面向FLNG的晃荡对泡沫金属上制冷剂冷凝与疏泄的作用机制研究

The operation efficiency of floating liquefied natural gas (FLNG) depends on the heat transfer between the refrigerant and seawater in the precooling stage of natural gas liquefaction process, but the existing seawater heat exchangers have the problems of low heat transfer coefficient of refrigerant side as well as easy damage of metal tubes. Employing metal-foam covered tubes instead of smooth tubes may obviously improve refrigerant-side heat transfer coefficient and tube strength, at the condition of well drainage of liquefied refrigerant from metal foam. This project proposes an idea to improve the liquid drainage ability by using low surface energy coating metal foam, and the mechanism of refrigerant condensation and drainage in low surface energy coating metal foam under sloshing conditions will be explored. A description model of surface characteristics of metal fiber will be developed based on surface infiltration experiments; a graph-theory based spatial topological structure model will be established by observations of surface asperities structure of metal fiber; a model of liquid drainage characteristics on metal foam will be developed by combining the Level-set method and experimental investigations on the mechanism of droplet movement and collision under sloshing condition; a model of droplet formation and growth characteristics during refrigerant condensation process will be developed based on the nucleation theory and the mixture diffusion theory; and finally a model reflecting the mechanism of coupling effect of refrigerant condensation and liquid drainage will be accomplished. The research achievements will provide a theoretical basis of designing high-efficiency heat exchangers for FLNG systems, and enrich knowledges of heat and mass transfer during the condensation process in porous medium.

海上浮式天然气液化装置（FLNG）高效运行依赖于天然气液化预冷流程中制冷剂向海水的充分散热，但现有海水换热器制冷剂侧传热系数较低且换热管易受冲击损坏；外镶泡沫金属管代替光管，能够大幅提高换热系数和抗冲击强度，其应用瓶颈是保证晃荡工况下制冷剂冷凝液从泡沫金属中及时疏泄。本项目提出利用低表面能改性增加泡沫金属对冷凝液体疏泄能力的思路，并探究晃荡对改性泡沫金属内制冷剂冷凝与疏泄特性的作用机制。通过金属纤维上浸润实验，建立纤维表面特性表征模型；基于金属纤维上微凸体结构特征的观测，开发基于图论的泡沫金属空间拓扑结构模型；基于晃荡对液滴运动和碰撞影响的实验，结合水平集方法，建立泡沫金属上制冷剂疏泄模型；通过经典成核和混合物扩散理论，开发制冷剂冷凝液形成及生长模型；建立反映泡沫金属上制冷剂冷凝与疏泄耦合机制的模型。研究成果可为设计高效的FLNG换热器提供理论依据，并丰富多孔介质内凝结相变热质传递理论。

海上浮式天然气液化装置（FLNG）由于空间受限且处于晃荡的海洋环境中，要求天然气液化预冷流程必须采用的 “高紧凑型”和“高可靠性”的冷凝器。外镶泡沫金属管代替光管，能够大幅提高换热系数和抗冲击强度，其应用瓶颈是保证晃荡工况下制冷剂冷凝液从泡沫金属中及时疏泄。本项目围绕晃荡对泡沫金属管外冷凝与疏泄作用机制展开研究,从泡沫金属单根纤维微观液滴、到泡沫金属胞元，再到整体泡沫金属管的疏泄特性与冷凝特性进行了实验、理论研究。搭建了单根纤维液滴生长机制观测实验台，建立了纤维液滴生长预测模型；通过测量晃荡工况下泡沫金属胞元内液体疏泄特性研究实验台，开发了晃荡工况下液体疏泄模型。在此基础上，提出了利用低表面能改性增加泡沫金属对冷凝液体疏泄能力的思路，并对晃荡工况下泡沫金属管外冷凝与疏泄特性的作用机制进行研究。至今共发表SCI英文论文13篇，EI论文1篇，国际会议1篇。研究成果可为设计高效的海上换热器提供理论依据，并丰富多孔介质内凝结相变热质传递理论。