集成冷能温差发电装置的空温式气化器纵向翅片管热动态特性研究、能效分析及结构优化

The ambient air vaporizer (AAV) integrating semiconductor thermoelectric generator, not only can make the power generation process utilizing LNG cold energy and the LNG gasification process simultaneously, it also can restrain the frost formation effectively. Aiming at the longitudinal finned tube integrating a power generation device for LNG cold energy utilization in AAV, this project intends to carry out an experimental and theoretical study on the frosting process on finned tube, clear the formation and growth mechanisms of the frost layer, reveal the law of heat and mass transfer on the outside surface of finned tube under frosting conditions, and establish an accurate prediction model for frost growth; on this basis, establish a energy balance-based model for the prediction of thermal dynamic characteristics by the coupling process analysis between the natural convection, heat radiation and sublimation on the outside surface of finned tube, the thermal conduction and thermoelectric power generation in tube wall, and the flow boiling or supercritical heat transfer in finned tube; in-depthly study the thermal dynamic characteristics, gasification efficiency and thermoelectric generation efficiency of the finned tube under frosting conditions; clear the influence mechanism of structure and operating parameters on the thermal dynamic characteristics, LNG gasification efficiency, thermoelectric generation efficiency and temperature difference between the hot and cold sides in PN junction; explore the method of improving LNG gasification efficiency and thermoelectric generation efficiency by enhancing the natural convective heat transfer around finned tube; finally realize the structure optimization design of longitudinal finned tube based on theoretical and numerical analysis, and lay a theoretical and technical foundation for the performance improvement of AAV and the exploration of effective utilization ways for LNG cold energy.

将半导体温差发电器集成在空温式气化器中，能够使LNG冷能发电和受热气化过程同步进行，同时有效抑制表面结霜。本项目拟针对集成冷能温差发电装置的LNG空温式气化器纵向翅片管，开展表面结霜实验及理论研究，明确翅片管表面霜层的形成和生长机制，揭示结霜条件下翅片管表面的热质传递规律，并建立精准的霜层生长预测模型；在此基础上通过对翅片管表面自然对流、热辐射及凝华结霜，管壁导热及温差发电与管内流动沸腾或超临界传热的耦合过程分析，建立基于能量平衡的热动态特性预测模型；并对翅片管在结霜条件下的热动态特性、LNG气化效率及冷能温差发电能效进行深入研究，明确结构和运行参数对热动态特性、气化效率、发电能效以及PN结冷热端温差的影响机制，探索强化自然对流传热提高气化效率和发电能效的方法，最终实现基于理论和数值分析的纵向翅片管结构优化设计，为提高空温式气化器的性能以及探索LNG冷能的有效利用途径奠定理论及技术基础。

空温式气化器是目前应用最广泛的LNG气化器之一。长期以来，翅片管表面结霜是影响空温式气化器效率的关键问题。与此同时，LNG在气化过程中浪费了大量冷能。将半导体温差发电装置集成在LNG空温式气化器中，能够使LNG冷能发电和加热气化过程同步进行，实现冷能回收利用并有效抑制气化器表面结霜。本项目针对集成半导体温差发电装置的LNG空温式气化器纵向翅片管在表面结霜条件下的热动态特性开展了深入研究，建立了低温表面霜层生长过程预测模型，揭示了表面结霜条件下传统纵向翅片管和集成半导体温差发电装置的新型纵向翅片管内部的复杂能量传输机理；明确了运行条件和结构参数对翅片管的热动态特性、LNG气化效率和冷能温差发电能效的影响规律以及对PN结冷热端温差的影响机制；提出了能够有效提高LNG气化效率和温差发电能效的结构改进方法。研究结果表明：1）集成冷能温差发电装置对纵向翅片管的表面结霜特性和LNG气化效率影响不大；2）在未结霜和结霜前期，传统纵向翅片管气化效率略高于新型翅片管，结霜后期则低于新型翅片管；3）翅片管发电量随结霜时间的增加呈递减趋势，未结霜时发电量为293.552W，结霜8h后，霜层参数趋于稳定，发电量为154.566W；4）管外自然对流传热和霜层导热热阻过大是导致气化效率、发电效率和发电密度较低的主要原因，及时除霜能够有效提高LNG气化效率，同时确保发电能效维持在较高水平；5）为提高LNG气化效率和发电能效，提出采用非连续顺排（或错排）纵向翅片强化空气侧自然对流传热，并通过纳米结构超疏水结构抑制结霜的结构改进方法。