Combined experimental and numerical studies on flow characteristic and heat transfer in ribbed channels with vortex generators of various types and arrangements

This work numerically and experimentally studies the heat transfer performances and flow characteristics of vortex generators (VGs) in a high aspect ratio rectangular ribbed channel with the Reynolds number ranging from 20000 to 100000. The steady liquid crystal thermography (LCT) method is adopted to link the images captured by experiments and the Nusselt numbers. Four different cases combining ribs and VGs are considered, and they are compared with a case with five continuous ribs in the channel. For the first time, the effect of winglet VGs and the tetrahedral VGs on heat transfer performance are compared. Simultaneously, two different arrangements of VGs, i.e. common-flow-down VGs and common-flow-up VGs are also studied to figure out which arrangement is better for improving the heat transfer performance. Simulations are conducted to systematically compare the fluid flow and local heat transfer characteristics to reveal the underlying thermo-fluid mechanisms of the considered cases by using three-dimensional CFD numerical simulations with a verified turbulence model, i.e., the SST k-ω model in the transition state. Results indicate that in the range of 0 < x/P < 1, the Nusselt number is enhanced to a large extent due to larger space for the flow reattachment. In addition, it is found that the winglet VGs perform better than the tetrahedral VGs. The winglet VGs with the common-flow-down arrangement give the best overall thermal performance at all Reynolds numbers in most cases. More specifically, the heat transfer performance can be improved up to 5.51% by adopting the common-flow-down VGs compared with the case having five continuous ribs. Furthermore, the flow characteristics reveal that longitudinal VGs can generate vortices to disturb the boundary layers, which can enhance the flow mixing and augment the heat transfer performance.