ABSTRACT

This paper presents the detailed study of parameter’s effect on Nusselt number (Nu), friction factor (f), and thermohydraulic performance parameter (η) of a rectangular duct through experiments using 45° V-down baffle blocks with staggered racetrack-shaped perforation geometry. The parameters investigated are the relative roughness height (e/H), relative pitch (p/e), and flow Reynolds number (Re). The results show that the secondary air jets issuing through racetrack-shaped perforations of baffle blocks with staggered holes strongly affect the duct’s flow pattern. The Nusselt number values show ups and downtrend with variation in the relative pitch and relative roughness height of the baffle blocks at all Reynolds number. The friction factor decreases with increased spacings but with variations up to a p/e value of 6 for different e/H of baffle blocks. The baffle block having e/H of 0.7 at p/e of 2 shows a maximum 456% rise in Nusselt number and an increase of 39 times in friction factor over the smooth duct. Baffle blocks having e/H of 0.5 and p/e of 4 obtain a 100% rise in thermohydraulic performance parameter value than the value for e/H of 0.6.

摘要

本文详细研究了参数对矩形管道努塞尔数 (Nu)、摩擦系数 (f) 和热工水力性能参数 (η) 的影响，通过使用具有交错跑道形射孔几何形状的 45° V-down 挡板块进行的实验。 . 研究的参数是相对粗糙度高度 (e/H)、相对螺距 (p/e) 和流动雷诺数 (Re)。结果表明，二次空气射流通过具有交错孔的挡板的跑道形穿孔发出，强烈影响管道的流动模式。Nusselt 数值显示了在所有雷诺数下挡板块的相对间距和相对粗糙度高度变化的上升和下降趋势。摩擦因数随着间距的增加而降低，但对于挡板的不同 e/H，ap/e 值的变化最高可达 6。在 p/e 为 2 时，e/H 为 0.7 的挡板块的努塞尔数最多增加 456%，摩擦系数比光滑管道增加 39 倍。e/H 为 0.5 和 p/e 为 4 的挡板块的热水力性能参数值比 e/H 为 0.6 的值提高了 100%。