The present experimental work is a comprehensive study of heat transfer and flow field characteristics inside a rectangular duct integrated with ribs of variable cross sections on the bottom wall. Four kinds of rib configurations, i.e., square (Case 1), pentagonal (Case 2), trapezium (Case 3), and truncated prismatic (Case 4), were deployed in the cooling passage to improve the thermal performance. The optical techniques, i.e., particle image velocimetry for flow field measurements and liquid crystal thermography for surface temperature measurements, were used to obtain reliable and accurate information about the flow and heat transfer features without disturbing the actual flow conditions. Transient experiments were conducted at a typical Reynolds number value, i.e., 42,500. The influence of the rib configurations and their relative spacing (P/e = 8, 10, and 12) were studied through the mapping of local- and spanwise-averaged enhanced heat transfer. Furthermore, the thermal performance parameters (overall Nusselt number augmentation, friction factor ratio, and thermohydraulic performance) are discussed in detail to select the best rib design. The truncated prismatic rib provided the best values of the thermal (27.91%), friction (32.75%), and thermohydraulic performance (45.16%) at P/e = 8, P/e = 12, and P/e = 8, respectively, when compared with square ribs. Moreover, the reasons for the variations in the heat transfer distribution inside the ribbed passages are elucidated through the flow structure information (mean velocities, mean streamlines, fluctuation statistics, mean vorticity, and turbulent intensity) at a relative spacing of 12. The heat transfer results are in harmony with the flow features, which helps in understanding the fundamental heat transfer mechanism.

中文翻译：

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各种肋骨安装的管道中增强的传热和流动特性

目前的实验工作是对矩形管道内部的传热和流场特性的全面研究，该矩形管道在底壁上集成了可变截面的肋骨。在冷却通道中部署了四种肋结构，即正方形（案例1），五边形（案例2），梯形（案例3）和截棱柱形（案例4），以提高热性能。光学技术，即用于流场测量的粒子图像测速技术和用于表面温度测量的液晶热成像技术，被用于获得有关流动和传热特征的可靠且准确的信息，而不会干扰实际的流动条件。在典型的雷诺数值（即42,500）下进行瞬态实验。肋骨结构及其相对间距的影响（P / e = 8、10和12）是通过局部平均和跨度平均增强传热的映射进行研究的。此外，详细讨论了热性能参数（总的努塞尔数增加，摩擦系数比和热工液压性能），以选择最佳的肋骨设计。截断的棱形肋在P / e = 8，P / e = 12和P / e时提供了最佳的热性能（27.91％），摩擦力（32.75％）和热工液压性能（45.16％）的值与方肋骨相比分别为= 8。此外，通过相对间隔为12的流动结构信息（平均速度，平均流线，波动统计，平均涡度和湍流强度）阐明了肋状通道内部传热分布变化的原因。结果与流动特征一致，有助于理解基本的传热机理。