EXPERIMENTAL AND NUMERICAL HEAT TRANSFER INVESTIGATION OF AN IMPINGING JET ARRAY ON A TARGET PLATE ROUGHENED BY CUBIC MICRO PIN FINS

A generic impingement cooling system for turbomachinery application is modeled experimentally and numerically to investigate heat transfer and pressure loss characteristics. The experimental setup consists of an array of 9 by 9 jets impinging on a target plate with cubic micro pin fins. The cubic micro pin fins have an edge length of 0.22 D and enlarge the target area by 150%. Experimentally heat transfer is measured by the transient liquid crystal (TLC) method. The transient method used requires a heated jet impinging on a cold target plate. As reference temperature for the heat transfer coefficient we use the total jet inlet temperature which is measured via thermocouples in the jet center The CFD model was realized within the software package ANSYS CFX. This model uses a steady state - 3D - RANS approach and the shear stress transport (SST) turbulence model. Boundary conditions are chosen to mimic the experiments as close as possible. The effects of different jet-to-plate spacing (H/D = 3-5), crossflow schemes and jet Reynolds number (15,000-35,000) are investigated experimentally and numerically. The results include local Nusselt numbers as well as area and line averaged values. Numerical simulations allow a detailed insight into the fluid mechanics of the problem and complement experimental measurements. A good overall agreement of experimental and numerical behavior for all investigated cases could be reached. Depending on the crossflow scheme the cubic micro pin fin setup increases the heat flux to about 134%-142% compared to a flat target plate. At the same time the Nusselt number slightly decreases. The micro pin fins increase the pressure loss by not more than 14%. The results show that the numerical model predicts the heat transfer characteristics of the cubic micro pin fins in a satisfactory way.