方法的正确性。本项目的研究不但有益于完善两相流力学理论，而且可为高性能熔盐泵的开发提供理论依据。

熔盐泵是太阳能高温传热蓄热中输送熔盐的关键装备。为了研究熔盐泵输送液-固两相介质时的内部流动特性及其外特性，以熔盐泵的内部流动为研究对象，分析了存在固相介质情况下的两相介质相间作用力，阐明了熔盐泵内潜热型液-固两相耦合的流动机理，建立了潜热型液-固两相耦合的计算流体动力学模型。以此为基础，探索了流道结构、介质属性和工作条件对熔盐泵外特性的影响规律，建立了基于潜热型液-固两相耦合的熔盐泵外特性预测模型。研究了高效智能优化算法，提出同时考虑熔盐泵能量损失、汽蚀余量和径向力的多目标优化方法。开展了熔盐泵内部流动可视化测量，进行了熔盐泵性能试验，验证了所建立模型和提出方法的正确性。研究结果表明，适当减小出口安放角2和出口宽度b2，适当增大叶片出口厚度su，可以使Ht-Qt曲线变陡峭，以避免H-Q曲线出现驼峰。输送低粘度介质时，H-Q性能曲线容易出现驼峰；相反，输送高粘度介质时，H-Q性能曲线不太容易出现驼峰。输送粘度小于0.01453Pa.s的熔盐与输送水时泵的性能相比，扬程和效率下降均小于5%，可近似采用输送水时的H-Q和-Q性能曲线。熔盐泵固相为单分散颗粒群时，熔盐泵内粒径小于0.02mm的颗粒跟随性较好，在泵内分布非常均匀，粒径为0.15mm以上时，随着粒径的增大，泵内固相离析现象越来越明显，叶片工作面和蜗壳壁面处聚集的颗粒越来越多，这些部位的磨损也愈加严重。熔盐泵内奇异点的位置不随着粒径、体积分数和密度的改变而改变。按照相似准则设计的模化方案理论上均可行，在选择最优方案时，应考虑转速、几何尺寸、流量和扬程等综合因素，以便实验能够有效开展。当雷诺数小于1.0107时，比扬程和效率随着雷诺数的减小迅速下降，可用此雷诺数作为泵运行的临界雷诺数ReQcr，泵不宜在低于临界雷诺数的工况下运行。采用粒子群优化算法优化以后的熔盐泵的性能有了很好的提升，不仅能量损失减小而且抗汽蚀性能和运行稳定性得到提高。研究结果有益于完善两相流力学理论，为准确预测熔盐泵的性能提供理论依据。