Heat Transfer in Multiple Parallel High Aspect Ratio Ducts With Triangular Trench Enhancement Features

Detailed heat transfer coefficient distributions and pressure drop have been obtained for high aspect ratio (AR = Width/Height = 12.5) ducts with triangular trench enhancement features oriented normal to the coolant flow direction. Numerical and experimental approaches analyze the performance of triangular trenches for six geometrically identical ducts branching from a common plenum. The numerical approach is based on a Reynolds Averaged Navier Stokes (RANS) turbulence model with an unstructured mesh. A transient liquid crystal (TLC) technique is used to experimentally calculate Nu on the ducts surfaces. Reynolds number (Re = 7080, 14800, and 22400, with respect to the duct hydraulic diameter are explored. As Computational Fluid Dynamics (CFD) and TLC results are both detailed, qualitative and quantitative comparisons are made. Experimental results show the closest and furthest ducts from the entrance of the plenum are considerably affected, as recirculation zones develop which partially choke the inlet the respective ducts. Results from the experiments are compared to CFD predictions from Duct 4. In addition, the experimental data are recalculated with the maximum bias in TLC temperature to indicate an improved matching between CFD and experimental methods to demonstrate that CFD captures the wall heat transfer coefficient trends similar to experimental results. The triangular trenches enhance heat transfer in the ducts two-fold compared to smooth wall Dittus-Boelter Nusselt number correlation for flow in tubes.