Abstract: In the literature survey on twisted tubes (TTs), it can be found that many documents believe that TTs are processed from round tubes based on the method of equal cross-sectional area, ignoring the fact that the cross-sectional perimeter of TTs is approximately constant during processing. In addition, the research on the cross-sectional shape on the heat transfer characteristics in the TT is relatively rare. Based on this, the heat transfer characteristics of the fluid in the TT with typical cross-sectional shape under low Reynolds number (Re) are analyzed by simulation on the basis of experimental validation. The results show the regularly spiral deformation of the TT induces periodic spiral flow of the fluid inside it, and the secondary flow is generated in the direction perpendicular to the mainstream, which reduces the synergy angle between temperature gradient and velocity and intensifies the convective heat transfer of the TT in contrast to that of round tube with equal cross-sectional circumference. When Re ranges from 650 to 1550, the TTs corresponding to the convective heat transfer coefficient from high to low are twisted triangle tube, twisted rectangular tube, twisted oval tube, twisted square tube and plain tube, respectively. The convective heat transfer coefficient and flow resistance of the twisted triangle tube increases 1.94~1.97 times and 2.96~3.06 times than plain tube, respectively. All the TTs outperform the plain tube in terms of comprehensive heat transfer performance and the comprehensive heat transfer performance evaluation factor of twisted triangle tube is the highest, with an average of about 1.86, and the rest are twisted rectangular tube, twisted oval tube and twisted square tube, which can be summarized that the twisted triangle tube performs the best convective heat transfer performance. Although the optimal tube shape is the twisted triangular tube, cold-rolling the cross-section into a triangular shape requires high toughness and is not easy to form. In practical applications, extruding the round tube into a rectangular or elliptical cross-section can be considered. The above research on the influence of cross-sectional shape on the heat transfer characteristics in TTs has practical significance for guiding the optimization design of novel TTs.

Key words: heat transfer enhancement, flow resistance, twisted tube, secondary flow

摘要： 为对比分析典型扭曲管内传热及流动阻力性能，以指导优化设计新型扭曲管，基于实验验证，采用数值计算方法，研究了典型横截面形状的扭曲管内流体在低雷诺数时的换热特性。结果表明，扭曲管的规律性螺旋形变诱导其内流体产生周期性螺旋流动，在垂直主流方向上产生二次流，增强了温度梯度与速度矢量间的协同程度，使得扭曲管的传热性能强于等横截面周长的普通圆管；在雷诺数为650~1550时，对流传热系数由高到低对应的换热管依次为扭曲三角形管、扭曲矩形管、扭曲椭圆管、扭曲方形管和普通圆管，扭曲三角形管的对流传热系数和流动阻力损失分别比普通圆管增大1.94~1.97倍和2.96~3.06倍，扭曲管的综合传热性能均优于普通圆管，扭曲三角形管的综合传热性能评价因子是最高的，平均约为1.86，其余依次为扭曲矩形管、扭曲椭圆管和扭曲方形管，扭曲三角形管具有最优的对流传热性能。

关键词: 强化传热, 流动阻力, 扭曲管, 二次流