中低温液态金属磁流体发电系统两相流型与传热研究

The theoretical and fundamental research on the multiphase flow in the sustainable energy conversion and utilization process is one of the key and supportive subjects listed among the strategy report for the academic development of the thermal physics engineering and energy utilization. Based on the combination of the numerical simulation, theoretical analysis, and experimental verification, a fundamental research on the flow regimes and heat transfer in the liquid metal MHD power generation system for lower-temperature heat resources will be implemented in the present proposal. Firstly, a numerical investigation will be carried out on the mixing process of the liquid metal and low-boiling point working medium, and on the flow regime, heat transfer and power generation performance under the magnetic field. The mixer and MHD channel will also be designed optimally. Secondly, the differential pressure signals will be processed, which may establish a relationship between the signal spectrum and flow regime. A characteristic parameter reflecting the flow regime can therefore be obtained and be employed as the flow regime criterion. Finally, in order to improve the numerical model and the flow regime criterion, experimental verification will be conducted on an experimental setup of the gas-liquid two-phase flow and heat transfer in the LMMHD power generation system. By this way, the mechanism influencing the flow regimes and heat transfer characteristics can be revealed. Implement of this project will improve the two-phase flow theory of the liquid metal and low-boiling point working medium under the magnetic field, and thus provide theoretical and technological support for the design and operation of LMMHD power generation systems.

可再生能源转化利用过程中的多相流基础研究是工程热物理与能源利用学科发展战略报告中列出的重点支持方向之一。本申请将采用数值模拟、理论分析和实验验证相结合的研究方法，开展中低温液态金属磁流体发电系统（LMMHD）两相流型与传热问题的基础研究。首先，对液态金属/低沸点工质的两相混合过程，以及磁场作用下的气液两相流型、传热及发电性能进行数值研究，并进行混合器和发电通道的最优化设计；其次，对气液两相流动过程的差压（压力）数据做信号处理，建立信号频谱特征与流型的关联，并提取可反映流型差异的特征参数，形成流型判据；最后，在LMMHD发电系统气液两相流动与传热实验台上开展验证工作，修正数值模型并完善流型判据，从而全面掌握中低温液态金属磁流体发电系统两相流型与传热特性及其影响机理。项目的实施将完善磁场作用下液态金属流动与传热的基础理论，为LMMHD发电系统的设计和运行提供理论和技术支撑。

能源是经济发展和社会进步的重要基础，在能源消耗不断增加而带来诸多社会和环境问题的现实背景下，发展可再生能源与节能减排已成为当今人类的共识。液态金属磁流体发电系统由于其工作温度范围宽、可利用能源种类多和流体导电率高等优势，可适用于各类中小型发电装置，发展前景广阔。.本课题基于多场耦合下两相磁流体动力学理论，对发电系统的关键部件（混合器和发电通道）进行设计和研究，利用低沸点工质的相变来强化两相混合与输运效果，深入研究混合器进口条件对混合效果与出口流型的影响，利用Hilbert-Huang变换分析建立信号频谱特征与流型的关联。然后，进一步研究发电通道内部的三维流场特性，总结特定流型下发电通道内的流型变化规律，并基于研究结果对发电通道进行优化设计，最后从微观角度揭示气泡特征对发电通道内两相流动行为的影响。.研究表明，不同工况下，混合器出口处的流型分为分层流，搅混流及环状流流型。进口速度较低的液态金属容易产生分层流动，随着速度的逐渐增大，分层流转变为搅浑流。在液态金属进口速度恒定的情况下，提高低沸点工质进口速度会导致环状流的产生。随着流型由搅浑流向环状流的转变，压力波动信号的能量特征值k在高频段的占比会逐渐降低。在发电通道内部，随着空泡率的增大，湍流强度逐渐减弱。尽管发电通道进口的流型不同，但发电通道内的流型最终向搅浑流转变。此外，顶部带有液态金属进口的发电通道的设计可以有效地将分层流转化为搅混流和改善系统输出功率。当有磁场存在时，发电通道内的气泡会破裂而后逐渐靠近两侧电极壁面。气液两相混合过程及两相流动特性的研究有助于实现液态金属的高效输运，从而提升发电系统的效率和运行可靠性，为实际应用提供一定的理论指导。