晃荡条件下复杂缠绕管通道内相变传热机理研究

The spiral wound heat exchanger is the key equipment in the cold box of the floating liquefied natural gas. It has been indicated that the sloshing under ocean conditions has important effects on the flow and heat transfer performance of the spiral wound heat exchanger. But the mechanism of the complex channel, multi-stream and phase change is not clear yet. This project intends to study heat transfer enhancement in the complex spiral wound tube channel under sloshing condition, which will be performed by combining experiment and numerical simulation method. The following listed are the main research contents of this project. (1) The internal relations of the heat transfer among the local heat transfer units as well as between the local heat transfer units and the entire spiral wound tube channel are investigated. The computational model extrapolating the heat transfer characteristics of a local unit to the entire channel is built to clarify the heat transfer law among the local heat transfer units as well as between the local units and the entire channel. (2) The effects of the sloshing parameters on the multi-stream distribution in the complex spiral wound tube channel are studied to reveal the law of the effect of the sloshing on the multi-stream distribution. (3) The coupled model of the phase change heat transfer on both sides of the tube in the spiral wound tube channel under the sloshing conditions is built to reveal the effect mechanism of the sloshing on the phase change heat transfer. The multi-parameter dimensionless correlations of the phase change heat transfer in the spiral wound tube channel are built including the multi-stream. Those results can provide theoretical supports for the high efficiency technology of heat transfer enhancement under the sloshing conditions, and promote the development of the LNG industry, which has important academic significance and engineering application value.

缠绕式换热器是浮式天然气液化冷箱的关键设备，研究表明海洋条件下的晃荡对其流动传热性能影响较大，但其内部的复杂通道、多股流分配与相变传热机理尚不清晰。本项目拟通过数值模拟和实验研究相结合的方法，针对晃荡条件下复杂缠绕管通道内的传热强化问题展开研究，主要内容包括：（1）探究各局部传热单元之间以及局部单元与缠绕管通道整体之间热量传递的内在联系，建立通过局部单元传热特性外推通道整体传热特性的计算模型，阐明复杂缠绕管通道局部单元之间以及局部单元与通道整体之间热量的传递规律；（2）研究晃荡参数对复杂缠绕管通道内多股流分配的影响，揭示晃荡对多股流分配的影响规律；（3）建立晃荡条件下缠绕管通道中管内外两侧相变传热的耦合模型，揭示晃荡对相变传热的影响机理，并构建包含多股流与相变传热的多元无量纲关联式。研究结果可为晃荡条件下的高效强化传热技术提供理论支持，将促进LNG产业的发展，具有重要的学术意义和应用价值。

以当前“双碳目标”下国家在能源领域对LNG的重大需求为牵引力，基于海上浮式天然气液化（FLNG）装备的重大需求为背景，本项目主要针对晃荡条件下FLNG冷箱用缠绕式通道中复杂的流动状态、多股流分配、相变传热等关键技术与机理问题，采用了数值模拟方法、实验研究、理论分析、人工智能算法预测等相结合的方法，重点对晃荡条件下复杂缠绕管通道中的气液两相分配与相变传热问题展开了研究。开展了LNG缠绕式换热器壳侧的流动状态分析研究，建立了水平管外混合制冷剂降膜滴状流动数值模型，获得了管外径、流量大小等参数对水平管外混合制冷剂降膜滴状流动的流型、分离长度、换热系数的影响规律。基于采用Lee模型对制冷剂相变传热研究的基础，提出了基于温度加权和松弛时间参数的新型传质模型，在减少假设的条件下能够准确地计算出松弛时间参数的值，提高了相变传热的数值精度。通过搭建气液两相流分配实验台与建立两相流分配数值模型，对LNG缠绕式换热器壳侧混合制冷剂气液两相流动分配进行了研究，揭示了制冷剂在LNG缠绕式换热器壳侧的气液两相流分配规律，并对分配结构进行了优化，提出了新的分配结构，解决了LNG冷箱混合制冷剂的气液两相分配问题。建立了缠绕式通道相变传热研究的数值模型，获得了主要几何参数、运行参数、多组分比例等对缠绕式通道中相变传热的影响规律。采用UDF建立了实现晃荡的数值模拟条件，搭建了六自由度晃荡实验系统，获得了晃荡幅度、频率对缠绕管通道中相变传热的影响规律。基于已有椭圆管翅式换热器的实验数据，利用人工神经网络算法对其流动传热性能进行了预测，验证了该方法用于缠绕管通道中相变传热与多股流分配性能预测的有效性。本项目的研究成果可以为海洋晃荡条件下复杂缠绕管通道中的气液两相流动分配、传热强化等理论研究与性能提升提供支持，为FLNG工艺技术的提升提供数据支撑，并将促进海洋条件下天然气液化产业的发展，具有重要的学术价值和工程意义。