折耳型轴向分隔螺旋折流板换热器的强化传热机理研究

The axial separation helical baffle heat exchanger with folded ears is a modified novel helical baffle heat exchanger based on circumferential overlap helical baffle heat exchanger. It not only inherits all the merits of circumferential overlap one, but also merges the additional new techniques of axial separation and folded ears. The axial separation technique adopts sleeve tubes between adjacent incline baffles to fit the flow rate with larger cross-sectional area. The advantages of folded ear technique are that the adjacent folded ears are perpendicular and connected to sleeve tubes. In this project, the flow characteristic, heat transfer enhancement mechanism and other main influence factors of the axial separation helical baffle heat exchanger with folded ears will be conducted by experimental tests and numerical simulation. The key research contents of this project mainly focus on (1) the influence of separation sizes and folded ears on secondary flow, shell-side helical flow and the performance of the whole heat exchanger; (2) the effect of the difference between equivalent inclined angle and inclined angle on heat transfer and flow resistance; (3) depicting the leakage pattern at trapezium area of adjacent two baffles and nearby distribution of flow field; (4) obtaining correlation criterion formulae of the shell side heat transfer coefficient and flow resistance coefficient of the axial separation helical baffle heat exchanger with folded ears from the experimental and simulation data, revealing the heat transfer enhancement mechanism, and developing engineering design and application system by providing design methods and theoretical bases for popularization and engineering application of the axial separation helical baffle heat exchanger with folded ears.

折耳型轴向分隔螺旋折流板换热器是一种在周向重叠螺旋折流板换热器基础上提出的新型螺旋折流板换热器。它不仅继承了周向重叠方案的优良特征，还融合了轴向分隔和折耳两种新技术。轴向分隔技术通过在相邻折流板之间加装分隔套管来实现较大的通流面积。折耳技术有利于相邻折流板在折耳区被分隔套管垂直并压紧。本项目将通过实验研究和数值模拟的方法探索该换热器的流场特性、强化传热机理及其他影响因素。重点研究：(1) 轴向分隔度和折耳对壳侧二次流、螺旋流及整个换热器性能的影响；(2) 当量倾斜角与倾斜角的差值对传热与流动阻力性能的影响；(3) 相邻折流板梯形区的泄漏模式及附近流场分布；(4) 分析和关联实验和模拟数据，拟合出折耳型轴向分隔螺旋折流板换热器壳侧对流换热系数、阻力系数的准则数关联式，揭示其强化传热机理，建立起更加完善的螺旋折流板换热器工程设计与应用体系，为工程应用和推广提供设计方法和理论依据。

为了研究折耳型轴向分隔非连续螺旋折流板换热器的流动和传热性能，进行了系列研究。集中对折流板倾斜角为10°、15°和20°的三分扇形折流板，折流板倾斜角为15°的三分椭圆折流板和折流板倾斜角为20°的轴向搭接方案进行测试分析；对倾斜角为20°、24°、28°和32°的周向重叠三分螺旋折流板换热器进行传热特性研究。对周向重叠、首尾相连、轴向搭接和缺口堵死等方案进行对比；最后对折流板倾斜角取28.5°，折耳区垂直拉杆，轴向分隔间距为零的折耳型轴向分隔三分螺旋折流板换热器以及作为对比的弓形折流板换热器进行水-水传热性能研究。借助数值模拟的优势，构建了一系列特殊切片，通过切片的不同位置和组合结构，深入剖析螺旋通道内清晰的局部流场特性和传热性能。结果表明：在研究范围内，折耳型周向重叠螺旋换热器的壳侧换热系数比弓形方案的对应值高4.88%到5.84%，而弓形方案的压降却比螺旋方案高57.14%到59.14%，尤其在大质量流量区间，弓形方案的压降增速更加明显，即折耳型周向重叠螺旋方案的壳侧综合性能(hs/Δps)、壳侧单位泵功综合性能(ρs·hs)/(Δps·Gs)的平均值比弓形方案分别高66.30%和66.23%。影响折耳型轴向分隔螺旋折流板换热器传热与流动的因素主要有螺旋折流板倾斜角、周向重叠、折流板数量、折流板组装方式、折耳以及轴向分隔量等结构影响因素。折耳结构封闭了相邻折流板之间的缺口，可有效抑制三角区的内部泄漏并促进迪恩涡二次流的发展壮大，增强壳侧对流换热系数。轴向分隔结构为非固定螺旋导程换热器提供了应用方案，但单独分隔间距加大时会降低传热系数和壳程流动阻力，影响用户对较高换热量的需要。那么将轴向分隔和折耳结构相融合，就能很好的实现高效低阻的功效。一系列水水传热性能参数为螺旋折流板换热器的热力设计计算、完善通用的螺旋折流板换热器的设计程序的应用和推广提供了理论分析数据和工程应用价值。为寻求新的螺旋折流板换热器通用计算模型提供预测方法，为管壳式换热器的新型结构的演变创造研究基础。