A Numerical Study of Turbulent Heat Transfer in Unconfined Impinging Slot Jets

This paper presents a numerical study on the prediction of turbulent heat transfer in an unconfined single slot jet impingement on an isoflux flat plate. Governing equations are solved with a finite-volume approach in which the k–ε model and Reynolds-Stress Model (RSM) with enhanced wall functions are employed for the turbulence closure. Computations are performed at four jet Reynolds number based on the hydraulic diameter of the nozzle, Re_j = 15000, 22500, 30000 and 40000, where the non-dimensional nozzle-to-plate spacing, H/W varies between 2 and 8. Local Nusselt number, Nu predictions are compared with the corresponding experimental data of Singer et al. [6]. It was shown that the magnitude and distribution of Nusselt number is significantly affected by the shape of velocity profiles at the nozzle exit, therefore the profiles obtained from nozzle flow simulations are imposed as inlet boundary conditions. Off-center peaks occurring at low nozzle-to-plate spacings exhibited by the experiments are not fully captured by the computations. These secondary peaks are more pronounced at high Re_j. The center-line jet velocity, and therefore the potential core length plays an important role on the stagnation Nusselt number, yielding an optimum nozzle-to-plate spacing for the given Re_j range. It is show that there is a significant discrepancy between the experimental data and the predictions from the k–ε model with standard wall functions, while the k–ε model and RSM with enhanced wall functions demonstrated significantly better agreement with the experiments.