CFD Simulation of Impinging Jet Flows and Boiling Heat Transfer

Circular jets impinging vertically on flat surfaces have many practical applications in industry. Nozzle height-to-diameter ratio plays an important role in the performance of this type of jet. In this thesis a step by step approach has been followed to cover different aspects of impinging jets. In the first step, a steady Reynolds-Averaged Navier-Stokes simulation has been carried out on impinging jets with different nozzle stand-off distances. A strong dependency of the jet characteristics on the nozzle height-to-diameter ratio was observed. The simulations show that an increase in this ratio results in larger shear stress and more distributed pressure on the wall. In the second step, an unsteady simulation using Large Eddy Simulation has been performed on an impinging jet with large stand-off distance. Good agreement was observed between the mean value results obtained from the current simulations and experiments. Unlike impinging jets with small stand-off distance, where the ring-like vortices keep their interconnected shape upon reaching the plate, no sign of interconnection was observed on the plate for the large stand-off distance case. A large deflection of the jet stagnation streamline was observed in comparison to the cases with small nozzle height-to-diameter ratios. Large fluctuations of the unsteady wall shear stresses were also captured. A boiling model was developed for impinging jets with heat transfer. An Eulerian-Eulerian two-phase flow model was implemented using an open source code for the simulation (OpenFOAM). Initially, an adiabatic two-phase model was developed for flow in a pipe. Following this, the energy equation was activated to account for non-adiabatic and boiling conditions. The simulation predictions were found to be in reasonable agreement with the experimental data and show significant improvement over previous numerical results. Finally, the model was upgraded for an impinging jet flow by implementing new correlations. The results obtained from the current model show reasonable agreement with the experimental results. The model can be confidently used for the evaluation of adiabatic and non-adiabatic impinging jet flows