Abstract

Numerical simulations are carried out to infer the heat transfer performances of perforated trapezoidal vortex generators (PTVG) in a turbulent regime, for Reynolds numbers ranging from 7500 to 15000. The flow geometry consists of a circular pipe fitted with seven arrays of perforated tabs, similarly, arranged as in the high efficiency vortex static mixer (HEV™) used in the industry. Four configurations using the PTVG are studied, differing by the flow direction, direct or inverse, and the arrangement of the tab arrays, aligned or alternate. The flow pattern shows the presence of primary pair of counter-rotating streamwise vortices at the tip of the tabs, as well as smaller secondary vortices near the wall region, well-known as the main transfer intensification mechanism. The perforation in the tab generates a jet-like flow structure which penetrates the dead zone behind the tabs and therefore, locally enhances the heat transfer and the global performance of the device. It is found that the heat transfer relative to empty pipe is enhanced from 40 to 80%, for the same pumping power. The new proposed PTVG exhibits better performance than classical HEV™, especially for Reynolds numbers greater than 10,000. This study is fundamental for highlighting the effect of perforating the vortex generators on heat transfer performance. Moreover, the novel PTVG would be of great benefit to enhance commercial multifunctional heat exchangers/reactors.

摘要

进行数值模拟以推断在湍流状态下穿孔梯形涡流发生器 (PTVG) 的传热性能，雷诺数从 7500 到 15000 不等。流动几何结构由装有七个穿孔凸片阵列的圆管组成，类似地, 布置在工业中使用的高效涡流静态混合器 (HEV™) 中。研究了使用 PTVG 的四种配置，它们的不同之处在于流动方向，直接或反向，以及标签阵列的排列，对齐或交替。流动模式显示在翼片尖端存在一对反向旋转的流向涡流，以及在壁区域附近存在较小的次级涡流，这是众所周知的主要传递强化机制。接片中的穿孔产生了一种射流状的流动结构，该结构穿透了接片后面的死区，因此局部增强了传热和设备的整体性能。发现对于相同的泵送功率，相对于空管的传热从 40% 提高到 80%。新提出的 PTVG 表现出比经典 HEV™ 更好的性能，尤其是对于大于 10,000 的雷诺数。这项研究对于突出涡流发生器穿孔对传热性能的影响至关重要。此外，新型 PTVG 对增强商用多功能换热器/反应器大有裨益。发现对于相同的泵送功率，相对于空管的传热从 40% 提高到 80%。新提出的 PTVG 表现出比经典 HEV™ 更好的性能，尤其是对于大于 10,000 的雷诺数。这项研究对于突出涡流发生器穿孔对传热性能的影响至关重要。此外，新型 PTVG 对增强商用多功能换热器/反应器大有裨益。发现对于相同的泵送功率，相对于空管的传热从 40% 提高到 80%。新提出的 PTVG 表现出比经典 HEV™ 更好的性能，尤其是对于大于 10,000 的雷诺数。这项研究对于突出涡流发生器穿孔对传热性能的影响至关重要。此外，新型 PTVG 对增强商用多功能换热器/反应器大有裨益。