开架式气化器新型传热管强化传热机理研究及结构优化

Open rack type gasification technology is not only the most widely-used LNG heating gasification technology at present, but also a key technology for large-scale LNG gasification equipment in China. This project intends to carry out numerical simulation,theoretical calculation and experimental validation of LNG flow and heat transfer in three new-type heat transfer tubes of super open rack vaporizer (SUPERORV) with duplex configuration at different pressures, LNG flow rates, seawater temperatures and seawater/LNG flow ratios. The main purpose in this study is to in-depth study the turbulent flow field distribution and its effects on phase-change heat transfer process in heat transfer tubes under low-temperature and phase-change conditions; reveal the multi-scale secondary flow characteristics in heat transfer tubes and their evolution rules from microcosmic angle; make efforts to explore the complex thermodynamic and dynamic characteristics and their coupling mechanisms in heat transfer tubes; clarify the gas-liquid two-phase flow and phase-change heat transfer mechanisms in heat transfer tubes; establish, develop, and improve the theoretical model of complex flow and heat transfer process in heat transfer tubes; analyze the effects of structure parameters, including the fins on inner wall of outer tube, the jet openings and the rod baffles in inner tube, on flow and heat transfer characteristics in heat transfer tubes; on this basis, put forward a structural optimization method for heat transfer tube based on numerical simulation, and develop a new-type heat transfer tube with high heat transfer performance. The implementation of this project could reveal the heat transfer enhancement mechanisms in heat transfer tubes of SUPERORV with duplex configuration profoundly, obtain new structure of heat transfer tube, and lay a theoretical and technical foundation for open rack vaporizer design in China.

开架式气化技术是目前应用最广泛的LNG加热气化技术，也是实现我国大型LNG气化设备国产化的关键技术。本项目拟对超级开架式气化器3种具有双层结构的新型传热管在不同压力、LNG流量、海水温度、海水/LNG流量比条件下的复杂流动传热过程开展实验、理论计算与数值模拟，深入研究低温相变条件下传热管内的湍流流场分布及其对相变传热过程的影响规律；从微观角度揭示传热管内的多尺度二次流特性及其演变规律；努力探索传热管内复杂的热力学与动力学特性及其耦合机制；阐明传热管内的气液两相流动及相变传热机理；建立、发展和完善其复杂流动传热过程的理论模型；分析外管内翅片、内管射流孔和扰流杆等结构参数对传热管流动传热特性的影响规律；在此基础上，确立基于数值模拟的传热管结构优化方法，并开发出具有优秀传热性能的新型传热管。项目的实施能够深刻揭示双层结构传热管的强化传热机理，并获得新型传热管结构，为我国开架式气化器设计奠定理论和技术基础。

开架式气化技术是目前应用最广泛的LNG加热气化技术，也是实现我国大型LNG气化设备国产化的关键技术。本项目对超级开架式气化器（SuperORV）传热管的强化传热机理开展了深入研究并对其进行了结构优化。主要研究内容如下：1）对受热圆管内超临界压力氮的流动传热过程进行了实验研究，揭示了超临界氮在受热圆管内的传热特性，明确了流速、压力和热流密度对超临界氮传热特性的影响规律；2）分别针对SuperORV传热管气化段和加热段传热过程建立了基于能量平衡的分布参数计算模型，并对SuperORV传热管的传热性能进行了数值计算及分析，讨论了运行压力、LNG流量和进口分配比、海水/LNG流量比以及内翅片、螺旋纽带等强化传热措施对SuperORV传热管传热性能及传热效率的影响；3）对SuperORV传热管中LNG的流动传热特性进行了数值模拟研究，深入分析了SuperORV传热管中LNG的受热气化过程，明确了LNG在超临界压力下的热物理性质变化及其对传热管内流场和温度场分布特性的影响规律，探讨了及SuperORV传热管在受热条件下内部复杂的耦合传热机理；4）针对SuperORV传热管提出了能够有效提高LNG气化效率的结构改进方法。研究结果表明：1）SuperORV传热管具有良好的传热性能，其双层套管结构和强化传热措施能够有效抑制传热管外侧海水结冰，并提高LNG气化效率；2）相比亚临界压力，超临界压力下SuperORV传热管具有更好的传热性能，LNG气化效率更高；3）运行压力、LNG流量、LNG流量分配比、海水/LNG流量比等运行参数对SuperORV传热管最小管长、传热管表面冰层长度和平均厚度等热特性参数均具有显著影响；4）采用内翅片和螺旋纽带能够有效强化传热并提高传热管的传热性能。在两种强化传热措施同时应用时，传热管最小长度缩短了40%以上；5）提高内外管间环形通道的LNG流量能够有效提高气化段上部的传热效率，但会导致气化段下部结冰更加严重，可采用逐渐减小内管管径同时使内管内LNG在旋流作用下从内管上的小孔流向环形通道的结构改进方法。