螺旋流动和倾斜折流板疏液强化凝结传热研究

The proper film pattern and effective drainage flow are key factors to increase the heat transfer efficiency for film condensation. This project mainly focuses on the scientific issues and conducts the relative basic research work of changing the condensate film pattern of condensation heat transfer in shell side of vertical helical baffle condensers by the effects of shell side spiral flow, condensate drainage and tube surfaces refreshing with the inclined sector baffles. Through research with both numerical simulation and performance test on the process of condensation heat transfer in helical baffle condensers of diverse geometrical structure factors such as variable inclination angles of baffle plates, conjunction styles of adjacent baffle plates of with or without circumferentially overlap, with or without bent hem as drip catching tray at baffle outlet edges, with or without liquid discharge gap at baffle plate periphery, single or multiple baffle helix(es). Explore the morphological evolution of condensation and local influence of thermodynamic characteristics of those factors. Describe the basic phenomena of thermodynamic non-equilibrium as well as vapor and liquid flow and heat transfer rules with steam flow and condensate film coupling coexistence pattern during the condensation process. Seek the relevant analysis and forecasting methods based on a deep understanding of basic physical phenomena and processes. Compare the results of abovementioned schemes with those of the conventional segmental baffle heat exchanger scheme. Complete the technical and the basic theory, and thus lay solid foundation for the relevant technique improvement and applications.

改善冷凝液液膜形态和有效疏液流动是提高冷凝器膜状凝结传热效率的关键，本项目重点围绕由立式螺旋折流板冷凝器壳侧螺旋流动以及倾斜折流板对管束上液膜的引导疏液与对传热表面的更新作用相关的凝结液膜形态变化对传热影响这一科学问题开展相关基础探索，通过数值模拟、可视化试验与传热性能试验，研究螺旋折流板冷凝器在折流板倾斜角变化，相邻折流板有无周向重叠，折流板出口有无挡液边，折流板外围有无排液缺口，单头与多头螺旋等几何结构因素对凝结过程传热的影响，探索各因素对凝结形态演化与局部热力学特征的影响；描述在此凝结过程中汽流与液膜形态耦合共存的基本现象、热力学非平衡性和汽液流动与传热规律，寻求相关分析预测方法，较深层地认识相关基础物理现象与过程，并将上述方案的结果与传统的弓形折流板换热器方案进行对比，完善相关技术和基础理论，为相关技术改进和应用奠定基础。

立式三分螺旋折流板冷凝器的螺旋折流板将管束分隔成短管段，不断将管束上的冷凝液刮下；在倾斜的折流板上设置挡液堰和疏水缺口，将凝结液沿壳体内壁排到底部，有效减薄液膜厚度，提高换热系数。.围绕立式冷凝器中倾斜折流板对竖直管束上凝结液的疏导和螺旋流动离心力的气液分离强化凝结传热的作用展开研究。计算了含有不凝性气体的三种不同倾斜角(15°、25°、35°)立式三分螺旋折流板冷凝器和作为比较的立式弓形折流板冷凝器和无折流板冷凝器方案的管外液膜厚度、蒸汽微分凝结量、蒸汽凝结量及凝结换热系数沿管长的分布情况和纯蒸汽凝结条件下Nusselt经典解数据。采用Fluent多相流模型中的混合(Mixture)模型进行模拟分析。获得了蒸汽在变角度单、双头三分螺旋折流板与弓形折流板三种方案的立式冷凝器内的速度矢量和速度云图叠加图、凝结液体积分数分布图和管子表面局部换热系数分布图。表明双头方案呈现较均匀的螺旋流动，螺旋折流板方案的凝结换热系数比弓形折流板方案的高得多。 .进行了立式冷凝器试验台的搭建，对螺旋折流板立式冷凝器的不同折流板结构形式的强化凝结传热性能进行了试验研究。试验比较分析了6件三分螺旋折流板芯体和1件弓形折流板芯体。结果表明，三分螺旋折流板立式冷凝器的壳侧换热系数是弓形折流板方案的1.48倍~2.65倍，其中最佳的双头变角度带挡液堰方案的壳侧换热系数比弓形折流板方案平均提高131.8%。以壳侧换热系数为评价指标，单头变角度方案比单头定角度对应方案平均提高25.47%；双头变角度方案比单头变角度对应方案平均提高15.74%；带挡液堰方案比不带挡液堰对应方案平均提高6.37%。.此外还在螺旋折流板折耳、轴向分隔、激光切割加工技术、管束与丝网交替结构的吸收强化、斜日字布管螺旋折流板电加热器、卡林纳循环与氨水朗肯循环组合系统、双蒸发压力卡林纳循环、LNG/O2燃气蒸汽混合工质动力循环等方面展开研究。

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