International Journal of Thermal Sciences ( IF 4.5 ) Pub Date : 2021-08-10 , DOI: 10.1016/j.ijthermalsci.2021.107203 Prashant Wasudeo Deshmukh 1 , Siddini Venkatesh Prabhu 2 , Rajendra Prasad Vedula 2
Measurements of local heat transfer coefficients on the circumference of a circular tube, fitted with two modified versions of an already existing axially inline curved Vortex Generator (VG) element insert are reported in this study. Measurements for average pressure drop are also presented and the air was used as the working fluid. The first modified insert is manufactured with a pair of two VG elements spaced symmetrically 180° apart but with the subsequent pairs along the axis staggered at an angle of 90°. The geometric features for the staggered insert were identical to the optimal one for the existing inline one. The staggered insert gives a more uniform circumferential and axial Nusselt number distribution. The ratio of the highest and lowest Nusselt number values for the staggered and inline case is equal to approximately 1.3 and 1.6 respectively. The average Nusselt number ratio at constant Reynolds number (10,000 < Re < 45,000) and constant pumping power however remained the same at about 2.6 and 1.5 respectively. The second modified insert was manufactured with three vortex generators placed symmetrically 120°apart at each axial location with all subsequent locations in line with one another. Two angles of attack 30°and 45° were used for the vortex generator elements and the pitch to projected length ratio of the VGs was varied between 1.6 and 12.2. The average heat transfer coefficient augmentation ratio using this insert at the equal Reynolds number and constant pumping power was obtained in the range of 1.5–5.5 and 1.0 - 1.8, respectively. The experimental data is presented in the form of empirical correlations for Nusselt number, and friction factor as a function of tube flow parameters, and non-dimensional geometrical parameters of VG inserts, which predict the data with an accuracy equal to ±20 %.
中文翻译:
使用带有多个弯曲涡流发生器元件的插件增强圆管中湍流的传热
本研究报告了对圆管圆周上局部传热系数的测量,该圆管装有两个改进版本的现有轴向内嵌弯曲涡流发生器 (VG) 元件插件。还提供了平均压降的测量值,并且使用空气作为工作流体。第一个改进的刀片制造有一对两个 VG 元件,它们对称地间隔 180°,但随后的对沿轴线以 90° 的角度交错排列。交错刀片的几何特征与现有内嵌刀片的最佳几何特征相同。交错插入提供更均匀的周向和轴向努塞尔数分布。交错和内联案例的最高和最低 Nusselt 数值之比大约等于 1.3 和 1。6 分别。恒定雷诺数 (10,000 < 关于 < 45,000)和恒定泵送功率分别保持在大约 2.6 和 1.5 左右。第二个改进的插入件制造有三个涡流发生器,这些涡流发生器在每个轴向位置以 120° 对称放置,所有后续位置彼此对齐。涡流发生器元件使用了两个攻角 30°和 45°,VG 的节距与投影长度之比在 1.6 和 12.2 之间变化。在相同的雷诺数和恒定的泵送功率下,使用该插件的平均传热系数增加率分别在 1.5-5.5 和 1.0-1.8 的范围内获得。实验数据以 Nusselt 数的经验相关性形式呈现,摩擦系数作为管流参数的函数,以及 VG 插件的无量纲几何参数,